The Kynix Blog

  After 20 years, your life may be like this:The electronic skin on your pulse can monitor your heart rate and blood sugar at any time to realize intelligent pulse detection;The electronic skin on your throat can "voice" for the deaf and mute by feeling the pressure changes produced by the movement of the throat muscles;Your whole body may become a network center, and the sensors in your body will connect with the outside world...All this seems very far away, but these technologies are quietly gestating, and are very likely to become disruptors of new technologies.Flexible Electronics: The Future of TECHNow is the era of smart phones, but the current smart electronic products are still rigid electronic devices. In the future, mankind is about to enter a new era, the era of flexible electronics. Flexible electronic devices that are as soft as human skin will be the next development trend of the electronics industry, and may even subvert human life. Catalog I What is Flexible electronics?II Applications of flexible electronics2.1 Flexible electronic display2.2 Thin film solar panels2.3 RFID2.4 Electronic skinIII ConclusionFAQ  I What is Flexible electronics? The concept of flexible electronics started in the 1980s, when people tried to replace inorganic semiconductors such as silicon with organic semiconductors, so that organic electronic devices have flexible characteristics.Flexible electronic technology is a brand-new electronic technology revolution. It is an emerging electronic technology that makes organic and inorganic materials electronic devices on flexible, malleable plastic or thin metal substrates. It has a wide range of fields in information, energy, medical treatment, and national defense.  Applications of flexible electronics In addition to integrating electronic circuits, functional materials, micro-nano manufacturing and other fields of technology, flexible electronic technology also spans industries such as semiconductors, packaging, testing, materials, chemicals, printed circuits, and display panels. Not only that, it can also help the transformation and upgrading of traditional industries, such as plastics, printing, chemicals, and metal materials.By improving its performance and industrial added value, flexible electronics will frequently appear in human life, bringing revolutionary changes to the industrial structure and future life. As technology upgrades, flexible electronics materials research and development and rich application products have emerged.II Applications of flexible electronicsWith the development of flexible electronic technology, various electronic products have emerged. Just as microelectronics technology provides a technology platform for large-scale integrated circuits and computer chip technologies, flexible electronic technology provides a brand-new technological platform for the research and development of new products. 2.1 Flexible electronic displayThe flexible electronic display is a brand-new product developed on the flexible electronic technology platform. Unlike traditional flat-panel displays, such displays can be repeatedly bent and folded, thus bringing great convenience to our lives.For example, all visual materials, including books, newspapers, magazines, and video files, can be presented on this display and can be viewed anytime, anywhere. Although current popular MP4 players and personal digital assistants (PDAs) can meet such use needs, the display screen cannot be bent and folded, and can only be read and viewed in a small screen area. And video, visual effects are greatly constrained. In contrast, flexible electronic displays have unparalleled advantages. They are like newspapers. When they are needed, they are unfolded. When they are used, they are curled or even folded. This guarantees the convenience of portability while giving full consideration to the visual effects.Flexible electronic displaySamples of flexible electronic displays have been successfully developed and it is believed that it will be a long way from entering the market. It is worth mentioning that flexible electronic displays use more lightweight organic materials instead of inorganic materials, so their weight is lighter than traditional displays, and this feature helps to improve their portability. In addition, the use of high molecular organic materials offers possibilities for reducing costs. In addition, the flexible electronic display has the characteristics of a thin thickness, and its thickness can be much smaller than that of the popular liquid crystal display. Therefore, another name of the flexible electronic display is a paper-like electronic display.2.2 Thin film solar panelsThin film solar panel is another specific application of flexible electronics technology. In today's world, energy has become a topic of global concern. China not only faces energy shortages but also faces environmental pollution. As a clean energy source, solar energy can effectively alleviate the contradiction of energy shortage under the premise of zero environmental pollution.As the most common way to use solar energy, solar panels can cover a large area at the lowest cost to effectively use solar energy. At present, thin film amorphous Sili-Con solar panels have been successfully developed and marketed. Thin film solar panel Thin-film solar panels based on flexible electronic technology can meet high-power generation needs, such as the use of thin-film solar panels in solar power plants in sunny desert areas.In addition, it can also make full use of its flexible and lightweight features to integrate it into clothing. Putting on such clothes to walk or exercise in the sun, the power of small appliances (such as MP3 players and laptops) that are carried around can be supplied by the thin-film solar panels on the clothes, thus achieving the purpose of saving and environmental protection.2.3 RFIDRadio frequency identification (RFID) technology can be used to complete information input and processing, fast and convenient operation, and rapid development without manual contact, and is widely used in production, logistics, transportation, medical, food, security and other fields. RFID systems usually consist of transponders and readers.The electronic tag is one of many forms of transponder, and can be understood as a transponder with a thin film structure, which has the characteristics of convenient use, small size, thin and light, and can be embedded in the product. More and more electronic tags will be used in future RFID systems.Flexible Electronics in RFIDIn this response to Covid-19, flexible electronic technology has played a huge role in body temperature measurement.Group body temperature measurement has problems such as huge number of monitoring people, cumbersome temperature measurement work, and difficulty in continuous temperature recording. Wearable temperature measuring stickers made by introducing flexible electronic technology can record and analyze the body temperature data of the target population. In this way, potential threats can be discovered and eliminated through long-term monitoring, thereby helping management departments to achieve personnel management monitoring.2.4 Electronic skinAnother important application of flexible electronics is electronic skin. Electronic skin, also called skin-like electrons, is basically characterized in that various electronic components are integrated on a flexible substrate to form a skin-like circuit board, which has high flexibility and elasticity like skin and can be used in many other applications. electrical equipment.It can be said that the potential of flexible electronic skin is great. With the popularization of technologies such as smart medical care, virtual reality, and artificial intelligence, the demand for wearable devices has surged, and flexible electronic skin is a perfect combination of wearable devices. Think about an electronic component installed on the body and used as a skin, isn't it sci-fi?Electronic skinIII Conclusion Folding computers, folding mobile phones, and wearable digital products are in the ascendant. With the development of science and technology, flexible electronic devices have received more and more attention from the society. Such devices can still work under bending, folding, twisting, compression or stretching conditions. In the future, flexible electronic equipment will have a very broad development space in the fields of energy, medical, information and communication.Pieces of work brought by flexible electronics are interpreting the integration of innovation and tradition in the era of the Internet of Everything, and the era of science and technology connecting everything is approaching.You can boldly imagine that in 20 years, your life might be like this:In the morning, the flexible electronic skin watch on your body wakes you up and reports the quality of your sleep. Put on your glasses, and the day’s schedule has been displayed for you on the transparent screen. After washing, the robot has prepared breakfast for you and your family; After going out, the smart watch on your wrist shows that the air quality is excellent; the smart assistant called "Flying" for you and has parked outside the house, waiting for you to start your day's itinerary... FAQ 1. Why are electronics flexible?The key advantages of flexible electronics, compared with current silicon technologies, are low-cost manufacturing (e.g. ink-jet printing and roll-to-roll imprinting) and inexpensive flexible substrates (e.g. plastics). ... In principle, flexible electronics is ideal for integration. 2. Where are flexible electronics used?Consumer electronics devices make use of flexible circuits in cameras, personal entertainment devices, calculators, or exercise monitors. Flexible circuits are found in industrial and medical devices where many interconnections are required in a compact package. 3. How could Flexible Electronics benefit the consumer?Among the benefits of flexible electronics (compared to traditional, rigid alternatives) are size, weight, portability, and energy efficiency. Above all, they make previously impossible designs and technologies (such as wearable devices) possible. 4. When was flexible electronics invented?1960s. Flexible electronics have a long history. The first flexible device was made in the 1960s by thinning crystalline silicon solar cells for use in extraterrestrial satellites. Today, smart credit cards carry bendable microchips which are made using stretchable Silicon. 5. What are flexible electronics made of?Flexible Electronics: generally refers to a class of electronic devices built on conformable or stretchable substrates, usually plastic, but also metal foil, paper and flex glass. 6. What are the two major approaches of making flexible electronics?(1) Transfer and bonding of completed circuits to a flexible substrate(2) Fabrication of the circuits directly on the flexible substrate  7. What makes flexible electronic display attractive?One property of flexible electronics which deserves to be highlighted is their robustness. This makes a great difference for applications such as wearables, notebooks and other consumer electronics which traditionally feature glass-based displays or sensors. 8. How flexible electronics are made?Compared with conventional microelectronics, flexible electronics does not require extrinsic packages such as ceramics. Instead, flexible circuits and packages can be manufactured and integrated together using only plastics. ... These layers can then be stacked together to complete the flexible electronic systems. 9. Why are flexible electronics important?Among the benefits of flexible electronics (compared to traditional, rigid alternatives) are size, weight, portability, and energy efficiency. Above all, they make previously impossible designs and technologies (such as wearable devices) possible. 10. Why do we need flexible materials?Not only does flexible packaging use less material than its rigid counterparts, leading to a lower overall packaging cost, it also creates less waste. Fres-co states that flexible packaging formats create 50 percent less waste than rigid ones, while also reducing greenhouse gas emissions and BTU consumption. 

