As we all know, the analog circuit is difficult to learn. In the most common transistor, we must analyze the DC offset first, and then analyze the AC output voltage. It can be said that determining the working point is a rather cumbersome task (in practice), the parameters of the transistor are large, and the discreteness of the parameters is also large. But what deserves our attention is that analog circuits have built the foundation of the electronics industry, and so far, electronic technology has developed to such a high level. But if we look at the development of various electronic circuits, we will find that almost all electronic technologies are not open to big technology. Even inside the digital chip, its basic unit is a complementary source grounding amplifier circuit. The importance of analog electronic technology is not to be treated.
What the analog circuit says is that the key is to learn more and do more, and to make a film, you naturally know which knowledge points need to be mastered. Here we mainly talk about the four knowledge parts of learning analog circuit requirements. To become the designer of analog circuits, we must master the following four basic components:
(1) Design of transistor components
It refers to the knowledge of semiconductor engineering. Any IC chip designed will eventually return to it. It is usually drawn from Schrödinger's wave equation (complicated), but it has little direct connection with the actual design circuit. This part cannot be lacking and is the theoretical basis.
(2) Design of transistor circuit
In order to engage in analog circuit design, you must actually master the basic knowledge of transistor circuits. It is recommended to study and simulate while learning, PSPICE and the like. You can do it one by one, and you should pay more attention to it. After a long time, I can naturally master the design technology of the transistor circuit. After learning this, we will begin to master the experience. Transistors and FETs are the basis for building the entire circuit. Here, the schematics of many ICs are very straightforward.
(3) Design of functional modules
The functional modules are mainly based on a variety of op amps, including AD, DA, PLL, voltage regulator, etc., which are mainly composed of transistors, and the functional module design engineering will properly idealize the components. This part of the study is very important. Generally speaking, it is to learn analog circuits from here. This part is relatively easy to understand and is also the entry point for analog circuit learning.
(4) System design
This part needs a considerable height and needs to be considered.
In fact, to be honest, if you have actually done one or two films, you will be able to get through most of them. The key is to experiment and do it.
Fudan has been working on the microelectronics professional analog chip design. He has been working for five years and has been working for five years. He has listened to many domestic and foreign experts. Recently, at the invitation of a friend, I wrote a little experience and shared it with everyone.
I remember that when I graduated from the undergraduate course, I was going to study the sensor. Later, I went into the State Key Laboratory of Fudan Yifu Building Special Integrated Circuit and System for graduate students. Now I want to come to this lab name with great meaning, but it was awkward at the time.
Circuits and systems seem to be two concepts, two levels. My classmates have graduated from the Department of Electronics and Information Systems. At that time, they knew that they were "systems", and we were doing analog "circuit" design, and naturally we were biased towards the circuit. The analog chip design beginners are always admired for the singularity of the circuit, especially the most authoritative magazine JSSC (IEEE Journal of solid state circuits) in this field. I used to like it very much. I decided to watch it for nearly 20 years. The article, through the eight classics of the classics, is always a time to sip an article, then the domestic articles published in this magazine is very rare, is to read a doctor abroad, can also be published on the above is also excellent.
When I was studying, my tutor was Professor Zheng Zengqi. Lilian was retired at that time. Yifulou invited Mr. Li to come and guide each week. Mr. Zheng is rigorous in his studies and is a heroic woman. Mr. Li is a domestic pioneer in analog circuits and is now employed as an expert or consultant in many companies. A book written by Teacher Li in 1987 (optical amplifier design); even now it seems to be a classic. Teacher Li and Teacher Zheng are classmates, so it is very good. I am naturally lucky to get the guidance of Teacher Li relative to my classmates.
The training plan that Teacher Li and Teacher Zheng gave me was: Learn from the operational amplifier first. So I remember that I just started designing from a small current source. At that time, I felt that the design was to adjust the parameters by simulation. But I always remember the words of Teacher Li's words: the op amp is the foundation, the op amp design is done, and the others are easy. I didn't understand it at the time. My classmates' topics were AD/DA, phase-locked loops and other "high-end" stuff, while Teacher Li and Teacher Zheng asked me to do "raw" modules. I only have (solid electronics). A paper published by the domestic junk magazine is a rail-to-rail amplifier. I was very depressed during the process, and I envied my classmates' project very much, but I felt that there was always reason for Mr. Li and Teacher Zheng to talk about it, so I specifically looked at the JSSC op amp article, which was basically seen in nearly 20 years.
