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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. 

IntroductionDo you know buffer amplifier or isolation amplifier? The operational amplifier is an extremely efficient and versatile device. As we all known, the op amp is a component that amplifies the weak signal, which can be made into different forms according to the circuit requirements, and the voltage follower is one of them. Most voltage follower circuit will use an Op-amp. A follower is specifically an op amp wired to have a gain of +1. IE, the output is the same polarity and voltage as the input. That is, the output signal is exactly the same as the input signal. Here op amp voltage follower is used to isolate the signal and enhance load capacity. Op-amp as Voltage FollowerIntroductionⅠ Voltage Follower OP AmplifierⅡ Voltage Follower Characteristics2.1 Op Amp Impedance Matching2.2 Buffer Amplifier & Isolation AmplifierⅢ Op Amp Follower Circuit Analysis3.1 Op Amp Voltage and Load3.2 Op Amp Voltage Follower Stability3.3 Op Amp Phase Difference Problem3.4 Adding Feedback ResistanceⅣ Op Amp Voltage Follower ApplicationⅠ Voltage Follower OP AmplifierThe op amp follower sacrifices the voltage amplification factor in exchange for the performance of increasing the input impedance and reducing the output impedance. Because the gain of the op amp is extremely high, the input impedance of the op amp follower tends to be infinite, and the output impedance tends to zero. Within the rated output current range, the feedback voltage is equal to the output voltage, the output voltage is in phase with the input voltage, and the output voltage is slightly smaller than the input voltage. It should be noted that voltage follower is a special case of negative feedback amplifier (voltage series).Op amp voltage follower is actually a simple circuit structure which play a role in impedance matching. When a weaker signal is used to drive a relatively high current, voltage follower is often added in the middle, so that it can make weak signal stronger. It improves the load capacity to a considerable extent, while ensuring that the waveform and amplitude of the signal remain unchanged.For example, a single-chip microcomputer outputs a PWM signal to control LED lights. One LED does not require much current, so there is generally no big problem, however, when multiple LEDs need to light, current may definitely not large enough. If the current output is not enough, which may affect the signal output by the single-chip microcomputer, in this way, the voltage follower comes in handy.Ⅱ Voltage Follower Characteristics2.1 Op Amp Impedance MatchingWhen the op amp gain is approximately 1, that is, the magnification is approximately 1. The "follow" in the follower means that the voltage remains unchanged before and after, and the output waveform is almost not lost. It can be composed of transistors or operational amplifiers (best). Because the op amp input impedance is large and the output impedance is small, voltage follower can reduce the impact on the signal and improve the load capacity.2.2 Buffer Amplifier & Isolation AmplifierHere is a question, how to understand the buffering effect? Is the voltage of the former having a small impact on the back circuit? No, it is equivalent to a constant voltage source. Within the design requirement, no matter how the circuit connected to the subsequent stage changes, the output voltage is constant and does not change. In this way, the magnification or other performance of the previous stage can be kept unchanged. Otherwise, if the previous-stage input impedance is large, and the latter stage is small, the signal will definitely be distorted. For example, if a sinusoidal voltage waveform with a peak value of 10V, the sinusoidal peak value loaded to the latter stage may only be 8V. After adding a voltage follower, the waveform loaded on the input of the voltage follower will basically not change, and the input-output stage voltage ratio is very close to unity. So there will be no distortion.Since the output impedance of the voltage amplifier is generally relatively high, usually in the range of several kiloohms to tens of kiloohms. If the input impedance of the subsequent stage is relatively small, part of the signal will be lost in the output resistance of the previous stage. At this time, a voltage follower is needed to buffer from it. Another advantage of applying a voltage follower is that the op amp input impedance is increased, so that the capacity of the input capacitance can be greatly reduced, which provides a prerequisite guarantee for the application of high-quality capacitors.Another question, what about isolation? Because the op amp input impedance of the voltage follower is very large, it can be approximated as an open circuit. Of course, this open circuit is for the previous circuit. In this case, the previous circuit will not affect the subsequent circuit. However, "open circuit" means what, is it really open? No, the previous voltage is transmitted, but the corresponding current is not transmitted. This is the isolation effect.For example, if the MCU outputs a PWM waveform, you want to use it to control the brightness of a small light bulb. However, the output capacity of the IO port of the general MCU is limited. You can directly use the PWM output from the IO port to drive one light bulb. More than one doesn't work. In this case, you can add a voltage follower, so that the voltage is still the original voltage, but the driving ability has improved. Of course, the output capacity is not increased out of thin air, but comes from the input power of the op amp. In electronics, the diode has current amplification capability, and its source of amplification capability also comes from the power supply.In Hi-Fi circuits, the controversy about negative feedback has been around for a long time. In fact, if there is no negative feedback, most amplifying circuits will not work well. However, due to the introduction of a large loop negative feedback circuit, the back EMF of the speaker will pass through the feedback circuit and be superimposed with the input signal. The sound quality is blurred and the clarity is reduced. Therefore, some of the final stages of the power amplifier adopt a circuit without large loop negative feedback, trying to eliminate the disadvantages by disconnecting the negative feedback loop. However, since the operating current of the final stage of the amplifier varies greatly, its distortion is difficult to control. Here, the function of the voltage follower is just for the application. Putting the circuit between the front stage and the power amplifier can cut off the interference effect of the back electromotive force of the speaker on the front stage, so that the clarity of the sound quality is greatly improved. Ⅲ Op Amp Follower Circuit Analysis3.1 Op Amp Voltage and LoadFigure 1. Op Amp Voltage Follower SchematicThe output and the inverting input terminal are connected in series with a 10k resistor to ensure excellent characteristics. An ac signal is input at the non-inverting input terminal. Of course, dc and ac are all okay, so you will get a very high voltage at the output terminal. AC voltage that is similar and has excellent load capacity, with buffering and isolation effects.3.2 Op Amp Voltage Follower StabilityThe problem of using a voltage follower to keep the operational amplifier stable, that is, how to reduce the oscillation in the amplifier circuit using negative feedback to maintain stability, there is still no final conclusion. The ideal operating state of the op amp is that the output voltage and the input voltage are in phase, that is, when the applied voltage at the negative input causes the output to increase, the op amp can reduce the increased voltage accordingly. However, there is always a difference in phase between the input and output in reality. When the phase difference between the output and the output is 180°, the negative input and the positive input are exactly the same, but the output that should have been reduced is enhanced. It becomes a state of positive and negative collapse. If it falls into this state in a specific frequency band and still maintains the original amplitude, then the output frequency and oscillation state will continue.Figure 2. Feedback Loop3.3 Op Amp Phase Difference ProblemThe main reason for the phase difference between the input and the output:1) Due to the inherent characteristics of op amps.2) Due to the characteristics of the other feedback loop in circuit.Figure 3. Gain-frequency, Phase-frequency CurveFig 3(a), Fig 3(b)and Fig 3(c) respectively represent the voltage gain-frequency characteristic and phase-frequency characteristic of the operational amplifier. As shown in the figure, the voltage gain and phase vary with frequency. The difference between the op amp gain and the gain after feedback (0dB when using a voltage follower) is the gain (feedback gain) of the feedback loop. If the feedback gain is less than 1 time (0dB), then, the phase changes by 180° and returns to the positive feedback state, the negative gain will gradually attenuate in the circuit and theoretically will not cause oscillation.On the contrary, when the phase changes by 180°, if the loop gain corresponding to the frequency is 1 time, the original amplitude will be maintained. If the loop gain corresponding to the frequency is greater than 1, the amplitude will gradually diverge. In most cases, in the process of amplitude divergence, the amplitude is limited due to the influence of nonlinear elements such as the maximum output voltage, and the oscillation state will be maintained.Therefore, the difference between the phase corresponding to the frequency when the loop gain is 0dB, 180° is an important factor for judging the stability of the negative feedback loop, and this parameter is called the phase margin. Unless otherwise specified, when a single amplifier is used as a voltage follower, sufficient phase margin must be maintained (Fig 3b.).3.4 Adding Feedback ResistanceWhen the operational amplifier is used as a follower, when the internal resistance of the signal source is large, adding a feedback resistor with the same resistance as the internal resistance of the signal source can reduce the output offset voltage and improve the follow accuracy. The follower with feedback resistance has a certain current limiting protection effect on the circuit when the circuit is "blocked", which is its advantage.The voltage follower is originally a non-inverting operational amplifier. One of the common features of it is that a common-mode voltage is added to the non-inverting terminal and the inverting terminal.Once this common-mode voltage exceeds the allowable common-mode input voltage range, for example, if the inverting terminal signal is too large, it will cause the input stage transistor to saturate. The inverting terminal signal will be directly added to the second stage of the op amp, making the inverting input becomes non-inverting input, that is, negative feedback becomes positive feedback, and the output signal passes through the feedback loop to further saturate the input stage transistor. As a result of this, the amplifier is of course no longer in normal working condition. Even if the input signal is canceled, it will not immediately return to the normal state. This phenomenon is called blocking.When it occurs, if the feedback loop resistance is not large enough, the current in the feedback loop may burn the input stage transistors and even harm the second stage. In order to avoid blocking, in addition to choosing an op amp with a large common-mode input voltage range, a clamp circuit is often added to the input of the amplifier to ensure that the common-mode voltage at the input does not exceed the allowable range.Of course, in a small-signal inverting operational amplifier, especially in circuits with capacitive elements such as integrating operational amplifiers, blocking may also occur. The processing method is the same as that of the non-inverting amplifier. Ⅳ Op Amp Voltage Follower ApplicationIn many typical circuit designs, there will be an op amp follower before the AD converter. Whether this follower is necessary or not depends on the requirements of the circuit based on the understanding of the function of the follower. First analyze the role of the voltage follower here:The function of the voltage follower here is impedance transformation.Impact 1: The input impedance becomes very high, so that the impact on the input signal can be small.Impact 2: The output impedance becomes very low, and the impact of AD input impedance on the input signal can be very small.It can be seen that the follower is very meaningful. Secondly, analyze your own circuit and the signal under test to make a decision whether to use a follower. Here are some rules to confirm:1) If the output impedance of the signal is very small, then the Impact 1 can be ignored.2) If the input impedance of AD converter is very large, then two impacts can be ignored.3) If both impacts can be ignored, no voltage follower is necessary.4) If there is an impact, a voltage follower is needed. Frequently Asked Questions about Op Amp Voltage Follower1. Which amplifier is called as voltage follower Why?This means that the op amp does not provide any amplification to the signal. The reason it is called a voltage follower is because the output voltage directly follows the input voltage, meaning the output voltage is the same as the input voltage. 2. What is the use of voltage follower?A voltage follower can be used as a buffer because it draws very little current due to the high input impedance of the amplifier, thus eliminating loading effects while still maintaining the same voltage at the output. 3. What do you mean by voltage follower circuit?A voltage follower is also known as a unity gain amplifier, a voltage buffer, or an isolation amplifier. In a voltage follower circuit, the output voltage is equal to the input voltage; thus, it has a gain of one (unity) and does not amplify the incoming signal. 4. What is an op amp buffer?An op-amp voltage buffer mirrors a voltage from a high-impedance input to a low-impedance output. 8 min read. A voltage buffer, also known as a voltage follower, or a unity gain amplifier, is an amplifier with a gain of 1. It's one of the simplest possible op-amp circuits with closed-loop feedback. 5. What is an op amp buffer circuit used for?A buffer is a unity gain amplifier packaged in an integrated circuit. Its function is to provide sufficient drive capability to pass signals or data bits along to a succeeding stage. Voltage buffers increase available current for low impedance inputs while retaining the voltage level.

