In the second paragraph, you start to know what is circuit design.
Every day, holding this textbook is mad at the draft paper. You also often start to mention some technical parameters, such as Vdsat, lamda, early voltage, GWB, ft and so on. I always feel that sometimes the circuit and the hand are almost the same, and sometimes the difference is quite big. You are also beginning to care about voltage, temperature and process variations. For example, low voltage, low power systems or something. Or what is the super high-speed and high-precision stuff, from time to time also come to the last two sentences. When you design the circuit, you start planning to go out, although the tape out looks quite far away. At this stage, you feel that the spice is very powerful, but it is often a big headache because the AC simulation results are wrong.
You have been fighting PVT for a while in the third paragraph,
But in general, there are basically few successful design experiences. You think it's really hard to design a circuit that works. You are anxious to build your confidence, but you don't know what to do. You start reading some JSSC or doctoral thesis, but you think they are talking about the same thing, the real chip is not the same thing. What do you think Vdsat's metrics are not accurate enough, the default settings of the emulator are not enough to meet your requirements, so you try to adjust the parameters of the emulator, or try to change the emulator, but the results they give are still Sometimes it is sometimes not allowed. You go to the forum and hope to get the guidance of the master. But they are also unclear, and sometimes things are sometimes wrong. At this stage, you think that the spice is very good, but the help manual is too unclear.
In the fourth paragraph, you have had a relatively large failure experience.
You know that to do a good circuit, you need to keep improving, you need to carefully check every detail. You find that there are a lot of problems that you have never imagined in the design process. To complete the circuit, you need to grasp every aspect. So you begin to systematically relearn the textbooks that have been sold at the time of college graduation. You have carefully looked at the relevant information that you can find, hoping to find some more inspiring ideas. You already know the circuit specifications and performance you need to achieve, and you know that circuit design essentially requires a lot of reasonable trade-offs. But you can't figure out how this "reasonable" is determined, and how to choose between the different indicators is good. You think it's really hard to design a proper working circuit. You don't believe that in this world, someone can do what they claim to be so good, because smart people feel that they are helpless in the face of such a complicated choice. How can they do it? At this stage, you feel that the spice function is still too limited, and often stunned by the "TIme step too small" error message. Occasionally you will create huge simulation files to crash everyone and the computer.
In the fifth paragraph, you think that many competitors have nothing more than that.
You start to have a familiar design approach. But you don't know how to optimize your tools at hand. You have used some scripting languages ​​compiled by others, but you can't think of it with awk or perl when you encounter a lot of problems. You start to take a lot of simulation time of the server, and you believe that after a lot of simulation, you can clearly adjust the module you designed to the right look. Sometimes you think that circuit design is too boring. If you can't do it, you are considering whether to give up. At this stage, you think that the spice is good, but it is far worse than the fast spice series of emulators; you don't believe in AC emulation, instead a lot of transient simulation.
Six paragraphs you begin to understand that there are only the most suitable designs in this world, and there is no best design.
You start to have a set of design methods that are truly your own. You will prefer one or two simulation tools and be able to use them to evaluate your design. You start thinking about PVT changes in your design. You know the evolution of a circuit from start to now and can tailor them to different applications. You start to pay attention to power consumption and area, and your tape out chip starts to meet some of the product requirements. But sometimes you still can't fully understand the design of some complex systems, and make some stupid mistakes and lead to catastrophic consequences. When you start reading JSSC, you should not only pick one or two articles to look at. It may be a good choice for you to use JSSC as a toilet reading. At this stage, you think that spice is a great tool, you know how to simulate the accuracy and speed in the spice, and make the most suitable choice at any time.
Seven segments, you begin to really understand the nature of analog circuit design,
Both high-precision systems and high-speed systems have their own unique perspectives and experiences. You can trade off different module metrics at the system level for the best performance. You will understand a potential market and start your own product definition, and you know that as long as the method is correct, the products you design will be very competitive. You can carry out the function and index division of the whole circuit from head to toe. You know every technical detail and how their compromise will affect your product. You start to pay attention to the reliability of the design. At this stage, you think that spice is a very useful tool and likes Monte Carlo simulation, but you often complain that the server is too slow, although you often run the simulation in the middle of the night.
It is a common practice for you to make a chip at this time. It is like a driver driving a car. When you encounter a red light, you will stop and the green light will do. The design of a product is almost unconscious for you. You don't need to adjust the parameters and optimizations constantly to the simulation results. More often, you need a small amount of simulation to end the design of a module. You can clearly feel that the circuit module of a certain indicator is technically possible or impossible. You don't have to care about the noise figure or signal-to-noise ratio or distortion of a particular module. You just need to know that it can be designed, and more detailed technical indicators are meaningless to you. You start to think that the things on JSSC are actually making up the number. Sometimes JSSC is considered unqualified even if it is used as toilet paper (too thin and too brittle). You think that spice is used very often, but it is not reliable. Many times, it is enough to look at the work point.
At this time of the nine paragraphs, you are familiar with many circuits.
You can predict in advance the direction of the next round of technology. You only run a few simulations a year, or you can simulate for a few years. When you rarely draw circuit diagrams, most of the time you are playing golf or fishing on a small island in the Pacific Ocean. Except for occasional fun on the ISSCC, you never talk about circuit matters with others, because you know no one can understand. It has been eight years since Fudan studied the design of microelectronics professional analog chip design and has been working for five years now. During this period, he has heard many domestic and foreign experts. Recently, at the invitation of a friend, I will share a little experience and share it with everyone. I remember that when I graduated from the undergraduate course, I was planning to study the sensor. Later, I went into the State Key Laboratory of Fudan Yifu Building Specialized 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. 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. At the time of studying, my tutor was Professor Zheng Zengqi, and Li Li was retired at that time. Yifu Building invited Mr. Li to come and guide each week. Mr. Zheng is rigorous in his studies and a heroic woman. Ms. 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. However, I felt that there was always reason for Teacher Li and Teacher Zheng, 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. 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 Chang Zhongyuan in it, and Dr. Leuven Catholic University 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. During 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 surprised. 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, and they just 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.
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 the tiger. It should be said that I 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 remember the experience that I always told me when I was chatting. He said that there are three realms for analog circuit design: the first is to calculate the hand, 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 am careful about 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 adjustable. It is not good here. Add a capacitor here, add a resistor there. If you try a few times, you will 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 Mr. Chang, and I also know the power of intuition. 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, the amplifier was finally able to understand thoroughly, and I felt that I had learned it. After I found 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, that 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. I made a phase-locked loop before leaving Xintao. I haven't done it before, then I took my classmate's master's thesis, as well as a book and a lot of papers to study it. After 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 I proposed the modification plan, because the basis of my op amp was solid, it was easy to understand the filter signal flow when I read the article, so I can propose the analysis and modification of the chip circuit principle in a short time. The final report was written (and one of my other smug works), and it was given to TI. TI. The audience was awesome. 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 run the company 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 Chinese, and he has superb ability in products. 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. On 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 systematic project involving all aspects of work. N people work together to finally bring products to market. In the field of chips, I used to admire scholars in the academic world. Now I find that the industrial level is still ahead of the academic world. Dr. Zhu said that he had done research for half a year at the Swiss Institute of Technology Huang Qiuting (IEEE's famous Fellow), which was very admired by Huang. Dr. Fang has a higher level. So like (Dragons and Eight), a nameless old man is the top master. But regardless of industry or academia, these four realms are common. Every analog chip designer should step by step and step through the four realms.
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