The Kynix Blog - Amplifiers

Summary As we all know,originally developed to support analogue computers,the op amp has an elegantly simple core design. The industries are contining to spare no effect in creating‘ideal op-amp'.     Simply by wiring in different feedback configurations using passives,op amp can be massaged into roles that include buffers and integrators as well has high-gain amplifiers. It is little wonder the op amp has been as successful as it has been. What's more, people in the industry expect a few core parts to do almost any job and for the circuit to be ripe for integration cause the op amp is so readily tunerable.In practice,the choice of discrete op amps has never been wider. Steve Logan, executive business manager for Maxim Integrated’s core products groups, says: “If you don’t need terribly high bandwidth, high voltage for industrial systems or very low voltage for portable designs, those are times when op amps can be integrated.”   Subtly different edge cases push designer to discrete options Op amps often interface electronics to the outside world, so they need to take account of numerous subtly different edge cases, which pushes designers to discrete options. Each variant uses a specific choice of process and circuit topology to take on a job. Logan cites the wrist-worn heart rate monitor, which measures the light reflected back from a green LED. In these systems, input current noise has a large effect on signal quality, calling for op amps that can deliver much lower levels than generic options.   Signal-Conditioning of Systems Signal-conditioning of systems can turn out to be more complex than first appears. Logan says "“One application that’s not immediately obvious is driving a high-speed, high-resolution SAR A/D converter; it can be pretty demanding circuitry. The difference between a SAR and sigma-delta is in how it takes a big gulp of current. The op amp has to settle quickly, so you are talking settling time, slew rate and total harmonic distortion. You may need multiple stages to get the settling time, along with an input buffer, plus a gain stage and filter stage in front of that. You might think at first: how tough can it be? Then it turns into a two- or three-stage op-amp circuit.”   Dwight Byrd, marketing manager at Texas Instruments, says: “As demand for further sensors and signals increases, better conditioning and amplification of the sensor becomes paramount, thus making the proliferation of op amps possible.”     Art Eck, senior product marketing manager at Microchip Technology, adds: “We see a trend toward more designer op amps: op amps that are built for a particular application or set of applications.” At the same time,Kevin Tretter,the product marketing manager of Microchip notes that changes in application needs are creating new problems for op-amp components to address. “With the rapid expansion of wireless capabilities the industry has seen over the years, the presence of electromagnetic interference is becoming a larger issue. Sensitive analogue sensor circuits commonly sit next to wireless communication modules. More and more amplifier manufacturers are trying to combat the adverse effects by implementing on-chip filtering.”   Demand for Futher Sensors A lot of designs call for sensors to be added but for boards to be shrunk cause increasing noise is partly a by-product of the shrinking size of many designs as well ass the recent focus on making systems more aware of their surrounding environment.   Byrd notes: “Where the biggest driver in further technology trends comes in is package size. Previously, an SC-70 package was considered one of the smallest one-channel op amps available. Now, SOT553 is becoming commonplace.”   Logan says the trend continues all the way to wafer-level packages, measuring just more than 1mm on the longer side. Such tiny packages support the idea of an ‘analogue insurance policy’, where op amps and similar parts provide additional conditioning and protection such as buffering to integrated mixed-signal SoCs. “For a little extra size and cost, you can add these functions and make them more robust. The wafer-level package lets you do that.”   Renesas subsidiary Intersil Engineer Tom Kugelstadt said there is otential for circuit-level advances that could reduce the need for op-amp proliferation and so aid integration. “The biggest inevitable tradeoff is between low-power and high-bandwidth, or high-speed. In general, high-speed amplifiers require the fast charging and discharging of the gate capacitances of the internal transistors. This requires increases in bias and supply currents, which often leads to increased offset current and voltages. While high-speed op amps have improved significantly in these parameters, they still tower a magnitude above their low-speed, precision counterparts.