CatalogⅠ IntroductionⅡ Types of sensors in the phone  2.1 Acceleration sensor  2.2 Gravity sensor  2.3 Light sensor  2.4 Proximity sensor  2.5 Magnetism Sensor  2.6 Gyroscope  2.7 GPS position sensor  2.8 Hall Sensor  2.9 Air pressure sensor  2.10 Heart rate sensor  2.11 Blood oxygen sensor  2.12 UV sensor  2.13 Temperature sensor  2.14 Fingerprint sensorⅢ Integrated application of sensors in the phoneⅣ SummaryⅤ FAQⅠ IntroductionThe development speed of smartphone technology is unimaginable, which includes sensor technology. Sensors in mobile phones have the ability to make a big difference in our way of life.Sensors in mobile phones refer to those components that can be sensed by chips, such as response distance, light value, temperature value, brightness value and pressure value. Like all electronic components, these sensors are getting smaller and smaller, with stronger performance and lower cost. Through the various data collected by the sensor, through the analysis and calculation of the program software of the mobile phone, various applications are generated. Today's mobile phones have provided extremely convenient functions in our social, financial payment, sports monitoring, entertainment, learning and other aspects.Ⅱ Types of sensors in the phone2.1 Acceleration sensorThe concept of acceleration sensor and gravity sensor overlap slightly, but in fact, they are different. Acceleration sensor is measured in multiple dimensions, which refers to the acceleration values in X, y and Z directions. It mainly measures some actions of instantaneous acceleration or deceleration.  For example, measuring the speed and direction of the mobile phone, when the user holds the mobile phone, it will swing up and down, so that the acceleration can be detected to change back and forth in a certain direction, and the steps can be calculated by detecting the number of times of the change back and forth. In the game, the acceleration sensor can trigger special instructions. This sensor is also used in some daily applications, such as shaking and cutting songs, turning and muting. The power consumption of acceleration sensor is small but its accuracy is low. Generally used in mobile phones, it can be used to measure steps and judge the direction of mobile phones. 2.2 Gravity sensorThe gravity sensor is realized by piezoelectric effect. There are a heavy object and piezoelectricity piece integrated into the gravity sensor. The horizontal direction is calculated by the voltage generated in the two orthogonal directions. The gravity sensor used in the mobile phone can be used to switch between horizontal and vertical screen directions.In some games, gravity sensors can also be used to achieve more interactive control, such as balance ball, car games and so on. 2.3 Light sensorThe light sensor is similar to the eye of a mobile phone. The human eye can adjust the light entering the eye in a different light environment. And the light sensor can let the mobile phone sense the intensity of the ambient light, which is used to adjust the brightness of the mobile screen. Because the screen is usually the most power-consuming part of the mobile phone, the use of light sensors to help adjust the brightness of the screen can further extend the battery life. The light sensor can also be used with other sensors to detect whether the phone is placed in the pocket to prevent accidental contact. 2.4 Proximity sensorIt is composed of an infrared LED lamp and an infrared radiation light detector. The distance sensor is located near the handset of the mobile phone. When the mobile phone is close to the ear, the system uses the distance sensor to know that the user is on the phone and then turns off the display to prevent the user from affecting the call due to misoperation. The working principle of the distance sensor is that the invisible infrared light emitted by the infrared LED is reflected by nearby objects and detected by the infrared radiation light detector. The distance sensor is usually used with the light sensor. 2.5 Magnetism SensorThe magnetic field sensor uses magnetoresistance to measure the plane magnetic field, so as to detect the intensity and direction of the magnetic field. Magnetic field sensor is usually used in the common compass or map navigation to help mobile phone users achieve accurate positioning. Through the magnetic field sensor, you can obtain the magnetic field intensity of the mobile phone in X, y and Z directions. When you rotate the mobile phone until the value in only one direction is not zero, your mobile phone points to the right south. Many compass applications on mobile phones use the data of this sensor. At the same time, the specific orientation of mobile phone in three-dimensional space can be calculated according to the different magnetic field intensity in three directions. 2.6 GyroscopeGyroscope can measure the angular velocity along one or several axes, which is an ideal technology to supplement the function of MEMS accelerometer. In fact, if the accelerometer and gyroscope are combined, the system designer can track and capture the complete action of 3D space, and provide a more real user experience, accurate navigation system and other functions for end users. "Shake and shake" function in mobile phone (for example, shaking mobile phone can draw lots), body sensing technology, as well as VR angle adjustment and detection are all applied to gyroscopes. The gyroscope sensor is a necessary component for some induction games. With this sensor, the interaction of mobile games has a revolutionary change. Users can feedback the game with multi-directional operation of their bodies, not just simple buttons. Usually, the standard mobile phone is equipped with three-axis gyroscope, which can track the displacement changes in six directions. The three-axis gyroscope can get the angular acceleration of the current mobile phone in X, y and Z directions, which is used to detect the rotation direction of the mobile phone. Some functions of turning the mobile phone and answering the phone are realized by the change of angular acceleration. 2.7 GPS position sensorThere are 24 GPS satellites running in a specific orbit above the earth. They will continuously broadcast their position coordinates and time stamps(the total number of seconds since January 1, 1970, 00:00:00 GMT) to all parts of the world. The GPS module in the mobile phone starts from the instantaneous position of the satellite, and calculates the distance between the mobile phone and the satellite by the time difference between the time stamp of the satellite transmitting coordinate and the time of receiving. It can be used for positioning, speed measurement, distance measurement and navigation and so on.  GPS module is mainly used to receive the satellite coordinate information through the antenna to help users locate. With the popularization of 4G network, GPS is used in more scenarios, such as remote location monitoring with intelligent hardware, or location search after device loss. 2.8 Hall SensorThe function principle of Hall sensor is hall magnetoelectric effect. When the current passes through a conductor located in the magnetic field, the magnetic field will produce a force perpendicular to the direction of electron motion on the electrons in the conductor, thus generating potential difference at both ends of the conductor. The main function of the hall sensor installed on the mobile phone is to use the smart leather case (magnetic leather case). After the leather case is buckled, the screen will display a small window interface in the small window left on the leather case, which is used to answer calls or read short messages. 2.9 Air pressure sensorWhen the air pressure changes, the value of resistance or capacitance will change, so as to measure the air pressure data. GPS can also be used to measure altitude, but there will be an error of about 10 meters. If the air pressure sensor is installed, the error can be corrected to about 1 meter, which is helpful to improve the accuracy of GPS (Global Positioning System). In addition, when some outdoor applications need to measure air pressure, the mobile phone with air pressure sensor can also be used. In IOS health applications, you can calculate how many floors you have climbed. 2.10 Heart rate sensorIrradiate fingers with high brightness LED light, because the brightness (the depth of red light) will change periodically when the heart sends blood to capillaries. Then capture these regular changes through the camera, and transfer the data to the mobile phone for calculation, and then judge the heart contraction frequency to get the number of heartbeats per minute. The user's heart rate data is obtained by detecting the number of pulsations per minute of the blood vessels on the user's fingers. Heart rate sensors are common in wearable devices. 2.11 Blood oxygen sensorLike heart rate sensors, hemoglobin and oxyhemoglobin in blood have different absorption ratios for the red light. Infrared light and red light LED are used to irradiate fingers at the same time, and the absorption spectrum of reflected light is measured to measure blood oxygen content. Blood oxygen sensors can be used in sports or health applications. 2.12 UV sensorThe photoelectric emission effect of some semiconductors, metals, or metal compounds will release a large number of electrons under ultraviolet irradiation. The ultraviolet intensity can be calculated by detecting this discharge effect. UV sensor is also used in the field of sports and health and in detecting radiation levels in the environment.At present, there are few mobile phones using this kind of sensor, and the stability of the measurement needs to be further observed. 2.13 Temperature sensorMany smartphones are equipped with temperature sensors, and some have more than one. The difference is that their purpose is to monitor the temperature inside the phone and the battery. If it is found that the temperature of a certain part is too high, the mobile phone will be turned off to prevent damage. In terms of extended functions, the temperature sensor can also detect the temperature change in the outside air, even the user's current temperature. 2.14 Fingerprint sensorAt present, the mainstream technology is capacitive fingerprint sensor, but ultrasonic fingerprint sensor is also gradually popular. When the capacitive fingerprint sensor works, the finger is one pole of the capacitance, and the other is a silicon chip array. Through the microcurrent generated between the human body's micro-electric field and the capacitance sensor, the distance between the fingerprint's peak and valley and the sensor forms the capacitance height difference to describe the fingerprint pattern. The principle of ultrasonic fingerprint sensor is similar, but it will not be interfered by sweat and oil, and the recognition speed is faster. It can be used in mobile phones to unlock, encrypt, pay and so on. It can automatically collect user fingerprint to protect privacy, which is usually used as a security measure.