In ancient Asia and Europe, "cutting the flesh to cure a boil" has a history of nearly 2500 years, but considering the level of medical treatment and anesthesia at that time, this seems to be more of torture. For irreparable damage to skin tissue, skin grafting is almost the only option considering the body's repulsive reaction. Doctors mainly rely on the removal of the patient's own skin or the skin of others for transplantation repair. Not to mention the unbearable pain, it will also leave new wounds on the patient's skin.In addition, the source of skin grafts for patients with large-area skin injuries is also a problem. The skin after transplantation is very fragile, with sequelae such as weakened sense of touch and decreased immunity.With the efforts of scientists from all over the world, the super-simulation electronic skin model is maturing. If it is put into human trials, this will be a good news for patients. This is a video introducing electronic skin Based on the development of electronic skin in recent years and the shortcomings of current wearable devices, this blog will introduce you to the structure of electronic skin and its future applications in the field of mobile health. Catalog  Ⅰ Introduction to electronic skinⅡ Development of electronic skinⅢ Electronic skin system architecture3.1 Flexible substrate3.2 Flexible battery3.3 Wireless communicationsⅣ Electronic Artificial Skin for   ApplicationⅤ ConclusionFAQ   Ⅰ Introduction to electronic skin Electronic skin, a system that allows robots to produce tactile sensations. It is not only simple in structure, but also can be processed into various shapes, and can even be attached to the surface of the device like clothes, allowing the robot to perceive information such as the location, orientation, and hardness of the object.Basic functions of electronic skin:From obtaining physical stimulation to distributed sensor array;Preprocess the sensor signal;The signal is transmitted wirelessly to higher-level systems (such as smart phones)The electronic skin is equipped with highly sensitive conductive nanomaterials, which can accurately cause slight tremors of the electrical changes of the muscle group. At the same time, the electronic skin is extensible (for example, it supports joint movement), and can even form integrated chemical sensors and biosensors.Therefore, electronic skin enables us to perceive different shapes and textures, temperature changes and different contact pressure levels. And, this is an integrated, scalable sensor network that can provide tactile and thermal signals to the brain, allowing us to operate safely and effectively in the surrounding environment. Human skin with distinctive features is a physical barrier to our interaction with the surrounding environment. Inspired by these features of human skin, researchers are working hard to create a flexible, scalable, and highly sensitive electronic device. Therefore, the development of electronic skin has become a research hotspot, especially in the fields of intelligent robots and electronic medicine.Ⅱ Development of electronic skinThe development of electronic skin technology could be divided into two stages:1）From 1970s to 1990s, the concept of e-skin appeared for the first time and got a preliminary development.2）Since 2000s, more researchers have been involved and have made a significant progress in recent years.In 1974, Clippinger demonstrated the feedback of a discrete sensor for a prosthetic hand. In 1985, General Electric first built a robotic arm sensitive skin which enabled to interact with the environment, placed on a flexible, curved sheet using discrete infrared sensors. In the 1990s, more and more teams began to create large-area, ultra-thin, multi-sensor flexible sheets. Jiang et al. first proposed a bent sensor sheet which obtained by etching thin silicon wafers and then integrating them on flexible polyimide film. In 2000, the organic transistor electronic nose was developed. Later, more achievements were made, such as scalable inverters, flexible active matrix technology, high resolution optical sensors, microstructured pressure sensors and so on. In 2003, the research team at the University of Tokyo in Japan made thin films by using low molecular organic compounds and realized the pressure of electronic skin through the pressure sensors on its surface. In 2010, the University of California, Berkeley, developed a technology to attach nanowire transistors to a sticky substrate, the resulting e-skin therefor could apperceive less than 50 grams of fine pressure and has been subjected to bending 2000 times. A woman scientist of Stanford University Bao Zhenan and her team have developed a highly sensitive flexible plastic film material that mimics human skin and senses subtle pressure. At the same time, the team developed the world's newest stretch solar cells, allowing electronic skin to self-generate electricity. In 2011, a researcher named John A.Rogers introduced an electronic patch for monitoring patient vital signs which described as "electronic skin." This device embedded the sensors in a film and placed the film on a flexible polyester substrate, like a kind of tattoo on the body. Physiological indexes of human health In 2014, electronic skin, developed by a researcher from the Chinese Academy of Sciences, was pasted on the human skin by static electricity, enabling real-time monitoring of physiological indexes of human health such as pulse, heartbeat, body temperature, muscle group vibration and so on, to promptly make a respond with feedback on changes of human health data. Ⅲ Electronic skin system architectureCompared with the current intelligent wearable devices, electronic skin has the characteristics of high sensitivity, ultra-thin, bendability and comfort in guardianship and monitoring the important physiological information of human body. E-skin system is a new type of flexible and extensible sensing system. By making sensors and circuits built on flexible substrates, e-skin systems can obtain unique ductility and more sensible to the various physical, chemical and biological signals. In the field of health care, the emergence of electronic skin will change the imprecise measurement of wearable devices, reduce the number of heavy monitoring equipment in the ward, and enable medical staff obtain the patient's physiological parameters in real time.Figure 1. Architecture of electronic skin systemFigure 2. E-skin structureFigure 3. Relationship between modules of e-skin system in medical applicationsThis system provides flexible circuits on flexible substrate, including microprocessors, Bluetooth and a variety of sensors (temperature, humidity and pressure sensors, blood oxygen, skin impedance and ECG sensors, etc.), which are connected to smart phones via Bluetooth. With the help of big data technology and cloud computing analyzes the data,  giving the diagnosis and treatment in time.Figure 4. Application scene of electronic skin system in mobile healthcareFigure 5. Electronic skin attached to temple to track brain wavesJohn Rogers, a professor of materials at the University of Illinois, Urbana-Champaign, has developed an e-skin called Biostamp, which can track brain waves in real time by sticking a flexible small sensor to a user's temple, able to show your deepest thoughts and feelings and translate them into information.Figure 6. Industrial designers of wearable health-monitoring electronicsIn the above structures, different applications have different requirements for sensors, and microcontrollers are becoming more and more lightweight in the field of electronic skin. So the following three parts of flexible substrate, power management and wireless communication technology will be described in detail.3.1 Flexible substrateOne of the most basic properties of electronic skin is that it has bending property, which can better attach to a large area of surface of human body One of the most basic properties of electronic skin is that it has bending property, which can better attach to a large area of human body surface. To achieve this property, the choice of materials is crucial. Advances in technology have enabled e-skin to be manufactured largely through the development of new materials and new processing methods. At present, polydimethylsiloxane (PDMS) and nanomaterials are commonly used as substrate materials:3.1.1 PDMSPDMS film is one of the most popular flexible substrates, including the advantages of good chemical inertia, being stable in a wide range of temperature, high transparency, variable mechanical properties and good adhesion to silicon wafer. At present, many research groups use PDMS as a flexible substrate. Sigurd Wagner and others used PDMS as a flexible substrate and found that wavy wires built into the film greatly enhanced its extensibility, such as obtaining skin tactile sensor arrays by printing silk screen on the PDMS film. The hypersensitive electronic skin equipment was fabricated by combining homogeneous microcosmic PDMS films with carbon nanocrystalline films.3.1.2 Nanophase materialsNanomaterials are a new type of materials developed in recent years. The current technological trends in the field of new materials are as follows:1. Carbon nanotubes: Compared with the zero-dimensional nanostructures such as carbon black, the one-dimensional carbon nanotubes have higher draw ratio and better electrical conductivity, which are used as conductive filler and then filled with the polymer composite can show lower resistivity and higher electrical conductivity.Figure 7. Schematic of carbon nanotube2. Graphene: Graphene is a hexagonal honeycomb structure consisting of a single layer of carbon atoms. It is the thinnest and strongest superconducting material ever known, which has a superior thermal, mechanical and electrical properties to carbon nanotubes, and with the tunneling effect it obtains a tactile sensor with high sensitivity, having a great application prospect in the field of conductive composite materials. Carbon nanotubes and graphene can be used not only as flexible substrates, but also as various good materials for high sensitivity sensors and flexible batteries. There are teams have so far made achievements in these areas and we are believing that nanomaterials will dominate in the near future.Figure 8. Graphene's atoms arranged in honeycomb pattern3.2 Flexible batteryLightness and softness are two of the most basic characteristics of e-skin. Traditional batteries can no longer meet the requirements of e-skin, but the  foldable and bendable flexible cell has become an indispensable part of e-skin equipment.Table 1. Comparison of current flexible batteryResearch instituteCellPerformanceProLogium Corporation, TaiwanUltra-Thin、Flexible FPC Lithium-Ceramic BatteryCuttable like paper, but cause no fire or explosion under bending, hammering, piercing, and 700-1300 ℃ high temperature gun fireImprint Energy, California, USAFlexible ultrathin zinc polymer battery3D printers in general use can be mass-produced at lower costRice University, USASuper-thin, High -performance flexible lithium free BatteryAfter 10,000 times of charge and discharge, or a thousand bends, it still maintains a capacity of 76%New Jersey Institute of TechnologyFlexible carbon nanotube cellIt can be made into various shapes and sizes, even DIY at homeSamsung Corp.Flexible bendable cellOrganic thin-film solar cellsFraunhofer Institute for Applied Polymer Research, GermanyOrganic thin film solar cellOrganic thin-film solar cellsNorthwestern University,USAFlexible stretchable lithium batteryStretchable, bendable, foldable and rechargeable wirelessly In addition to the flexible batteries mentioned above, a wireless charging technology developed in recent years also provides an alternative to the realization of electronic skin, including kinetic energy (motion, vibration, rotation) thermal energy, piezoelectricity and even radio waves (which can be viewed as wireless energy recovery) can be converted into usable electricity to provide a long-time even permanent energy supply. While it is still hard to really apply it to reality at the moment, it will be a new and innovative breakthrough in the future.3.3 Wireless communicationsIn recent years, in order to meet the requirement of intelligent equipment short-range communication, the automation short-range wireless technology emerges as the times require. At present, among all kinds of short-range wireless communication technologies, several mainstream of it such as Wi-Fi, ZigBeec, NFC, BLEID, UWB and so on become the main means for intelligent devices to communicate with each other at present. In e-skin system, wireless communication is still an indispensable part, and even has a higher requirements in communication performance, application environment and low power consumption.Table 2 Comparison of Wireless Communication TechnologyWireless technologyTransmission range / mMaximum transmission rate /MbpsTransmitting power / MWWi-Fi10-3054<50Zigbee10-100250kbps30NFC<20cm424kbps Bluetooth(BLE)10-1001~10RFID(UHF)<30~100kbps UWB3-10480 Wi-Fi is widely used in smart phones, and its fast transmission speed is an obvious advantage. Bluetooth is a wireless technology with low power consumption, ideal transmission distance and low cost. With the popularity of smart phones and the integration of Bluetooth modules, along with its gradually enhanced storage and computing capabilities, continuous real-time monitoring of the human body becomes possible. At the same time, the smart phone is used in the wearable health monitoring system as the information gateway to transmit the received physiological information, therefore the real-time monitoring of patients' health status has realized together with the emergence of big data technologies and cloud Computing. Bluetooth technology is the first choice for human-body monitoring system to transmit physiological signals in electronic skin. Ⅳ Electronic Artificial Skin for Application Figure 9. Electronic skin to monitor heart rateBiological tissue tends to be curved and soft, and most of the current wearable health monitoring devices are hard, rigid and difficult to achieve a large area of surface attachment. From an application point of view, this is not conducive to obtaining physiological signals from the human body. However because the e-skin has a flexible substrate which can be attached to a large area of tissue surface, and its sensors with high sensitivity can obtain the physiological signals of human body more accurately. Due to the unique properties of e-skin and the development of miniaturization technology, e-skin has great application potential in the fields of health monitoring, prosthesis, robot and so on.Figure 10. Intrinsically stretchable transistorIn the field of health care, electronic skin will have more applications, as shown in figure 11: Blood glucose detection;Speech recognition;Infant temperature monitoring;Intelligent Drug Administration, etc.Figure 11. Applications of electronic skin in health careIt is important for diabetics to be able to know their blood sugar changes all the time. Continuous blood glucose monitoring system can measure the patients’ blood glucose concentration with sensors containing specific enzymes.Speech recognition system(ASR) is an e-skin device attached to the throat of human body. It can monitor the weak pressure changes produced by muscle movement and transform them into speech, helping the deaf and mute to realize their dream of "speaking".Infant monitoring system can monitor the temperature, heart rate and other physical status of the baby in real time, and meanwhile feed back to the intelligent terminal in time.The intelligent drug delivery system can inject drugs regularly and quantitatively by placing them into the e-skin and monitoring the recovery of wounds by intelligent terminal control.With the combination of electronic skin and intelligent equipment, it is only necessary to transmit and analyze the signals obtained by e-skin to the intelligent equipment through wireless communication technology, then it has been able to monitor and provide feedback on the health condition of the human body in real time and in long distance. Electronic skin, as a new type of wearable device, will in the future provide real-time detection of blood pressure, blood sugar, heart rate, body temperature and etc. It is the best choice for real-time diagnosis and evaluation of human health. Ⅴ Conclusion The application prospect of e-skin is very extensive, not only in the field of health care, but also in the fields of consumer electronics, military affairs and even the more sci-fi robot "imitation of human skin", which will bring about revolutionary breakthroughs.With the endless emergence of wearable electronic devices, high sensitivity and miniaturization will become the mainstream trend. The emergence of electronic skin will undoubtedly bring about major technological breakthroughs and innovation opportunities for flexible wearable electronic devices.  