oscillator Related Articles

Ⅰ IntroductionA Colpitts oscillator is one of several designs for LC oscillators, which employ a combination of inductors (L) and capacitors (C) to produce an oscillation at a specific frequency. It was invented in 1918 by American engineer Edwin H. Colpitts. The voltage divider made up of two capacitors in series across the inductor serves as feedback for the active device in the Colpitts oscillator.   CatalogⅠ IntroductionⅡ What a Colpitts Oscillator Contains?Ⅲ How the Colpitts Oscillator Works?Ⅳ Colpitts Oscillator vs Hartley OscillatorⅤ Types of Colpitts Oscillator5.1 Common Base Colpitts Oscillator5.2 Common Emitter Colpitts Oscillator5.3 Buffered Colpitts OscillatorⅥ Advantages of Colpitts OscillatorⅦ Applications of Colpitts OscillatorⅧ ConclusionⅨ Frequently Asked Questions about Colpitts OscillatorⅡ What a Colpitts Oscillator Contains?The Colpitts circuit, like other LC oscillators, is made up of a gain device (such as a bipolar junction transistor, field-effect transistor, operational amplifier, or vacuum tube) with its output connected to its input in a feedback loop containing a parallel LC circuit (tuned circuit) that serves as a bandpass filter to set the oscillation frequency. The amplifier's input and output impedances will be different, and these must be linked into the LC circuit without overdamping it. Ⅲ How the Colpitts Oscillator Works?The Colpitts oscillator is commonly used in RF applications, with a frequency range of 20KHz to 300MHz. The capacitive voltage divider configuration in the tank circuit serves as the feedback source in the Colpitts oscillator, and this arrangement provides superior frequency stability than the Hartley oscillator, which uses an inductive voltage divider system for feedback. The circuit diagram of a typical transistor-based Colpitts oscillator is shown below. Colpitts oscillator The resistors R1 and R2 in the circuit schematic provide a voltage divider biasing for the transistor. The transistor's collector current is limited by the resistor R4. The input DC decoupling capacitor is Cin, and the output decoupling capacitor is Cout. The emitter resistor, Re, is used to ensure thermal stability. The emitter by-pass capacitor is denoted by Ce. The emitter by-pass capacitor's job is to keep the amplified AC signals from crossing Re. If the emitter by-pass capacitor is missing, the amplified AC signal will drop across Re, causing the transistor's DC biasing conditions to change, resulting in lower gain. The tank circuit is made up of capacitors C1, C2, and inductor L1. Tank circuit in a Colpitts oscillator When the power source is turned on, the capacitors C1 and C2 begin to charge. They start discharging through the inductor L1 when they are completely charged. The electrostatic energy stored in the capacitors is transmitted to the inductor as magnetic flux when the capacitors are fully drained. The inductor begins to discharge and the capacitors are re-charged. Oscillation is caused by energy being transferred back and forth between capacitors and inductors. The voltage across C2 is in phase opposite that of C1, and the voltage across C2 is sent back to the transistor. The enhanced feedback signal at the transistor's base emerges across the collector and emitter. The transistor compensates for the energy lost in the tank circuit, maintaining the oscillations. One 180° phase shift is produced by the tank circuit, and the other 180° phase shift is produced by the transistor. That means the input and output are in phase, and positive feedback requires to keep oscillations going for long periods. The equation below can be used to calculate the frequency of the Colpitts oscillator's oscillations. Where L is the inductance of the tank circuit's inductor and C is the effective capacitance of the tank circuit's capacitors. The effective capacitance of the serial combination C= (C1C2)/(C1+C2) if C1 and C2 are independent capacitances. The Colpitts oscillator can be made variable by utilizing ganged variable capacitors in place of C1 and C2. Ⅳ Colpitts Oscillator vs Hartley OscillatorThe Colpitts oscillator is extremely similar to the Hartley oscillator, however they are constructed differently. The Colpitts oscillator employs a single inductor in parallel with two capacitors in series, whereas the Hartley oscillator utilizes the exact opposite, one single capacitor in parallel with two inductors in series. In high-frequency operation, the Colpitts oscillator is more stable than the Hartley oscillator. Colpitts Oscillator vs Hartley Oscillator In high-frequency operation, the Colpitts oscillator is an ideal choice. It can generate output frequencies in the Megahertz and Kilohertz ranges. Ⅴ Types of Colpitts Oscillator5.1 Common Base Colpitts OscillatorA typical Colpitts oscillator design is shown below. The Colpitts LC tank circuit operates similarly to the Hartley oscillator, however it only has a single inductor and two capacitors. Instead of the tapped inductor used in the Hartley, the capacitors create a single 'tapped' capacitor. The total capacitance in series (CTOT) of the two capacitors (connected in series) is calculated as follows: common base Colpitts oscillator The total capacitance required for the tank circuit to achieve parallel resonance at the specified frequency is given. The oscillation frequency is calculated using the same formula as the Hartley oscillator. However, in this case, the number C is the sum of the values C2 and C3 in order (CTOT). C2 and C3's values are chosen so that their ratio delivers the required proportion of feedback signal. The ratio of voltages across two capacitors in series, on the other hand, is inversely proportional to the ratio of their values, implying that the smaller capacitor has a higher signal voltage across it. The fundamental advantage of the Colpitts design is that the single inductor in the tuned circuit eliminates any mutual inductance between two coils, where the alternating magnetic field generated up around one inductor drives a current into the inductor of the other coil. This alters the resonance frequency of the tuned circuit by changing the total inductance of the coils. 5.2 Common Emitter Colpitts OscillatorThe Colpitts analog of the Common Emitter Hartley Oscillator is shown below.                              common emitter Colpitts oscillator It employs a common emitter amplifier, and because the tuned (tank) circuit tapping point is connected to the ground in this design, the tank circuit generates anti-phase waves at the top and bottom of L2, ensuring proper phase relationships for positive feedback between collector and base. The feedback is delivered to the base via C1, which also functions as a DC block, preventing the greater voltage on L1 from causing the base bias voltage to be thrown off. The supply rail (+Vcc) is connected to the tank circuit (L2, C2, and C3) through L1. Because the DC supply is significantly decoupled by huge capacitors in the DC Power supply, if the tank circuit were connected directly to the supply, there would be no anti-phase AC signal present at the top of the tank circuit. As a result, between the tuned circuit and the supply, an RF choke (L1) with a high impedance at the oscillation frequency is provided. This permits the development of a signal voltage across L1 for feedback purposes. Automatic class C bias is utilized, with the emitter only partially disconnected by a small amount of C5 to provide the previously mentioned "slide bias." The Colpitts oscillator, like the Hartley, can produce an excellent sine wave shape and has the added benefit of improved stability at very high frequencies. It's easy to spot because it's always got a "tapped capacitor" on it. The fact that any load placed on the output by circuits that the output is supplying essentially inserts a dampening resistance across the tank circuit complicates the design of a sine wave oscillator. This can have an adverse influence on both the wave shape and frequency stability of the oscillator waveform, as well as lowering the amplitude of the oscillator output by lowering the Q factor of the tuned tank circuit. 5.3 Buffered Colpitts OscillatorAs demonstrated below, feeding the oscillator output into an emitter follower buffer amplifier is a standard technique. buffered Colpitts oscillator TR1's load impedance has been changed to the RF choke, and the tank circuit is now isolated from TR1 by two DC blocking capacitors, C1 and C4. As a result, instead of a tuned amplifier, this variant of the Colpitts oscillator uses a tuned feedback channel. The emitter follower stage (R4, TR2 and R5) has a very high input impedance, which has no effect on the oscillator, and a very low output impedance, which allows it to drive loads with impedances as low as a few tens of ohms. Variations in supply voltage can also affect the frequency stability of oscillators. When good frequency stability is required, it is typical to use a stabilized power supply. Extra decoupling capacitors may be required for oscillator supplies to reduce undesired 'noise.' Automatic class C bias, which is given in this circuit by only partially disconnecting the emitter of TR1 by C5, is generally used to achieve stable amplitude. Ⅵ Advantages of Colpitts OscillatorThe Colpitts oscillator may produce very high-frequency sinusoidal pulses.It can tolerate extreme heat and cold.There is a lot of frequency stability.Both variable capacitors can be used to change the frequency.A small number of components is all that is required.Over a certain frequency range, the output amplitude remains constant.The Colpitts oscillator was created to address the shortcomings of the Hartley oscillator and is known to have no unique flaws. As a result, a Colpitts oscillator has a wide range of uses. Ⅶ Applications of Colpitts OscillatorThe Colpitts oscillator is mostly employed for fixed frequency generation due to the challenges in achieving a smooth variation of inductor and capacitor.The Colpitts oscillator is most commonly found in mobile phones and other radio frequency-controlled communications devices.The Colpitts oscillator is a great choice for high-frequency oscillation. Colpitts Oscillator is used in high-frequency oscillator-based systems.Colpitts Oscillator is utilized in a few applications where continuous and undamped oscillation is required as well as thermal stability.For applications that require a broad range of frequencies with minimal noise.Colpitts oscillator is used in a variety of SAW-based sensors.The Colpitts oscillator is used in a variety of metal detectors.A Colpitts oscillator is used in frequency modulation radio frequency transmitters.It has a wide range of uses in both military and commercial items.Signal masking-related chaotic circuits are also required in microwave applications Colpitts oscillator in various frequency ranges. Ⅷ ConclusionTo summarise, the Colpitts Oscillator consists of a parallel LC resonator tank circuit whose feedback is achieved by way of a capacitive divider. The Colpitts oscillator exists in several forms like most oscillator circuits, and the most common form is the transistor circuit. The tank sub-center circuit's tap is made at the junction of a "capacitive voltage divider" network, which feeds a fraction of the output signal back to the transistor's emitter. The 180o phase shift produced by the two capacitors in series is inverted by another 180o to produce the requisite positive feedback. The resonance frequency of the tank circuit determines the oscillation frequency, which is a purer sine-wave voltage. Ⅸ Frequently Asked Questions about Colpitts Oscillator1.What is the use of Colpitts oscillator?It is used for generation of sinusoidal output signals with very high frequencies. The Colpitts oscillator using SAW device can be used as the different type of sensors such as temperature sensor. As the device used in this circuit is highly sensitive to perturbations, it senses directly from its surface. 2.What is the basic principle of oscillator?There are many types of electronic oscillators, but they all operate according to the same basic principle: an oscillator always employs a sensitive amplifier whose output is fed back to the input in phase. Thus, the signal regenerates and sustains itself. This is known as positive feedback. 3.What is meant by Colpitts oscillator?A Colpitts oscillator, invented in 1918 by American engineer Edwin H. Colpitts, is one of a number of designs for LC oscillators, electronic oscillators that use a combination of inductors (L) and capacitors (C) to produce an oscillation at a certain frequency. 