Ⅲ Integrated application of sensors in the phoneNowadays, the technology level of smartphones is rapidly updated, which is largely due to the innovation and breakthrough of sensor technology in mobile phones. With the integrated application and software support of basic sensors, mobile phone researchers have developed many cool mobile phone functions. ① Super safe 3D ultrasonic fingerprint recognitionThe mobile phone integrates Xiaolong 820 chipset and Xiaolong sense ID. Among them, Xiaolong sense ID adopts the latest ultrasonic technology developed by Qualcomm to realize 3D fingerprint recognition. Fingerprint press recognition technology has become the standard equipment of some smartphones. Different from the previous technology, Qualcomm snapdragon sense ID can work even when there is a little dirt or moisture in the user's fingers, and can even penetrate glass, aluminum, stainless steel, sapphire, plastic and other equipment for identification. This means that mobile phone manufacturers can integrate sensors and devices without having to make fingerprint identification units into a single button. Therefore, ultrasonic fingerprint recognition technology can be put into the screen window of the flat panel. In addition, in terms of security, it has been greatly improved. Ultrasound has been used in the field of professional biometrics for a long time. It can penetrate the epidermis and detect the three-dimensional details of fingerprint, making it difficult for hackers to copy fingerprint and invade users' mobile phones. ② Iris recognition of mobile phoneThe iris of human eye is more complex than fingerprint, so it is safer to use iris recognition to unlock mobile phone than fingerprint recognition. Users only need to capture the eyeball through a special app, log the iris pattern of the eye onto the terminal, and then they can use it safely. Iris mobile phone will become the wallet for everyone to pay, the gold card of the bank, the key to open the door, the certificate for customs clearance and the evidence for medical insurance, opening a new generation of Internet identity authentication. The mobile phone's built-in micro iris recognition product consists of imaging module, lighting module and software algorithm. It can scan the user's iris features through the built-in camera, and the user only needs to stare at the screen for a short time. The effective recognition distance is 20 ~ 30cm, and the recognition speed is 1s. Based on the capsaic security chip and metacentric dual operating system independently developed by Spreadtrum, the iris recognition scheme is optimized from the aspects of system imaging, feature description and matching, security and anti-counterfeiting, user interaction, etc., to achieve accurate recognition. ③ RWB technology creates an intelligent and beautiful imageThe mobile phone with RWB technology is equipped with f1.8 aperture and 6p lens. Compared with the photos taken by the previous RGB technology models, the noise reduction ability is increased by 80%, the sensitivity is increased by 40%, and the area is reduced by 23%. The smaller rear camera mirror volume is used to obtain more light, and the details under weak light will be better. The image sensor of Bayer array usually uses RGB (red, green and blue) technology. On average, the whole sensor will block two-thirds of the incident light, resulting in a great waste. RWB (red, white and blue) has the greatest improvement compared with the traditional Bayer array sensor, which is the high sensitivity shooting performance. As the green pixel is replaced by the white pixel, the effective light intensity received by the sensor almost doubles, and the RWB's high sensitivity index has also been significantly improved. ④ Leica dual cameraLeica Summit Series dual lens with better brightness and clarity makes it easier to take photos and videos. The rear 12 megapixel black-and-white and color dual cameras have more than just two 12 megapixel lenses. In the process of photographing, the dual cameras work at the same time, and the black and white lens capture the details to make the image clearer; the color lens capture the color to make the color fuller, and the image synthesis algorithm makes the details and the colors more integrated, so the picture is lifelike and amazing. By using the hybrid focusing technology of laser focusing, depth focusing and contrast focusing, we can take the wonderful pictures with clear picture and clear layers in an instant. Mobile phone for comprehensive health exercise monitoringThis mobile phone attaches great importance to the health of users. It is equipped with ten major professional sensors, with low power consumption, which can realize users' 24-hour use of professional sports applications. In addition, more sensors allow the phone to restore the user's real movement, accurate to three steps of movement, while also measuring heart rate, blood oxygen and ultraviolet. With the support of the application algorithm, the user's stride and stride frequency can also be accurately identified. ⑤ 3D visual sensory experience of eye-tracking technologyThe concept of "full display mobile phone" has two cameras in front of it. One is used for taking photos like ordinary mobile phones, while the other is used for eye tracking and capturing the position of human eyes. According to your eye position and pupil distance, a reasonable visual angle image matching the position of human eyes is customized and generated in real-time. Whether it's left and right or front and back movement, you can get a comfortable and clear 3D visual sensory experience all the way. "One screen, two cores and three cameras" is standard for full display mobile phones. ‘One screen’ is the naked eye 3D cylindrical grating LCD screen, users can experience the shock of 3D and VR vision without wearing 3D glasses, and they can realize the free switching of 2D / 3D. ‘Two cores’ is that in addition to the CPU, there is an independent VR visual motion chip to improve the 3D / VR rendering speed. ‘Three cameras’ is that in addition to conventional cameras, eye-tracking cameras are added. ⑥ Video integrated mobile phone’s free conversion of 2D / VR The mobile phone realizes the integration of VR camera and mobile phone. It is equipped with four cameras, two at the front and two at the back, which can meet the demand of 360-degree panoramic shooting, realize 3D stereo effect, and also can freely switch between VR lens and 2D plane lens at the same time. The pixels of CMOS image sensor in VR camera module reach 26 million, and Sony photosensitive device is used. The thickest part of the camera module of ultra-thin VR panoramic lens is only 23.8mm, which is the thinnest mobile VR camera module in the world. VR mobile camera uses a single binocular zigzag two in one super wide angle camera module. This VR camera module contains two imaging systems with the same structure. Each imaging system is composed of a 200 degree super wide angle lens and an imaging sensor. The lens optical path adopts 90 degree zigzag double optical path design. The optical axis of the two cameras is the same, greatly reducing the lens volume to achieve ultra-thin and ultra light integrated structure. VR camera module also integrates the front and rear VR camera scenes into a sphere through image recognition, splicing and other algorithms, so that the pixel size, color, brightness and other parameters of the two hemispheres are the same, which is the first in terms of technology.Ⅳ SummaryThe development of sensors in the future is sure that they will know more about the surrounding environment, that is to say, the types of sensors will be far more than these. The bolder assumption is that in the future, sensors will not only perceive but also have certain processing capacity. What sensors transmit is not only data, but also some intelligent operation and judgment. In terms of sensor technology, it is the common understanding of the whole industry that sensor integration is getting higher and higher. The higher integration degree leaves more possibilities for the expansion of sensors, and greatly saves the equipment space, which is more conducive to the development of mobile devices towards portability. I believe that in the foreseeable future, the perception of our mobile phone to users will be more accurate, and its application in the future will be far richer than we think now. Ⅴ FAQ1. What sensors does a phone have?• Accelerometer.• Ambient Light Sensor.• Ambient Temperature Sensor.• Air Humidity Sensor.• Barometer Sensor.• Finger Print Sensor.• Gyroscope Sensor.• Harmful Radiation Sensor and so on. 2. How many sensors are there in mobile?Today's mobile devices are packed with nearly 14 sensors that produce raw data on motion, location and the environment around us. This is made possible by the use of micro-electromechanical systems (MEMS). 3. How many types the capacitive touch sensors are classified?There are two types of capacitive touch sensors: surface capacitive sensing and projected capacitive sensing. In surface capacitive sensing, an insulator is applied with a conductive coating on one side of its surface. On top of this conductive coating, a thin layer of the insulator is applied. 4. What is the proximity sensor on phone?In Android, the proximity sensor is primarily used to detect when the user's face is close to the screen. ... This is how the phone screen seems to know to switch off when you hold it up to your ear during phone calls, preventing any errant button presses. 5. Do phones have a motion sensor?Most Android-powered devices have an accelerometer, and many now include a gyroscope. The availability of software-based sensors is more variable because they often rely on one or more hardware sensors to derive their data. 6. Which sensor is used in the touchscreen?Optical touchscreens use infrared emitters combined with infrared image sensors to continuously scan the touchscreen. When an object comes into contact with the touchscreen, it blocks some of the infrared light being received by the sensors. 7. What is a simple touch sensor?The Touch Sensor is sensitive to touch, pressure as well as force. The Touch Sensor works similar to that of a simple switch. When there is contact or a touch on the surface of the Touch Sensor. It acts like a closed switch and allows the current to flow through it. 8. How do I find the sensor code on my phone?To get the ball rolling, simply open your Samsung phone app. From there, enter *#0*# using the dial pad, and the phone will immediately go into its secret diagnostic mode. Note that the process is automatic, so there's no need to tap on the green call button to enter the command. 9. How accurate are phone gyroscopes?They used an algorithm designed for repetitive, well-defined, and bounded pedaling leg movement. Their results show that the achieved accuracy of gyroscope angular tracking in pedaling is in the range of 2.2°–6.4°. Many works have been published on golf swing motion tracking. 10. What is a depth sensor in mobile?The DepthVision Camera is a Time of Flight (ToF) camera on newer Galaxy phones including Galaxy S20+ and S20 Ultra that can judge depth and distance to take your photography to new levels. ... With Quick Measure, the camera acts as a 3D camera, judging width, height, area, volume, and more when you put an object in the frame. 