FAQ 1. What is electronic skin used for?Flexible circuits inspired by human skin offer options for health monitoring, prosthetics and pressure-sensing robots. 2. What are the advantages of an e-skin?It helps the body to adjust after the transplant. It can make robots more sensitive. The use of tiny electronic wires allows the skin to generate impulses, similar to that of the body's own nervous system. It could lead to advancements in medical equipment. 3. What electronic skin is flexible?Electronic skin refers to flexible, stretchable and self-healing electronics that are able to mimic functionalities of human or animal skin. ... Advances in electronic skin research focuses on designing materials that are stretchy, robust, and flexible. 4. What is the main difference between flexible skin like sensors and the human skin?Like human skin, AISkin also is quite durable; however, while human skin can only stretch about 50 percent, the sensor-based skin can stretch up to 400 per cent of its length without breaking, making the material useful in wearable technology applications. 5. Who invented electronic skin?Researchers from the National University of Singapore have developed an 'electronic skin', capable of recreating a sense of touch thanks to more than 100 small sensors. They hope the technology can be applied to prosthetic limbs, allowing users to feel texture, temperature and pain. 6. Where has electronic skin been developed?National University of Singapore. A team from the National University of Singapore created the skin device, which measures 1 square centimeter. The system contains 100 small sensors that attempt to recreate things like texture, temperature and even pain. The researchers call the device Asynchronous Coded Electronic Skin, or ACES. 7. What can the skin sense?Receptors that let the body sense touch are located in the top layers of the skin - the dermis and epidermis. The skin contains different types of receptors. Together, they allow a person to feel sensations like pressure, pain, and temperature. ... They may sense pain, temperature, pressure, friction, or stretch. 8. What is a skin sensor?Electronic skin sensors, also known as the wearable thin film sensors, can be directly placed on the human body to measure body parameters such as body temperature, heartbeat, sweat composition etc. ... Electronic skin sensors have applications in many areas such as healthcare, sports, robotics and prosthetics, etc. 9. How do you replicate human skin?It was found that the most common materials used to simulate skin are liquid suspensions, gelatinous substances, elastomers, epoxy resins, metals and textiles. Nano- and micro-fillers can be incorporated in the skin models to tune their physical properties. 10. How is electronic skin made?Research into conductive electronic skin has taken two routes: conductive self-healing polymers or embedding conductive inorganic materials in non-conductive polymer networks. ... embedded silver nanoparticles (AgNPs) into a polymer matrix, making the e-skin conductive. 

 Resistors are used and manufactured by thousands of organizations and people all over the world. So we should know what it is and its functions.  Therefore, it has many classifications based on different standards. In today's blog, we are going to talk about the color-band resistors. Hope it can be helpful. How to read a resistor? Catalog I What is resistor?II How to read resistor color code?III Uses and applications of resistorVI What do the colored bands on a   resistor mean?4.1 Four-band-code resistor4.2 Five-band-code resistor4.3 Six-band-code resistorFAQ I What is resistor? II How to read resistor color code?To identify the value of color-band resistors, a resistor color code is used. This color code consists of several colorful bands. Surface mount resistors are identified by a numerical resistor code. The nominal values of resistors are also standardized. Several ranges of preferred resistor values are available. Another important aspect of resistor standardization is the use of standardized resistor symbols. The IEC standard symbol of a fixed value resistor is shown.Color-band resistor is the most commonly used electronic component in electronic circuits. The color-ring resistor is used to distinguish the resistance value of the resistor by coating the color band with different colors on the ordinary resistor package. Ensure that resistance can be clearly read in any direction when installing the resistors. The basic units of the color ring resistor are: ohms (Ω), KΩ, MΩ, 1MΩ= 1000KΩ = 1000000Ω.An electronic color code is used to indicate the values or ratings of electronic components, usually for resistors, but also for capacitors, inductors, diodes and others. A separate code, the 25-pair color code, is used to identify wires in some telecommunications cables. Different codes are used for wire leads on devices such as transformers or in building wiring.A carbon-composition resistor can have 4 to 6 bands. A 5-band resistor is more precise compared to a 4-band type because of the inclusion of a third significant digit. A 6-band resistor is like a 5-band resistor but includes a temperature coefficient band (the 6th band).   4-Band5-Band6-Band1st Band1st significant digit1st significant digit1st significant digit2nd Band2nd significant digit2nd significant digit2nd significant digit3rd Bandmultiplier3rd significant digit3rd significant digit4th Bandtolerancemultipliermultiplier5th BandN/Atolerancetolerance6th BandN/AN/ATemperaturecoefficientResistor Color Codes mean that the resistance is represented by four or five color rings or six color rings above the resistor. The color information representing the resistance value can be read at any time at a time. So resistors with color codes is the most widely used in various electronic devices. No matter how it is installed, the repairman can easily read its resistance value, which is easy to detect and replace.Each color represents a number if it's located from the 1st to 2nd band for a 4-band type or 1st to 3rd band for a 5-band and 6-band type.Resistor color codes value 1If the color is found on the 3rd band for a 4-band type or the 4th band for a 5-band and 6-band type, then it's a multiplier.Resistor color codes value 2The 6th band for a 6-band type resistor is the temperature coefficient. This indicates how much the actual resistance value of the resistor changes when the temperature changes.Resistor color codes value 3 III Uses and applications of resistorColor band marks are mainly used on cylindrical resistors, such as carbon film resistor, metal oxide film resistor, fuse resistor, wire winding resistor.However, it has been found in practice that some color-band resistors are not arranged in a very clear order and are often easy to misread. In recognition, the following techniques can be used to judge:- Tip 1: Find the color band of the mark error first, and then arrange the color band order. The most commonly used colors to indicate resistance errors are: gold, silver, brown. In addition, gold and silver rings, which are rarely used as the first ring of a resistor color ring, so long as there is a gold band or a silver band on the resistor, this can basically be recognized as the last band of color-band resistor.- Tip 2: Brown band is usually identified as an error mark. Brown band is often used as error band or as effective number band, and it often appears in the first band and the last band synchronously, which makes it difficult to identify who is the first band. In practice, it can be judged by the gap between the color bands: for example, for a five-band-code resistor, the gap between the fifth and fourth band is wider than that between the first and second band. Based on this, the arrangement order of color bands can be determined.- Tip 3:In the case that the color band order can not be determined by the color band spacing alone, it can also be judged by the production sequence value of the resistor. For example, there is a color band reading order of resistance: brown, black, black, yellow, brown, its value is: 100 × 10000mΩ, the error is 1%, belonging to the normal resistance series value, if read in reverse order: brown, yellow, black, black, brown, its value is 140 × 1Ω = 140Ω, the error is 1%. Obviously, the resistance values read out in the latter order is wrong according to production standard of resistors, so the order of the latter color loops is incorrect. Color codes valueVI What do the colored bands on a resistor mean?In the early days, when the surface of the resistor was not sufficient to display all resistor values by numbers, the resistance, tolerance, and specification of the resistor were expressed by the color band marking method. There are two main parts.- Part one: a group near the front end of the resistor is used to indicate the resistance value.The resistance value of a two significant numbers, represented by the first three color rings, such as 39Ω, 39KΩ, 39MΩ.The resistance value of the three significant resistance numbers is represented by the first four color rings, such as: 69.8Ω, 698Ω, 69.8KΩ, which is generally used to express the precision resistor.- Part two: a color band near the rear end of the resistor is used to represent tolerance accuracy.Each color ring in the first part is equidistant and easily distinguished from the second color band.Resistor color code4.1 Four-band-code resistorFour-band-code resistorThe four-color band resistor is identified as follows: the first and second band represent the resistance of the two-digit significant number; the third band represents the multiplier; and the fourth band represents the error.Example：brow, red, red, goldIts resistance value is 12 × 10 ^ 2= 1.2kΩ, the error is ±5%.The error also represents, it fluctuates around the standard value of 1200, about 5% × 1200, this resistance is acceptable, that is, the resistance is good between 1140~1260.The first and second ring represent the first two digits of the four-color resistor respectively; the third ring represents the multiplier; the fourth band represents the error. The key to fast recognition is to determine the resistance value within a certain order of magnitude according to the color of the third band, for example, when the number is a few Ks or dozens of K, and then connect with the numbers in the first and second band, so that the final resistance can be read out quickly.For the four-band-code resistor, the method of calculating the resistance value is as follows:Resistance= (first color-ring value * 10+second color+ring value) * the multiplier represented by the 3rd color band.4.2 Five-band-code resistorFive-band-code resistorThe recognition of five-band-code resistors: the first, second and third bands represent the resistance of the three-digit significant number respectively; the fourth band represents the multiplier; the fifth ring represents the error. If the fifth color band is black, it is generally used as a wire wound resistor, and the fifth color band, if white, is generally used as a fuse resistor. If the resistor has only a black color band in the middle, it represents zero ohmic resistance.-Example: red, red, black, brown, goldIts resistance is 220 × 10 ^ 1 / 2.2KΩ, the error is ±5%.- The first color band is hundreds digit, - The second color band is tens digit number;- The third color band is the single digit, - The fourth color band is the color power;- The fifth color band is the error rate.For the five-band-code resistor, the method of calculating the resistance is as follows:Resistance= (first color-band value * 100+second color band value * 10+third color-band value) * the multiplier of the fourth color band.4.3 Six-band-code resistorThe identification of this resistor is the same as the above mentioned resistors, but the sixth color ring represents the temperature coefficient of the resistor. Followings are examples:-Example 1: when the four color rings are yellow, orange, red and gold, because the third band is red, the resistance range is single digit kΩ. According to the number "4" and "3" of yellow and orange respectively, the reading number is 4.3 kΩ. The fourth band is gold representing the error of 5%.-Example 2: when the four color bands are brown, black, orange and gold in turn, because the third band is orange and the second ring is black, the resistive value should be tens of kΩ, the number "1" of brown is substituted, and the reading number is 10 kΩ. The fourth band is gold, and the error is 5%. In some indistinguishable cases, you can also compare the colors of the two ends, because the first color, will not be gold, silver, or black. If these three colors are close to the edge, they need to be calculated backwards.There are two ways to identify the colorful resistor. One is to label the color band with 4 color rings, the other is to label the color bandwith 5 color bands. The difference between the two is that the first two bits of the four-color band represent the effective number of the resistor, but the first three bits of the five-color band resistor represent the effective numbers, and the last but one represents the multiplier of the effective number of the resistor. The last bit represents the error of the resistor.4/5/6-band color code FAQ 1. What do the Coloured bands on a resistor mean?The color code is given by several bands. Together they specify the resistance value, the tolerance and sometimes the reliability or failure rate. The number of bands varies from three till six. As a minimum, two bands indicate the resistance value and one band serves as multiplier. 2. How do you determine the color of a resistor band?Hold the resistor with the gold or silver band to the right and read the color codes from the left to the right. Select the color codes from the bands on the resistor. Read the colors from left to right. The resistance value based on the color code provided is now displayed. 3. What resistor do I need for LED?LEDs typically require 10 to 20mA, the datasheet for the LED will detail this along with the forward voltage drop. For example an ultra bright blue LED with a 9V battery has a forward voltage of 3.2V and typical current of 20mA. So the resistor needs to be 290 ohms or as close as is available. 4. What is an axial resistor?The most common through-hole resistors come in an axial package. The size of an axial resistor is relative to its power rating. A common ½W resistor measures about 9.2mm across, while a smaller ¼W resistor is about 6.3mm long. A half-watt (½W) resistor (above) sized up to a quarter-watt (¼W). 5. How are axial resistors made?Wirewound resistors are commonly made by winding a metal wire, usually nichrome, around a ceramic, plastic, or fiberglass core. The ends of the wire are soldered or welded to two caps or rings, attached to the ends of the core. 6. What do the colors on a resistor mean?The color code is given by several bands. Together they specify the resistance value, the tolerance and sometimes the reliability or failure rate. The number of bands varies from three till six. As a minimum, two bands indicate the resistance value and one band serves as multiplier. 7. What are series 100 and 200 axial leaded resistors for?Series 100 & 200 Axial Leaded Non-Inductive Bulk Ceramic Resistors provide excellent performance where high peak power or high-energy pulses must be handled in a small size. 8. How can you tell the difference between axial and surface mounted resistors?To identify resistors, first look at the shape of the resistors to find out which type they are. Axial resistors are cylindrical with a group of color bands, while surface mounted resistors are rectangular with alphanumeric codes. 9. Where are the color bands on an axial resistor?Axial resistors are cylindrical with leads extending from each end. Look at the resistor so the group of 3 or 4 color bands are on the left side. These are sometimes followed by a gap, then an additional color band. Read the color bands from left to right. 10. What is the nominal power of CS and SR resistors?CS and SR resistors are axial wirewound ceramic resistors with a silicone based coating. The nominal power ranges from 2 till 15W. They are used in a wide variety of applications. Standard tolerance is 5%. Available on request is 1%. CS and SR resistors follow the E24 Ohmic values series. 

