circuit Related Articles

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  

Ion Transistors for the transport of both positive and negative ions, as well as biomolecules had been previously developed by a group of Organic Electronics research team at Linköping University. Now Tybrandt has now succeed in developing circuits using these Transistors similar to traditional silicon electronics. In essence of this technology we can build computer chips that can directly interface with our body cells.The major advantage of chemical circuit is that the charge carrier consists of chemical substances with various functions and this gives us new opportunities to regulate and control signal paths of Human Body Cells.In a conventional transistor there are three terminals Gate, Source and Drain. When signal is applied to Gate terminal, electrons flow from Source to Drain. Electrons are the charge carrier in conventional transistor, but in the new Ion Transistor the ionic neurotransmitter acetylcholine is the charge carrier. NAND gates and Inverters can be created using these Ion transistors, which means that it can be used to implement any logic function.Magnus Berggren, Professor of Organic Electronics and leader of the research group says that, it can be used to send signals to muscle synapses when our muscle signalling system may not works for some reasons and our chips works with common signalling substances such as acetylcholine.The research in Ion Transistors which can control and transport ions and charged biomolecules was begun before 3 years by Berggren (professor in Organic Electronics at the Department of Science and Technology at Linköping University) and Tybrandt (a doctoral student). Researchers at Karolinska Institute then used this Transistors to control the delivery of the signalling substance acetylcholine to individual cells. It hopes that it can restore the lost movement of paralysed peoples.Mr. Tybrandt in conjunction with Robert Forchheimer (Professor of Information Coding at LiU) has taken the next steps by developing chemical chips which contains logic gates, that allows the construction of all logic functions.Ref:KY56-C4706KY56-KSC5024RTUKY56-MJL21193G

As integrated circuit components are coming up against size limits, manufacturers are turning to new approaches based on stacking extremely thin wafers. However, the thin wafers easily warp under the stresses involved in fabrication, and measuring the stress and warpage has so far proven challenging.In a paper published in the Journal of Applied Crystallography, Professor Patrick McNally's team at Dublin City University, together with collaborators Brian Tanner at Durham University and Andreas Danilewsky at the University of Freiburg, report on a new technique using the Test beamline (B16) at Diamond Light Source to accurately, precisely, and verifiably measure the stress and warpage in individual silicon wafers. The researchers are now cooperating with industry partners to translate their approach into a tool which can be used for quality assurance and to improve fabrication processes. Meanwhile, they continue to work at Diamond to improve the technique and adapt it to different contexts and materials.A stack of measurement troubleIn a 1965 paper, Intel co-founder Gordon Moore observed that the density of transistors in integrated circuits doubled every 18-24 months, a trend which has held well in the decades since. However, manufacturing techniques are nearing the limits of 'Moore's law' as the components printed onto integrated circuits approach atomic dimensions. To continue improving performance, manufacturers are exploring a new direction by combining different chips, each with a specialised function, into a vertical package in a 'more than Moore' approach known as heterogeneous integration.The new technique involves using wafers less than a tenth as thick as those currently in use. Since they are so thin – just 25 to 100 µm – the wafers are extremely flexible, but they are also subjected to extreme stress during the fabrication process. "Imagine you glue together four or five pieces of silicon, each thinner than a human hair, then heat them up to 100-200° C, and then stand on top of them with your boot. Maybe you jump up and down a bit. That's the sort of damage that's done as part of semiconductor processing," explains Professor Patrick McNally of Dublin City University. The stress and resulting warpage of the wafers during manufacturing can lead to malfunctions, altered performance, and silicon 'real estate' lost to stress-related 'keep out zones' on the chip. To avoid these pitfalls, manufacturers are eager to understand how to manage stress and warpage in their design and fabrication processes.So far, measuring the warpage of the individual silicon wafers without damaging them has been impossible, forcing people to use the warpage of the entire package as a proxy. Using the Test beamline (B16) at Diamond, the trio have developed a non-destructive technique to precisely and accurately measure the warpage of each wafer in a package through transmission X-ray diffraction imaging. To confirm their measurement technique, the team included samples with known curvature and displacement from IMEC in Belgium. "We've proven that it can be done reliably and verifiably," said Professor McNally.To industry and beyondWhile the new technique shows great promise, "no one in the semiconductor business is going to back a synchrotron into their fabrication facility," noted Professor McNally. The team has already successfully carried out preliminary trials with a commercial tool as an X-ray source, and work is underway with X-ray metrology companies to bring the technique into industry as a quality assurance tool. Improving the measurement speed of the commercial tools is a major outstanding challenge – measurements done in minutes at Diamond can take hours with commercial tools – but the team is pursuing avenues to improve this.The technique offers an opportunity not only to measure warpage during fabrication but also to improve the design process. Mechanical engineers at a large chip company are working with the team to test the finite element models they use to predict stress and warpage in their designs. "The idea is that we provide a 'sanity check' on their modelling so they can use it to improve their designs," said Professor McNally.Meanwhile, the team is continuing to develop the approach using the facilities at Diamond, which underpins any advancements. The team has recently tested their new technique on chips, which were receiving power to measure how the warpage might change under different usage conditions. "We do our top end development at Diamond," said Professor McNally, explaining that the ability to rapidly test and explore ideas at the synchrotron is crucial before they can be adapted for industry applications.Ref:KY32-MAX1490AEPG+KY32-LMX4169AQFXN      