This article is an introduction article on the resonator, information like its working principle, types, and some main parameters will be introduced in detail, also including the analysis of the difference between resonator and oscillator.     Catalog I. What is A Resonator? II. The Working Principle of Resonator      2.1 The Structure of Resonator      2.2 Piezoelectric Effect III. Resonator Types IV. Main Parameters of Resonator V. What’s the Difference Between Resonator and Oscillator? 5.1 General Difference Between Resonator &   Oscillator 5.2 Pros and Cons Analysis of Resonator &   Oscillator FAQ   I. What is A Resonator? This video introduce resonator in details.   A resonator refers to an electronic component that generates a resonant frequency.   A resonator refers to an electronic component that generates a resonant frequency. It is a typical passive device and requires a peripheral circuit to drive its work to generate a clock output.   Crystal resonators are commonly divided into quartz crystal resonators and ceramic resonators. The function of generating frequency has the characteristics of stability and good anti-interference performance and is widely used in various electronic products.   The frequency accuracy of quartz crystal resonators is higher than that of ceramic resonators, but the cost is also higher than that of ceramic resonators. The resonator mainly plays the role of frequency control, and all electronic products involve frequency transmission and reception require a resonator. The types of resonators can be divided into the in-line type and patch type according to their appearance. II. The Working Principle of Resonator   2.1 The Structure of Resonator   Quartz crystal resonator is a kind of resonant device made by using the piezoelectric effect of quartz crystal (a crystal of silicon dioxide).   Its basic composition can be roughly described as follows: cut a thin slice (referred to as a wafer, which can be square, rectangular or circular, etc.) from a piece of quartz crystal at a certain azimuth angle, and coat silver layers as electrodes on its two corresponding surfaces. Weld a lead wire on each electrode to the pin, and add a package shell to form a quartz crystal resonator. Its products are generally packaged in metal shells, but also in glass, ceramic or plastic packages.   2.2 Piezoelectric Effect   If an electric field is applied to the two electrodes of the quartz crystal, the wafer will be mechanically deformed. Conversely, if mechanical pressure is applied to both sides of the wafer, an electric field will be generated in the corresponding direction of the wafer. This physical phenomenon is called the piezoelectric effect.   If an alternating voltage is applied to the two poles of the wafer, the wafer will produce mechanical vibration, and at the same time, the mechanical vibration of the wafer will produce an alternating electric field. In general, the amplitude of the mechanical vibration of the wafer and the amplitude of the alternating electric field is very small, but when the frequency of the applied alternating voltage is a certain value, the amplitude is obviously increased, which is much larger than the amplitude at other frequencies. This phenomenon is called piezoelectric resonance, which is very similar to the resonance phenomenon of the LC circuit. Its resonant frequency is related to the cutting method, geometry, and size of the wafer. III. Resonator Types   Quartz crystal resonators are composed of quartz crystal resonators (ie resonators and oscillation circuits) with extremely high-quality factors. The quality of the crystal, the cutting orientation, the structure of the crystal oscillator and the circuit form, etc., jointly determine the performance of the resonator.   The International Electrotechnical Commission (IEC) divides quartz crystal resonators into 4 categories: ordinary crystal oscillator (SPXO), voltage-controlled crystal resonator (VCXO), temperature compensated crystal oscillator (TCXO), and thermostatically controlled crystal oscillator (OCXO). Digitally compensated crystal loss oscillation (DCXO) is currently under development.   (1) Ordinary crystal resonator (SPXO) can produce frequency accuracy of the order of 10-5～10-4, the standard frequency is 100MHZ, and the frequency stability is ±100ppm. SPXO does not use any temperature and frequency compensation measures are low in price and are usually used as a clock device for microprocessors. The package size ranges from 21×14×6mm and 5×3.2×1.5mm.   (2) The accuracy of the voltage-controlled crystal resonator (VCXO) is in the order of 10-6 to 10-5, and the frequency range is 1 to 30 MHz. The frequency stability of the low-tolerance resonator is ±50ppm. Usually used in phase-locked loops. The package size is 14×10×3mm.   (3) The temperature-compensated crystal resonator (TCXO) uses temperature-sensitive devices for temperature and frequency compensation, with a frequency accuracy of 10-7～10-6, a frequency range of 1-60MHz, and frequency stability of ±1～±2.5ppm, The package size ranges from 30×30×15mm to 11.4×9.6×3.9mm. Usually used in handheld phones, cellular phones, two-way wireless communication devices, etc.   (4) The thermostatically controlled crystal resonator (OCXO) places the crystal and oscillation circuit in a thermostat to eliminate the influence of environmental temperature changes on the frequency. The frequency accuracy of OCXO is in the order of 10-7～10-8, even higher for some special applications. The frequency stability is the highest among the four types of resonators. IV. Main Parameters of Resonator   The main parameters of the crystal oscillator are nominal frequency, load capacitance, frequency accuracy, frequency stability, etc. Different crystal oscillators have different nominal frequencies, and most of the nominal frequencies are marked on the crystal housing.   For example, the nominal frequencies of common ordinary crystal oscillators are 48kHz, 500 kHz, 503.5 kHz, 1MHz～40.50 MHz, etc. The frequency of crystal oscillators with special requirements can reach 1000 MHz or more, and there are also non-nominal frequencies, such as CRB, ZTB, Ja, etc.   The load capacitance refers to the sum of all the effective capacitances inside and outside the IC block connected by the two leads of the crystal oscillator, which can be regarded as the series connection capacitance of the crystal oscillator in the circuit. The different load frequency determines the different oscillation frequency of the resonator. For crystal oscillators with the same nominal frequency, the load capacitance may not be the same.   Because the quartz crystal resonator has two resonant frequencies, one is a low-load capacitance crystal of a series resonant crystal oscillator, and the other is a high-load capacitance crystal of a parallel resonant crystal. Therefore, when the crystal oscillators with the same nominal frequency are exchanged, the load capacitance must be the same, and they cannot be exchanged rashly, otherwise, it will cause the electrical appliances to work abnormally.   Frequency accuracy and frequency stability: Because the basic performance of ordinary crystal oscillators meets the requirements of general electrical appliances, certain frequency accuracy, and frequency stability are required for high-end equipment. Frequency accuracy varies from magnitude to magnitude. The stability varies from ±1 to ±100ppm. Choosing the appropriate crystal oscillator according to the specific equipment needs, such as communication network, wireless data transmission and other systems require a more demanding quartz crystal resonator.   Therefore, the parameters of the crystal oscillator determine the quality and performance of the crystal oscillator. In practical applications, the appropriate crystal oscillator should be selected according to specific requirements. Because of the different prices of crystal oscillators with different performances, the higher the requirements, the more expensive the price. Generally, the choice only needs to meet the requirements. V. What’s the Difference Between Resonator and Oscillator?     5.1 General Difference Between Resonator & Oscillator   The so-called resonator includes not only quartz crystal resonators but also ceramic resonators, LC resonators, and so on. A crystal oscillator is the abbreviation of the crystal oscillator. It is an oscillator component composed of a combination of a crystal resonator and a circuit, especially an oscillator component made of a quartz crystal.   So the complete naming should be "Quartz Crystal Resonator" and "Quartz Crystal Oscillator". In addition, the resonator is a passive device, which requires a peripheral circuit to drive its work and generate a clock output. The oscillator is an active device with its own built-in circuit to provide a more stable clock output.   A crystal oscillator is an oscillating circuit that uses a crystal as a frequency-selecting component. Compared with other oscillating circuits, it has the advantages of good frequency selection characteristics (high Q value) and high-frequency stability.   The fundamental difference between a resonator and an oscillator is active and passive, which can also be said to be active and passive. The oscillator has one more control circuit than the resonator.   Crystal resonators have some equivalent parameters, and different use environments may have different requirements. For example, some users require load capacitance C0 / C1. When selecting, consider the environmental temperature, load capacitance, frequency accuracy, and even DLD requirements. This requires some control of the parameters of the peripheral oscillator circuit to output a stable frequency.   The crystal oscillator avoids these troubles. The oscillating circuit has been completed by the manufacturer, and only a stable power supply is needed to have a stable output. In addition, the oscillator has some auxiliary functions, such as voltage-controlled crystal oscillator (VCXO), temperature-compensated crystal oscillator (TCXO), constant temperature crystal oscillator (OCXO), etc. These oscillators can meet some precision controls that are difficult to achieve when directly using resonators. . The frequency accuracy of OCXO can reach the order of E-9.   Secondly, the crystal oscillator is made of a crystal resonator, in order to be used as a signal carrier or timing on other components. To meet the requirements of the products produced.   An oscillator is simply a frequency source and is generally used in a phase-locked loop. In detail, it is a device that can convert DC power into AC power without external signal excitation. Generally divided into two types: positive feedback and negative resistance.   The so-called "oscillation", its meaning implies exchange, the oscillator includes a process and function from no oscillation to oscillation. It can complete the conversion from DC power to AC power. Such a device can be called an "oscillator."   Any communication or electronic system should have a level value within a normal range at some given point. The components that are adjusted to the normal level value are amplifiers and attenuators. The point of excessively low level is the point where noise is introduced, and the point of excessively high level will cause overload and make the amplifying component appear intolerable nonlinear distortion. It is not difficult to understand the role of the attenuator. There are two types of attenuators: fixed and variable.     5.2 Pros and Cons Analysis of Resonator & Oscillator   In this sector, we are going to analyze the pros and cons of crystal resonator and ceramic resonator, resonator, and oscillator.   (1) pros and cons of crystal resonator and ceramic resonator   The introduction of the crystal resonator has been mentioned above, so I won't repeat it here. Let's take a look at ceramic resonators.   A ceramic resonator is a piezoelectric ceramic device used to oscillate at a specific frequency. The materials used to make such devices excite resonance characteristics during the production process.   Because this resonance characteristic is within the production error range, and its quality factor is much lower than that of quartz, the frequency stability that ceramic resonators can provide is not as good as crystal resonators. Generally, ceramic resonators are used in occasions where the cost is low and the performance requirements are not high.   Pros: Compared with crystals, the cost of ceramic resonators is only half that of crystals and the size is smaller.   Cons: Compared with crystals, it lacks frequency and temperature stability. Its accuracy is poor, probably between 1% and 0.1%.     (2) pros and cons of resonator and oscillator   The oscillator is an energy conversion device that converts DC power into AC power with a certain frequency. The circuit formed by it is called an oscillator circuit. The oscillator is an active device. The oscillator has one more control circuit than the resonator.   Oscillators are electronic components used to generate repetitive electronic signals (usually sine waves or square waves). The circuit formed by it is called an oscillating circuit. An electronic circuit or device that can convert direct current into an alternating current signal with a certain frequency.   There are many types. According to the oscillation excitation mode, it can be divided into the self-excited oscillator and separately excited oscillator; according to the circuit structure, it can be divided into the resistance-capacitance oscillator, inductance-capacitance oscillator, crystal oscillator, tuning fork oscillator, etc.; according to the output waveform can be divided into It is a sine wave, square wave, sawtooth wave, and other oscillators. It is widely used in the electronics industry, medical treatment, scientific research, etc.   Pros: The crystal oscillator signal quality is good, relatively stable, and the connection method is relatively simple (mainly to do a good job of power filtering, usually a PI filter network composed of a capacitor and an inductance is used, and the output terminal uses a small resistance resistor to filter the signal. Yes), no complicated configuration circuit is required. For applications with sensitive timing requirements, the performance of crystal oscillators is relatively good.   Cons: Compared with the crystal resonator, the defect of the crystal oscillator is that its signal level is fixed, and the appropriate output level needs to be selected. It is less flexible and expensive. In addition, the quartz oscillator takes a long time to start.   Volume: Compared with passive crystals, crystal oscillators are usually larger in volume. With the improvement of technology, some crystal oscillators are now surface-mounted, and the volume is comparable to crystal resonators.   Summary: The typical initial accuracy of ceramic resonators is in the range of 0.5% to 0.1%, and drift caused by aging or temperature changes may change this accuracy range.   The tolerances of cheap ceramic resonators are only ±1.1%, and the accuracy of higher-end automobiles is ±0.25% and ±0.3%, respectively. The future application lies in the automotive CAN (controller area network) bus application with an operating temperature of -40°C to +125°C. Low-cost ceramic resonators with frequencies ranging from 200 kHz to about 1 GHz are suitable for embedded systems that do not have strict timing requirements.   Ceramic devices start faster and are generally smaller than quartz devices. They are also more able to withstand shock and vibration.     FAQ   1. What does a resonator do? A resonators' sole purpose in life is to change a vehicle's engine noise before it reaches the muffler for a final decibel reduction.   2. What is a resonator in electronics? A resonator is a device or system that exhibits resonance or resonant behavior. ... Resonators are used to either generate waves of specific frequencies or to select specific frequencies from a signal. Musical instruments use acoustic resonators that produce sound waves of specific tones.   3. What does removing the resonator do? A resonator delete changes the way that the pulses generated by your vehicle move through the exhaust system. Think of this device as if it were a large echo chamber. It takes those pulses, optimizes their frequencies, and this makes it possible to achieve better power production.   4. Which is better muffler delete or resonator delete? If you want a louder and lighter vehicle, you'll be better off with the muffler delete. If you're after a good sound and a little more power, the resonator delete is the way to go. ... After all, the difference between a resonator delete and muffler delete isn't that significant.   5. What is difference between crystal and resonator? The ceramic resonator utilizes a frequency within the electrical component but unlike the crystal which has a frequency tolerance of 10~30 PPM , a ceramic resonator carries a 0.5% or 5,000 PPM frequency tolerance which is generally used in microprocessor applications where absolute stability is not important.   6. Is intake resonator necessary? An air intake resonator is a crucial component to an automobile engine's intake system. It allows the engine to run more quietly as well as more efficiently. ... An air intake resonator is a crucial component to an automobile engine's intake system. It allows the engine to run more quietly as well as more efficiently.   7. Do resonators restrict airflow? Magnaflow resonators dont restrict flow at all, its just like adding a section of straight pipe as they are straight through. magnaflow's design uses no chambers, but rather a perforated straight pipe surrounded by a sound-absorbing material.   8. Which is the best frequency for a noise resonator? The resonator is designed to work best in the frequency range where the engine makes the most noise; but even if the frequency is not exactly what the resonator was tuned for, it will still produce some destructive interference.   9. Will a resonator quiet my exhaust? Mufflers and resonators work together to quiet your car's exhaust and reduce annoying sounds. While they function differently, they both help improve your exhaust note. Mufflers and resonators can also be deleted for a louder, more aggressive exhaust sound.   10. Does removing the resonator increase horsepower? As a rule; the quieter an exhaust system is, the more horsepower it is stealing from your engine. ... Removal of all mufflers and resonators will provide slightly greater increases but remember as the restrictions are removed the exhaust grows louder.  