In addition to magnetic element design, feedback network design is also the least known and very troublesome work of switching power supply. It involves analog electronic technology, control theory, measurement and computing technology and other related issues.CatalogI Frequency response1.1 Basic concept1.2 Frequency response of basic circuits1. 3 Characteristics of LC filter circuitII Time-domain response of basic circuits2.1 Step-function signal2. 2 Step response of single time constant2. 3 Step response of LC circuitIII PluralIV Complex functionV Exchange C and LThe purpose of switching power supply loop design is to achieve the required output (voltage or current) accuracy within the range of input voltage and load variation, and meanwhile, makes equipment to work stably under any circumstances. What’s more, achieve fast response and small overshoot when load or input voltage changes. At the same time, it can reduce the low frequency pulsation component and the switch ripple and so on.To better understand the feedback design method, the basic knowledge of frequency characteristics, negative feedback and operational amplifier in analog circuits is reviewed importantly. Here the basic design method of feedback compensation is discussed with the example of forward converter. It also introduces how to test the open loop response by using analyzer HP3562A, and then design and correct the network according to the test characteristics and verify the design results. Finally, introduce the simulation test.I Frequency responseIn electronic circuits, reactance (inductor and capacitor) elements are inevitable. For different frequencies, their impedance varies with frequency. Their electrical signals not only change in amplitude, but also in phase. The relation between output and input of sinusoidal signals with different frequencies is called frequency response.1.1 Basic conceptThe output-to-input ratio of the circuit is called a transfer function or gain. The relation between the transfer function and the frequency, that is, the frequency response can be represented by the following expression: G=(f)∠φ(f), while G(f) is the relation between the modulus (amplitude) of the transfer function and the frequency, which is called the amplitude-frequency response; ∠φ(f) is the relation between the phase difference of the output signal and the input signal and frequency, which is called the phase frequency response.The typical logarithmic amplitude-frequency response is shown in Fig. 1, and Fig. 1 (a) is the amplitude-frequency characteristic. It is drawn on the logarithmic coordinate with logarithmic frequency f as the transverse coordinate, and the longitudinal axis gain is represented by 20logG(f). Fig. 1 (b) is the phase frequency characteristic, and the vertical axis represents the phase angle φ on the single logarithmic coordinate with logarithmic frequency f as the transverse coordinate. This diagram is called Potier graphs.Fig. 1 Potier graphsIn terms of amplitude-frequency characteristics, there is a frequency range in which the gain is basically constant, and when the frequency is higher or below than a certain frequency, the gain will decrease. When the high frequency increases, if the gain is lower than the constant part of the 3dB, the frequency is called the upper limit frequency or the upper limit cut off frequency, representing by fH, while the frequency is larger than the cut-off frequency is called the high frequency region. At low frequency, when the gain is lower than the constant part of 3dB, the frequency is called the lower frequency or the lower rate limit, representing by fL, where the frequency is lower than the lower cut-off frequency is called the low frequency region. Between the high-frequency cut-off frequency and the low-frequency cut-off frequency is called the intermediate frequency region. In this area, The gain is basically unchanged. The definition of it: BW=fH-fL1.2 Frequency response of basic circuits1.2.1 High frequency responseFig. 2 High - frequency responseIn the high-frequency region, the circuit that affects the high-frequency response of the system (circuit) is shown in Fig. 2. Taking Fig. 2(a) as an example, the ratio of output voltage to input voltage decreases with the increase of frequency, and meanwhile the phase lags.Using complex variables to obtainAs for the actual frequency, s=jw=j2πf , making(F-0)The high-frequency voltage gain of the circuit can be obtained: The relationship between the frequency and phase angle, and the mode (amplitude) of the gain in the high frequency region are obtained:The logarithmic amplitude-frequency is(F-1)1.2.1 Amplitude-frequency response1) when f<<fH,The gain value is 1, a horizontal line at the horizontal coordinates;2) when f>>fH,It can be seen that for the logarithmic frequency coordinate, the upper formula can be represented by an oblique line, the slope is -20dB/ tenth frequency (- 20dB/dec), and intersects with the 0dB line at f=fH, so fH is called turning frequency. When f=fH, that is  , the high frequency response takes the 0dB line and-20dB/dec as the asymptote, and the maximum difference at the turning frequency is-3dB. The amplitude-frequency characteristic is shown in Fig. 3(a)Fig. 3 High - frequency potier diagramWhen the frequency is equal to the turning frequency, the capacitor reactance is exactly equal to the resistance. When the frequency increases continuously, the impedance of capacitor C decreases by-20dB/dec, that is, the frequency increases by 10 times and the capacitive reactance decreases by 10 times, so the output attenuates with-20dB.1.2.2 Phase-frequency characteristic The relationship between phase and frequency can be made in the following ways according to formula (F-2).- When f<<fH, φ closes to 0 ° , getting a straight line.- When f>>fH, φ closes to 90 ° , getting a straight line.- When f=fH, φ=45 °.- When f=0.1fH, and f=10fH, φH is -5.7 °and -84.3 °respectively, so the slope is represented approximately by 45/dec oblique line. The phase frequency characteristics are shown in the following figure.Fig. 3 High - frequency potier diagramFrom the amplitude-frequency and phase-frequency, it can be seen that when the frequency increases, the gain of the circuit becomes smaller and the phase lag becomes larger. When the phase reaches 90 °, the gain is 0. Both amplitude-frequency and phase-frequency characteristics are determined by upper frequency fH. It can be seen from formula (F-0) that the upper cut-off frequency is determined by the time constant (RC) of the circuit. If the time constant L /R of Fig. 2(b) is equal to the time constant RC of Fig. 2(a), the porter diagram of Fig. 2(b) circuit is exactly the same as that of Fig. 2(a).As can be seen from Fig. 3, the high frequency signal attenuates greatly, while the low frequency signal is preserved. Therefore, this circuit is also called a low-pass filter. For Fig. 2(a) circuits, if the time constant is much larger for the time studied, that is, the resistance and capacitance values are large  Uo=Uc，From  it can get This is an integrator. It can be seen that the same circuit has different functions for different research purposes.1.2.3 Low Frequency CharacteristicWe study the characteristics of the two circuits in the low frequency region shown in Fig. 4. Fig. 4 Low -frequency regionUsing the complex variables, from Fig. 5 (a), Fig. 5 Low - frequency potier diagramwe can getAccording to actual frequency and s=jw, makingGettingThus the gain (mode) and phase angle of the low frequency region of the circuit are respectively:Use the linear approximation method which is similar to the high frequency response, the potier diagram of the low frequency response can be drawn, as shown in Fig. 5. The fH in the diagram is the lower limit frequency, that is, the low turning frequency. Below the turning frequency, the gain of the circuit decreases with the decrease of the frequency, and the characteristic slope is 20dB/dec. When the phase reduces with the frequency, using the forward input phase. Maximum advance 90 °, gain 0 (- ∞, dB).The lower limit transition frequency is also related to the circuit time constant RC (L/R). If the time constants of Fig.4 (a) and Fig.4 (b) are the same, their potier graphs are identical.It can also be seen from Fig.5 that the circuit attenuates the low frequency signal, while the high frequency signal passes smoothly due to the reduction of capacitance. So this circuit is also called a high-pass filter. For Fig. 4(a), when the time constant of the Fig. 4(a) circuit is much smaller than the time interval we studied, the output obtains the variable input signal, then the circuit is a differential circuit.1. 3 Characteristics of LC filter circuitFig. 6 Frequency characteristic of LC filter circuitIn the switching power supply, the forward output filter (Fig. 6) is a LC network with a load resistor in parallel with the output capacitor, and the load resistor can be changed from a certain value (full load) to infinity (no load). For Fig. 6, we can also use complex variables to getAccording to actual frequency and s=jw, makingGetting (F-2)The characteristic impedance of the circuit is, at small range of f close to f0,, making , so The gain amplitude-frequency and phase-frequency characteristics are as follows respectively:(F-3)The Potier diagram of the LC filtering circuit can be made by the expressions (F-3), as shown in Fig.. When f <f0, the formula (F-3) tends to 1, that is 0db, φ≈ 0°; When f >f 0, the second term in the denominator (F-2) is much larger than the other two, the inductive reactance is increased by 20dB/dec, the capacitive reactance by 20dB/dec is decreased, the load impedance is far greater than the capacitive reactance, and the amplitude-frequency is decreased by 40dB/dec, φ tends to -180 °. When f is close to f0, different D values and amplitudes do not increase. The greater D value is equivalent to the light load, that is circuit underdamping, the higher the amplitude. With the increase of the load, the equivalent load resistance decreases, the D value decreases, and the peak value of lifting decreases. When D=1, at critical damping, amplitude-frequency increases slightly from low frequency to f0, at f=f0, it returns to 0dB, and when f >f0, the gain tends to -40dB/dec. When D < 1, the damping is equivalent to full load or overload. In the vicinity of f →f0, the amplitude doesn’t raise, but also attenuates with the increase of frequency, and the slope of attenuation is about 20 times of f0. The relationship between phase shift and f/fc and different D values is shown in the Fig. 8 of amplitude-frequency reaching-40dB/dec. It can be seen that the phase difference between the output and the input is 90 °at the turning frequency point f 0, regardless of the D value. For the high underdamped filter (Ro > 5Zo), the phase frequency characteristic changes rapidly with the frequency. For Ro=5Zo, when frequency at 1.5f0, the phase shift is almost 170 °. But in the circuit with gain slope of-20dB/dec, it is impossible to produce phase shift greater than 90 °, and the phase frequency characteristic changes with the frequency. The change rate of phase shift of in Fig. 8 is much lower than that of -90 °/dec in Fig. 8.Fig. 7 Frequency amplitude of LC filter circuitFig. 8 Phase frequency of LC filter circuitIf the output capacitance in Fig. 7. has ESR , is equivalent series resistor Resr. It is generally very small and the low frequency characteristic will not be affected by 1/ωC<<Resr, in low frequency band. When the frequency increases to At this time  ,the phase is raised by 45°. As the frequency continues to rise, the output filter circuit becomes a LResr circuit. The LC filter attenuates from-40dB/dec to-20dB/dec after the frequency fesr, and the phase shift tends to lag by 90 ° instead of 180 °. This means that the capacitance of the ESR provides a zero point.II Time-domain response of basic circuitsThe circuit analysis includes steady state analysis and transient analysis. The frequency response of the amplitude and phase of the circuit is analyzed with sine wave as the basic signal, which is the steady-state response. This method is called frequency domain analysis method.Another method of circuit analysis is transient analysis. The step-function signal is used as input signal to study the variation of circuit output with time, which is called step response. It is judged by the rising time of the waveform and the flat-top drop size. It's called time domain analysis.2.1 Step-function signalThe graph represents a step voltage that can be represented as:It can be seen that the change rate of step signal waveform is infinite, but it is a constant during the conversion. From the point of view of frequency analysis, the extremely fast rate of change includes harmonic components from DC to very high frequency. Whether the output of the circuit can repeat the waveform of the input signal: the rising time of the output reflects the high frequency response of the circuit, while the flat top drop reflects the low frequency response of the circuit.2. 