At that time, I thought I understood this very well. Later I found out that I didn't understand it. The so-called understanding is to truly integrate, otherwise there will be more knowledge in the head, and it is also dead. However, the operational amplifier is the cornerstone of the analog circuit. Only when the foundation is solid can it flourish, and the two teachers can understand it after working hard. In general, in Fudan, what I feel most deeply is the rigorous academic style of Teacher Zheng and the words of Teacher Li.
After graduating from master's degree, I went to work, and there were several offers at the time. My brother Sun Liping, Li’s close disciple, recommended me to Xintao Technology. He said that there is a Chang Zhongyuan, a Ph.D. student at the Catholic University of Leuven, which is very powerful. I followed the advice of my brother and went. Xintao was acquired by IDT for 85 million US dollars at that time, becoming the first successful chip company in China. Interview with me is the general manager of the company, Howard. C. Yang (Yang Chonghe). Howard is a Ph.D., phase-locked loop expert at Oregon State University. At the interview, he asked me to draw a two-stage amplifier with Miller compensation. I am very skilled. He said that you have a zero on the surface. I am very strange. I have never heard it. In the fog, I realized that this was first proposed by Howard in the world. There is a resistor in the equivalent model. He named himself Yang. resistance. At that time, out of courtesy, nodded. However, they are still very satisfied, so they went in like this. For me, the only regret of the interview was that I didn’t see Chang Zhongyuan, probably he was on a business trip.
After entering Xintao, he made up his mind to prepare for the surgery industry. Because undergraduate and graduate students like physics, mathematics, and philosophy, they have spent some energy on these. After work, I have to do a real knife. Every day after work simulation and after work, I read the original English book. The first book is the popular Razavi book. Read it three times. It feels great. At that time, in Xintao, the newborn calf was not afraid of tigers. It should be said that I still did a very good job, so I was appreciative of Chang, and he was rated as the most potenTIal person in the company. Occasionally, I always come over and give pointers, others are envious. In fact, I remembered the experience that I always told me when I was chatting. He said that there are three realms in analog circuit design: the first is to calculate, meaning that pensile-to-paper, the circuit should actually be In the calculation, the simulation is only the result of the hand calculation. The second is to think about it and turn the circuit into an intuitive thing. The third is to create circuits.
I basically followed the trilogy. I carefully calculated the exercises behind Razavi's book. In the company's project, I also tried to focus on the hand calculation first. The parameters of the amplifier are first calculated and compared with the simulation results. Over time, my hand calculation ability has been greatly improved, and some small signal analysis calculations feel very comfortable. Here is a small episode. Once in a project, a protection loop AC simulation is always unstable, and it is not adjusted. It is not good here. Add a capacitor here, add resistance here, try it for a few times, and find it. . Because this loop is very large, it feels like a scorpion. Chang always puts it in three, five, and two, and he looks at it carefully. Then he draws a formula and finds the main pole and bandwidth expression. Through this incident, I admire Chang’s five-body cast, and also know the intuitive power. So when you look at the book, you will carefully derive the formula in the book, and then intuitively think about the signal flow, not intuitive. After more than a year, I finally understood the amplifier thoroughly. I feel that I have learned it. After I passed it, I found a pass. Finally, the amplifier has two difficulties, one is frequency response and the other is feedback.
In fact, the so-called circuit is intuitive, it is to think about the circuit from the perspective of feedback. Every time I analyze some "weird" circuits on the book or JSSC, I will sigh: feedback, feedback! Then write the analysis of the experience on the paper.
Learning to pass through a field and then learning other related fields will have some sort of "acceleration". The usual way is to let the following people study and study each time they make a new project. Before I left Xintao, I made a phase-locked loop. I haven't done it before, then I took my classmate's master's thesis, as well as a book and a lot of paper, to study it for a month and a half. I often came over and asked me: What is the 3dB bandwidth of the phase-locked loop? I smiled and said: I have already understood it.
The knowledge of the frequency response of my powerful op amp is used on the phase-locked loop. I have already studied the deep phase noise and jitter at this time. Soon after, a 30-page English study report was sent out, and I always praised it! . Later at COMMIT, there was a project to modify an RF Transceiver chip from WCDMA to TD-SCDMA. There is a baseband analog filter inside. I have never touched the filter before, it took me two months to read three original English books, the first one has more than 900 pages, and N more paper, all of a sudden on the entire filter field, switched capacitors, GmC, AcTIve RC understands. When proposing the modification plan, since the basis of my op amp is solid, it is easy to understand the filter signal flow when reading the article, so the chip circuit principle analysis and modification scheme can be proposed by one person in a short time. The final report was written (and one of my other smug works), and it was given to TI. TI. It was awe-inspiring here. When the conference call, they first said that the report was "Great job!" Didn't understand, Julian praised me and said, "They rate you very much." Later, I went to Dallas. TI was very respectful to us. When I was reporting, many people came to listen. In short, now know that everything is fundamental, and the foundation is solid and easy to cut, and the faster you learn.