“However, there are circuit topologies that aim for increased precision while trading only a minute portion of their high-speed performance. These designs, known as composite amplifiers, consist of a precision amp in open-loop and a high-speed amp in a closed-loop differentiator configuration.”   Complesity of Picking Right Op-amp The multiple novel circuit topologies that have appeared over the past few decades to deal with problems such as temperature drift and power consumption can have unexpected side effects that designers need to take into account. That adds to the complexity of picking the right op amp.   Logan points to the use of chopper-stabilised amplifiers. “These are great for low offsets, but push the noise out to a single frequency. One that pushes it out to 60kHz is great for DC, but if you have signals that reach 50kHz, you start to get into the noise skirt. These are nuanced things you might not see immediately from the datasheet.”   Frequency-related interactions often need careful examination, says Byrd, and datasheets should show them. “If the output impedance is relatively low and unchanging over a frequency range, it is normally indicative that the op amp will be more stable than one that does have a wide varying output impedance. The output impedance will be interacting directly with the op amp load, and normally a capacitor, it would create various filters as the frequency and therefore the output impedance changes.”   Kugelstadt says interactions with manufacturing choices at the PCB level can introduce unforeseen issues. “High-precision designs using auto-zeroing amplifiers can suffer in precision from asymmetric circuit design. Here, the solder joints around the amplifier form thermocouples that contribute more differential input voltage than the specified offset in the data sheet. Customers unfamiliar with this pitfall blame the device manufacturer for overstating its device performance. The remedy is good application support, such as including layout guidelines in the application section of the data sheet.”   Design Issues TI marketing manager Ying Zhou points out that the need to consider how the op amp is designed, particularly if the op amp is being co-opted for a secondary purpose. “If a dual- or quad-channel op amp is already used elsewhere on the board, sometimes the engineers would assign the left channels for comparator functions,” she says.Although many op amps have input clamping diodes to protect the input transistors but these can affect their behaviour as comparators. Zhou says ‘mux friendly’ versions of op amps that remove the clamps make them more suitable for use as comparators.   Logan notes: “Getting an evaluation kit and putting it on the board is a great thing to do. There is a lot of pin compatibility out there, so you can easily drop another one in to check its performance. But, you do have the issue of having a lot to choose from.”   The industry continues to strive to create the ‘ideal op amp’ and, although we continually get closer to that ideal, there will always be design trade-offs among speed, noise, power usage, size, et cetera. These trade-offs, coupled with continually growing application specific needs, will continue to drive a variety of amplifier types.”  

In this article today, we will introduce 9 simple audio amplifier circuit design schematic diagram with detailed explanation, complemented with some knowledge about amplifier.     Catalog   I. What is an Audio Amplifier? II. Nine Simple Audio Amplifier Circuit Design Schematic Diagrams III. Some Knowledge about Amplifier FAQ     I. What is an Audio Amplifier? Let's watch a video first. This video shows us how to make a great sounding LM386 audio amplifier with bass boost An audio amplifier is a device that reconstructs an input audio signal on an output element that produces sound. The reconstructed signal volume and power level are ideal. They are truthful, effective, and low distortion. The audio range is from 20Hz to 20 kHz, so the amplifier must have a good frequency response within this range. Depending on the application, the power varies greatly. From milliwatts of headphones to several watts of TV or PC audio, to dozens of watts of mini home stereo and car audio, to hundreds of watts or more of more powerful household and commercial audio systems, until the power is big enough to meet the sound requirements of an entire cinema or auditorium.   The development of audio amplifiers has gone through three times. They are electron tube (vacuum tube) time, bipolar transistor time, and field-effect transistor time. The electronic tube audio amplifier has a round and sweet timbre, but it has the disadvantages of large volume, high power consumption, unstable operation, and poor high-frequency response. For the bipolar transistor audio amplifier, it has the advantages of a wide frequency band, large dynamic range, high reliability, long life, and high-frequency response is good. However, its static power consumption and on-resistance are very large, and the efficiency is difficult to improve. The third one is the field-effect transistor audio amplifier. It has the same round and sweet timbre as the electron tube and its dynamic range is wide. More importantly, it has a small on-resistance and can achieve high efficiency. Figure 1 II. Nine Simple Audio Amplifier Circuit Design Schematic Diagrams Next, I would like to introduce nine simple audio amplifier circuit design schematic diagrams.   