2 Step response of single time constantLet's study the step response of Fig. circuit. The step response is represented by the rise time tr and the flat-top landing δ. Fig. 9 Step response of single time constantRise time trWhen the step signal is added to the input of Fig. (a) circuit, according to the general law of RC circuitU0-initial value;  U∞-terminal value; τ= RC- time constant. The capacitance initial voltage U0  is zero.In the formula τ = L/R, Ui is the voltage value of the flat top part of the step signal. The relation between Uo/Ui  and time is shown in Fig. 10. The three elements of RC circuit: initial value, final value and time constant. The input rises to the final value in a very short time, and the output voltage changes with time exponentially, which takes a period of time to reach the final value. This phenomenon is called frontier distortion. The interval between 10% of the output end value and 90% of the final value is generally defined as the rising time tr.Fig. 10 The relation between Uo/Ui and tAs can be seen from the expressions (6-18), when t=t1according to the same principle, when t＝t2Because ofSo the rise timeHigh frequency response of circuit f 1/(2πRC)H，gettingTherefore, the rise time is inversely proportional to the upper bound frequency. The higher the is, the smaller the rise time tr is and the lower the front distortion is. For example, the bandwidth of a circuit is 1MHz, and the step-up time is tr=0.35 rt μs. We use Fig. (a) to study flat-top landing. When step input, the output isThe relationship between and time is shown in Fig. 11. If the time tp is small than τ, the output voltage will still decrease according to the exponential law, though the input voltage is invariable, and the decreasing speed is related to the time constant. This phenomenon is called flat-top descent. Fig. 11 Flat-top descentBecause of tp < τ, it can be approximately obtained:Considering that fL=1/ (2πRC), then getsIt can be seen that the flat-top drop δ is proportional to the lower limit frequency fL, and the lower the fL , the smaller the flat-top fall. In switching power supply, the sudden change of load and input power supply voltage is also a step-by-step response. In the above research, the system is still in the linear state, but in the switching power supply, there are high gain amplifiers, under the action of the step signal, the system usually enters the nonlinear state, the large signal response is often lower than the small ones.2. 3 Step response of LC circuitFig. 12 Step response of LC circuitThe LC circuit is shown in Fig. 12. If the circuit loss resistance is zero,  initial voltage of the inductance initial current and capacitance are zero, under the action of step-up signal, getting the formulas are as follows:Ui as step input signal; resonant angular frequency of LC circuitCharacteristic Impedance of resonant CircuitThe peak value of inductance current isDifferent initial values, excitation and circuit conditions, initial and final values of the waveform amplitude are different, but the phase relationship is fixed.Note: plural conceptIII PluralThe complex number is composed of real part and imaginary part, that is,, gettingSince a complex number is composed of two numbers, we can use the x axis as the real number and the y axis as the imaginary axis, as shown in Fig 13. Redraw the Fig. 13 as Fig. 14, and you can see that the complex number can be expressed in two quantities: one is the distance to the coordinates (0,0) , and the other is the angle  from the counterclockwise to the point . The value r is called the modulus of the complex number, and the angle φ is called the amplitude angle of the complex number.Fig. 13 Complex graphic methodFig. 14 Expressing complex number by distance and angleIn electricity, we naturally think of using complex numbers to express values and phases. For example, if you represent a sinusoidal quantity of electricity, the sine is projected on the imaginary axis with the coordinate distance, and the cosine is projected on the real axis, so a complex number can also be represented as (F-4)According to Euler's formula The upper form can be solved as  (F-5), or simplified to (F-6)It can be seen that a complex number can be expressed in the following ways: (F-4) is a complex cartesian coordination, (F-5) is exponential, and (F-6) is polar coordinate. The three can be converted to each other. The complex number can be added or subtracted by cartesian coordination, and the multiplication and division operations by the exponential or the polar coordinates.According to the above mentioned formulas, if φ==90°, soAny phasor multiplied by j, phase rotation 90°: + represents counterclockwise rotation; - represents clockwise rotation. If the virtual axis is j, times j, then rotates to the solid axis to change to -1, then , so is the imaginary unit.IV Complex functionThe instantaneous amplitude and phase can be expressed by a complex number. If a sinusoidal quantity is expressed, the complex number in the circuit is frequency dependent. There are two aspects of interest in steady-state design: what are the parameters of a function that are zero? And where is the function infinite? These two cases represent the zeros and poles of the function respectively.For example It is obvious that x=2 in this function while phase is zero, that is, the complex amplitude is 2, the phase is 0, in other words, the real part is 2, and the imaginary part is 0 (Fig. 15), and the x=3 function becomes infinite. Its complex image value 3 and phase value 0 as another example, we can see that the capacitance has frequency dependent complex 1/sC (s as an complex variable, frequency-dependent), while the inductance is sL. Fig. 15 shows the switching power output filter (capacitor has ESR, inductor has coil resistance, not considered here). Form a voltage divider with an output to input ratio of Fig. 15 Complex impedance of inductor and capacitorThis function will not be zero, but when, that is, there are two poles. The two poles appear at the resonant frequency point and the phase angles are 90 °and 270 °(pure imaginary number, no real part, as shown in Fig. 16 ). Of course, the physical meaning here is that the LC network resonates at this frequency and the output is amplified infinitely at this frequency. In fact, there is always resistance in the actual circuit, so the magnification is not infinite, that is, the two poles are not on the virtual axis and the real part is not zero.Fig. 16 Poles of LC resonant frequencyV Exchange C and LFor capacitive currentIf Us=Uest，the voltage is a sine wave [because of ]，we can getGetting the resistance is: In the definition of Laplace transformation, we do not have to actually solve the integral because the integral is implicit in solving the differential equation. Similarly, we can get the inductance impedance: Similarly, use  to replace  to get: So the resistance is Z=sL

In this article, we will provide you the basic introduction to FPGA and ASIC, illustrate their differences in the design, and many other complement content. CatalogI. What is FPGA?II. What is ASIC?III. What is the Difference Between FPGA and ASIC?      3.1 Difference in RTL Design      3.2 Difference in Development ProcessIV. Difference SummaryFAQI. What is FPGA?The circuit design with hardware description language (Verilog or VHDL), which can be easily synthesized and distributed, can be quickly made to FPGA for testing. It is the mainstream of modern IC design verification technology. These editable elements can be used to implement basic logic gates (such as AND, OR, XOR, NOT) or more complex combinatorial functions such as decoders or mathematical equations. In most FPGA, these editable components also contain memory elements such as triggers (Flip-flop) or other more complete memory blocks.System designers can connect blocks of logic inside FPGA via editable connections as needed as if a circuit test board had been placed in a chip. The logic blocks and connections of a finished FPGA can be changed according to the designer, so FPGA can meet the required logic functions.The speed of FPGA is generally slower than that of ASIC, and the area of realizing the same function is larger than that of ASIC. But they also have many advantages, such as quick production, modification to correct errors in the program, and cheaper costs. Vendors may also offer cheap but poorly edited FPGA. Because these chips have poor editable capabilities, the development of these designs is done on an ordinary FPGA, and then the design is transferred to a chip similar to ASIC. Another way is to use CPLD (Complex Programmable Logic Device). Learn the basics of what is an FPGA. This video discusses the history of FPGAs and how they have advanced over time. It discusses some applications that are possible. Finally it will introduce the two languages used to program FPGAs: VHDL and Verilog.  FPGA StateFPGA (Field Programmable Gate Array) is the product of further development on the basis of PAL, GAL, CPLD, and other programmable devices. As a semi-custom circuit in the field of ASIC, it not only solves the deficiency of custom circuits but also overcomes the shortcoming of the limit of the gate of the original programmable device, that is, FPGA allows unlimited programming. FPGA Parts ExplainationFPGA adopts the concept of LCA (Logic Cell Array), which includes three parts: configurable logic module (CLB), Input-Output Block(IOB), and Interconnect. FPGA is a programmable device with different structures compared with traditional logic circuits and gate arrays (such as PAL, GAL, and CPLD devices). FPGA uses a small lookup table (16×1RAM) to implement combinatorial logic. Each lookup table is connected to the input of a D-trigger, which drives other logic circuits or drives the I / O. Therefore, the basic logic unit module can realize both combinational logic function and sequential logic function. These logic units connect with mental wires or I/O contracts. In addition, the logic of FPGA is to load programming data into internal static storage units. The value stored in the memory cell determines the logical function of the logical unit and the connection between modules or between modules and I / O contracts and ultimately determines what FPGA can achieve.II. What is ASIC?An application-specific integrated circuit(ASIC) is a microchip designed for a special application, such as a special kind of transmission protocol or a hand-held computer. People might contrast it with general integrated circuits, such as the microprocessor and the random access memory chips in PCs. ASIC is used in a wide range of applications, including auto emission control, environmental monitoring, and personal digital assistants (PDAs).Mining was for a long time a GPU only game, but with ASIC miners seemingly everywhere these days, are they actually profitable? ASIC StateAt present, ASIC is considered to be a kind of integrated circuit designed for special purposes in the field of integrated circuits. An integrated circuit is designed and manufactured at the requirement of a specific user or a particular electronic system. That is, the ASIC is characterized by a request for a specific user. The ASIC is smaller in volume and lower in power consumption than that of a general integrated circuit in mass production, also has the advantages of improved reliability, improved performance, enhanced confidentiality, lower cost, and so on. Full Customization and Semi-customizationASIC is divided into full customization and semi-customization, so an ASIC can be pre-manufactured for a special application or it can be customized (typically using components from a "building block" library of components) for a particular requirement of customers.Full customization design requires designers to complete the design of all circuits, so it requires a lot of manpower and material resources, although it has good flexibility the