IntroductionIn electronics, operational amplifiers are generally dual/quadruple configurations. So users can consider using the extra amplifier as a comparator. Electrical symbols of the comparator and the operational amplifier are very similar. They are devices with one input inverting terminal and one non-inverting terminal, and one output terminal. In addition, the output voltage range of the output terminal is generally between the rail-to-rail power supply. Meanwhile, they have same features of low bias voltage, high gain and high common-mode rejection ratio. When an op amp is used as a comparator, its own gain bandwidth product, group delay, slew rate and other parameters are likely to be changed due to internal frequency compensation and saturation effects. For an optimized single device, this change can be seen as an economical solution. This article discusses the specifications and characteristics to consider when using op-amps as comparators and provides design advice. How operational amplifier be a comparator and what the difference between them.Op Amp vs ComparatorCatalogIntroductionⅠ Operational Amplifier and Comparator1.1 Electronic Op Amp1.2 Electrical ComparatorⅡ Circuit Structure Comparison2.1 Op Amp2.2 ComparatorⅢ Difference between Amplifier and Comparator3.1 Total Difference Summary3.2 Distinctions between Op-amp and ComparatorⅣ Basic Use of Comparators and Op AmpsⅤ Op-amp Comparator5.1 Technique5.2 Op Amp Comparators DisadvantagesⅥ Using Op Amps as Comparators NotesⅦ ConclusionⅠ Operational Amplifier and Comparator1.1 Electronic Op AmpThe operational amplifier is a kind of differential amplifiers with high input resistance, low output resistance, high open gain (open-loop gain), and has the function of amplifying the voltage difference between the active input pin and the negative input pin. Operational amplifiers and voltage comparators are indeed the same in principle and diagram symbol. That said, they have 5 pins: two of which are power supply (+) and supply power (-), another two pins are non-inverting input (+) and non-inverting input terminal (-), and the last pin is the output terminal.Figure 1. Op Amp Symbol1.2 Electrical ComparatorComparing two or more data items to determine whether they are equal, or determining the  relationship and arrangement order between them is called comparison. A circuit or device that can realize this is called a comparator. Specifically, it is a circuit that compares an analog voltage signal with a reference voltage. The two inputs of the comparator are analog signals, and the output is a binary signal 0 or 1. When the difference of the input voltage increases or decreases and the sign of the positive and negative remains unchanged, the output remains constant. Comparing the voltages of the two input terminals, if the voltage at the positive input terminal is a and the voltage at the negative input terminal is b, when a>b, the output is high level(logic 1); when a<b, the output is low level(logic 0). The schematic diagram is shown below (the voltage at the input terminals of the comparator is IN1 and IN2, the power supply is VCC/GND, the pull-up resistor is 1K, and the pull-up voltage is VCC.).Figure 2. Volatge ComparatorWhen output voltage IN1＞IN2, positive input is in high level with high voltage.When output voltage IN2＞IN1, negative input is in low level with high voltage.A reference voltage is usually applied to an input terminal. Then the output will indicate the  signal applied to the other input. Comparators are often used to determine whether a signal is above or below the reference level. And meawhile, the comparator can form a non-sinusoidal waveform conversion circuit and be used in fields such as analog and digital signal conversion.When the reference voltage is zero, the comparator is called a zero-crossing detector. It uses to convert a sine wave into a square wave. Two comparators can form a "window" circuit, which is used to determine whether a signal is between two limited values. In an output state of the comparator changes as quickly as possible, and sometimes the output of the comparator is required to have a certain logical relationship with the input, a dedicated strobe pulse is required. At this time, the op amp comparator only has an output during operation. In general, a dedicated comparator IC has better performance. And it replaces the operational amplifier in some applications. The most common advantage is that the comparator IC operates with a single power supply.The comparator has a wide range of uses, and can be used for discrete control of voltage signals such as thermistors and photosensitive sensors. For example, the voltage value of the photoresistor is collected by a comparator to determine whether it is day or night. What’s more, the comparator can also be used for voltage adjustment in an analog negative feedback circuit.Figure 3. TLC311 ComparatorIt can be seen from the diagram that the difference between the operational amplifier and the comparator lies in the output circuit. The operational amplifier uses a dual-transistor push-pull output. While the comparator uses only one transistor, the collector is connected to the output terminal, and the emitter is grounded. In addition, the comparator requires an external pull-up resistor from the positive power supply terminal to the output terminal, which is equivalent to the collector resistance of the transistor. Op amp can be used for linear amplifying circuit (negative feedback), as well as the non-linear signal voltage comparison (open-loop or positive feedback). The comparator can only be used for signal voltage comparison, not for linear amplifier circuits (because it has no frequency compensation). Both can be used for signal voltage comparison, but the comparator is designed as a high-speed switch, which has a faster conversion rate and a shorter delay than an operational amplifier. Ⅱ Circuit Structure Comparison2.1 Op AmpFigure 4. Op Amp CircuitOp amp circuit generally consists of input segment, gain segment, and output segment. The input  is composed of a differential amplifier section for amplifying the voltage difference between two pins. In addition, the in-phase signal component (the state where there is no potential difference between the pins and the input voltage is some) is not amplified to take a cancellation effect. If only relying on the differential amplifier circuit, the gain is insufficient, so the gain section is used to further increase the open gain of the operational amplifier.The anti-vibration phase compensation capacitor is connected between the gain section of the ordinary operational amplifier. In order to avoid changes in the characteristics of the operational amplifier due to loads such as resistors connected to the output pins, a compensation capacitor is connected with the output as a buffer.The change (distortion, voltage drop, etc.) in output characteristics caused by the load is mainly determined by the circuit structure and current capability of the output section.Generally, types of output circuit stages are A, B, C, and AB type, which are classified according to the amount of drive current flowing in the output (the difference in bias voltage). Depending on the amount of drive current, the level of distortion coefficient in the output section will change. The order of general circuit distortion from small to large is type A, type AB, type B, and type C. 2.2 ComparatorFigure 5. Comparator CircuitThe comparator circuit structure is basically the same as that of an operational amplifier. Because a negative feedback circuit is not used, there is no built-in phase compensation capacitor for vibration isolation. Owing to it can limit the operating speed between the input and output, the response time is significantly improved compared with the operational amplifier.The output circuit form of the comparator is mainly divided into open collector (open drain) type and push-pull output type. The figure shows the internal equivalent circuit of BA10393, it is also an open collector output circuit. Ⅲ Difference between Amplifier and Comparator3.1 Total Difference Summary(1) The main difference between amplifier and comparator is the closed-loop characteristic. Most of the amplifiers work in a closed loop state, so it is required that they cannot be self-excited after the closed loop. Most of the comparators work in an open loop state and pursue speed. For the case of relatively low frequencies, the amplifier can completely replace the comparator (the output level should be considered), but in most cases, the comparator cannot be used as an amplifier.In order to increase the speed, the comparator optimization will reduce the range of closed-loop stability. While the op amp is optimized for the closed-loop stable range, so the speed is reduced. If an amplifier used as a comparator, as for performance, you may pay more than an amplifier price for its closed-loop stability.In other words, whether an op amp is used as a comparator or not is to see the negative feedback depth of the circuit. Therefore, a shallow closed-loop comparator may work in the amplifier state and will not have self-excited state. However, a lot of experiments must be done to ensure that the op amp is stable under all working conditions.