Circuit Diagram 1 This circuit makes full use of the conventional LM317 voltage adjustment chip,  so that it not only completes the voltage stabilization function of the unstabilized voltage after filtering but also realizes the function of amplifying the audio signal picked up by the electret capacitive microphone. The electret capacitive microphone contains an impedance converter based on JFET, which converts the speech signal into a current form and adds it to the RP resistor, causing the corresponding voltage change. 220V AC output 36V unstable DC through transformer and bridge rectifier, and after filtering by the capacitor, the low resistance audio amplification signal input by the LM317 on the DC is fed into the capacitor and output to the loudspeaker. The implementation circuit is shown in figure 2.   Figure 2 After the circuit is installed, the voltage difference between the two inputs of the electret capacitive microphone should be adjusted first. This voltage difference is required to be less than 1.25VDC. By connecting an adjustable resistor between the LM317 adjustment end and the ground, the required limit can be achieved by adjusting the resistance by Rp. Secondly, the audio signal picked up by the microphone is easy to be interfered with by external noise. The addition of C1 can filter out part of the interference signal, but the required signal is also attenuated. Because the internal gain of the LM317 can compensate for the attenuation part, the loss caused by the introduction of C1 is negligible.    In order to avoid excessive loss, the capacity of C1 should be as low as possible, this circuit takes 15F. Finally, it should be noted that the minimum operating current requirement of the LM317 chip is 4 mA when the circuit is working normally, and a load resistor is used to absorb the 4mA current. If a low impedance loudspeaker is used, this load resistance must also be introduced to compensate for the signal distortion. In a practical circuit, if an 8Q impedance loudspeaker is used, at least 420Q load resistance is used to compensate for the possible signal distortion.   Circuit Diagram 2 Figure 3     Circuit Diagram 3 Adjust R1 so that the signal is not distorted at the maximum output, and reduce R2 to output more power. If there is a multimeter, the collector voltage of the transistor can be adjusted to about half of the power supply voltage. Figure 4     Circuit Diagram 4 In this design, the gain control of the preamplifier adopts DC volume control mode is realized as shown in figure 5. The preamplifier is an inverse proportional amplifier composed of a fully differential operational amplifier and resistor. Its gain is determined by the ratio of feedback resistance to input resistance. The external input DC analog control signal Vc is converted into control data through the gain control module (GainCon-troD), which is used to control the ratio of the feedback resistance of the preamplifier to the input resistance, and then adjust the change of the gain. Figure 5   The operational amplifier adopts a two-cascade structure, as shown in figure 6. In the first stage, a folded common-source common-gate amplifier with PMOS input is used to provide a large gain. At the same time, the common-mode range of the input is increased and the flicker noise is reduced. The load of the folded input tube adopts a current source load with a source feedback structure to increase the output impedance and reduce noise. The second stage uses a common-source amplifier to provide a large swing.    In order to maintain the stability of the closed-loop, Miller compensation capacitance is added. At the same time, in order to counteract the influence of the zero points of the right half-plane, the zero adjusting resistance in series with the compensation capacitor is inserted into the feedforward path of the compensation capacitor. In the design of the common-mode feedback circuit, the common-mode feedback structure with resistance distributor and amplifier is adopted.     Figure 6   Circuit Diagram 5 The audio amplifier uses very few peripheral components and works well at 2v. （The circuit is shown in figure 7）   The TDA7052 is a mono amplifier designed for battery-powered portable tape recorders and radios with an internal gain set at 40dB. Now the recorder and radio tend to be miniaturized and the battery consumption is reduced, which means that the power supply voltage is reduced, and the output power is also reduced. In order to compensate for this loss, TDA7052 uses the bridge drive load (ETL) principle, which can make the output power of 8 EU load up to 1.2 w.   