As circuits become smaller and more densely populated with circuit protections, electrical characteristics of the components become more prone to the influence of the heat generated. "The interaction between thermal and electrical phenomena is one of the most troublesome problems in analog and digital integrated circuits," explain Ryo Ishikawa, Junichi Kimura and Kazuhiko Honjo from the University of Electro-communications in Chofu-shi, Japan.     In this paper, the researchers report on the world's first method to compensate the disturbed electrical characteristics by using an electric circuit that cancels signal distortion caused by thermal behaviour of a heterojunction bipolar transistor. This research should help design devices that are better equipped to handle heat effects. A modulated high-frequency signal is distorted by the thermal behaviour through complex intermodulation phenomena, although the temperature response of the circuit is slow. The researchers modelled the thermal effects of a heterojunction bipolar transistor in an integrated circuit using thermal resistors and thermal capacitors. The circuit elements were arranged in a 'ladder circuit' comprising repeating units of thermal resistors and thermal capacitors. To compensate the signal distortion on the integrated circuit, an electric 'ladder circuit' was connected. Although the validity of the electric ladder circuit to compensate the signal distortion has already been confirmed by experiments and simulations, a theoretical derivation for the behaviour has so far been lacking. Honjo and his team derived nonlinear expressions describing the circuit parameters, and solved the expressions using series expansions. The model compared well with experiments and simulations. Experiments for an InGaP/GaAs heterojunction bipolar transistor power amplifier operating at 1.95GHz provide compelling validation for their analytical design, emphasising its potential for designing circuits that cope better with heat effects. Reference: KY438-PN-DESIGNKIT-38 KY438-PN-DESIGNKIT-37    

The latest buzz in the information technology industry regards "the Internet of things"—the idea that vehicles, appliances, civil-engineering structures, manufacturing equipment, and even livestock would have their own embedded sensors that report information directly to networked servers, aiding with maintenance and the coordination of tasks.Realizing that vision, however, will require extremely low-power sensors that can run for months without battery changes—or, even better, that can extract energy from the environment to recharge.Last week, at the Symposia on VLSI Technology and Circuits, MIT researchers presented a new power converter chip that can harvest more than 80 percent of the energy trickling into it, even at the extremely low power levels characteristic of tiny solar cells. Previous experimental ultralow-power converters had efficiencies of only 40 or 50 percent.Moreover, the researchers' chip achieves those efficiency improvements while assuming additional responsibilities. Where its predecessors could use a solar cell to either charge a battery or directly power a device, this new chip can do both, and it can power the device directly from the battery.All of those operations also share a single inductor—the chip's main electrical component—which saves on circuit board space but increases the circuit complexity even further. Nonetheless, the chip's power consumption remains low."We still want to have battery-charging capability, and we still want to provide a regulated output voltage," says Dina Reda El-Damak, an MIT graduate student in electrical engineering and computer science and first author on the new paper. "We need to regulate the input to extract the maximum power, and we really want to do all these tasks with inductor sharing and see which operational mode is the best. And we want to do it without compromising the performance, at very limited input power levels—10 nanowatts to 1 microwatt—for the Internet of things."The prototype chip was manufactured through the Taiwan Semiconductor Manufacturing Company's University Shuttle Program.Ups and downsThe circuit's chief function is to regulate the voltages between the solar cell, the battery, and the device the cell is powering. If the battery operates for too long at a voltage that's either too high or too low, for instance, its chemical reactants break down, and it loses the ability to hold a charge.To control the current flow across their chip, El-Damak and her advisor, Anantha Chandrakasan, the Joseph F. and Nancy P. Keithley Professor in Electrical Engineering, use an inductor, which is a wire wound into a coil. When a current passes through an inductor, it generates a magnetic field, which in turn resists any change in the current.Throwing switches in the inductor's path causes it to alternately charge and discharge, so that the current flowing through it continuously ramps up and then drops back down to zero. Keeping a lid on the current improves the circuit's efficiency, since the rate at which it dissipates energy as heat is proportional to the square of the current.Once the current drops to zero, however, the switches in the inductor's path need to be thrown immediately; otherwise, current could begin to flow through the circuit in the wrong direction, which would drastically diminish its efficiency. The complication is that the rate at which the current rises and falls depends on the voltage generated by the solar cell, which is highly variable. So the timing of the switch throws has to vary, too.Electric hourglassTo control the switches' timing, El-Damak and Chandrakasan use an electrical component called a capacitor, which can store electrical charge. The higher the current, the more rapidly the capacitor fills. When it's full, the circuit stops charging the inductor.The rate at which the current drops off, however, depends on the output voltage, whose regulation is the very purpose of the chip. Since that voltage is fixed, the variation in timing has to come from variation in capacitance. El-Damak and Chandrakasan thus equip their chip with a bank of capacitors of different sizes. As the current drops, it charges a subset of those capacitors, whose selection is determined by the solar cell's voltage. Once again, when the capacitor fills, the switches in the inductor's path are flipped."In this technology space, there's usually a trend to lower efficiency as the power gets lower, because there's a fixed amount of energy that's consumed by doing the work," says Brett Miwa, who leads a power conversion development project as a fellow at the chip manufacturer Maxim Integrated. "If you're only coming in with a small amount, it's hard to get most of it out, because you lose more as a percentage. [El-Damak's] design is unusually efficient for how low a power level she's at.""One of the things that's most notable about it is that it's really a fairly complete system," he adds. "It's really kind of a full system-on-chip for power management. And that makes it a little more complicated, a little bit larger, and a little bit more comprehensive than some of the other designs that might be reported in the literature. So for her to still achieve these high-performance specs in a much more sophisticated system is also noteworthy."Related products:XC7Z100-2FFG900IXC7Z010-1CLG400IA2F200M3F-1FGG256 