(2) In general speaking, the comparator is an open-loop application of the op amp, but the comparator is designed for voltage threshold comparison. The required comparison threshold must be accurate, and the rise or fall time of output edge after comparison should be short. It conforms to TTL/CMOS level/or OC, etc., does not require the accuracy of the intermediate links, in addition, the driving capability is also different. In short, using op amps as comparators cannot achieve full-scale output in most cases, or the edge time after comparison is too long. So it is better to use special comparators in the design.Figure 6. Op Amp and Comparator Symbol3.2 Distinctions between Op-amp and ComparatorAlthough the electrical symbols of the comparator and the op amp are the same on the circuit diagram, the two devices have big differences and are generally not interchangeable. The differences are as following:1. The flipping speed of the comparator is fast, on the level of ns, while the flipping speed of the op amp is generally us level(except for special high-speed op amps).2. The op amp can be connected to the negative feedback circuit, but the comparator cannot use negative feedback. Although the comparator also has two input terminals of the inverting and non-inverting phase, when connecting negative feedback, the circuit cannot work stably without phase compensation circuit inside. But it is the main reason why the comparator is much faster than the op amp.3. The output stage of the operational amplifier generally adopts a push-pull circuit and a bipolar output. The output stage of most comparators is an open collector structure, so pull-up resistors and unipolar output are needed, which are easy to connect to digital circuits.4. Based on input, many operational amplifiers have built-in protection circuits to prevent large voltages from damaging the chip. When a large differential voltage is input, the input work will become abnormal, because the differential input voltage range of the op amp is usually limited. In addition, the common-mode input voltage range of non-rail-to-rail op amps cannot reach the positive power rail, but the comparator supports the positive power rail. Op amps and comparators have many similar parameters. It is more convenient to choose op amps instead of comparators in applications that require low offset voltage, low offset current, and high common mode rejection. Ⅳ Basic Use of Comparators and Op AmpsFigure 7. Operational Amplifier and ComparatorThe comparator is an open-loop circuit. Its function is to compare the voltage of the output terminal. When the voltage at the positive input terminal is large (IN2>IN1), the output is in high level (note: The comparator is an OC output, and the output terminal needs a pull-up resistor. A few volts will be pulled up to output a few volts, otherwise, the output will be an open circuit). When the negative input terminal voltage is large (IN1>IN2), the output will be in low level (GND). The voltage comparator input signal is an analog voltage, and the output signal generally only has two steady-state voltages of high level and low level. The voltage comparator can convert various periodic signals into rectangular waves.Operational amplifier can be used in linear amplifying circuit, and can also be used in non-linear circuit (used as comparator). It is widely used in electrical circuits, such as non-inverting amplification, inverse proportional amplification, difference, addition circuit, subtraction circuit, integral and differential circuit.  Ⅴ Op-amp Comparator5.1 TechniqueThe functions of the operational amplifier are more complicated, but the comparator is relatively simple. When the frequency requirement is not high, the operational amplifier can also be used as a low-performance comparator in practical applications.In theory, an operational amplifier with an open-loop configuration (no negative feedback) can function as a low-end comparator. When the voltage of the non-inverting input terminal (V+) is higher than the inverting input terminal (V-), due to the higher open-loop gain, a positive saturation voltage +U is output. When the voltage of the inverting input terminal (V-) is higher than the positive input terminal (V+), a reverse saturation voltage -U is output. For an op amp that works in a linear negative feedback configuration and is powered by a separate voltage (±V), is different from a non-linear comparator without negative feedback. 5.2 Op Amp Comparators DisadvantagesIn practice, the use of op amp comparators has the following disadvantages compared with the use of dedicated comparators:1) The op amp is designed to work in a linear segment with negative feedback, so saturated op amps generally have a slower flip speed. Most op amps have a compensation capacitor used to limit the slew rate of high-frequency signals. This makes the op amp comparator generally have a propagation delay on the level of microseconds, but a dedicated comparator is on the level of nanoseconds.2) The op amp does not have a built-in hysteresis circuit and requires a special external network to delay the input signal. 3) The static operating current of the op amp is stable only under negative feedback conditions. When the input voltage is not equal, there will be a DC offset.   4) The function of the comparator is to generate the input signal for the digital circuit. When using the op amp comparator, it is necessary to consider the compatibility with the digital circuit interface.5) Interference may occur between different frequencies of multiple op amps.6) Many op amps have diodes connected in reverse series at the input. The input of the two poles of the op amp is generally the same, which will not cause operational problems. But the two poles of the comparator need to be connected to different voltages, which may cause unexpected breakdown of the diode.7) Integrated circuits of dedicated comparator, which better combine the characteristics of analog and digital. It provides an output representing the logic state related to two analog voltages, one of which is a fixed reference quantity. When another voltage exceeds the reference value, is less than the reference value, or is in a specified range, the comparator can send a signal. It has an optimized combination of high gain, wide bandwidth and large flip rate to quickly change the output state. And the conversion time of digital signals is usually very fast. Ⅵ Using Op Amps as Comparators NotesThere are many points should remember when using op amps as comparators in circuits. You must consider five main op-amp characteristics to ensure expected performance:1) Power SupplyIf the logic and operational amplifier share the same power supply, the rail-to-rail operational amplifier can drive CMOS and TTL logic. but if they do not share the same power supply, an additional interface circuit is required.2) Input impedance and Bias CurrentWhen the operational amplifier is used as a comparator, it must meet the high input impedance condition. The input impedance of the CMOS voltage feedback operational amplifier is in the megohm level, which meets the requirement. As for current feedback (transconductance) operational amplifiers, the inverting input terminal has extremely low impedance, which cannot be used as a comparator.3) Differential Input CharacteristicsThe original intention of operational amplifier design is to cooperate with negative feedback to reduce the differential input as much as possible. In specific applications, the actual differential input voltage and the maximum differential input voltage that the op amp can actually provide should be considered.4) Common-mode Input CharacteristicsFor the old FET-type input operational amplifier, when the input exceeds the common-mode voltage range allowed by the device, a phase reversal will occur. At present, the op amps produced by various manufacturers use various methods to prevent the op amps from phase inversion. If the actual common-mode voltage range exceeds the allowable input common-mode voltage range of the op amp, you need to actually verify whether it is working properly.5) StabilityBecause there is no negative feedback externally, the open loop gain of the op amp used as a comparator is very high. Therefore, parasitic capacitance of the PCB and ground impedance of the non-inverting input terminal may cause the output to oscillate.Figure 8. Window Comparator CircuitⅦ ConclusionAlthough op amps are not designed to be used as comparators, nevertheless, many applications where the use of an op amp as a comparator is an economical engineering decision. It is important to make an reasonable decision to ensure that the op amp chosen performs as expected.That said, it is necessary to read the data sheets carefully and to consider the effects of op amp parameters on the application. Because the op amp is being used in a nonstandard manner, it may not reflect actual behavior, and some circuit experiment is advisable. Furthermore, because not all devices are typical in their behavior, some pessimism is warranted when interpreting the experimental results. Frequently Asked Questions about Operational Amplifier as Comparator1. Can an op amp be used as a comparator?However, op amps can also be used as comparators, which causes them to operate non-linearly. The inputs are driven hard and the output voltage slams to the power supply rail. 2. How does a comparator op amp work?A comparator circuit compares two voltages and outputs either a 1 (the voltage at the plus side; VDD in the illustration) or a 0 (the voltage at the negative side) to indicate which is larger. Comparators are often used, for example, to check whether an input has reached some predetermined value. 3. How op amp can be used as comparator in open loop configuration?Thus, an op-amp operating in open loop configuration will have an output that goes to positive saturation or negative saturation level or switch between positive and negative saturation levels and thus clips the output above these levels. This principle is used in a comparator circuit with two inputs and an output. 4. What is the difference between a comparator and an amplifier?Unlike operational amplifiers that usually operate with the input voltages at the same level, comparators typically see large differential voltage swings at their inputs. But some comparators without rail-to-rail inputs are specified to have a limited common mode input voltage range. 5. What is the difference between op amp and comparator?The difference between an op-amp comparator and a voltage comparator is in the output stage as a standard op-amp has an output stage that is optimized for linear operation, while the output stage of a voltage comparator is optimized for continuous saturated operation as it is always intended to be close to one supply.