CatalogCatalogⅠ Oscillation DefinitionⅡ Definition of Voltage Controlled OscillatorⅢ Types of Voltage Controlled Oscillator  3.1 Harmonic Oscillators  3.2 Relaxation OscillatorsⅣ Working Principle of Voltage Controlled OscillatorⅤ Voltage Controlled Oscillator Requirements  5.1 VCO tuning range  5.2 VCO tuning gain  5.3 VCO V/f slopeⅥ Voltage Controlled Oscillator FeedbackⅦ Colpitts & Clapp Voltage Controlled Oscillator CircuitsⅧ Voltage Controlled Oscillator Varactor Issues  8.1 Abrupt  8.2 Hyper-abruptⅨ FAQⅠ Oscillation DefinitionAn oscillator is a circuit that, without any input, generates a continuous, repeated, alternating waveform. Basically, oscillators transform unidirectional current flow from a DC source into an alternating waveform that, as determined by its circuit components, is of the desired frequency. By observing the behavior of the LC tank circuit shown in Figure 1 below, which uses an inductor L and a completely pre-charged capacitor C as its components, the basic theory behind the operation of oscillators can be understood. In this case, the capacitor initially begins discharging through the inductor, which results in the conversion of its electrical energy into an electromagnetic field that can be stored in the inductor. There will be no current flow in the circuit until the capacitor discharges fully.The stored electromagnetic field, however, would have created a back-emf by then, which results in the flow of current through the circuit in the same direction as before. This flow of current through the circuit continues until the electromagnetic field collapses, resulting in the electromagnetic energy back-conversion into electrical form, allowing the cycle to repeat. Now, however, the capacitor would have been charged with the opposite polarity, because of which an oscillating waveform is obtained as the output. However, because of the resistance of the circuit, the oscillations that occur due to the inter-conversion between the two energy-forms will not continue indefinitely as they will be subject to the impact of energy loss. The amplitude of these oscillations gradually decreases to zero as a result, making them damp. This means that the energy loss needs to be balanced to achieve continuous oscillations and constant amplitude. However, in order to achieve oscillations of constant amplitude, it should be noted that the energy supplied should be precisely regulated and must be equal to that of the energy lost.Ⅱ Definition of Voltage Controlled OscillatorA voltage-controlled oscillator (VCO) is an output signal oscillator whose output can be varied over a particular frequency range that is controlled by the DC voltage input. It is an oscillator whose output frequency is directly connected by its input to the voltage applied (FM control).A main parameter of the VCO is the sweeping time: this is the minimum time required to turn or sweep from minimum frequency to maximum frequency or reverse. From an external analog signal, the VCO can be modulated by amplitude (AM). To produce the requested RF power level, an external power amplifier may be required.Ⅲ Types of Voltage Controlled OscillatorThe VCOs can be categorized based on the output waveform:• Harmonic Oscillators• Relaxation Oscillators3.1 Harmonic OscillatorsThe output waveform that harmonic oscillators generate is sinusoidal. This can also apply to the oscillator that regulates the linear voltage. The LC and Crystal oscillators are examples. Here, the capacitance of the diode varies according to the voltage around the diode. This in turn alters the LC circuit's capacitance. Hence, the frequency of the output will change. The advantages are frequency stability in terms of power supply, noise and temperature, and frequency control precision. The only downside is that this form of the oscillator on monolithic ICs can not be implemented effortlessly.3.2 Relaxation OscillatorsThe waveform output produced by harmonic oscillators is a screwed tooth. Using the decreased amount of components, this type may provide a wide range of frequency. It can primarily be used in ICs that are monolithic. The oscillators for relaxation may have the following topologies: • Delay-based ring VCOs • Grounded capacitor VCOs • Emitter-coupled VCOs Here: In delay-based ring VCOs, in a ring shape, the gain stages are connected. As the name implies, in every single point, the frequency is connected to the delay. The VCOs of the second and third types act almost equally. The time taken in each stage is directly linked to the capacitor's charging and discharging time.Ⅳ Working Principle of Voltage Controlled Oscillator Using several voltage regulation electronic components such as varactor diodes, transistors, Op-amps, etc., VCO circuits can be built Here, using Op-amps, we are going to address the function of a VCO. Below, the circuit diagram is shown.A square wave is going to be the output waveform of this VCO. The output frequency is, as we know, connected to the control voltage. The first Op-amp will act as an integrator inside this circuit. The arrangement of the voltage divider is applied here. Because of this, half of the control voltage given as input is supplied to the Op-amp 1 positive terminal. At the negative terminal, the same voltage level is retained. This is to maintain the voltage drop, R1 as half of the control voltage, across the resistor. The current flowing from the R1 resistor passes through the MOSFET when the MOSFET is in good condition. The R2 has half of the resistance, the same drop in voltage and twice the current as of the R1's. So, the attached capacitor is charged by the extra current. To supply this current, the Op-amp 1 should have a gradually increasing output voltage. The current flowing from the R1 resistor passes through the capacitor and gets discharged when the MOSFET is out of order. The output voltage obtained at this time from the Op-amp 1 will decrease. A triangular waveform is therefore produced as the output of Op-amp 1. The Op-amp 2 will act as a catalyst for Schmitt. A triangular wave that is the output of the Op-amp 1 is the input to this Op-amp. If the input voltage is greater than the threshold level, VCC will be the output from the Op-amp 2. If the input voltage is lower than the threshold level, the Op-amp 2 output is zero. The output of the Op-amp 2 is therefore going to be square waves. LM566 IC or IC 566 is an instance of VCO. In fact, it is an integrated 8-pin circuit that can generate double-square wave and triangular wave outputs. Below, the internal circuit is depicted.Ⅴ Voltage Controlled Oscillator RequirementsThere are several parameters that must be considered before the design begins when designing a voltage-regulated oscillator, VCO. These describe the parameters of key performance required for the VCO. 5.1 VCO tuning rangeIt is clear that the oscillator that is powered by voltage must be able to tune over the range that the loop is supposed to work over. This requirement is not always simple to satisfy and, in certain extreme situations, can require the VCO or resonant circuit to be switched. 5.2 VCO tuning gainThe gain of the oscillator regulated by voltage is important. It is calculated per Hz (or V/MHz, etc) in terms of volts. It is the tuning shift for a given change in voltage, as indicated by the units. Any of the overall loop design factors and measurements are influenced by the voltage-controlled oscillator gain.At lower frequencies, the VCO response curves can be shown to be relatively straight. They typically flatten out at higher voltages, however, where the capacitance changes from the variable diodes decrease. 5.3 VCO V/f slopeFor any voltage-driven oscillator used in a phase-locked loop, it is a crucial requirement that the voltage to frequency curve is monotonic, i.e. it always shifts in the same context, usually increasing voltage frequency. If ti alters, as can generally occur in some instances due to spurious resonances, etc., this can cause the loop to become unstable. This must therefore be avoided if the phase-locked loop is to work satisfactorily. This curve shows a slight dip which will result in an unstable phase-locked loop.Phase noise efficiency: In some PLL applications, the phase noise performance of the voltage regulated oscillator is of particular importance - particularly where it is used in frequency synthesizers. Outside of the PLL loop bandwidth, the phase noise output of the voltage-regulated oscillator is the dominant factor in phase noise. While the operation of the PLL reduces close-in noise, there is no reduction in VCO phase noise outside the loop bandwidth. These are some of the main specifications that must be understood from the outset of the VCO design. Careful optimization of the tuned circuit Q, especially the use of variable diodes with as high a Q as possible, selection of the active system, optimization of the oscillator feedback.Ⅵ Voltage Controlled Oscillator FeedbackA VCO can be considered, like any oscillator, as an amplifier and a feedback loop. It is possible to denote the amplifier's gain as A and the feedback as B. For the circuit to oscillate, 360 ° must be the complete phase shift around the loop and unity must be the gain. Signals are fed back around the loop in this manner so that they are addictive and, as a result, any slight disturbance in the loop is fed back and builds up. Because the feedback network is frequency-dependent, the signal is based on one frequency, the feedback network is resonant, and a single frequency signal is produced. A typical emitter circuit is used by many oscillators and thus by VCOs. This in itself generates a 180° phase shift, leaving a further 180° to be given by the feedback network. A typical base circuit where there is no phase shift between the emitter and collector signals (assuming a bipolar transistor is used) can be used by other oscillator or VCO circuits and the phase shift network must provide either 0 ° or 360 °. The device requires a resonant circuit for the oscillator to oscillate on a given frequency to ensure that the oscillation happens on a given frequency. The resonant circuit may be one of a variety of LC resonant circuit configurations, depending on the circuit, or a quartz crystal, etc., in either series or parallel resonance.Ⅶ Colpitts & Clapp Voltage Controlled Oscillator CircuitsThe Colpitts and Clapp oscillator circuits are two commonly used formats for the VCO. Of the two, the most commonly used is the Colpitts circuit, but both are somewhat similar in their configuration. These circuits serve as oscillators because an active device such as a bipolar transistor with capacitors positioned between the base and the emitter (C1) and the emitter and the ground (C2) has been found to fulfill the requirements needed to provide adequate feedback for the output of the oscillator in the correct step. The C1:C2 ratio must be greater than one for the oscillation to take place. The resonant circuit is rendered between the base and ground by adding an inductive function. This consists of only an inductor in the Colpitts circuit, while an inductor and capacitor in series are used in the Clapp circuit.The resonance conditions are that:The capacitance for the overall resonant circuit consists of a series of combinations of the two C1 and C2 series capacitors. The capacitor in the series with the inductor is also used in the series with C1 and C2 in the case of the Clapp oscillator.The capacitance of the series is thus:It is important to change the resonant point of the circuit to make the oscillator tune. This is better accomplished in the case of the Colpitts oscillator, by inserting a capacitor across the indicator. Alternatively, the capacitor may be in series with the inductor for the Clapp oscillator. A circuit where the inductive reactance is located between the base and ground is often favored for high-frequency applications because it is less vulnerable to spurious oscillations and other anomalies.