Figure 7 lists the working parameters of TDA7052. Except for special instructions, the power supply is 6 v, the load impedance is 80, the input signal frequency is 1 kHz and the ambient temperature is 25 degrees.   Figure 7   Circuit Diagram 6   TDA2822 Fabrication of microphone Power Amplifier Circuit The circuit has few peripheral components, simple fabrication, but surprisingly good sound quality. A dual audio amplifier integrated circuit is used and its main characteristics are high efficiency and low power consumption. The typical value of static working current is only about 6mA. The integrated circuit has strong voltage adaptability (from1.8V to 15V DC) and will still have a power output of about 100mW even if it is used at a low voltage of 1.8V. The specific circuit is shown in figure 8. Figure 8   The electret microphone MIC converts the picked sound signal into an electrical signal, which is introduced from the foot 2 of U1 by C2 and W, and amplified by U1 audio to promote the loudspeaker pronunciation. The machine is connected with a BTL output circuit, which is good for improving sound quality and reducing distortion. At the same time, the output power is increased fourfold. When a 3v voltage is used, the output power is 350mW.   The resistance R1 and R2 are 1/4W metal film resistance, W is a small carbon film potentiometer and C2 is preferably a monolithic capacitor. If there is no good quality ceramic capacitance, select high quality, voltage resistant, and low leakage current electrolytic capacitor for C1, C4, and C3. Choose high sensitivity electret microphone as MIC, choose small button switch or toggle switch for K and choose TDA2822M or TDA2822 or D2822 for U1. According to the numerical value in figure 7, it can work normally without debugging.     Electret microphone detection For example, the R*100 of MF 47 multimeter is used to measure the Great Wall CZ Ⅲ electret microphone. When the black watch pen is connected to the core line and shell of the electret microphone, the multimeter pointer refers to the value at 3k Ω. When blowing hard, the pointer refers to the value at 4k Ω (and the resistance value of some microphones becomes smaller). If you blowhard and the multimeter pointer wobbles very little, you can adjust the two watch pens and try again. If the multimeter needle is still wobbling very little, the electret microphone is damaged.   In application, the drain D of the electret microphone must be connected to the positive electrode of the power supply through a resistance of 4.7 to 10k Ω, and then connected to the amplifier circuit, as shown in figure 9. Figure 9   Circuit Diagram 7    Add an amplifying circuit to the microphone  The electronic components are as follows：                                                                    resistance R1：1k Ω resistance R2：1m Ω resistance R3：1k Ω transistor vT：9014 capacitance：4.7 UF capacitance C2 ：4.7 UF battery：AA size battery     Figure 10    Working principle of amplifier circuit  Fig. 10 is a circuit diagram of the entire microphone amplifier circuit. As you can see from fig. 10, there are only six or seven originals of the whole circuit. The following is a brief description of how it works, in which the resistor R1 is responsible for providing the operating voltage to the microphone, R2 and R3 are responsible for providing the bias voltage for the transistor, and the capacitor C1 is responsible for coupling the signal of the microphone to the transistor for amplification. Finally, the amplified signal is coupled through capacitance C2 and sent back to the positive pole of the microphone line, that is, the outermost shielding layer of the microphone line (that is, the outer layer of copper mesh). Figure 10 is the material or electronic component we use to make it.    Considerations in production  The specifications of the electronic components required for the whole amplifier circuit are as follows: resistance R1：1K Ω resistance R2 ：1m Ω resistance R3 ： 1K Ω transistor VT ：9014 capacitance C1：4.7 μ F capacitance C2 ：4.7 μ F battery： a general AA size battery. △ Generally speaking, it can be used for about half a year if it is used normally.    Pay attention to the following points in the production process： 1. The pin of the transistor must be connected correctly; otherwise, it will not play the role of amplification. The pin distinguishes the following transistors lead down and the flat side facing itself. The transistors are E (emitter), B (base), and C (collector);   2. The microphone head is also polar. (see figure 4 for a specific distinction);   3. The polarity of the coupling capacitance can be distinguished by marking, and the pin with an arrow and marked "-" is a negative electrode, and the positive electrode is generally not marked   Because the components are few or can be directly welded in the shed, the circuit board can be directly installed into the base of the microphone, and the power lead of the circuit board can be connected to the battery slot reserved by the microphone.     