IntroductionAs everyone knows, in order to create a passive low pass filter, combing resistive elements with reactive elements happens often. Put simply, a typical circuit composed of resistors and capacitors or inductors. According to theories, the resistor–inductor (RL) low-pass topology is equivalent to the resistor-capacitor (RC) low-pass topology in terms of filtering capability. However. in fact, RC low pass filters are more common, so this article will focus on first-order RC low pass filters.In this video, Passive RC Low Pass Filter has been discussed. CatalogIntroductionⅠ Typical RC Circuit1.1 Time Domain1.2 Frequency DomainⅡ First-order Low Pass Filter on Software2.1 Basic Filtering Algorithm2.2 Basic Algorithm of First-order RC Digital FilteringⅢ Optimization Method- Filtering Coefficients AdjustmentⅠ Typical RC CircuitThe RC circuit has thousands of uses and is a very important circuit to study. Not only can it be used to time circuits, it can also be used to filter out unwanted frequencies in a circuit and used in power supplies, like the one for your computer, to help turn ac voltage to dc voltage.Figure 1. Typical RC Circuit (DC, AC, and Pulse Signals can all use it)1.1 Time DomainCapacitor Current:According to Kirchhoff’s Voltage Law:Where, the unit of Ui is volts, the unit of RC is seconds, and τ=RC, get:Suppose the initial voltage of the capacitor is 0, where:R=1000ΩC=4.7uFUi=1Vt=0.0001~0.1sτ=RCVc(τ)=0.632 Figure 2. Step Response Curve of a First-order RC System1.2 Frequency DomainTaking the capacitor voltage as the output, the network function of the circuit is:Where u1=Ui, u2=UoLet ωc be equal to:, which is the cut-off frequency.Amplitude and phase angle function:Value of variables:R=1000ΩC=4.7uF |A(fc)|=0.707θ(fc)=-45, f=0.001, 1, …….100000.Amplitude and phase frequency characteristics:Figure 3.Figure 4.Logarithmic representation of amplitude-frequency characteristic:Figure 5.Analysis:When ω<ωc, the amplitude is a straight line parallel to the coordinate, and there is no attenuation.　When ω>ωc, it is a straight line whose slope is proportional to -20dB/decade.When ω=ωc, the gain is attenuated to 0.707, which is -3dB, and the phase lags by 45 degrees, corresponding to a low-pass filter. This frequency is usually called the cutoff frequency. Disadvantages:When using this analog filter to suppress low-frequency interference, the filter is required to have a larger time constant and a high-precision RC network. Increasing the time constant requires increasing the value of R, and meanwhile, the leakage current increases accordingly, thereby reducing the filtering effect.Figure 6. RC CircuitⅡ First-order Low Pass Filter on SoftwareAdvantages1) The use of digital filtering algorithms to achieve dynamic RC filtering can well overcome the shortcomings of analog filters.2) This kind of algorithm is more practical when the simulation constant is required.3) It has a good inhibitory effect on periodic interference.4) Save RAM space Disadvantages1) Exit phase lag, resulting in low sensitivity.2) It cannot filter out interference with a frequency higher than half of the sampling frequency (called the Nyquist frequency. For example, if the sampling frequency is 100 Hz, it cannot filter out interference signals above 50Hz). In this case, an analog filter should be used.3) For the single-chip microcomputer without multiplication and division running instructions, the workload of the program operation is relatively large.2.1 Basic Filtering AlgorithmOrigin of the AlgorithmThe transfer function of the first-order RC low-pass filter in the S domain for frequency analysis:Through z-transformation (there are many methods, such as first-order forward difference, bilinear transformation, etc. Here, the first-order backward difference method is used): Into the S-domain Transfer Function After the derivation is transformed into the difference equation, we can get:The transfer function in the S domain can be transformed into a difference equation in the time domain through the Z transformation.2.2 Basic Algorithm of First-order RC Digital FilteringX is the input, Y is the output value after filtering, then: a is a parameter related to the RC value, called the filter coefficient, its value determines the weight of the new sample value in the filtering result of this time, and its value is usually far less than 1, when the sampling interval t is small enough:1) The smaller the filtering coefficient, the smoother the filtering result, but the lower the sensitivity.2) The larger the filtering coefficient, the higher the sensitivity, but the more unstable the filtering result.3) The output value this time mainly depends on the last filtered output value, and the current sampled value has a relatively small effect on this output, which plays a corrective role.4) Cutoff frequencyFor example: t=0.5s (f=2Hz), a=1/32where fl=(1/32)/(2*3.14*0.5)=0.01Hz Basic ProgramWrite the program according to the basic principles and formulas of first-order filter, as follows:/*In the program, integer arithmetic is faster than decimal arithmetic. In order to speed up the processing speed of the program, for calculation convenience, a is an integer (from 0~255), 1-a is replaced by 256-a, which means that the new sample value is being filtered. The weight in the result (you can also change the base of 1-a to 100-a, and the calculation result will be processed accordingly)*/#define a 128 char value; //Last filtering valuechar filter(){    char new_value;    new_value=get_ad();//Sampling value    return(256-a)*value/256+a*new_value/256；}Initial Optimization of the ProgramReduce the number of operations of multiplication and division to increase the speed of operations.Specific optimization methods:First compare the new sampled value with the previous filtering result, and then use different formula calculations based on the comparison, so that the calculation efficiency of the program is doubled.Resolve the basic formula to get: ProcessNotes:S → New Sampling ValueR → Previous Filtering ResultC→ Filter CoefficientN→ New Filtering Result Program/*Int: NEW_DATA     New sampling values       OLD_DATA       Last filtering result       k        Filter coefficient (0~255)  Out:         The filtering results */ char filter_1(char NEW_DATA,char OLD_DATA,char k){    int result;    if(NEW_DATA<OLD_DATA)    {        result=OLD_DATA-NEW_DATA;        result=result*k;        result=result+128;//+128 Round Up        result=result/256;        result=OLD_DATA-result;    }    else if(NEW_DATA>OLD_DATA)    {        result=NEW_DATA-OLD_DATA;        result=result*k;        result=result+128;//+128 Round Up        result=result/256;        result=OLD_DATA-result;    }    else result=OLD_DATA;    return((char)result);} Filtering AnalysisWhen the filtering coefficient is 30:Figure 7.When the filtering coefficient is 128:Figure 8.When the filtering coefficient is 200:Figure 9.It can be seen that the smaller the filtering coefficient, the smoother the filtering result, but the lower the sensitivity. On the contrary, the larger the filtering coefficient, the higher the sensitivity, but the more unstable the filtering result.Insufficient1) The contradiction between sensitivity and smoothness2) Errors caused by discarding decimals.For example: the current sampling value=25, the last filtering result=24, and the filtering coefficient=10;According to the algorithm, the filtering result of this time = 24.0390625In single-chip microcomputers, floating-point numbers are rarely used, and the fractional part is either discarded or needs to round up. In this way, the result is 24. If the sampling value is always 25, the result will always be 24. Because the filtering result and the actual data will always have an error that cannot be eliminated. Sometimes it will cause the filtering result curve to deviate from the actual value when the sampling data is stable at a certain value (that is, there is a large error between the filtering result and the actual result although in a stable case). Be Careful1) Changing the filtering coefficient, increasing it will reduce the smoothness, and if it is too large, the filtering will lose its meaning.2) The use of decimal part in calculations will bring heavy computational pressure to the CPU. Ⅲ Optimization Method- Filtering Coefficients AdjustmentRealize the Function1) When the data changes rapidly, the filtering results can be followed up in time, and the faster the data changes, the higher the sensitivity should be (sensitivity priority principle).2) When the data becomes stable and oscillates within a range, the filtering result can become stable (the principle of stability first).3) When the data is stable, the filtering result can be approximated and finally equal to the sampling data (eliminate the error caused by decimals in the calculation). Judgment before Adjustment1) Whether the data changes consistently. For example, when the two consecutive sampling values are larger than the previous filtering result, it is normal, otherwise it is regarded as inconsistent.2) Whether the data changes quickly, which is to judge the difference between the sampling value and the previous filtering result.Adjustment Principle1) When the two data changes are inconsistent, it means there is jitter. Clear the filtering coefficient to zero, and delete the new sampling value.2) When the data changes consistently, gradually increase the filtering coefficient to provide the weight of this sampling.3) When the data changes quickly (difference value> debounce count acceleration response threshold), the filtering coefficient should be increased quickly. Adjusting Filter Coefficient Process① Calculate the difference (absolute value) between the current sampling value and the last filtering result; Set the data change direction flag.② Two changes in the same direction?③ First order filter coefficient + coefficient increment (the maximum value is taken when the result is greater than the maximum value). Several Constant Parameters and Their Ranges1. Debounce counting acceleration response threshold is determined according to the actual situation.2. The maximum value of debounce count, which is generally 10.3. The increment of filtering coefficient range is 10~30.4. The maximum value of the filtering coefficient is generally 255.Before starting the first-order filtering program, open the adjustment filter coefficient program to adjust the coefficients in real time. Filtering Effect1. When the sampled data is accidentally interfered, the interference in the filtering result is completely filtered out.2. When the data oscillates within a range, the filtering result curve is very smooth, almost a straight line.3. When the sampling data has real changes, the filtering results can be followed up in a relatively timely manner.4. When the sampling data becomes stable, the filtering result gradually approaches and is finally equal to it.Finally, improve the algorithm. Taking into account the requirements of sensitivity and stability; and meanwhile, it does not consume too much RAM space. As long as a few constants are adjusted reasonably, the algorithm is more suitable for practical applications. Frequently Asked Questions about RC Low Pass Filter1. What is RC low pass filter?A low pass filter is a filter which passes low-frequency signals and blocks, or impedes, high-frequency signals. ... Low pass filters can be constructed using resistors with either capacitors or inductors. A low pass filter composed of a resistor and a capacitor is called a low pass RC filter. 2. Why RC circuit is low pass filter?Then by carefully selecting the correct resistor-capacitor combination, we can create a RC circuit that allows a range of frequencies below a certain value to pass through the circuit unaffected while any frequencies applied to the circuit above this cut-off point to be attenuated, creating what is commonly called a rc low pass fiter. 3. What is difference between RC low pass filter and RC high pass filter?Low pass filter is the type of frequency domain filter that is used for smoothing the image. It attenuates the high frequency components and preserves the low frequency components. High pass filter: ... It attenuates the low frequency components and preserves the high frequency components. 4. What is the transfer function of a low pass filter?Low Pass Filters and their Transfer FunctionsAs its name implies, a low pass filter is an electronic device that allows low frequency AC signals to pass a current through the filter circuit. The output from the filter circuit will be attenuated, depending on the frequency of the input signal. 5. How is low pass filter frequency calculated?The cut-off frequency or -3dB point, can be found using the standard formula, ƒc = 1/(2πRC). The phase angle of the output signal at ƒc and is -45o for a Low Pass Filter.