Ⅷ Voltage Controlled Oscillator Varactor IssuesIn order to ensure that the drive frequency in the tuned circuit is not too high, caution must be taken in the design of the circuit when varactor diodes are used inside a voltage-driven oscillator. If this is the case, then the varactor diodes, reducing the Q and increasing the number of spurious signals, can be forced into forwarding conduction. Within a VCO, there are two main types of varactor diode that can be used-the name refers to the diode junction and this impacts their output.8.1 Abrupt: Abrupt diodes have a relatively sharp transition between the areas of the diode, as the name implies. They are able to give a higher Q than their hyper-abrupt relatives, while abrupt varactor diodes do not offer such a high tuning range or linear transfer characteristic. This results in a better oscillator phase noise output regulated by voltage. The other point to note is that in order to have the appropriate tuning range, abrupt varactor diodes may need a high tuning voltage, as certain diodes may need a tuning voltage for the VCO to differ up to 50 volts or slightly more. This can cause problems with supplying the drive circuits with a voltage supply with a sufficiently high voltage.8.2 Hyper-abrupt: There is a relatively linear voltage for hyper-abrupt diodes: the capacitance curve. As a consequence, in some applications, they give a very linear tuning characteristic that may be needed. They can also tune over a wide range, and can normally tune over an octave range with less than a 20-volt tuning voltage shift. They do not give an especially high Q standard, however. Since this will deduct from the tuned circuit's overall Q, this will mean that the output of the phase noise is as good as that which can be obtained using an abrupt varactor diode. Despite the apparent simplicity of the circuit, the voltage-controlled oscillator design is far from trivial. A design would also involve careful optimization of the levels of input coupled with the system and layout. The VCO's design will need to carefully balance the requirements of sometimes conflicting requirements, such as a large tuning range and low noise phase. The standards of efficiency that can be achieved are surprisingly good once the design has been completely configured and the design has been completed.Ⅸ FAQ1. What is a Voltage Controlled Oscillator?A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscillation frequency. 2. What is the use of VCO in PLL?VCO stands for Voltage Controlled Oscillator. PLL operation is simple. VCO creates a high-frequency clock that is divided by some factor. This divided frequency is compared against a stable, reference, frequency using a phase comparator and difference (in-phase or frequency) is converted into voltage and fed back into VCO.Depending on voltage difference VCO frequency will be higher or lower.For example, let’s suppose we have VCO generating 10000 at 5V and divide by 100 dividers. The reference frequency is 90. The phase comparator will subtract two frequencies, 100 - 90 = 10 and will produce some voltage proportional to the frequency difference. This voltage is fed back into VCO and will increase 5V to 6V. Voltage increase will result in frequency drop. The process will continue as long as VCO generated frequency is equal to reference, in our case 9000.From above we see PLL output frequency is: Out = Ref * DividerVCO in RF is produced using varicap diodes - diodes which capacity depends on reverse voltage. Varicap diodes are available with capacities ranging from 1pF up to 500pF and capacity change 2 - 20. How PLL is stable depends on the reference clock and a phase comparator. In the simplest case phase comparator are the XOR gate and RC filter. 3. Why is VCO better than DCO?Of course, the real answer depends on the application. But one important application for a VCO is to implement a so-called phase-lock-loop. In that application, the smoothly continuous frequency vs voltage characteristic of a VCO would allow the VCO to track some variable reference frequency much more precisely. A 'typical' DCO in the same application could only achieve a step-wise approximation to tight tracking. Another, historically more important, application of a VCO is as the primary component of an FM broadcast transmitter. Using a conventional DCO in this application would typically produce an unacceptable amount of weird, noisy distortion in the demodulated audio as the DCO control input attempted to track the audio signal. But yes, it is possible to conceptualize, and even practical to design, a DCO whose frequency control steps are so fine and rapid that, used in an FM broadcast transmitter, the listener would not notice the step-wise tuning of the carrier. 4. What is the function of a VCO voltage-controlled oscillator?A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscillation frequency. 5. How does voltage control oscillator work?A voltage-controlled oscillator is an oscillator with an output signal whose output can be varied over a range, which is controlled by the input DC voltage. It is an oscillator whose output frequency is directly related to the voltage at its input. The oscillation frequency varies from few hertz to hundreds of GHz. 6. How do you make a voltage-controlled oscillator?To make a VCO, the oscillator needs to be tuned by a voltage. This can be achieved by making the variable capacitor from varactor diodes. The tuning voltage for the VCO can then be applied to the varactors. 7. What is the output of VCO?The VCO has an output power level of -3 dBm into 50 Ω with phase noise of -101 dBc/Hz typical at 100 kHz offset. The control voltage range is 0.4 to 2.4 volts, and load pulling is typically 0.75 MHz, pk-pk. Power supply pushing is 280 kHz/volt (typical). 8. What is the VCO tuning range?The VCO is linearly tunable from 806 to 1,113 MHz with a 34% tuning range controlled linearly by the tuning voltage. The phase noise of the VCO is -100.4 dBc/Hz at 100-kHz offset frequency from a 903 MHz carrier. 9. What is VCO phase noise?Characterizing Phase Noise. The term phase noise is widely used for describing short-term random frequency fluctuations of a. signal. Frequency stability is a measure of the degree to which an oscillator maintains the same value. 10. Which is the input terminal in a VCO?It generates the square wave at the output whose frequency is determined by a control voltage. The first op-amp works as an integrator. The control voltage is applied at the input terminal and due to the voltage divider arrangement, half the control voltage is applied at the positive terminal of the first op-amp. 

IntroductionSimply put, an oscillator is a device that can convert DC power into AC power without external signal excitation. The so-called "oscillation" implies alternating current. This article will mainly explain the circuits of different sine wave oscillators, including their working principles, how to realize their functions, circuit composition and comparison of advantages and disadvantages of different forms of circuits. This article uses a large number of circuit diagrams and formulas to explain in detail, which can help you understand in a better way.Basics of oscillators and their different typesCatalogIntroductionCatalogI The Principle of Feedback Oscillator1.1 How Does the Feedback Oscillator Work?1.2 Equilibrium Conditions1.3 Starting Conditions of the Oscillator1.4 Stable Conditions of the Oscillator1.5 General Composition of Sine Wave OscillatorII LC Oscillator Circuit2.1 The Composition Principle of the Oscillator2.2 Capacitive Feedback Oscillator2.3 Inductive feedback oscillatorIII RC Oscillator Circuit3.1 Brief Introduction of RC Oscillator and its Circuit3.2 RC Phase Shift Oscillator3.3 Wien Bridge OscillatorIV Quartz Crystal Oscillator Circuit4.1 What is a Quartz Crystal Oscillator?4.2 Quartz Crystal4.3 Quartz Crystal Oscillator CircuitV Non-sine Wave Generating Circuit5.1 What is a Non-sine Wave Generating Circuit?5.2 Rectangular Wave Generator5.3 Triangle Wave and Sawtooth Wave Signal GeneratorVI QuizⅦ FAQI The Principle of Feedback Oscillator1.1 How Does the Feedback Oscillator Work?The feedback oscillator is when the power is turned on, the various electrical disturbance signals in the loop are selected by the frequency selection network, and the signal of a certain frequency is fed back to the input terminal, and then the cycle of amplification → feedback → amplification → feedback , The amplitude of the signal increases continuously, and the oscillation is established from small to large. As the signal amplitude increases, the amplifier will enter a non-linear state, and the gain will decrease. When the feedback voltage is exactly equal to the input voltage, the oscillation amplitude will no longer increase and enter a balanced state. As can be seen from the figure below, the feedback oscillator is a closed loop composed of an amplifier and a feedback network. The amplifier is usually a tuned amplifier with an oscillation circuit as a load. The feedback network is generally a linear network composed of passive components.Figure1. Block Diagram of Feedback OscillatorIn order to generate self-oscillation, there must be positive feedback, that is, the signal fed back to the input terminal and the signal at the input terminal of the amplifier have the same phase. For the above figure, suppose the voltage amplification factor of the amplifier is K(s), the voltage feedback coefficient of the feedback network is F(s), and the closed-loop voltage amplification factor is Ku(s), thenby We can writeIf a certain frequency ω1=ω, then T(jω1) is equal to 1. From the above formula, we can see that Ku(jω) will tend to infinity. This shows that there is no external signal, and self-excited to produce signal output, namely self-oscillation. Therefore, the condition of self-oscillation is that the loop gain is 1.Definition:1.2 Equilibrium ConditionsThe equilibrium condition of the oscillator isthis can also be expressed asIf a certain frequency ω1=ω, then T(jω1) is equal to 1. From the above formula, we can see that Ku(jω) will tend to infinity. This shows that there is no external signal, and self-excited to produce signal output, namely self-oscillation. Therefore, the condition of self-oscillation is that the loop gain is 1. The above two formulas are the amplitude and the phase equilibrium conditions respectively. Equilibrium conditions are also called "two conditions for maintaining self-oscillation". The amplitude balance condition determines the amplitude of the oscillator output signal, and the phase equilibrium condition determines the frequency of the oscillator output signal. But it must be pointed out that the loop can only meet the phase equilibrium condition at a certain frequency (f), which is the resonant frequency (f0) of the loop.1.3 Starting Conditions of the OscillatorWhen the oscillator is in actual application, there should be no external signal Us(s) shown in Figure 1. The initial source of oscillation is electrical signals such as electrical shock and various thermal noises that inevitably exist when the oscillator is switched on.It can be seen from the establishment process of the oscillation that in order to make the oscillator start-up, the feedback voltage Uf and the input voltage Ui should be in phase at the beginning of the oscillation (that is, positive feedback); Uf>Ui should be required in amplitude, that is:Vibration conditions: φA+φF=2nπ(n=0,1,2,•••)AF>1 Simply put, as we know, the condition of unity gain must be met to make the oscillation continue. But to start the oscillation, the voltage gain of the positive feedback loop must be greater than 1, so that the amplitude of the output voltage can reach the required potential. Then the gain must be reduced to 1, so that the output voltage can be maintained at the required potential and the oscillation phenomenon can continue. Transition from |T(jω)|>1 to |T(jω)|=1 when the oscillator is workingThe amplifier must work in the linear amplification region of the transistor when amplifying small signals.When the oscillation is started, the amplifier works in the linear region. At this time, the output of the amplifier increases linearly with the increase of the input signal; as the amplitude of the input signal increases, the amplifier gradually enters the saturation or cut-off region from the amplification region, and enters a nonlinear state. The closed-loop gain of will decrease with the increase of the input signal, as shown in the figure below:Figure2. Graphical Representation of Amplitude ConditionsWhen the loop gain drops to |T(jω)|=1, the growth process of the amplitude will stop, and the oscillator will reach a balanced state and perform constant amplitude oscillation. It can be seen that the transition of the oscillator from amplified oscillation to steady amplitude oscillation is realized by the non-linear characteristics of the amplifier. When the oscillating circuit is powered on, the current of the transistor increases abruptly from zero, and the sudden change current contains a wide spectrum component. The start-up process of the circuit is very short! As long as the circuit satisfies the starting conditions, after the oscillator is powered on, there will be an output signal with stable amplitude at the output.Figure3. Circuit Start-up Process1.4 Stable Conditions of the OscillatorIf the loop gain characteristic has two equilibrium points A and B, among them, point A is stable and point B is unstable.Figure4. Stable Conditions of the OscillatorIt can be seen from the above discussion that in order to stabilize the equilibrium point, |T(ω0)| must have a negative slope change near UiA.Stable conditions are divided into amplitude stable conditions and phase stable conditionsTo make the amplitude stable, the oscillator must have the ability to prevent amplitude changes at its equilibrium point. Then the amplitude stability condition should beSince the feedback network is a linear network, which means the size of the feedback coefficient does not change with the input signal, so the amplitude stability condition can be written asThe phase stability depends on the increase of ω, and the decrease of , meaning that the phase characteristic of the parallel oscillator circuit ensures the phase stability.Therefore, the phase stability condition is. The higher the Q value of the loop,  the larger of the value of , and the better phase stability.1.5 General Composition of Sine Wave Oscillator(1) Amplifying circuit-realize energy control.