Effect Test After trial, the effective distance of the microphone can reach 5 to 6 meters, and the effect is also obvious with the voice input function of Office Word 2003, and the speech can also be accurately recognized about 1 meter away from the microphone.   Circuit Diagram 8 A transistor is required. First, output the MP3 signal and use a lower power tube to amplify it. Then push medium power tube. This can achieve small distortion and have the coupling undone. This transistor circuit is simple, practical, and also easy to make.     Figure 11 The circuit is powered by a 9V single power supply. The input signal is coupled to the base of 9014 through 47uF capacitance. 9014 is responsible for preamplifier, and works in Class A state. 5.6K and 1.5K resistors are bias resistors of 9014, and 5.6K resistors are negative feedback resistors at the same time. 22 Ω resistors is a current series negative feedback resistor, which is used to increase the input impedance and reduce the linear distortion by 9014. The 470 Ω resistor is a 9014 collector load resistor used to convert the 9014 amplified current into a voltage, and two 1N4148 diodes are used to set the post-stage complementary tube in the pre-conduction region. OTL complementary output circuit is composed of 8050 and 8550. 3.3 Ω resistors are negative feedback resistors in series with emitters, which act the same as 22 Ω resistors. The 1000uf capacitor is the output capacitor, which is used to separate the DC and allow the AC signal to pass through. 8050 and 8550 are used as power output tubes to form a complementary push-pull output circuit, and the amplified current of 9014 is further amplified to push the loudspeaker. The static bias current of the push-pull circuit is set by two 1N4148, and the two 1N4148 are temperature compensation elements of two power output transistors at the same time. The voltage at the positive contact of the 1000uF electrolytic capacitor shall be half of the supply voltage. Because the conduction voltage of the silicon transistor base is 0.7 V, the base voltage of 8050 can be obtained to be about 5.2 V. From this, the static bias current of 9014 is (9- 5.2) / 470 =8 [mA]. The emitter voltage of 9014 is 8*22=0.176 V, and the base voltage is 0.176+0.7≈0.87V. Circuit Diagram 9 As long as R3 is increased, the gain of the amplifier can be increased. The parallel capacitor C4 at both ends of R3 is used to provide low resistance path filtering to high frequency to prevent high frequency self-excitation. J1 is a jumper, when J1 is turned on, foot 1 is grounded and the full power amplifier works; when J1 is disconnected, foot 1 is VDD, micro-power off, and the amplifier does not work. Jumper J2 can also control the operation of the amplifier. When J2 is disconnected, the + IN end is unbiased and the amplifier does not work. But if it is connected,  the amplifier works. LM4819 high gain audio amplifier circuit is shown in figure 12. Figure 12   III. Some Knowledge about Amplifier      Distortion  Also referred to as THD+N, Total Harmonic Distortion + Noise is simply a measure of the effect that an amplifier will have on sound output. The lower the distortion is, the closer your amp’s output will be to the original recording’s sound. The more distortion that there is, the more coloration there will be to the sound. Just keep in mind that your speakers will also have an impact upon sound, so choose them wisely by matching them with the right amplifier for the clearest sound.    Left and Right Signals  Crosstalk is a term that refers to the measure of how much of the right signal is mixed with the left signal. Amps come as a single unit, but they need to send signals out separately to the speakers so that you can hear things like a piano on the right and a singer to the left. If there is a lot of crosstalk, though, it will be much more difficult to decipher where the different sounds are coming from.    Power  When you look at an amp’s specs, you will also notice that there is a number for the power output, which is basically how loud the music can go. For the average listener, a 10W amp would be sufficient, as it will let you play your music loudly without creating any distortion. If you are really looking for a super loud amp, though, you can go as high as 100W. It really depends upon what your preferences are, what you will be using your amp for, what speakers you have, and how much room you have.    Connections  Your amp should have plenty of inputs for anything and everything that you wish to plug into it. You could have a 3.5mm connection for your iPod, and you could have a USB connection for your laptop, as a couple of examples. Just don’t sacrifice sound quality for more inputs.    