development efficiency is low. If the design is ideal, full customization can run faster than semi-custom ASIC chips. When using the standard cell, the semi-custom can select SSI (gate), MSI (such as adder, comparator, etc.), data path (such as ALU, memory, bus, etc.),. memory and even system-level modules (e.g. multipliers, microcontrollers, etc.) ) and the IP core from the standard logic unit library. When these logic units have been laid out and designed reliably, the designer can easily complete the system design. Modern ASIC often contains a 32-bit processor, storage units like ROM, RAM, EEPROM, Flash, and other modules. Such ASIC is often called SoC(system in the chip).ASIC DevelopmentProgrammable ASIC is another characteristic branch of ASIC development. It mainly uses programmable integrated circuits such as PROM, GAL, PLD, CPLD, FPGA, or logic array to get ASIC. Its main feature is to provide software design and programming directly, completes the function of ASIC circuit, and it does not need to be processed by IC process line.There are many kinds of ASIC designs for programmable devices, which can meet different requirements. PLD and FPGA are commonly used programmable devices. It is suitable for the design of digital circuits with a short development cycle, certain complexity, and circuit scale, especially for electronic system design engineers using EDA tools for ASIC design.III. What is the Difference Between FPGA and ASIC? 3.1 Difference in RTL DesignThere are many differences between FPGA and ASIC. The logic of ASIC is usually much larger than that of FPGA. There is an order of magnitude difference in gate numbers, and the running clock is much higher than FPGA. Moreover, FPGA is relatively flexible than ASIC because it can be programmed, but only in terms of RTL design: (1) ASIC tends to be more conservative, any changes to logic needed careful consideration, and make alternative choices in case of a correction. Any modification to RTL is almost incremental, and even if the previous logic is wrong, it will not be deleted, but one more branch is made.(2) ASIC has higher requirements for coding style. Coding style requirements for all modules are consistent, thus favoring the fault check.(3) ASIC design pays more attention to the clock and reset. In particular, clocks are critical to the design of ASIC, and reset is critical to BIST testing. ASIC uses libraries to design in this respect. ASIC usually does not use a counter to divide frequencies, which can lead to unclean clocks. Unless it's a very low-frequency clock, ASIC is also much more cautious about signal processing across clock domains. The closing and opening of the clock also need to be strictly checked.(4) ASIC has to consider the problems of SCAN testing and BIST, so it is necessary to do BIST insertion for SRAM when designing and to reserve interfaces for SCAN. Although most of the interfaces are done by tools, RTL authors often have to do some top-level complex work manually, logic such as the source of the SCAN clock.(5) FPGA often uses existing IP, it needs to consider the balance of resources because there is a problem of resource waste in FPGA. ASIC rarely needed to consider this problem, the main consideration of it is its performance and power consumption, except SRAM and CLK which is related to reset in logic choice, the other are handwritten. So the logic is basically no waste, and more compact.(6) ASIC timing is more predictable and adjustable, so it can write a lot of logic. 3.2 Difference in Development ProcessThe differences between FPGA and ASIC development processes: ASIC and FPGA Design Flow ASIC and FPGA Implementation StepsThe first step is to implement functionality in a way that is generally described in HDL, such as Verilog, VHDL. Of course, small-scale circuits can also use circuit diagram input mode.The second step is to ensure the correctness of circuit functions, also known as verification. It can be realized by software simulation, hardware simulation, and so on. Software simulation is generally intuitive and easy to debug because the state of every moment can be seen, this is like debugging software programs. Hardware simulation generally refers to FPGA verification, that is, the circuit is implemented with FPGA, and then run it. The advantage of this is that it is very fast. For example, a video decoding core is used to solve a frame of the image, and software simulation can even use the best server, it still takes a lot of seconds to run, but in FPGA, it basically needs milliseconds. For a large mode verification of the circuit, is essential.The first two steps for digital IP,  the ASIC and FPGA are basically the same, unless some implementation techniques are different.The third step is, once the correctness of the circuit you describe is ensured, to implement it by turning the code you write into a real circuit, such as a register or a NAND gate, which is called synthesis. Because the circuit is becoming more and more complex, the most basic circuit is made into cells, such as register, and non-gate, so it will not be refined to the problem of how to use triode. The difference of this step is the smallest unit of the FPGA and the ASIC. FPGA is a well-made circuit, generally considering universality and efficiency, so the basic circuit unit is relatively large, such as LUT, consist of a register and NAND gate, although it uses one gate, it will take up such a unit. For ASIC, the two-input NAND gate is a simple gate circuit, even in order to distinguish the driveability and the timing characteristic difference, there are several grades, some area is small, some driveability is strong. In general, this step is to make sure your description turned into a library-based circuit description.The fourth step is, when you get a description of the circuit based on the library, you have to consider how these units are placed, which is called layout and wiring. The wiring resources of FPGA are limited, so you need to constantly adjust it to ensure the timing requirements. Map your circuit to the middle of its fixed resource map. ASIC's words are generally based on peripheral circuit requirements, timing requirements, your circuit to a certain location on the chip. After the arrangement, we have to consider whether the connection can pass, whether the delay at all levels can meet the circuit establishing and maintaining time requirements, and so on.The fifth step is output. FPGA is to output a configuration file to make the FPGA chip configure its circuit so that it can achieve the desired function. This file can be downloaded by PC after FPGA power-up, or stored in Flash, when the circuit is powered on, the automatic configuration will make. ASIC is to output a layout file to tell the manufacturer how to corrode silicon chip, how to connect metal, and so on.The sixth step is cost. ASIC has a great advantage in terms of recurring costs with less material is wasted due to the fixed number of transistors in the design. As for FPGAs, a certain number of transistor elements are always wasted although these packages are standard. This means that the cost of an FPGA is often much higher than that of an ASIC. Although the recurring cost of an ASIC is quite low, its non-recurring cost is relatively high. Although it is non-recurring, its value per IC decreases with increased volume.  A Field Programmable Gate Array can be seen as the prototyping stage of Application Specific Integrated Circuits: ASIC is very expensive to manufacture, and once it's made there is no going back (as the most expensive fixed cost is the masks [sort of manufacturing "stencil"] and their development). FPGA can reprogrammable many times, however because of the fact that a generic array of gates is connected to accomplish your goal, it is not optimized like ASIC. Also, FPGAs are natively dynamic devices in that if you power it off, you lose not only the current state but also your configuration. Boards now exist though that add a FLASH chip and/or a microcontroller to load the configuration at startup so this tends to be a less important argument. Both ASIC and FPGA can be configured with Hardware Description Languages, and sometimes FPGA is used for the end product. But generally, ASIC kicks in when the design is fixed.If you analyze the cost of production in relation to the volume, you would find that as you go lower in production numbers, using FPGA actually becomes cheaper than using ASIC.There are, of course, various auxiliary steps in the process. In general, it's all about making sure that the circuits you design are correct and implemented correctly.IV. Difference Summary FPGAASICReconfigurable circuitOne-time circuitDesign mainly with hardware description languages (HDL)Similar to the FPGAFPGA is relatively flexibleASIC tends to be more conservativeFPGA is not strict with the coding because of its programming featureASIC has higher requirements for coding styleFPGA uses small LUT to combine logic configurationASIC design pays more attention to clock and resetFPGA designers generally do not need to care for back-end designThe problems of SCAN testing and BISTFPGA uses existing IPperformance and power consumptionAnalog designs are not possible with FPGAASIC can have complete analog circuitThe speed is generally slowerRun fast than FPGAAllow unlimited programmingAn integrated circuit for a special purposeMore power consumptionMuch more power efficient than FPGA Visual Comparsion(√ means better to select)FPGAASICNRE√Performance√Design Flow√Barrier to entry√Time to market√Analog Blocks√Unit size√Power consumption√Cost per unit√FAQ 1. How do FPGAs work?In general terms, FPGAs are programmable silicon chips with a collection of programmable logic blocks surrounded by Input/Output blocks that are put together through programmable interconnect resources to become any kind of digital circuit or system. ... Unlike processors, FPGAs are truly parallel in nature. 2. What is FPGA and why it is used?FPGAs are particularly useful for prototyping application-specific integrated circuits (ASICs) or processors. An FPGA can be reprogrammed until the ASIC or processor design is final and bug-free and the actual manufacturing of the final ASIC begins. Intel itself uses FPGAs to prototype new chips.3. What is the function of FPGA?The field-programmable gate array (FPGA) is an integrated circuit that consists of internal hardware blocks with user-programmable interconnects to customize operation for a specific application.4. Is FPGA faster than GPU?Compared with GPUs, FPGAs can deliver superior performance in deep learning applications where low latency is critical. FPGAs can be fine-tuned to balance power efficiency with performance requirements.5. Is Raspberry Pi a FPGA?The main difference between the Snickerdoodle and other single-board systems like the popular Arduino and Raspberry Pi products is the inclusion of a Field Programmable Gate Array (FPGA). 6. Does FPGA have memory?The FPGA fabric includes embedded memory elements that can be used as random-access memory (RAM), read-only memory (ROM), or shift registers. These elements are block RAMs (BRAMs), LUTs, and shift registers. ... The data of the ROM is written as part of the FPGA configuration and cannot be modified in any way.7. Is FPGA a microprocessor?Microprocessor vs FPGA: A microprocessor is a simplified CPU or Central Processing Unit. ... An FPGA doesn't have any hardwired logic blocks because that would defeat the field programmable aspect of it. An FPGA is laid out like a net with each junction containing a switch that the user can make or break.8. What is FPGA and ASIC?ASIC stands for Application Specific Integrated Circuit. ... The difference in case of ASIC is that the resultant circuit is permanently drawn into silicon whereas in FPGAs the circuit is made by connecting a number of configurable blocks.9. Is FPGA better than ASIC?In general, we can say that for lower volumes' designs, FPGA flexibility allows to save costs and obtain better results; while ASICs chips are more efficient and cost effective on high volume applications.10. Which one is faster ASIC or FPGA?A single unit of an FPGA chip will be relatively larger than an ASIC chip unit. Because FPGA has its internal structure and a certain size that cannot be changed – while ASIC consists of exactly the amount of gates required for the desired application. FPGA boasts a faster time to market than ASIC.11. What are the main differences between ASIC and FPGAs?Performance and Efficiency. ASICs offer superior performance and are more efficient than FPGAs. Factors like faster speed and the ability to layer multiple functionalities onto a single chip make ASICs outperforms FPGAs. 