(2) Positive feedback network-meets the conditions for starting vibration.(3) Frequency selection network-only one frequency satisfies the oscillation condition to obtain a sine wave output of a single frequency. Commonly used frequency selection networks include RC frequency selection and LC frequency selection(4) Amplitude stabilization link-makes the circuit easy to start and oscillate stably, with little waveform distortion. Examples of oscillation circuits:High frequency resonant amplifier and sine wave oscillatorFigure5. High Frequency Small Signal Resonant AmplifierFigure6. Mutual Inductance Coupled OscillatorII LC Oscillator CircuitLC oscillators can be divided into three types: mutual inductance coupled oscillators, inductive feedback oscillators and capacitive feedback oscillators according to their different feedback networks.This section focuses on different types of feedback LC oscillators and three-point oscillators.2.1 The Composition Principle of the OscillatorFigure7. General Form of Three-terminal OscillatorThe basic circuit is the so-called three-terminal (also called three-point) oscillator, which means the circuit formed by connecting the three terminals of the LC loop and the three electrodes of the transistor respectively, as shown in the figure. The three-terminal LC oscillator is a feedback type LC oscillator. In order to obtain positive feedback, the feedback circuit must make the instantaneous polarity of the transistor's AC voltage meet a certain phase relationship: when Vbe is negative, Vce should be positive, namely, Vbe and Vce are in reverse phase, and Veb and Vce are in phase. Only when the reactance Xce and Xeb have the same properties can they be guaranteed to be in phase. When the resistance of the loop element is very small, its influence can be ignored, and the influence of the input impedance and output impedance of the transistor can also be ignored. To maintain oscillation, the circuit must meet the requirements. Otherwise, the loop resonance condition cannot be met.The criteria for the three-terminal oscillator circuit to meet the phase equilibrium condition is as follows:(1) The reactance properties of Xce and Xeb are the same, but the reactance properties of Xcb are opposite. That is, ce and be are the same resisting piece, and cb resisting piece.(2) The oscillation frequency should satisfy 1Xo+Xcl-XolBased on this criterion, it can be quickly judged whether the oscillating circuit composition is reasonable or not.Three-terminal LC oscillatorThe three-terminal LC oscillation circuit is often used, and its operating frequency is about a few MHz to a few hundred MHz. The frequency stability is also higher than that of the transformer coupled oscillation circuit, which is about 10-3~10-4. After some frequency stabilization measures, it can be higher. There are many types of three-terminal LC oscillators, mainly: Inductance three-terminal type, also known as Hartley oscillator; capacitor three-terminal type, also known as Colpitts oscillator; series type improved capacitor three-terminal type, also known as Clapp parallel type improved capacitor three-terminal type , Also known as Sellier oscillator. The three-terminal oscillator has two basic circuits, as shown in the figure below.Figure8. Capacitive Feedback Oscillator and Inductive Feedback Oscillator2.2 Capacitive Feedback OscillatorCapacitive feedback three-terminal oscillator is an electronic component, also called Colpitts oscillator, which is a kind of self-excited oscillator. It is composed of a series capacitor, an inductance circuit and a positive feedback amplifier. It is named because the three end points of the two series capacitors of the oscillating circuit are connected to the three pins of the oscillating tube respectively.Figure9. Capacitive Feedback OscillatorAs shown in the figure, use C2 to feed back part of the voltage of the resonant tank to the base. The three end points of the LC resonant tank are respectively connected to the three electrodes of the transistor, so it is called a capacitive feedback three-terminal oscillator, or Colpitts oscillator. The vector analysis method can be used to prove that the circuit meets the phase balance condition. As long as the ratio of C1 and C2 is appropriately selected and the amplifier has enough amplification, the circuit can oscillate.Figure10. Capacitive Feedback OscillatorAdvantages of Colpitts circuit:(1) Good oscillation waveform;(2) The frequency stability of the circuit is high. If the capacitance of the circuit is increased appropriately, the influence of unstable factors on the oscillation frequency can be reduced;(3) The operating frequency of the three-terminal circuit of the capacitor can be made higher. The output and input capacitors of the oscillator tube can be directly used as the oscillation capacitor of the loop, and the operating frequency can reach a very high frequency range of tens of MHz to hundreds of МHz. Disadvantages of Colpitts circuit:When adjusting C1 and C2 to change the oscillation frequency, the feedback coefficient will also change, which will affect the starting conditions and working status. But as long as a variable capacitor is connected to both ends of L and C1 and C2 are fixed capacitors, the feedback coefficient will not be affected when the frequency is adjusted.2.3 Inductive feedback oscillator(1) Circuit compositionIn order to overcome the shortcomings that the transformer primary coil and the secondary coil in the transformer feedback oscillation circuit are not tightly coupled, the N1 and N2 of the transformer feedback oscillation circuit can be combined into one coil. As shown in the figure below, in order to strengthen the resonance effect, the capacitor C is connected across the entire coil. This is the inductive feedback oscillator circuit, or Harley oscillator.Figure11. Inductive Feedback Oscillator Circuit(2) Working principle✿The circuit includes four parts: amplifier circuit, frequency selection network, feedback network and non-linear element (transistor), and the amplifier circuit can work normally.✿Use the instantaneous polarity method to judge whether the circuit meets the phase condition of sine wave oscillation: disconnect the feedback, add the input voltage with frequency f0, give its polarity, and judge that the polarity of the feedback voltage obtained from N2 is the same as the input voltage , So the circuit satisfies the phase condition of sine wave oscillation.✿As long as the circuit parameters are selected properly, the circuit can meet the amplitude condition and produce sine wave oscillation. The following figure shows the AC path of the inductive feedback oscillation circuit. The three ends of the primary coil are connected to the three poles of the transistor, so the inductive feedback oscillation circuit is called an inductive three-point circuit.Figure12. AC Path of Inductive Feedback Oscillator Circuit(3) Advantages and disadvantagesThe coupling between N2 and N1 in the inductance feedback oscillation circuit is tight, the amplitude is large, and it is easy to oscillate; when C uses a variable capacitor, a wide adjustment range of oscillation frequency can be obtained, and the highest oscillation frequency can reach tens of MHz. Since the feedback voltage is taken from inductance, it has greater reactance to high-frequency signals, and the feedback signal contains more high-order harmonic components, and the output voltage waveform is not good. The following introduces two improved capacitor three-terminal oscillation circuits:Clap oscillator:The following figure (a) is the principle circuit of the Krapper oscillator, and (b) is its AC equivalent circuit. Its characteristic is that a capacitor C3 is added to the inductance branch of the aforementioned capacitive three-point oscillating resonant tank. Its value is relatively small, requiring C3<< C1, C3<< C2.Figure13. Clapp OscillatorRegardless of the influence of the capacitance between the poles, the total capacitance CΣ of the resonant circuit is the series connection of C1, C2 and C3, namely. Thus, the oscillation frequency is .The condition for the above formula to be true is that C1 and C2 must be selected relatively large. It can be seen that the influence of C1 and C2 on the oscillation frequency is significantly reduced, so the influence of the capacitance between the transistors connected in parallel with C1 and C2 is also very large. It is smaller, and the stability of the oscillation frequency is improved. Sellier oscillator:Figure14. Sellier Oscillator so the oscillation frequency:L is the inductance of the inductance coil of the resonant amplifier circuit; C is the total capacitance of the resonant circuit. In the LC resonance circuit, the inductance L(H)/capacitance C(F)=105~106, which can achieve better results.III RC Oscillator Circuit3.1 Brief Introduction of RC Oscillator and its Circuit● What is an RC oscillator?(1) The sine wave oscillator has no input signal and is a positive feedback amplifier with a frequency selection network. If resistors and capacitors are used to form a frequency selection network, it is called an RC oscillator, which is generally used to generate 1Hz-1MHz low-frequency signals. The frequency selection effect of the RC frequency selection network is not as good as that of the LC resonant circuit, so the waveform and stability of the RC oscillator are worse than that of the LC oscillator.(2) RC oscillator can be divided into sine wave oscillator and non-sine wave oscillator according to whether the output wave type is sine wave.(3) There are many kinds of RC oscillation circuits: bridge type, phase shift type, double T type, the most commonly used is bridge type oscillation circuit, namely RC series-parallel frequency selection network. ● Features of RC oscillator(1) RC phase-shift oscillator features: simple, poor frequency selection, unstable amplitude, inconvenient frequency adjustment, generally used in occasions with fixed frequency and low stability requirements. Frequency range: several hertz-tens of kilohertz(2) RC series-parallel network oscillator features: it can easily and continuously change the oscillation frequency, it is convenient to add negative feedback to stabilize the amplitude, and it is easy to get a good oscillation waveform.