Introduction 18650 is a lithium-ion battery, where 18 means a diameter of 18mm, 65 means a length of 65mm, and 0 means a cylindrical battery, that is, they get their name from their size. As for scale, it is larger than an AA battery. 18650 battery is a rechargeable battery, has voltage of 3.7V and has capacity between 1800mAh and 3500mAh. You may also know 26650 battery and 21700 battery, what are they? and what is the difference between them? Intro To 18650 Li-ion Cells Catalog Introduction Ⅰ 18650 Battery Basic 1.1 Characteristic 1.2 Protective Function 1.3 Basic Parameters 1.4 Merits and Drawbacks Ⅱ 26650 Battery 2.1 Intro Info 2.2 Basic Parameters 2.3 18650 Battery vs 26650 Battery Ⅲ 21700 Battery 3.1 Info about 21700 3.2 Basic Parameters 3.3 21700 Battery Advantages 3.4 18650 Battery vs 21700 Battery Ⅳ Technical Specifications Comparison Ⅴ FAQ Ⅰ 18650 Battery Basic 1.1 Characteristic ① Large capacity: The capacity of a lithium battery is at least 1200mah or more, or even 3600mah, while the average battery cell is only about 500mah.② High energy storage efficiency and good stability: It can still maintain full performance output under 70°, and there is generally a protection circuit inside to prevent the battery from burning out.③ No memory effect: It is not necessary to discharge all the remaining power before charging, and it can be charged and discharged at any time, which is convenient to use.④ High charge and discharge cycle life: The number of cycles of lithium batteries is tens of thousands and the high temperature resistance is very good.⑤ Environmental protection, no toxic substances: Non-toxic, harmless, non-polluting, certified by RoHS quality. Figure 1. 18650 Battery 2200mAh 3.7V 1.2 Protective Function ① Overcharge protection: When the lithium battery is overcharged, the internal temperature rise of the battery will continue to rise, and a detection system for the battery voltage is added. When the battery overcharge voltage reaches a certain value or time period, the overcharge function will work and stop automatically to protect the battery.② Over-discharge protection: It means that the battery is always in an overloaded output state. Generally, there is discharge protection. At this time, the battery will be in a standby mode.③ Overcurrent protection: The overcurrent protection value can be adjusted, some are a few amperes, and the setting is selected according to the actual situation.④ Short-circuit protection: When the battery is short-circuited, the overcurrent protects the battery from burning.In addition to these four protection functions, some also have functions such as temperature and balance. Generally, the battery has a built-in PCM protection system with multiple protection functions. 1.3 Basic Parameters Number Item Parameter 1 Standard Voltage 7.4V 2 Rated Capacity 2200mAh 3 Continuous Working Current 1-3A 4 Overcurrent Protection Value 2-5A(adjustable) 5 Affordable Equipment Power ≤22V 6 Overcharge Protection Voltage 4.25±0.025V/Cell 7 Discharge Protection Voltage 2.50±0.05V/Cell 8 Charging Mode Constant-current and Constant-voltage 9 Maximum Charging Voltage 8.45V-8.55V 10 Recharging Current 0.2℃-0.5℃ 11 Charging Temperature 0~45℃, 45~85%RH 12 Discharge Temperature -20~55℃, 46~85%RH 13 Storage Temperature and Humidity Range Short term: more than one month -20℃~+55℃, 45~85%RH Medium term: more than three months -20℃~+45℃, 45~85%RH Long term: within one year -5℃~+20℃, 45~85%RH 14 Dimensions Brightness Reference Sample Length Reference Sample Thickness Reference Sample 15 Weight <120g   1.4 Merits and Drawbacks ✅Merits1) Large capacityThe capacity of 18650 battery is generally between 1200mah ~3600mah, and the general battery capacity is only about 800mah. If combined into a 18650 battery pack, it can easily break through 5000mah.2) Long LifeThe 18650 battery has a long service life, and the cycle life can reach more than 500 times during normal use, which is more than twice that of ordinary batteries.3) High Safety PerformanceThe 18650 battery has high safety performance. In order to prevent the short circuit of the battery, the positive and negative electrodes of the 18650 batteries are separated. Therefore, the possibility of short-circuiting has been reduced to the extreme. A protection board can be added to avoid overcharging and overdischarging of the battery, which can also prolong the service life of the battery.4) High VoltageThe voltage of 18650 lithium battery is generally 3.6V, 3.8V and 4.2V, which is much higher than the 1.2V voltage of nickel-cadmium and nickel-metal hydride batteries.5) No Memory EffectIt is not necessary to empty the remaining power before charging, which is convenient to use.6) Small Internal ResistanceThe internal resistance of the polymer battery is smaller than that of the general liquid battery, and the internal resistance of the domestic polymer battery can even be below 35mΩ, which greatly reduces the self-consumption of the battery and prolongs the standby time of the mobile phone. This polymer lithium battery that supports large discharge current is an ideal choice for remote control models, and has become the most promising product to replace nickel-metal hydride batteries.7) It can be combined in series or in parallel to form a 18650 lithium battery pack.8) Wide Range of Use18650 batteries can be employed in Notebook computers, walkie-talkies, portable DVDs, instrumentation, audio equipment, model aircraft, toys, video cameras, digital cameras and other electronic equipment.❎Drawbacks1) The biggest disadvantage of the 18650 battery is that its size has been fixed, and it is not very well positioned when it is installed in some notebooks or some products. Of course, this can also be said to be an advantage, which is compared to other polymer lithium batteries, etc. This is a disadvantage in terms of the customizable and changeable size of lithium batteries. Compared with some products with specified battery specifications, it has become an advantage.2) The production of 18650 batteries requires a protection circuit to prevent the battery from being overcharged and causing discharge. Of course, this is necessary for lithium batteries, which is also a common drawback of lithium batteries, because the materials used in lithium batteries are basically lithium cobalt oxide materials, and lithium batteries made of lithium cobalt oxide materials cannot be discharged at large currents, and their safety is poor.3) The production conditions of 18650 batteries are high, compared with general battery production, they have high requirements for production conditions, which undoubtedly increases the production cost.   Ⅱ 26650 Battery 2.1 Intro Info The 26650 battery is a cylindrical lithium battery with a diameter of 26mm and a length of 65mm. It is used in power tools, lighting, wind and solar energy storage, electric vehicles, toys, instrumentation, ups backup power supply, communication equipment, medical equipment and military lights. Figure 2. 26650 Battery Size 2.2 Basic Parameters Cycle performance: 2000 times (1C charge/1C discharge, capacity retention rate ≥80%, 100% DOD)Maximum continuous discharge current: 9.6APulse discharge current: 15A, 5sOperating temperature: Charge: 0°C ~ 55°C, discharge: -20°C ~ 60°CStorage temperature: -20°C ~ 45°CBattery weight: 86g (approx.)Nickel-cobalt-manganese ternary lithium-ion 26650 single-cell nominal voltage is generally: 3.6VNominal capacity: 4500mAh (capacity range 4500-4650mAh)AC internal resistance: ≤30mΩ (plus PTC type)Charging conditions: Cut-off voltage 4.2±0.05V, cut-off current 0.01C. (Note: Charge with 0.5C constant current to 4.2V, and charge with constant voltage until the current drops to 0.01C and cut off)Discharge cut-off voltage: 2.75VCycle performance: 500 times (1C charge/1C discharge, capacity retention rate ≥70%, 100% DOD)Maximum continuous discharge current: 13APulse discharge current: 15A, 5sOperating temperature: Charge: 0°C ~ 55°C, discharge: -20°C ~ 60°CStorage temperature: -20°C ~ 45°CBattery weight: 92g (approx.) 2.3 18650 Battery vs 26650 Battery 1) Different Rated CapacityThe rated capacity of IFR26650 is 3000mAh, and the rated capacity of IFR18650 is 1100~1400mAh.2) Different DiametersThe diameter of the IFR26650 is 26mm, and the diameter of the IFR18650 is 18mm. 3) Different Reference QualityThe production test quality of IFR26650 is 94 grams, and the IFR18650 is 45 grams.18650 lithium batteries are used in lighting, industrial supporting lithium battery packs, power tool batteries, electric bicycle batteries, power lithium battery packs, etc., while 26650 batteries are used in integrated solar street light lithium battery packs, energy storage stations, solar energy storage batteries and so on.The 26650 battery will gradually replace the 18650 battery in the application of power batteries. And with the large-scale use of lithium batteries, it will inevitably be a trend that larger-capacity 26650 batteries replace the trendy 18650 lithium batteries in the 3C era.   Ⅲ 21700 Battery 3.1 Info about 21700 The 21700 battery is a cylindrical battery with a diameter of 21mm and a height of 70.0mm. Its charge density is currently the highest energy density and lowest cost battery in the world, and it is cost-effective. Figure 3. 