12. Why do we need FPGA?Why Use an FPGA? ... FPGAs are particularly useful for prototyping application-specific integrated circuits (ASICs) or processors. An FPGA can be reprogrammed until the ASIC or processor design is final and bug-free and the actual manufacturing of the final ASIC begins. Intel itself uses FPGAs to prototype new chips.13. Is ASIC a CPU?CPUs and microprocessors are the same thing. ASIC is just a general term for a microchip. CPUs are technically ASICs, but much simpler devices can be implemented on an ASIC too.14. What is the most preferred FPGA variant?Verilog is currently the most popular. Verilog creates a level of abstraction to hide away the details of its implementation. Verilog has a C-like syntax, unlike VHDL.15. What is ASIC technology?An application-specific integrated circuit (ASIC /ˈeɪsɪk/) is an integrated circuit (IC) chip customized for a particular use, rather than intended for general-purpose use. ... ASIC chips are typically fabricated using metal-oxide-semiconductor (MOS) technology, as MOS integrated circuit chips. 16. When should ASIC and FPGA devices be used?If your application requires constant bug fixes, feature and design changes, and software flexibility, then FPGAs may be the right solution. If your end application requires high performance, smaller device footprint, and significantly lower power consumption, then ASICs are your best bet. 17. How does an ASIC work?ASICs allow miners to use hardware made specifically for Bitcoin or other SHA-256 algo coins. An ASIC has benefits over CPU, GPU and FPGAs due to being designed for one specific task. They are able to mine Bitcoin at a higher hash rate (speed of processing transactions) than CPUs, GPUs and FPGAs.18. Why use an FPGA instead of a CPU or GPU?This is where FPGAs are much better than CPUs (or GPUs, which have to communicate via the CPU). With an FPGA it is feasible to get a latency around or below 1 microsecond, whereas with a CPU a latency smaller than 50 microseconds is already very good. Moreover, the latency of an FPGA is much more deterministic. 19. Why is ASIC needed?ASICs are designed specifically for one client to provide a function required by the client's end product. For example, a cell phone company may design an ASIC to combine the display backlight controller with the battery charging circuit into a single IC in order to make the phone smaller.20. What is better ASIC or GPU?In short: ASICs are best for mining Bitcoin, Litecoin, Dash, and coins that are based off these algorithms. GPUs are best for mining Ethereum, Monero, Ravencoin, and coins based off those algorithms. Note: Over time all of these coins will produce less thanks to halvings which cut the reward for mining blocks in half.You May Also LikeDiscussion on the influencing factors of clock in FPGA designNew SoM Combination Design Based on Processor and FPGA: FPGA and Processo

This is a technical article introducing what is operational amplifier, how does op amp works, how many types of op amp are there, and how to choose the right op amp for your circuit, and the last part, we will look at the example expressions of the op amp to better understand this device. Down below is an episode of Electronic Basics will explain the three golden rules when working with OpAmps and how to use them in order to understand and build all kind of OpAmp circuits. The main focus will be the noninverting and inverting amplifier and the comparator circuit.  Catalog  I. What is an Operational AmplifierII. How does Op Amp WorksIII. Seven Types of Op AmpIV. Op Amp Design ConsiderationV. Op Amp Examples ExpressionsVI. ConclusionFAQ  I. What is an Operational Amplifier In an actual circuit, an operational amplifier is a circuit unit with high magnification, which usually combines the feedback network to form a certain functional module. Since it was used in analog computers to realize mathematical operations, it is named "operational amplifier", more commonly known as op-amps.  An operational amplifier is a circuit unit based on its function, which can be implemented by discrete devices or semiconductor chips. With the development of semiconductor technology, the vast majority of operational amplifiers are in the form of a single chip. Nowadays, there are many kinds of operational amplifiers, which are widely used in almost all industries. Figure 1. Op Amp Diagram  II. How does Op Amp Works The operational amplifier has two input terminals a (inverse input), b (in-phase input), and one output.  There are also referred to as backward input end, non-backward input end, and output end respectively. When the voltage U- is applied to the terminal and the public end (the common end is a point where the voltage is zero, it is equal to the reference node in the circuit.), and meanwhile a terminal of the actual direction of the output voltage U is higher than that of the common terminal, the actual direction of the output voltage U is from the common end to the o terminal, that is, the direction of the two terminals is opposite.  When the input voltage U+ is added between the b terminal and the common terminal, the actual direction of U and U+ is exactly the same as that of the common terminal. For the distinction, end a and end b are divided “-” and “+”, also, don't mistake them for the positivity and negativity of the voltage reference direction. The positivity and negativity of a voltage should be marked separately or as an arrow. Figure 2. Op Amp Symbols and Terminals Inverting amplifiers and non-inverting amplifiers are shown below:Figure 3. Inverting Op Amp Fig. 4 Non-inverting Op Amp Generally, the operational amplifier can be simply regarded as a high gain direct coupling voltage amplifier unit with a signal output port (Out) and two in-phase, and inverse high impedance input terminals. Thus, an operational amplifier can be used to fabricate phase, inverse, and differential amplifiers. Operational amplifier power-supply mode can be divided into two types: dual power supply and single power supply. For a dual power-supply operational amplifier, the output can be changed on both sides of the zero voltage, and the output can also be set zero at the differential input voltage of zero. As for the single power supply, an operational amplifier that uses a single power supply, a range of input variations is between the power supply and the ground. The input potential of the operational amplifier is usually higher than a certain value of negative power supply, but lower than a value of positive power supply. Specially designed operational amplifiers can allow input potentials to vary throughout the range from negative to positive power, even slightly higher than positive power supply or slightly lower than the negative source. This operational amplifier is called a rail-to-rail input operational amplifier. The output signal of the operational amplifier is proportional to the voltage difference between the two inputs. In the audio band, the output voltage = A0 (E1-E2), where A0 is the low-frequency open-loop gain of the operational amplifier, E1 is the input signal voltage at the in-phase, and E2 is the input signal voltage at the inverse phase.  III. Seven Types of Op Amp General type: Its performance parameters are suitable for general use (low frequency and slow signal change), such asμ741A, LM358 (double OP Amp), LM324, and LF356  with FET as input stage. They are the most widely used integrated operational amplifiers. High-Z type: The characteristic of this kind of amplifier is that the input impedance of differential mode is very high and the input bias current is very small, general rid > 1GΩ~1TΩ, IB is several to dozens of picoamps. The main measure to achieve these targets is to make use of the high input impedance of FET, using FET as input stage not only has high input impedance and low input bias current but also has the advantages of high speed, wideband and low noise, however,  the input offset voltage of this kind of operational amplifier is larger. Such operational amplifier have LF356, LF355, LF347, CA3130, CA3140, etc. Low-temperature drift type: In precision instruments, weak signal detection, and other automatic control instruments, the bias voltage of the operational amplifier is small and does not change with the temperature. The low-temperature drift operation amplifier is designed for this purpose. At present, the commonly used operational amplifier has OP07, OP27, OP37, AD508, and ICL7650 composed of MOSFET devices and so on. High slew-rate type: In fast A/D converter, D/A inverter, and video amplifiers, the conversion rate of the operational amplifier must be high, and the BWG of the unity gain bandwidth must be large enough. The common operational amplifier has LM318, 175A, and so on, while the SR=50~70V/us, BWG>20MHz... Low-consumption type: Due to the wide application of portable instruments, low power supply, and low power consumption must be used. Commonly used low-power operational amplifier has TL-022C, TL-160C and so on. The operating voltage is ±2V~±18V, and the current consumption is 50 ~ 250μA. At present, the power consumption of some products has reached μW level, for example, the power supply of ICL7600 is 1.5V and the power consumption is 10mW, which can be supplied by a single battery.  High voltage and power type: The output voltage of the operational amplifier is mainly limited by the power supply. In an ordinary operational amplifier, the maximum output voltage is only dozens of volts and the output current is only dozens of Ma. In order to increase the output voltage and current, the auxiliary circuit must be added to the external circuit of the operational amplifier. High-voltage and high-power operational amplifier can output high voltage and high current without any additional circuit. For example, the power supply voltage of the D41 integrated operational amplifier can reach ±150 V, and the output current of μA791 integrated operational amplifier can reach 1A.  Programmable control type: In the usage of instruments will be involved in the measurement range problem. In order to get the fixed voltage output, we must change the magnification of the operational amplifier. For example, there is an operational amplifier with a magnification of 10 times, where the input signal is 1mv, the output voltage is 10mv when the input voltage is 0.1mv, the output is just 1mv. To obtain 10mv, the magnification must be changed to 100. A programmable control operation amplifier is to solve this problem. For example, the PGA103A changes the magnification by controlling the level of pin 1 and pin 2.  IV. Op Amp Design Consideration After knowing some basic types op amps, there are some basic questions you should ask before looking for a suitable op amp. Basics:（1）What is the input signal going to look like?（2）Current-input or voltage-input?（3）What is the expected operating frequency range? Maximum range?（4）What amplitude is needed? (Typical and maximum values.)（5）What’s the impedance of the circuit it’s going into?（6）What is an acceptable output signal going to look like?（7）What is the expected range of frequencies the output signal might cover?（8）What is the expected amplitude range?（9）Will the op-amp be driving another device? If so, how much power will be needed?