(3) Double T frequency selective network oscillator characteristics: good frequency selection characteristics, difficult frequency modulation, suitable for generating single frequency oscillation. ● RC oscillator circuitThe oscillating circuit composed of RC frequency selection network is called RC oscillating circuit, which is suitable for low-frequency oscillation, and is generally used to generate low-frequency signals of 1Hz~1MHz. The circuit is composed of four parts: amplifier circuit, frequency selection network, positive feedback network, and amplitude stabilization link. The main advantage is simple structure, economic and convenient. According to the different forms of the RC frequency selection network, the RC oscillator circuit can be divided into an RC lead (or lag) phase shift oscillator circuit and a Wien circuit oscillator circuit. For RC oscillator circuits, increasing the resistance R can reduce the oscillation frequency, and increasing the resistance does not need to increase the cost. The frequency of the sine wave generated by the commonly used LC oscillator circuit is relatively high. If a sine wave with a lower frequency is to be generated, the oscillation circuit must have a larger inductance and capacitance. This will not only cause the components to be bulky, heavy and inconvenient to install, but also difficult to manufacture. high cost.  Therefore, the sinusoidal oscillation circuit below 200kHz generally adopts an RC oscillation circuit with a lower oscillation frequency.3.2 RC Phase Shift OscillatorThe phase shift oscillator is an oscillator composed of an advanced phase shift or a lag phase shift circuit as a frequency selection network and an inverting amplifier. It has the advantages of simple circuit, economy and convenience, but the effect of frequency selection is poor, the amplitude is not stable enough, and the frequency adjustment is inconvenient. Therefore, it is generally used for occasions with fixed frequency and low stability requirements. Its oscillation frequency is:Figure15. RC Phase Shift Oscillator Schematic Diagram3.3 Wien Bridge OscillatorThe RC series-parallel frequency selection network and amplifier can be combined to form an RC oscillator circuit, and the amplifier part can be an integrated operational amplifier. As shown in the figure, the RC series-parallel frequency selection network is connected between the output of the operational amplifier and the non-inverting input to form positive feedback. Rt and R1 are connected between the output of the operational amplifier and the inverting input to form negative feedback. . The positive feedback circuit and the negative feedback circuit constitute a Wien bridge circuit, and the input and output ends of the operational amplifier are respectively connected across the diagonal of the bridge. Therefore, this kind of oscillation circuit is called a Wien bridge oscillation circuit.Figure16. Wien Bridge OscillatorThe oscillating signal is input from the non-inverting terminal, so a non-inverting amplifier is formed. The output voltage is in phase with the input voltage, and the closed-loop voltage amplification factor is equal to: When the RC series-parallel frequency selection network is ω=ω0=1/RC, Fu=1/3, εf=0, so as long as |Au|=1+(Rt/R1)>3, that is, Rt>2R1, oscillation The circuit can meet the self-excited oscillation amplitude and phase start-up conditions to produce self-excited oscillation, the oscillation frequency f0=1/2πRC. Using double adjustable potentiometer or double adjustable capacitor can easily adjust the oscillation frequency. In the commonly used RC oscillator circuit, the high stability capacitor is generally used to switch the frequency band (coarse frequency adjustment), and then the double variable potentiometer is used to fine-tune the frequency.IV Quartz Crystal Oscillator Circuit4.1 What is a Quartz Crystal Oscillator?Quartz crystal oscillator refers to a device made on the principle that the crystal resonates due to the piezoelectric effect when the frequency of the electrical signal is equal to the natural frequency of the quartz crystal. It is a key component of crystal oscillators and narrow-band filters.Although the appearance, size and frequency of the quartz crystal oscillator are different, the structure principle is basically the same. In order to improve the stable and reliable operation of the quartz crystal, the shell components of the quartz crystal oscillator will be sealed and evacuated. Or fill with nitrogen.4.2 Quartz Crystal(1) StructureFigure17. Structure of the Quartz Crystal(2) Basic characteristicsApplying an electric field between the plates→mechanical deformation of the crystalMechanical force is applied between the plates → the crystal generates an electric fieldPiezoelectric effect: alternating voltage → mechanical vibration → alternating voltageWhen the alternating voltage frequency = natural frequency, the amplitude is the largest → piezoelectric resonanceThe natural frequency of mechanical vibration is related to the size of the wafer, and the stability is high.4.3 Quartz Crystal Oscillator CircuitThe high quality factor of quartz crystal is used to form an LC oscillator circuit.(1) Parallel Type quartz crystal oscillatorFigure18. Parallel Type Quartz Crystal Oscillator Quartz crystal works between fs and fp, which is quite a large inductance, and forms a capacitive three-point oscillator with C1 and C2. Because the Q value of the quartz crystal is very high, which can reach more than several thousand, the circuit can obtain high oscillation frequency stability.Figure19. Frequency Characteristics of Parallel Quartz Crystal Oscillator (2) Series type quartz crystal oscillatorFigure20. Series Type Quartz Crystal Oscillator Circuit The quartz crystal works at fs, which is resistive and has the smallest impedance, the strongest positive feedback, and zero phase shift, which meets the phase balance condition of oscillation.For frequencies other than fs, the impedance of the quartz crystal increases, and the phase shift is not zero, then the oscillation condition is not met, and the circuit does not oscillate.Figure21. Frequency Characteristics of Series Quartz Crystal OscillatorV Non-sine Wave Generating Circuit5.1 What is a Non-sine Wave Generating Circuit?It is composed of an integrating circuit and a hysteresis comparator circuit. The role of the integrator circuit is to produce a transient process. The hysteresis comparator acts as a switch, that is, the steady state is destroyed by the continuous closing of the switch, and a transient process is generated.Commonly used non-sine wave generating circuits include rectangular wave generating circuits, triangular wave generating circuits and sawtooth wave generating circuits, etc. They are often used as signal sources in pulse and digital systems.5.2 Rectangular Wave GeneratorIt is composed of hysteresis comparison circuit and RC timing circuit. The output has no steady state and there are two transient states; if the output is high level, it is defined as the first transient state, and the output is low level as the second transient state.Basic components:(1) Switching circuit: The output has only two situations of high level and low level, called two states; therefore, a voltage comparator is used.(2) Feedback network: self-control, when the output is in a certain state, it breeds the condition of turning into another state. Feedback should be introduced.(3) Delay link: Make the two states maintain a certain period of time and determine the oscillation frequency. Use RC circuit to achieve.Circuit composition:Figure22. Rectangular Wave Generating Circuit5.3 Triangle Wave and Sawtooth Wave Signal GeneratorThe circuit structure of the triangle wave generator: hysteresis comparator + inverting integratorworking principle:Figure23. Circuit of Triangle Wave Generator Sawtooth wave generator: change the forward and reverse charging time constant of the integrator, thereby changing the duty cycle.Figure24. Circuit Diagram of Sawtooth Generator uo1=+UZ, D is cut off, charging time constant: R4C.uo1=-UZ, D is on, charging time constant: (R6∥R4)C≈R6C.Figure25. The Waveform of the Sawtooth GeneratorVI QuizLC resonant circuits are used in:a) RF and ultrasonic oscillators.b) AF and ultrasonic oscillators.c) LF sweep oscillators.d) Variable frequency crystal oscillators. Answer: aⅦ FAQ1. What are the uses of an oscillator?Oscillators have very high precision and accuracy usually <100 ppm variation at a max. So with this kind of accuracy, the oscillator can be used as a clock of the microcontroller (the clock is the most essential part of the microcontroller, without an accurate clock, the functionality will be erratic because we cannot expect the output at the same time we have designed it for). All the quartz-based watches use an Oscillator (32kHz quartz crystal) to keep the time. SO if your timekeeping devices are running with an oscillator, you can imagine the accuracy.Oscillators can additionally be used to generate waveforms required in test benches. In almost all the applications where timing and synchronization are very essential, an oscillator finds its place. For example, in communication systems (whichever electronic communication you consider let it be a telephone, lan, anything) an oscillator is the heart.An oscillator can be used in power systems to generate accurate power waveforms. 2. What is the function of a local oscillator?A local oscillator is used in transmitters and receivers to add or subtract an amount to a basic carrier and modulation. Very handy, as it’s easiest to build up a carrier and modulate it at a low frequency, like 445Kc or 10.7MHz, and then add to it a “LO” to get it up to the FM band or the Gigahertz Wifi or radar bands. The same thing on receive, you first use a 'LO' to subtract down to an intermediate frequency where it’s so much easier to amplify and filter. 3. How do you make a crystal oscillator?The simplest is to use a logic inverter. Put a crystal between the input and output. Some schematics show some caps from the crystal legs to the ground and some show a series resistor. 4. Which type of circuit is used in the oscillator?Types of Oscillators: Harmonic Oscillators & Crystal Oscillators. Harmonic or linear oscillators produce a sinusoidal output where a signal increases and decreases at a predictable level over time. Two basic types are RC, or resistor/capacitor circuits, as well as LC, or inductor-capacitor circuits. 5. What is an Oscillator and the types of oscillators?An oscillator is a type of circuit that controls the repetitive discharge of a signal, and there are two main types of the oscillator; a relaxation, or a harmonic oscillator. This signal is often used in devices that require a measured, continual motion that can be used for some other purpose. 6. What is the basic principle of an oscillator?There are many types of electronic oscillators, but they all operate according to the same basic principle: an oscillator always employs a sensitive amplifier whose output is fed back to the input in phase. Thus, the signal regenerates and sustains itself. This is known as positive feedback. 7. What is the working of the oscillator?Oscillators convert direct current (DC) from a power supply to an alternating current (AC) signal. They are widely used in many electronic devices ranging from simplest clock generators to digital instruments (like calculators) and complex computers and peripherals etc. 8. How does an oscillator work without input?An oscillator circuit uses a vacuum tube or a transistor to generate an AC output. ... For continuously generating output without the requirement of any input from the preceding stage, a feedback circuit is used. From the above block diagram, the oscillator circuit produces oscillations that are further amplified by the amplifier. 9. What causes oscillation?If a constant force such as gravity is added to the system, the point of equilibrium is shifted. ... In the spring-mass system, oscillations occur because, at the static equilibrium displacement, the mass has kinetic energy which is converted into potential energy stored in the spring at the extremes of its path. 10. What is the difference between oscillator and inverter?The oscillator is a generalized term for an active circuit that produces a periodic waveform. The inverter is a specialized term for a system that contains an oscillator and produces large amounts of power(such as AC) from a source (like a DC battery). The oscillator has no input and produces an oscillating wave as output. 