I was the COMMIT I went to in November 2002. At the time, I was interviewed by my current company owner, Julian. Julian asked me: Where do you think the SOC (system on chip) design is? I said: It should be an analog circuit, this is more difficult. Julian is wrong, it is the system. I was very dissatisfied at the time, and I felt that analog circuit engineers should spend their time analyzing and designing circuits. Julian later started the company's On-Bright and brought me, and also pulled two from TI. One is Dr. Fang. For me, I recommended Dr. Zhu to Julian. In the past two years, Dr. Zhu and Dr. Zhu have admired the five bodies. Dr. Fang is the top expert in TI ***, and has strong product capabilities. On-Bright is now working on a power chip. I have worked with Dr. Zhu for nearly two years and know the importance of the system.
Chip design must eventually go to the system, this is the fourth realm of chip design. The circuit is like a brick, and the system is like a building. The chip design engineer must consider the problem from a system perspective, otherwise it will only see the trees and not the forest. In the power chip, the amplifier and the comparator are the most common ones. The difficulty lies in the thorough understanding of the system. At On-Bright, I really saw the product, from definition to design, to debug, chip testing and system testing, and finally to RTP (release to production). Julian introduced TI's advanced product development process and project management approach to On-Bright. Dr. Zhu and I were an eye-opener and knew the hardships of making products.
Product and academics are two worlds, and academics can be arrogant. Making a sample is OK. Product development is a systems engineering that involves all aspects of the work.
Summary of analog circuit design experienceThe design of analog circuits is the most difficult and deadly design part of engineers. Although the development of digital circuits and large-scale integrated circuits is very fast, the design of analog circuits is still inevitable, and sometimes digital circuits cannot be replaced. , for example, the design of RF RF circuits! Here are some of the problems that should be paid attention to in the design of analog circuits. Some of them are purely experience, and we hope that we can add more and more criticisms! . . .
(1) In order to obtain a feedback circuit with good stability, it is usually required to use a small resistor or choke outside the feedback loop to provide a buffer for the capacitive load.
(2) The integral feedback circuit usually requires a small resistor (about 560 ohms) in series with each integrating capacitor greater than 10pF.
(3) Do not use active circuits outside the feedback loop to filter or control the EMC's RF bandwidth, but only passive components (preferably RC circuits). The integral feedback method is effective only when the open loop gain of the op amp is greater than the closed loop gain. At higher frequencies, the integration circuit cannot control the frequency response.
(4) In order to obtain a stable linear circuit, all connections must be protected using passive filters or other suppression methods such as opto-isolation.
(5) Use an EMC filter and the IC-related filters should be connected to the local 0V reference plane. (6) Input and output filters should be placed at the connection of the external cable. Any wire connection inside the shielded system is required for filtering because of the antenna effect. In addition, filtering is also required at the wire connections inside the shield system of the converter with digital signal processing or switching mode.
(7) High quality RF decoupling is required on the analog IC's power and ground reference pins, just like digital ICs. However, analog ICs typically require low frequency power supply decoupling because the power supply noise rejection ratio (PSRR) of the analog components increases little after being above 1 kHz. RC or LC filtering should be used on the analog power traces of each op amp, comparator, and data converter. The corner frequency of the line filter should compensate for the PSRR corner frequency and slope of the device to achieve the desired PSRR over the entire operating frequency range.
(8) For high-speed analog signals, transmission line technology is necessary depending on the connection length and the highest frequency of communication. Even with low frequency signals, the use of transmission line technology can improve its immunity to interference, but transmission lines that do not have the correct match will have an antenna effect.
(9) Avoid using high-impedance inputs or outputs that are very sensitive to electric fields.
(10) Balanced transmit and receive (differential mode) techniques are used in analog circuits since most of the radiation is generated by common mode voltages and currents, and because electromagnetic interference in most environments is a common mode problem. It will have good EMC performance and reduce crosstalk. The balanced circuit (differential circuit) drive does not use the 0V reference system as a return current loop, thus avoiding large current loops and reducing RF emissions.
(11) The comparator must have hysteresis (positive feedback) to prevent erroneous output changes due to noise and interference, and to prevent oscillation at the trip point. Do not use a comparator that is faster than needed (keeping dV/dt within the required range, as low as possible).
(12) Some analog ICs are inherently sensitive to RF fields, so it is often necessary to shield such analog components using a small metal shielded box mounted on the PCB and connected to the ground plane of the PCB. Be careful to ensure that it is cooled.
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