（10）How accurate or precise does the op-amp need to be? The operating environment:What supply voltage(s) are available?Is there a physical size limitation? You may need to make a list of packages of an acceptable size.What is your operating temperature range? Figure out a Max, Min, and Typical. Look at how the temperature affects your most critical parameters using the graphs in the datasheet. If the information you need is missing, you can contact the company or set it aside and move on to another spec that is more thorough. Buying:Are you restricted to certain manufacturers that your company deals with?Will you need to second source the op amp?What is the lifecycle of the op amp? Do not select any op amp that is Not Recommended for New Design (NRND), End of Life (EOL), or otherwise a special factory order (this might mean that it’s about to go EOL).Price might be a specification of a sort, but this should be one of the last parameters you look at when you are deciding between otherwise identical op amps. Other points:When selecting parameters, it's good to allow a margin of error on the specifications. Not every op amp will be precisely the values as listed, and op amp values change with temperature, age, and stress. Make sure the finalists in your part selection are actually for sale. “Vapor-ware” is when a manufacturer announces a part to be released in the near future, but some parts have been known as “about to release” for a year or more, depending upon the manufacturer. That’s why you second source your product, and why you confirm the product's lifecycle prior to finalizing. V. Op Amp Examples Expressions The ADC architecture, resolution, signal bandwidth, and other specific application details are at work when understanding the various types of operational amplifiers that determine the best way to choose the best amplifiers. We consider these issues in the context of driving SAR ADC in this article. SAR ADC is the mainstay of the A-D converter world. In general, this kind of ADC is located between high resolution, low-speed incremental ADC and high speed, low-resolution pipeline ADC. By virtue of its delay-free feature, SAR ADC is often a better choice than ΔΣ ADC and pipeline ADC in applications with multiplexed signals, or applications that need to implement accurate first-time conversions after an arbitrary idle cycle (such as ATE), what's more, applications where ADC is located in a loop that requires quick feedback. In most cases, the sensor output cannot be directly connected to the SAR ADC input. An amplifier is needed to obtain the optimal SNR and distortion.  SAR ADC to sample the input to the internal capacitor and to compare the input voltage with the reference voltage with a successive binary-weighted sequence. When the switch to the sampling capacitor is open, the charge is injected into the input node due to the voltage mismatch from the sampling capacitor to the input node. A simple monopole RC filter is arranged between the amplifier and ADC. It not only used to filtering high-frequency noise and aliasing components but also to absorb this injected charge. Care must be taken when selecting cutoff frequencies for such filters. Besides, the cutoff frequency should be set at a low frequency enough, which can effectively absorb the injected charge and filter the noise, but the frequency should be high enough so that the amplifier can achieve stability within the sampling time of the data converter. Since this filter can't limit noise alone, it is generally included at the amplifier input end, and a filter with a lower cut-off frequency is also installed simultaneously. Figure 5. LTC2379 18-bit 1.8Msps  Differential Input SAR ADCSINGLE-ENDED-INPUT SIGNALSINGLE-ENDED-TO-DIFFERENTIAL DRIVER  SAR ADC Drive Differential Input SAR ADC Many of the sound performance SAR ADC use differential input to maximize the dynamic range of low power supply voltage. One such example is the LTC2379-18 shown in Fig, which operates with a 2.5V power supply and a reference of up to 5V to achieve a peak-to-peak differential input range of 10V. If the input signal is differential, all that is needed to buffer the signal and drive the ADC, or maybe a low-noise, fast, and stable dual-channel operational amplifier such as LT6203. These amplifiers are configured which as unit gain buffers for the input signal provides a high impedance input. In many cases, however, the input is single-ended and must be converted to a differential signal. This task can be easily accomplished with amplifiers such as LT6350. This type of amplifier has two stages: the first stage generates a buffered non-invert input signal and the second stage generates an inverted output. If the input signal matches the input range of the ADC, the amplifier can be used to provide a high impedance buffer for the signal, as shown in the upper part of Fig. 6(a). If the signal needs to be expanded and shifted to match the input range of the ADC, it can be done as shown in Fig. 6(b) below.  In this example, a single-ended ±10V signal is converted into a differential signal from 0 to 5V (R2 and R3 are used to shift the signal, and RIN and R1 are used to expand the signal). What is often overlooked inaccurate analog circuits is the need for a high match between gain setting and level shift resistors. If a discrete resistor with 0.1% accuracy is used, the mismatch will vary with time, temperature, and common-mode voltage range, which makes it possible that it will be the main source of the fault circuit. Using precisely matched resistors such as LT5400 will help improve this situation. The amplifier needs space between the supply voltage and the output voltage. To maintain optimal accuracy and linearity, depending on the amplifier, the output must generally be within 0.5V or more of the power rail. This means that the amplifier must be provided with a power supply voltage range wider than the ADC input range, or that the ADC must accept a limited input range from the amplifier.  ADC such as LTC2379-18 includes a "digital gain compression" function. The function sets the full scale of the ADC from the inside and the difference between the ground voltage and the reference voltage is 0.5V. This allows the use of a single 5V amplifier that matches the full scale of the ADC.  Figure 6 (a): Single-to-difference conversion using LT6350 Fig. 6(b): Single-to-difference conversion using LT6350 ADC Driving Pseudo Differential ADC Another way is when converting a single-ended analog signal to a digital signal, skipping the differential conversion completely and using a new pseudo-differential ADC, such as LTC2369-18. The shortcoming is that the noise-signal ratio of SNR which up to 6dB is lost due to a smaller input range.  Besides, differential structures are inherently easier to eliminate even harmonics. However, using it also has some important advantages. The drive circuit is simpler: it can be as simple as using a low-noise, fast, stable operational amplifier, such as LT6202, while another operational amplifier and resistor are not required to establish the inverted input. Apart from using fewer groups, the power and noise of the circuit are generally low. Because a lower noise anti-aliasing filter behind the amplifier can have a higher cut-off frequency. This makes it easier for the amplifier to achieve stability within the ADC conversion time, making it a good choice in applications where successive conversions are likely to change throughout the scale, as is the case with multiplexed signals.  It is necessary to emphasize again that the space of the amplifier must be considered-the supply voltage must be far enough away from the output of the amplifier, which can drive the signal without distortion. In other words, this means that the amplifier must be provided with a negative orbit.  One way to solve this problem is to use products such as LTC6360. This new amplifier (Fig. 7) is optimized to drive the SAR ADC with an integrated ultra-low noise charging pump that generates its own internal negative voltage rail. Although it has a single positive source, this allows the output to swing to the ground, even slightly lower than the ground. The LTC6360 maintains excellent accuracy (250V misalignment, 2.3nV/Hz noise) and is fast and stable (16-bit, 150ns). Figure 7. When using a single power source, the LTC6360 wobbles to 0V  VI. ConclusionSeveral amplifier topologies can be used to drive SAR ADC. The best choice depends on the input signal, ADC input architecture, and application details, such as whether the input signal is multiplexed. Factors to be weighed include power, complexity, performance, and speed (conversion rate and stabilization time). Choosing an op-amp requires matching your requirement to the op-amp datasheet. Blindly assuming that any op-amp will work in any circuit is only going to result in frustration and disappointment. What's more, using the right op-amp can allow you to do things you never thought were possible.  FAQ 1. What is operational amplifier and its types?An operational amplifier (op amp) is an analog circuit block that takes a differential voltage input and produces a single-ended voltage output. Op amps usually have three terminals: two high-impedance inputs and a low-impedance output port. 2. Why is it called operational amplifier?Op-amp stands for operational amplifier. ... Originally, op-amps were so named because they were used to model the basic mathematical operations of addition, subtraction, integration, differentiation, etc. in electronic analog computers. In this sense a true operational amplifier is an ideal circuit element. 3. What is the difference between amplifier and operational amplifier?Amplifiers can be either electronic or mechanical in common definition whereas operational amplifiers are electronic amplifiers. Amplifiers, in general, have a limited capability of amplifying DC signals but all op-amps are capable of amplifying DC signals. 4. What is the main function of operational amplifier?An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins. 5. What are the advantages of operational amplifier?Advantages: 1. increased circuit stability2. increased input impedance 3. decreased output impedance 4. increased frequency bandwidth at constant gain. 6. What are op amps used for in real life?Op amps are widely used in amplifiers oscillators, filters, comparators, integrators and differentiation,voltage regulator, current regulator. Non linear applications include precision rectified log amplifier . It is also used in analog to digital and digital to analog converter. 7. Where are operational amplifiers used?Operational amplifiers are linear devices that have all the properties required for nearly ideal DC amplification and are therefore used extensively in signal conditioning, filtering or to perform mathematical operations such as add, subtract, integration and differentiation. 8. What is an ideal operational amplifier?Operational amplifier: The ideal op amp is an amplifier with infinite input impedance, infinite open-loop gain, zero output impedance, infinite bandwidth, and zero noise. It has positive and negative inputs which allow circuits that use feedback to achieve a wide range of functions. 9. Why op-amps are better than transistors?1 Answer. A transistor is a single electronic element. ... An operational amplifier is the equivalent of many transistors and is thus able to perform much better than a single transistor (e.g. higher input impedance, lower output impedance, higher gain, differential inputs and/or differential outputs, etc.). 10. Why does an operational amplifier need a power supply?Operational amplifiers have two power supply rails because they usually need to swing bipolar - output voltages that go either positive or negative in response to the normal range of input signals. ... Without the dual supplies the output signal would clip at the ground potential. 11. How op-amp can be used as a differentiator?An op-amp differentiator is an inverting amplifier, which uses a capacitor in series with the input voltage. ... Differentiators have frequency limitations while operating on sine wave inputs; the circuit attenuates all low frequency signal components and allows only high frequency components at the output. 12. Is an op amp a transistor?Well for starters, an op amp is simply a combination of transistors, so by varying the transistor you can get different properties. One thing to also remember is that op amps are class A amplifiers which basically means that they are always on and therefore drawing power which can be undesirable. 13. Why is op amp a versatile device?Op Amps or operational amplifiers, are fundamental building blocks in electronic design, mainly because these analog integrated circuits (ICs) are very versatile. ... The term “differential amplifier,” for instance, simply means that the op amp will try to amplify any difference between the signals. 14. Does op amp need ground?An Op Amp inverting input (-) is at zero potential (A virtual ground), even though it does not have a galvanic connection to ground. 15. What is the difference between real ground and virtual ground?Real ground is when a terminal is connected physically to the ground or earth. where as virtual ground is a concept used in Op-Amps in which a node is assumed to have the potential that of the ground terminal.   You May Also LikeOperational Amplifier(OP Amp) TutorialAbout Operational Amplifier LM358: 24 Classical CircuitsA Load Insensitive High-Power Balanced Power Amplifier