Signal vs. Noise  There will always be some background noise within your amplifier, just as there is always some background noise in your own environment. What you want is an amp that will ensure the background noise is not obvious or perceptible. This will ensure that you will hear all of the music but none of the noise. Checking the signal to noise ratio on an amp will give you clearer insight into how well the product will work in this area.   FAQ   1. What does an audio amplifier do? An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals such as the signal from radio receiver or electric guitar pickup to a level that is high enough for driving loudspeakers or headphones.   2. What is the difference between a speaker and an amplifier? Speakers are those things that make sound. The amplifier is what delivers sound to the speakers. Amps are usually radios and speakers are what you plug into the amp/receiver to hear the sound. ... The speakers plug into the sound card which in this case would loosly be called the amplifier.   3. Does amplifier improve sound quality? An amplifier simply increases(magnifies)the components of sound quality. If the quality of the input sound is poor, it will be a louder poor sound ; meaning you will hear the poorness of the sound more. It amplifies everything, the good and the bad.   4. Why do you need an amplifier? An amplifier is the device that turns the low voltage signals from your source equipment into a signal with enough gain to be used to power a pair of speakers. ... The second does the 'heavy lifting' and adds the gain to the signals in order to be used to power a pair of speakers. This is the power amplifier.   5. Which is better amplifier or receiver? A receiver is definitely the more convenient choice of the two, but that doesn't mean that it comes without any downsides. Usually a Lower Quality Amplifier - Though the quality of receiver amps is definitely increasing, you still don't have a completely dedicated amp with a receiver.   6. Which is more important speaker or amplifier? A speakers performance is highly variable and its sound will depend on the amp driving it. But the greatest amp (whatever that is) will sound like crap if the speaker sounds like crap. The quality of the speaker is the ultimate limitation of your system (assuming proper set up and room integration)   7. Can I hook up 8 ohm speakers to a 4 ohm amplifier? Yes, you can use 8 ohm speakers with a 4 ohm amplifier. Just wire two 8 ohm speakers of the same wattage in parallel.   8. How much money should I spend on an amp? If it's just for practicing in your bedroom, you can get a perfectly adequate little practice amp for under $200. If you'll be playing in a band or gigging out, yeah, you probably should expect to spend in the $500-700 range at least.   9. Do you need an amp for a subwoofer? Subwoofers are designed to increase the bass frequencies, resulting in a deep, thumping sound. In most cases, they are paired with an amplifier to boost the sound. If you do not have the funds for both components, you can still hook up a subwoofer without an amplifier; it simply involves a little more know-how.   10. Which transistor is used in amplifier? In most of the electronic circuits, we use commonly NPN transistor configuration which is known as NPN transistor amplifier circuit. Let us consider a voltage divider biasing circuit which is commonly known as a single stage transistor amplifier circuit.     Reference Component LM3886TF LM4652TA LM4765T  

The LTC2185 is a 125Msps 16-bit ADC with excellent noise and linearity performance while only consuming 185mW per channel. It is ideal for demanding low power applications that require excellent AC performance. A high performance ADC like the LTC2185 requires a high performance amplifier driving it to maintain the excellent performance. The ADA4927-1 delivers the linearity performance required by the LTC2185 while only consuming 215mW. The well designed package of the ADA4927-1 allows for a simple layout that reduces parasitic capacitance in the feedback path that can erode the phase margin of the amplifier. This combination of ADC and driver allows excellent performance from 62.5-125MHz a region where other high speed amplifiers are lacking.  The LTC2185 is a two-channel simultaneous sampling parallel ADC which offers a choice of full-rate CMOS, or double data rate (DDR) CMOS/LVDS digital outputs. Pin-compatible speed grade options include 25Msps, 40Msps, 65Msps, 80Msps and 105Msps with approximate power dissipation of just 1.5mW/Msps per channel. It includes popular features such as the digital output randomizer and alternate bit polarity (ABP) mode that minimize digital feedback when using parallel CMOS outputs.  