21700 Battery 4000mAh 3.7V   3.2 Basic Parameters The positive electrode is converted to nickel, the performance is not affected, the consistency is good, and it can be directly used as a battery pack.*Rechargeable Li-ion Cell*Size: Diameter 21mm, Length 70mm*Weight: about 65g*Rated voltage: 3.6V*Standard capacity: 4800mAh*Internal resistance: about 13 milliohms*Charging voltage: 4.2V*Discharge cut-off voltage: 2.5V*Discharge current: 10A (15-20A can be discharged instantaneously).*Applications: flashlights, scooters, LED lights, miner's lamps, lighting products, power banks, mobile power supplies, backup power supplies, computers, mobile devices, cars, bicycles, communications, medical, energy storage, solar energy, etc. 3.3 21700 Battery Advantages 1) The energy density of the 21700 type battery is higher than that of the well-known 18650 type battery. The number of single cells in use can be greatly reduced, and the cost will be reduced after grouping. The capacity of a 18650 battery is about 2600-3600 mAh, while a 21700 battery supports more than 4000 mAh, even 5000mAh has appeared on the market. And the larger capacity is increasingly beneficial to extend the battery life of modern devices.2) The single volume of the rechargeable battery is increased by 35%. Taking the Tesla 21700 rechargeable battery as an example, the energy of a single battery can be increased by 34.8ah, an increase of 35%.3) The net weight of the system software is estimated to be reduced by 10%. The total capacity is more than 21,700. With the increase of single volume and the increase of single energy ratio, the total number of batteries required under the same kinetic energy can be reduced by about 1/3, and the total number of metal components and electrical components selected for the battery pack can reduce the difficulty of managing information systems coefficient. After converting SDI (Samsung Digital Interface) to the new 21700 rechargeable battery, it was found that the system software reduced the net weight by 10% over the existing battery. 3.4 18650 Battery vs 21700 Battery The 18650 rechargeable battery has high reliability and stability, and the performance index of the 21700 battery is much higher than that of the 18650 battery. In addition, compared with other battery models, the raw materials, processing technology and technical steps of the 21700 rechargeable battery are more advanced than the 18650 rechargeable battery level. Therefore, the 18650 and 21700 production lines are the best match.   Ⅳ Technical Specifications Comparison 18650 Battery 26650 Battery 21700 Battery Nominal Voltage: 3.6V Voltage: 3.2V Voltage: 3.7V Nominal Capacity: 2,850 mAh Technologie: Lithium Iron Phosphate Capacity: 3500- 5600mAh Minimum Discharge Voltage: 3V Dimension: 26.2 (Ø) x 65.6 (H) mm Operating voltage: 2.5- 4.2V Maximum Discharge current: 1C Weight: 80g Cutoff voltage: 2 - 2.5V Charging Voltage: 4.2V (maximum) Standard capacity: 2300mAh - 0.5C (current value of 2300mA at 1C°) Weight: 55gms to 75gms Charging current: 0.5C Max. charge voltage: 3.65 ± 0.05 V Charge density (Energy per cell): 10.5- 13.7Wh Charging Time: 3 hours (approx) Inner resistance: ≤15mΩ Charge discharge cycle: 500 to 2000 Charging Method: CC and CV Max. discharge voltage: 2.0V Continuous discharge current: 20- 35 amps Cell Weight: 48g (approx) Cycle characteristic: 1500 (C/5) - 300 (10C) Optimum /Minimum charging time: 2.5 hrs to 3.5 hrs Cell Dimension: 18.4mm (dia) and 65mm (height) Working temperature: 0 ~ 55°C Discharge: -20°C ~ 60°C Charging voltage: 4.2V- 5V   Ⅴ FAQ 1. Are 18650 batteries banned?Consumers should not buy or use individual, loose 18650 lithium-ion battery cells without protection circuits due to possible fire risk, according to a warning just issued by the Consumer Product Safety Commission (CPSC). ... Samsung and Sony also warn consumers against using the cells. 2. What battery replaces the 18650?21700 battery18650 batteries are generally 3.6/3.7 volts and have capacity ratings from 2,300 to 3,600 mAh. 21700 – were designed to be a larger and higher capacity replacement for 18650 batteries. Like the 18650, the 21700 has a nominal voltage of 3.6/3.7V. The 21700 was designed to replace the 18650 in EV battery packs. 3. Are AA batteries the same as 18650?No, they are slightly larger and have completely different formula. The 18650 battery is a lithium-ion cell classified by its 18mm x 65mm size, which is slightly larger than a AA battery. They're often used in flashlights, laptops, and high-drain devices due to their superior capacity and discharge rates. 4. What makes 18650 batteries explode?The safety problem of 18650 lithium-ion battery is burning or even exploding. The root cause of these problems lies in the thermal runaway inside the battery. In addition, some external factors such as overcharge, fire source, extrusion, puncture, short circuit, etc. Will cause the battery to explode. 5. How many hours does a 18650 battery last?A standard lithium ion 18650 battery is rated to last between 300 to 500 cycles before noticing a large performance drop. That is a pretty wide range and we'll discuss some things you can do to extend your batteries life to 500 or even more cycles. 6. How can I charge my 18650 without a charger?You need a regulator to apply a minimal charge, and fortunately, small incandescent lamps in light bulbs and decorative lamps are the perfect regulators for this task. You must connect a cable to the lamp you are using and the other end of the cable will be connected to a hot battery, such as the car's battery. 7. Why are 18650 batteries so popular?The 18650 battery has a voltage of 3.6v and has between 2600mAh and 3500mAh (mili-amp-hours). These batteries are used in flashlights, laptops, electronics and even some electric cars because of their reliability, long run-times, and ability to be recharged hundreds of times over. 8. Are 21700 batteries better than 18650?The stronger heating and lower resistance of 21700 cells than the 18650 results in higher polarization in the 18650 and deviations between the voltage curves for the two formats at higher C rates. The 21700 has about 50% greater capacity and energy density than the 18650 for discharge rates up to about 3.75C. 9. Does Tesla use 21700 batteries?Tesla and Panasonic's 21700 cell was huge news when it was announced in 2017. Tesla doesn't currently use 18650 cells, though; it now uses the 21700 standard with cells measuring 21mm by 70mm. ... The new Tesla battery has gone up in size again, this time far more significantly to 4680 or 46mm x 80mm. 10. Does Tesla use 18650 batteries?Currently, Tesla mainly uses the Panasonic 18650 lithium-cobalt-acid battery, the entire battery contains thousands of independent cells, the battery costs about 135 $ / kWh, to provide 233 W / kg of energy. The future of Tesla plans to launch a new 20,700 lithium battery pack. 11. Are 18650 and 26650 batteries interchangeable?Based on their voltage and current outputs, yes, the 18650 and 26650 batteries are interchangeable. However, the two battery types are very different in size. The 26650 has a much greater diameter, so it will not fit in items designed for the slimmer 18650 battery. 12. What battery can I use instead of 26650?Well, 18650s rechargeable lithium-ion batteries can be used alone or with other batteries too including 26650 batteries in order to build battery packs and power banks or devices used for recharging a device. So, depending on the purpose, both 26650 and 18650 battery can be used together. 13. How long does it take to charge a 26650 battery?around 20 hoursIt may take around 20 hours to charge the 26650 battery fully. 14. Are 18650 batteries the same as AAA?AAA Batteries vs 18650 BatteriesAt first, AAA and 18650 batteries don't have much in common - AAA batteries are cylindrical batteries 10.5 mm (0.41 inch) in diameter and 44.5 mm (1.75 inches) in length, while 18650 batteries are cylindrical batteries 18.6 mm (0.73 inches) in diameter and 65.2 mm (2.56 inch) in length. 15. Can I use regular batteries instead of 18650?Technically yes, you can even buy an adapter that takes 3 AA's to replace an 18650, I use them in my tactical torch if the 18650 dies. However AA batteries are generally much lower capacity than an 18650 so they don't tend to last anywhere near as long. 16. Is 26650 battery same as C battery?They may appear the same and or the same size, but the C battery has a 1.5V nominal voltage while the 26650 lithium battery has a 3.6V or 3.7V nominal voltage. 17. What is the best 26650 battery for Vaping?The Hohm Grown 2 is our top pick for 26650s. It is an accurately rated 30A battery and its large capacity will have it running for much longer than your typical 18650 cell. The 26650 battery has been used for vaping for quite some time now. 18. How many 21700 batteries are in a Tesla?Currently, 4,416 (2170) cells are placed inside Tesla Model 3/Y Long-Range battery packs. In contrast, there will only be 960 cells required to fill the same space. 19.What does 18650 mean on a battery?lithium-ion batteryAn 18650 battery is a lithium-ion battery. The name derives from the battery's specific measurements: 18mm x 65mm. For scale, that's larger than an AA battery. The 18650 battery has a voltage of 3.6v and has between 2600mAh and 3500mAh (mili-amp-hours).