A bump circuit with flexible tuning ability that uses 500 times less power and is smaller than previous circuits has been demonstrated by researchers at the University of Tennessee in the US."The challenges and requirements of the analogue deep-learning system inspired us to come up with this radically new design," said Junjie Lu, the lead author. "We implemented the bump circuit by preceding the current correlator with a novel nano-power tunable transconductor to achieve variable width and height. By significantly reducing the power consumption of the bump circuit, this work makes possible the realisation of analogue learning and signal processing systems that achieve better energy efficiency than their digital equivalents, and ultimately fully autonomous systems, which are able to get both information and energy from the environment without external intervention."Towards flexible transferThe bump circuit is a family of circuits with bell-shaped, non-linear transfer functions. First appearing in 1991, they are widely used to provide similarity or distance measures in analogue signal processing systems such as support vector machines, neural networks and analogue machine-learning systems.The original bump circuit design lacked the ability to change the width of its transfer function, which is desirable in many applications to represent distributions with different variance or templates with different model parameters. A common approach to solve this is to pre-scale the input voltage, but the circuits required are physically large and consume a lot of power. Other approaches also have limitations such as complex circuitry, large physical size, and a restricted number of possible widths achievable.Hidden depthsThe researchers from the University of Tennessee designed their circuit as an important building block in an analogue deep-learning machine, which is able to perform unsupervised learning and extract salient features from high-dimensional input data, with a much better power efficiency than the existing digital machine learning implementations.Large-scale systems require the computational element, or bump circuit in this case, to be very efficient in both power and area. It is also important that the output features, which are the confidence scores that the current input belongs to each of the previous observations, take both the mean distances and probabilistic variances into account. A bump circuit that has a tunable centre for mean tuning, width for variance tuning, and height for normalisation is therefore highly desirable, and if these three bump parameters can be individually tuned and controlled by a single signal, this would greatly help with on-chip trainability.To achieve the variable height and width, the researchers designed and incorporated a novel transconductor, linearised using the drain resistances of saturated transistors. They adopted a pseudo-differential structure to allow operation with a low supply voltage, and designed a common mode feedback circuit to provide common mode rejection for the pseudo-differential structure to get a tunable bump height.The whole circuit uses 18.9 nW power from 3 V supply which is 1/500 th of the power of the next best bump circuit with tunable width. Implemented in 0.13 µm CMOS, it is smaller in area by 6%, and has maximum flexibility through the individual tunability of the three key bump function parameters. Another feature is that multiple bump circuits can be easily cascaded to represent multivariate probability.A vision of the futureWith power scaling in CMOS tapering off, there has been renewed interest in analogue computation recently, and the researchers expect to see some very exciting results in this area. They are currently working to integrate low-power circuits, such as their bump circuit, into larger systems for real-world applications."One application area we've been working on is machine vision," said Lu. "We've been working with image processing and machine vision researchers to build a complete pipeline using analogue circuits. This circuit helps to provide a path to implementing multi-dimensional kernel methods for machine learning."Systems using the bump circuit could find application in many areas such as healthcare monitoring, environmental monitoring, process control and battlefield surveillance. In addition, the nano-power tunable linear transconductor developed in this work, which has the advantages of ultra-low power, large input range and gm tunability, could be used in a huge range of applications such as amplifiers, filters and oscillators.Related products:LMV1031UR-20LM4889MALM4867MTE