Analog full power bandwidth of 550MHz and ultralow jitter of 0.07psRMS allows under-sampling of IF frequencies with excellent noise performance. To maintain this level of performance the LTC2185 needs to be driven with an appropriate amplifier like the ADA4927-1. The ADA4927 is a high speed differential current feedback amplifier. Fabricated on Analog Devices’ silicon-germanium process, the ADA4927-1 has excellent distortion and an input voltage noise of only 1.3nV/rtHz. This allows it to drive high speed ADCs like the LTC2185. The gain of the ADA4927-1 is set with external feedback resistors located next to the input pins.  By keeping the feedback pins and input pins close on the package, the ADA4927-1 provides a clean layout and minimizing the parasitic capacitance in the feedback network. This make the ADA4927-1 an ideal choice for driving high performance ADCs, like the LTC2185, from DC to 125 MHz. Figure 1 shows a schematic of the ADA4927-1 driving the LTC2185. The corresponding layout is shown in figure 2.  The feedback pins on the ADA4927-1 are adjacent to the input pins which minimizes the parasitic capacitance of the feedback node and improves the phase margin of the amplifier. It also Simplifier the layout by making it possible to place feedback resistors directly across the two pins and not having additional trace length in the feedback path. There is a simple filter between the amplifier and ADC that reduces the wideband noise of the amplifier and improves the SNR of the system. This filter also attenuates the sampling glitches from the ADC before they reach the amplifier. This helps keep the output network of the ADA4927 from oscillating in response to these glitches. This filter network can be modified to accommodate a wide range of input bandwidth requirements. (Figure 1:  Schematic showing an ADA4927-1 driving one channel of the LTC2185)(Figure 2:  Layout showing an ADA4927-1 driving once channel of the LTC2185)Figure 3 and figure 4 show the SNR and SFDR of the LTC2185 and ADA4927-1 combination. The SFDR stays above 67dB out to 125MHz while the SNR is better than 63dB to the same frequency. This combination only consumes 250mW. With a sample rate of 125Msps, this combination provides good performance through the entire 2nd Nyquist zone where other amplifiers begin to have poor linearity.  (Figure 3:  SNR of the LTC2185 driven with the ADA4927-1)(Figure 4:  SFDR of the LTC2185 driven with the ADA4927-1) Using the ADA4927-1 to drive the LTC2185 provides excellent linearity while keeping the power consumption low. The fact that the ADA4927-1 stays very linear out to 125MHz allows this ADC amplifier combination to be used in demanding communication and medical applications that require the use of the second Nyquist zone of the LTC2185. The pin out of the ADA4927-1 and filter design minimize the complexity of the layout while maintaining excellent performance on a low power budget. Ref.KY32-LTC2185KY362-ADA4927-1 

Researchers at Chalmers University of Technology, Sweden, have demonstrated an integrated amplifier with the lowest noise performance so far. The amplifier offers new possibilities for detecting the faintest electromagnetic radiation, for example from distant galaxies.Last year, Chalmers reported a world record for a low-noise amplifier in the prestigious journal Electron Device Letters. The amplifier exhibited a minimum noise figure of 0.018 dB across a bandwidth of 4-8 GHz. However, since the low-noise amplifier was designed in a hybrid solution, scaling up to larger quantities turned out to be very difficult.Chalmers has now in collaboration with a company called Low-Noise Factory published an article on an integrated ultra-low-noise amplifier. The scientists have developed a unique indium phosphide-based process for what is known as high electron mobility transistors (HEMT). Transistors and other semiconductor components have been fabricated on a monolithic chip on an indium phosphide wafer. All parts of the design such as semiconductor layers, components, process and circuit design have been optimised for the lowest noise performance.As a result, an integrated 2.0 x 0.75 mm amplifier with an ultra-low-noise figure of 0.045 dB was demonstrated. The amplifier had a very large bandwidth of 0.5-13 GHz and a high gain exceeding 38 dB across the frequency band. In order to show such extreme performance, the amplifier was cooled to minus 260 degrees of Celsius."The combination of high gain, large bandwidth and ultra-low-noise figure makes this circuit very attractive for large multipixel arrays containing thousands of antennas," says Jan Grahn, research group leader at Chalmers."The integrated ultra-low-noise process enables the fabrication of thousands of amplifiers with identical performance. One potential future application is in the world's largest radio telescope SKA (Square Kilometer Array) that is being planned, an international project where the Onsala Space Observatory at Chalmers is one of the acting members. In huge applications such as the SKA, even a small noise-figure reduction in the first low-noise amplifier in the receiver chain may potentially bring about major savings in the final system design." 