CategoryⅠ IntroductionⅡ Development Background  2.1 Limitations of Microwave Oscillators  2.2 Origin of OEOⅢ Working Principle of OEO  3.1 The basic structure of OEO  3.2 Principle-based improvement directionⅣ Operating Characteristics of OEO  4.1 Advantage Performance  4.2 Disadvantage PerformanceⅤ Application of Optoelectronic Oscillator  5.1 Light Pulse Output  5.2 Clock ExtractionⅥ SummaryⅦ FAQ Ⅰ IntroductionThe optoelectronic oscillator (OEO) represents the first practical microwave oscillator that uses optical energy storage elements to generate signals with high spectral purity in the frequency range of several hundred MHz to more than 100 GHz. Many light wave energy storage components, such as fiber Fabry-Perot resonators, fiber ring resonators, optical micro disc resonators, etc. can be used to form OEO. It is a long fiber loop. The use of optical resonators can greatly reduce the size of OEO. Especially the optical microdisk resonator, which is a key component of integrating OEO in a single chip.  Figure1. Opto-Isolator OscillatorⅡ Development Background2.1 Limitations of Microwave OscillatorsGenerally speaking, the quality of the microwave signal generated by the microwave oscillator depends on the energy storage performance of the oscillation cavity. To produce high-quality microwave signals, a high-Q and low-loss energy storage unit is required. Current microwave oscillators are mostly based on electronics (such as dielectric oscillators) and acoustic (such as crystal oscillators) energy storage elements. When these components operate at frequencies above GHz, the energy storage characteristics will drop sharply, and the phase noise and spectral purity of the high-frequency microwaves produced will be poor. 2.2 Origin of OEOIn 1996, XSYao and L. Maleki of the California Institute of Technology Jet Power Laboratory developed a microwave oscillator based on a photonic energy storage unit during the use of photonics technology to improve the performance of a microwave system. This oscillator was named optoelectronic oscillator (OEO). Compared with microwave oscillators based on electronics and acoustic energy storage units, optoelectronic oscillators can generate high-purity microwave or millimeter-wave signals from several MHz to hundreds of GHz, and the Q value of their energy storage elements is as high as 1010, which generates high-frequency signals. The phase noise is as low as -163dBc / Hz at a frequency offset of 10kHz, and has both optical and electrical outputs. It is a very ideal high-performance microwave oscillator and is expected to be widely used in the future. Ⅲ Working Principle of OEO3.1 The basic structure of OEOThe basic structure of the optoelectronic oscillator is shown in Figure 2. It is a positive feedback loop composed of laser, electro-optic modulator, high Q optical energy storage unit (such as a certain length of optical fiber), photodetector, bandpass filter, microwave amplifier, phase shifter and microwave coupler. The energy of the oscillation comes from the injected light in front of the electro-optic modulator. After the injected light is modulated by the electro-optic modulator, it becomes an optical signal carrying a specific frequency. This optical signal is converted into an electrical signal by a photodetector, amplified, and then band-pass filtered. The filter filters out a specific frequency, part of which is used for output, and part of which is fed back into the microwave input port of electro-optic modulation to complete a cycle. After continuous cycling, a stable oscillation is finally formed. Since the optical oscillator uses a high-Q optical energy storage unit such as a low-loss long fiber, the output signal has extremely low phase noise. Figure2. Basic Structure of OEO3.2 Principle-based improvement directionIn addition, the loss in the optical energy storage unit such as optical fiber does not change with the change of microwave frequency, so theoretically the performance of the output signal of the optoelectronic oscillator will not deteriorate with increasing frequency. After nearly two decades of continuous exploration, the research on opto-electronic oscillators has made rapid progress. In the United States, opto-electronic oscillators have been successfully applied in cutting-edge technologies such as drones as high-quality local oscillators.  Nevertheless, in order to obtain a wider range of applications, optoelectronic oscillators need to be continuously improved in terms of performance and stability. Current research on optoelectronic oscillators is mainly focused on reducing phase noise, improving side mode suppression ratio, improving frequency stability, expanding output frequency, improving frequency tuning performance, miniaturization and multi-frequency oscillation, etc.Details are as follows:  (1) Phase NoiseThe phase noise of the output signal of the optoelectronic oscillator mainly comes from the thermal noise, scattered noise, and relative intensity noise of active devices such as lasers, photodetectors, and amplifiers. Phase noise can be reduced by optimizing the structure of microwave photonic links and the way the devices work. In experiments by D. Eliyahu and some others that produced extremely low phase noise (-163 dBc / Hz @ 6kHz) signals, a high power Nd: YAG laser with low relative intensity noise and an array amplifier with low phase noise were used. P.S.Devgan et al. Used low-biased Mach-Zehnder modulators and optical amplifiers to achieve an all-optical gain optoelectronic oscillator.  Compared with optoelectronic oscillators using electric amplifiers, the phase noise of this solution has been improved by 10dB. In addition, the use of high-power photodetectors can effectively reduce white noise, while the use of photodetector arrays to receive signals can effectively reduce the effects of flicker noise.Figure3. Phase Noise Modulation(2) Side Mode SuppressionIn order to obtain microwave output with low phase noise, the resonator of the photo-electric oscillator must have a very high Q value (Q = 2πfτ, f is the center frequency, and τ is the energy decay time), that is, a very large energy decay time is required. A larger τ can be obtained by increasing the fiber length, but as the fiber length increases, the longitudinal mode spacing (Δf = 1 / τ) in the cavity of the photo-electric oscillator decreases（As low as several tens of kHz）, in order to effectively suppress the non-oscillation mode and select a single oscillation frequency, a relatively narrow microwave band-pass filter is required. ①Dual-loop optoelectric oscillatorOne way to suppress side modes is to use a dual-loop optoelectronic oscillator. Two optical fiber loops of different lengths are formed in the cavity of the photo-electric oscillator. Only modes that satisfy the conditions for selecting the two loops at the same time can start oscillation. By selecting appropriate loop lengths, single-mode vibration can be achieved. The dual-loop optoelectronic oscillator scheme can be divided into an optical-domain coupled dual-loop structure and an optical-domain coupled dual-loop structure.  This research group proposed a dual-loop optoelectronic oscillator based on polarization modulation and polarization division multiplexing. The polarization beam splitter not only realizes the conversion of polarization modulation to intensity modulation, but also realizes that the incident light wave is divided into two orthogonal polarization states to form a double loop. The side-mode rejection ratio of the 10GHz signal generated by this solution reached 78dB. Compared with the electric-domain coupled dual-loop scheme, the optical-domain coupled scheme requires only one photodetector. Optical domain coupling dual loop schemes can also be implemented using wavelength division multiplexing technology.Figure4. A Dual-loop Optoelectronic Oscillator②Coupled optoelectronic oscillatorAnother method to suppress side modes is to use a coupled optoelectronic oscillator (COEO). The coupled optoelectronic oscillator includes two parts: an actively mode-locked laser loop and an optical feedback loop. The active mode-locked fiber laser loop can effectively increase the Q value of the oscillator. Therefore, a shorter fiber length can be used to obtain low phase noise. This research group used a non-pumped erbium-doped fiber to achieve a 10.7GHz stable coupled photo-electric oscillator with a phase noise below -120dBc / Hz @ 10kHz. (3) Frequency StabilityThe factors that affect the frequency stability of the optoelectronic oscillator are mainly two aspects:  ①The high-Q components in the system (including long optical fibers and narrow-band electrical filters) are susceptible to changes in the environment, and the output frequency is changed to cause the output frequency. Instability, especially the change of equivalent cavity length caused by environmental factors such as temperature. ②Because the filters used in optoelectronic oscillators usually have a relatively large passband range, they are within the gain bandwidth of the loop. There will be many side molds. One of these side modes may obtain sufficient gain during the change of cavity length to replace the original starting frequency, resulting in unstable starting frequency. In addition, the bias point drift problem of common electro-optic modulators will also affect the stability of the output frequency, but isolating the optoelectronic oscillator from the environment or using a temperature control device can reduce the impact of environmental changes on the system. For example, in experiments of XSYao, the optoelectronic oscillator was placed in a foam-filled box to isolate the influence brought by vibration. The active phase-locked loop circuit control is used to lock the oscillation signal of the optoelectronic oscillator to an external reference source, which can also effectively improve the frequency stability of the optoelectronic oscillator.Figure5. Frequency Stability(4) Working FrequencyTheoretically, the optoelectronic oscillator can generate signals from several MHz to hundreds of GHz, and the phase noise has nothing to do with frequency, but the high-frequency millimeter wave optoelectronic oscillator is difficult to realize. This is mainly due to the use of microwave devices such as photoelectric modulators, microwave couplers, microwave phase shifters, microwave amplifiers, and microwave transmission lines in optoelectronic oscillators, whose operating frequency is limited by electronic bottlenecks. Although there have been recent reports of high-frequency microwave or millimeter-wave devices, these devices are generally expensive, consume large power, and have poor performance. In response to the above problems, M. Shin et al. Used the LiNbO3 Mach-Zehnder modulator's half-wave voltage to the proportional relationship between the wavelength to achieve the simultaneous generation of 10GHz fundamental frequency and 20GHz octave signal. (5) TunabilityIn order to generate a broadband adjustable microwave signal, the optoelectronic oscillator needs to use a broadband adjustable high Q filter, which can be a tunable electrical filter, an optical filter, or a microwave photon filter. Limited by the electronic bottleneck, the tuning range of the output signal of the optoelectronic oscillator using a tunable electrical filter is limited. Optoelectronic oscillators based on microwave photonic filters usually have a large tuning range.Figure6. Schematic of The Tunable Opto-electronic Oscillator(6) Miniaturization ResearchOptoelectronic oscillators usually include laser sources, intensity modulators, long fiber delay lines, photodetectors, electrical amplifiers, electrical phase shifters, electrical bandpass filters, and other electrical or optical devices. These discrete electrical and optical components make the optoelectronic oscillator bulky and cause large power losses. By using high-Q optical resonators (such as whispering wall mode resonators) to replace fiber lengths of several kilometers, the size of the energy storage unit of a photo-electric oscillator can be significantly reduced. (7) Multi-frequency OscillationOptoelectronic oscillators usually only produce a pure single frequency signal. In applications such as wideband channelized receivers and multi-band radars, signals of multiple frequencies are required. In 2012, F. Kong et al. Used a birefringence characteristic of a phase-shifted Bragg grating to implement a dual-frequency optoelectronic oscillator. The disadvantage of this solution is that it can only generate signals of two frequencies, and the system is very sensitive to the environment. If a multi-frequency optoelectronic oscillator based on a single-phase modulator and a multi-wavelength light source are used, a single-passband tunable microwave photon filter can be formed on each optical carrier. By increasing the number of optical carriers, it will be easy to obtain more channels of different frequency signal output. Ⅳ Operating Characteristics of OEO4.1 Advantage PerformanceOptoelectronic oscillator is generally a positive feedback loop composed of light source, intensity modulator, filter and photodetector (PD). It takes advantage of the low loss characteristics of modulators and optical fibers to turn continuous light into stable, clean spectrum RF/microwave signals. The continuous light emitted by the laser is transmitted to the photodetector through the optical fiber after passing through the electro-optic modulator. The photodetector converts the light into an electrical signal and enters the frequency selection, amplification, and feedback modulation device.  During this process, the active device will generate noise disturbances of different frequencies. These disturbances are filtered by the filter at the output to the desired frequency and used to feedback and control the electro-optic modulator. The amplifier in the loop provides gain, and after several cycles of the signal, a stable oscillation can be established, and its oscillation frequency is mainly determined by the passband characteristics of the filter. 4.2 Disadvantage PerformanceAlthough the performance of the optoelectronic oscillator is outstanding, its system composition also determines some of its shortcomings. First of all, in order to obtain a high Q signal output, a long fiber is generally used in the cavity. At this time, the length of the cavity also determines the interval between the oscillation modes. The longer the cavity, the smaller the mode interval. In theory, a sufficiently narrow filter can be used to filter out unwanted modes, but it is quite difficult to obtain the device.  