Fujitsu today announced the development of a gallium-nitride (GaN) high-electron mobility transistor (HEMT) power amplifier for use in W-band (75-110 GHz) transmissions.This can be used in a high-capacity wireless network with coverage over a radius of several kilometers. In areas where fiber-optic cable is difficult to lay, to achieve high-speed wireless communications of several gigabits per second, one promising approach is to use high-frequency bands, such as the W band, which uses a wide frequency band. In order to get good long-distance coverage in these frequencies, however, it is necessary to increase the output power of the power amplifier to the scale of watts. Fujitsu succeeded in developing a power amplifier for W-band transmissions using GaN-HEMT technology capable of high output at 100 GHz. Evaluations of the newly developed power amplifier confirmed it to have 1.8 times increased output performance than before, which would translate to an increase of over 30% in transmission range when used in a high-speed wireless network. A portion of this research was conducted as part of a project of the National Institute of Information and Communications Technology (NICT) on "Agile Deployment Capability of Highly Resilient Optical and Radio Seamless Communication Systems." Details of this technology are being presented at Power Amplifiers for Wireless and Radio Applications (PAWR2016), opening January 24 in Austin, Texas.High-frequency wireless communications, using the frequency band known as the W band (75-110 GHz), are drawing increasing interest, both as a way to temporarily set up high-capacity communications channels for handling special events where large numbers of people gather, or for responding to disasters, and also as a way to bring communications to remote areas where fiber-optic cables are difficult to lay. Compared to today's mobile phones, which use frequencies in the 0.8-2.0 GHz range, the W band uses a frequency band more than 50 times as broad with 50 times the speed, meaning it is a frequency band that is well-suited to these high-capacity wireless communications.In order to transmit wireless signals over a distance of several kilometers, the transmission antenna needs a power amplifier capable of a high output on the order of several watts. Existing power amplifiers for high-frequency transmissions in the millimeter-wave band (30-300 GHz), which are built using gallium arsenide or CMOS semiconductors, are limited by their operating voltage to an output of about 0.1 W, and it has not been possible to increase this. GaN-HEMT power amplifiers have achieved high output performance in the microwave range (3-30 GHz), but the problem up until now was that their output performance declined in the W-band range. To solve these problems, Fujitsu developed a GaN-HEMT device with a unique structure capable of increasing output in the millimeter band (Figure 1). This uses a layer of indium-aluminum-gallium-nitride (InAlGaN), and double-layer silicon nitride (SiN) passivation film to increase current density by a factor of about 1.4, resulting in 3.0 W of output power from a transistor per 1-mm of gate width, at a high frequency of 100 GHz. In developing this transistor, Fujitsu collaborated with Professor Yasuyuki Miyamoto of the Tokyo Institute of Technology in developing a device-simulation technology.Fujitsu succeeded in developing a power amplifier with the world's highest W-band output performance using this GaN-HEMT device with a proprietary structure (Figure 2). In order to successfully design a power amplifier with high output performance, Fujitsu precisely measured and modeled the characteristics of GaN-HEMT during high-frequency operation. Based on that, a circuit was designed where pairs of GaN-HEMTs were grouped together into compact, high-gain units with low power loss. In order to maximize the power from these units, GaN-HEMTs were connected in a series by the interstage circuit where the signal lines and the device layouts were carefully laid out. Using a model of these compact, high-gain units, Fujitsu conducted simulations to optimize the distributor and combiner matching circuits between the units, and their layouts and signal lines, resulting in a high-amplitude power amplifier (Figure 3). A prototype power amplifier had amplitude that multiplied its input by a factor of 80, producing 1.15 W of output power. Power output per transistor, a measure of power-amplifier performance, was 3.6 W per 1 mm of gate width, the highest in the world.The newly developed power amplifier achieved a 1.8 times increase in power-amplifier output over previous W-band power amplifiers, with the world's highest output performance (Figure 4). This translates to an improvement of over 30% in terms of range for wireless communications at speeds of several gigabits per second.Fujitsu plans to apply this power-amplifier technology to high-capacity long-range wireless communications, and to implement high-speed wireless communications systems that can be used for high-expediency temporary communications infrastructure for use during special events and when fiber-optic links have been broken in the event of disasters.  

LM4910LQ belonging to the Boomer series of National Semiconductors is an integrated stereo amplifier primarily intended for stereo headphone applications. The IC can be operated from 3.3V ans its can deliver 0.35mW output power into a 32 ohm load. The LM4910LQ has very low distortion ( less than 1%)   and the shutdown current is less than 1uA. This low shut down current makes it suitable for battery operated applications. The IC is so designed that there is no need of the output coupling capacitors, half supply by-pass capacitors and bootstrap capacitors. Other features of the IC are   turn ON/OFF click elimination, externally programmable gain etc. Stereo headphone amplifier LM4910LQCircuit diagram of the LM4910LQ stereo headphone amplifier is shown above.C1 and C2 are the input DC decoupling capacitors for the left and right input channels. R1 and R2 are the respective input resistors. R3 is the feed back resistor for left channel while R4 is the feed back resistor for the right channel. C3 is the power supply filter capacitor. The feedback resistors also sets the closed loop gain in conjunction with the corresponding input resistors. Notes:The IC is available only  in SMD packages and care must be taken while soldering.The circuit can be powered from anything between 2.2V to 5V DC.The load can be a 32 ohm headphone.Absolute maximum supply voltage is 6V  and anything above it will destroy the IC.A logic low voltage at the shutdown pins shut downs the IC and a logic high voltage at the same pin activates the IC.