Secondly, in terms of the phase noise of the signal, the relative intensity noise of the light source, the photodetector and the electric amplifier will all affects the phase noise of the resulting microwave signal. Excessive bandwidth of filters and amplifiers will also reduce the signal-to-noise ratio in the passband range and affect the quality of the oscillation frequency.  Finally, because the loop is mainly composed of optical fibers, its cavity length is easily affected by environmental conditions and stress. The change causes the change of the fundamental frequency of the oscillation to cause the output frequency to drift or hop. In addition, the long optical fiber occupies a relatively large volume, which causes obstacles to the miniaturization and integration of the entire optoelectronic oscillator system. Solving the above problems is some of the key work for the final practical use of optoelectronic oscillators. Figure7. Cristal Oscillator Ⅴ Application of Optoelectronic OscillatorThe basic function of the optoelectronic oscillator is to generate high-quality optical and electrical microwave signals, but after being updated, it has also derived some new applications. In these applications, the electrical output of the photo-oscillator basically keeps the microwave signal output, but some changes occur in the light output part.5.1 Light Pulse OutputIn 1997 and 2000, X. Steve Yao and others successively analyzed and demonstrated the hybrid structure (COEO) of the optical resonator and optical oscillator loop provided by SOA to generate electric microwave signals and light pulses. This solution is similar to a regenerative mode-locked laser.  The main difference is that the photoelectric loop of COEO needs to be oscillated, and the final output mode is constrained by the selection of the two loops. In 2007, Ertan Salik demonstrated a COEO structure based on erbium-doped fiber amplifier (EDFA) to provide optical path gain, and obtained a 9.4 GHz microwave signal with ultra-low phase noise of -150 dBc / Hz (at a frequency offset of 10 to 100 kHz). Output and light pulse output with only 2 fs jitter. The optical pulse output mechanism of this structure is based on a fiber mode-locked laser. Therefore, in order to obtain high-performance output, there are high requirements on the design of the cavity length stabilization, dispersion control, and polarization maintenance of the optical cavity. Another feasible solution is to generate light pulses by changing the photoelectric modulation characteristics in the optoelectronic oscillator loop. In 2003, Jacob Lasri et al. Used electro-absorption modulator (EAM) to replace Mach-Zehnder intensity modulation (MZM) in the traditional scheme. By controlling the bias of EAM, a narrow modulation transmission window was obtained. Electric microwave signal and light pulse output. If a multi-wavelength light source is used in the light source part, this structure can also conveniently generate multi-wavelength light pulses. The structure of this scheme is relatively simple, but EAM generally has a large insertion loss, and the resulting pulse width is also wide.Figure8. Electro Absorption ModulatorIn addition, using a semiconductor laser operating under gain switching conditions or using a large-signal direct-modulation as the light source of the photo-electric oscillator, it is possible to obtain an electric microwave signal and an optical pulse output without requiring an additional modulator.5.2 Clock ExtractionBecause the structure of the optoelectronic oscillator has the function of frequency selection and amplification feedback, no matter whether the optical or electrical signal is injected into the optoelectronic oscillator, its clock signal (or frequency-divided clock) can be changed as long as it falls within the passband of the filter. The output can be recovered after locking and regeneration.  The maximum recoverable clock frequency is determined by the center frequency of the filter in the loop and the bandwidth of the modulator and the photodetector. X. Steve Yao et al.  Later, Caiyu Loun and others analyzed the extraction scheme of the frequency-divided clock based on the optoelectronic oscillator in 2002. By using the output electrical signal of the optoelectronic oscillator as a trigger signal to observe the injected optical signal on an oscilloscope, the electrical signal at this time can be determined. Whether the output is a divided clock of the injected signal, and experimentally verified the divided clock extraction under the condition of 10 Gb / s injected signal. In 2005, Hidemi Tsuchida and his partners demonstrated a frequency-divided clock extraction experiment with an injected signal rate of 40 Gb / s and 160 Gb / s. Figure9. Clock RecoveryIt should be noted that this method also provides a new idea for clock extraction of non-return-to-zero (NRZ) signals. In theory, there is no obvious clock component for NRZ signals to be extracted, but as long as the frequency selection of the optical oscillator filter is carefully adjusted. The clock signal of the injected NRZ code signal can be found and generated by the window. Li Huo et al. proposed the clock of the injected 10 Gb / s NRZ code signal, and obtained the converted zero (RZ) at the same time in the optical output part of the optoelectronic oscillator. The EAM-based optoelectronic oscillator can also complete the clock recovery of the RZ code signal. In the experiments demonstrated by Jaoob Lasri et al., In order to obtain the optical clock pulse signal at the same time, a DC light with a wavelength different from the wavelength of the injected signal light was added. Since the power change of the injected signal light will form a periodic switching window on the EAM and transfer the clock information to the simultaneously injected DC light, the wavelength of this DC light is selected by the optical filter to complete the Oscillation can generate an electrical clock signal and simultaneously obtain an optical clock pulse at that wavelength. It should be said that in addition to optical and electrical microwave sources, pulse sources and clock extraction systems, there are other applications, such as generating dual-frequency signals, inserting encoders to form multi-function signal generators, and so on. However, various applications are based on the feature that the photo-electric oscillator structure can automatically generate stable low-phase noise microwave signals. Therefore, as long as it focuses on various fields that require high-quality microwave signals, many new applications can be developed. Ⅵ SummaryIt can be seen that as a high-quality optical and electrical microwave signal generator, the optoelectronic oscillator has great advantages and wide application prospects. Various unique application methods also lay the foundation for the multifunctionalization of the optoelectronic oscillator.  However, it is undeniable that the current optoelectronic oscillator is still mainly in the laboratory research stage. There is still a period of time before it can be practically applied in the national economic construction and the development of national defense science and technology. Its main constraints focus on how to make the optoelectronic oscillator system into a compact, integrated, and compact frequency control system. The realization of these requirements depends on the development and manufacturing process of new photonic microwave devices and corresponding active devices.  Although there are no direct targets for optoelectronic oscillators, recent literature reports show some opportunities. For example, utc-pd (uni-traveling -Carrier Photodiode) in optoelectronic detection can receive high optical power and have high power electrical signal output, which can reduce or avoid the use of electric amplifiers in optoelectronic oscillators. The development of integrated semiconductor laser and modulator technology makes it possible to miniaturize the light source and feedback modulation of the photoelectric oscillator. The high Q value photonic filter with semiconductor structure is helpful to realize the system integration and tunability of optoelectronic oscillator. It is believed that with the gradual maturity of these technologies, the optotoelectric oscillator will be applied in practice and play its due contribution.  Ⅶ FAQ1. What do you mean by optoelectronic devices?Optoelectronic devices are electrical-to-optical or optical-to-electrical transducers or instruments that use such devices in their operation. ... Optoelectronics is based on the quantum mechanical effects of light on electronic materials, especially semiconductors, sometimes in the presence of electric fields. 2. What are optoelectronic devices give example?Examples of optoelectronic devices are: laser diodes, superluminescent diodes and light-emitting diodes (LEDs), converting electrical energy to light. photodetectors (e.g. photodiodes and phototransistors), converting optical signals into electrical currents. 3. What is the working principle of optoelectronic devices?Optoelectronic devices are primarily transducers i.e. they can convert one energy form to another. These devices produce light by expending electrical energy. They can also detect light and transform light signals into electrical signals for processing by a computer. 4. What are Optoelectronics used for?Optoelectronic devices refer to components used to detect or emit electromagnetic radiation, typically in the visible and near-infrared (NIR) regions of the electromagnetic spectrum. Each of these functions exploits the photoelectric effect of materials, also known as light-matter interaction. 5. Is LDR an optoelectronic device?There are two types of optoelectronic devices. These are Photoconductive devices and Photovoltaic devices. Photoconductive devices detect variations in light intensity to activate or inhibit electronic circuits. LDR, Photodiodes and Phototransistors fall in this category. 6. What are optoelectronic junction devices?Optoelectronic junction devices are p-n junction devices in which, carriers are generated by photons. Photodiodes, light-emitting diodes (LEDs) and solar cells are examples of optoelectronic devices. A photodiode is a device that is used to detect optical signals. 7. Which substance has optoelectronic property?Unlike the majority of electronic devices, which are silicon-based, optoelectronic devices are predominantly made using III–V semiconductor compounds such as GaAs, InP, GaN, and GaSb, and their alloys due to their direct bandgap. 8. Who discovered optoelectronics?Three Bell Laboratories scientists, William Shockley, John Bardeen, and Walter Brattain, demonstrated the first transistor-based on point-contact germanium (Ge) device. On the other hand, the semiconductor laser was discovered 15 years later in 1962. 9. Is solar cell an optoelectronic device?Solar Cell is another example of an Optoelectronic device based on the p-n junction, and the operating mechanism of a solar cell is essentially the same as that of Photodiode in that, a p-n junction is illuminated by light and the photogenerated carriers are separated by the built-in electric field across the p-n junction. 10. What are optoelectronic devices Name any two optoelectronic devices?Examples of optoelectronic devices include telecommunication laser, blue laser, optical fiber, LED traffic lights, photo diodes and solar cells. The majority of the optoelectronic devices (direct conversion between electrons and photons) are LEDs, laser diodes, photo diodes and solar cells. 

As one of the world-leading research and innovation hub in nanoelectronics and digital technology,IMEC announced at the 2017 Symposia on VLSI Technology and Circuits that the world's first demonstration of a vertically stacked ferroelectric,AI doped HfO2 device for NAND applications.Using a new material and a novel architecture,imechas created a non-volatile memory concept with attractive characteristics for power consumption, switching speed, scalability and retention. The achievement shows that ferro-electric memory is a highly promising technology at various points in the memory hierarchy, and as a new technology for storage class memory. Imec will further develop the concept in collaboration with the world's leading producers of memory ICs.  Ferro-electric materials consist of crystals that exhibit spontaneous polarization; they can be in one of two states, which can be reversed with a suitable electric field. This non-volatile characteristic resembles ferromagnetism, after which they have been named. Discovered more than five decades ago, ferro-electric memory has always been considered ideal, due to its very low power needs, non-volatile character and high switching speed. However, issues with the complex materials, the breakdown of the interfacial layer and bad retention characteristics have presented significant challenges. The recent discovery of a ferro-electric phase in HfO2, a well-known and less complex material, has triggered a renewed interest in this memory concept.  "With HfO2, there is now a material with which we can process ferro-electric memories that are fully CMOS compatible. This allows us to make a ferro-electric FET (FeFET) in both planar and vertical varieties," noted Jan Van Houdt, imec's chief scientist for memory technology. "We are working to overcome some of the remaining issues, such as retention, precise doping techniques and interface properties, in order to stabilize the ferro-electric phase. We are now confident that our FeFET concept has all the required characteristics. It is, in fact, suitable for both stand-alone and embedded memories at various points in the memory hierarchy, going all the way from non-volatile DRAM to Flash-like memories. It has particularly interesting characteristics for future storage-class memory, which will help overcome the current bottleneck caused by the differences in speed between fast processors and slower mass memory." Imec recently presented the first, extremely positive results to its partners. The research center is now offering further development and industrialization of the vertical FeFET as a program to all its memory partners, which include the world's major companies producing memory ICs.  Van Houdt explained "FeFETs can be used as a technology to build memory very similar to Flash-memory, but with additional advantages for further scaling, simplified processing, and power consumption,with our longstanding R&D and processing experience on advanced Flash, we are uniquely positioned to offer our partners a head start in this exciting opportunity. They can then decide how best to fit ferro-electric memories in their products and chips." This is a breakthrough in CMOS-compatible ferroelectric memory, let's look forward to the CMOS-compatible ferroelectric memory together.