PCB News - The nine stages of analog integrated circuit design

The nine stages of analog integrated circuit design, how many stages have you reached?

This article is a long testimony from a doctoral student at Fudan University. I read it completely and felt it was well written. I couldn't help but share it on the ADI forum.

You have just started to enter this line. You only have a general understanding of PMOS/NMOS/BJT. You don’t know the characteristics of various devices. You don’t have any idea about the specific circuit design. Your circuit diagram Mainly look at articles in domestic magazines, or follow the existing circuits in textbooks, you always think they make sense. The circuits you make are mainly small-scale modules. If you do some differential op amps, or bandgap benchmark simulations, you can calculate and post, for fear that there will be not enough papers by then. In general, basically seeing the op amp is still frustrated. You think spice is a very difficult and weird thing to use.

In the second paragraph, you begin to know what circuit design is, holding this textbook and calculating it on the draft paper every day. You often start to mention some technical parameters, such as Vdsat, lamda, early voltage, GWB, ft and the like. I always feel that sometimes the circuit and the hand are almost the same, and sometimes the difference is quite big. You also start to care about changes in voltage, temperature and process. For example, low-voltage, low-power systems or something. Or something about ultra-high-speed and high-precision. You plan to tape out when you design the circuit, although the tape out seems to be quite far away. At this stage, you think that spice is very powerful, but you often get a lot of headaches because of incorrect AC simulation results.

You have been fighting PVT for a while, but generally speaking, there are still few successful design experiences. You think it is really difficult to design a circuit that can be used. You are anxious to build your confidence, but you don't know what to do. You start to read some JSSC or doctoral dissertations, but you think they are talking about the same thing, the real chip or not so. Do you think the Vdsat indicators are not accurate enough, and 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 accurate and sometimes inaccurate. You go to the forum, hoping to get expert guidance. But they are also vague, and they say things sometimes right and sometimes wrong. At this stage, you think spice is very good, but the help manual is too unclear.

In the fourth segment, you have had a major tapeout failure experience. You know that to make a circuit, you need to keep improving, and you need to carefully check every detail. You find that there are many unimagined problems in the PCB design process, and every aspect of the circuit needs to be fully grasped. So you start to systematically re-learn the textbooks that you had sold when you graduated from college. You take a close look at the relevant information you can find, hoping to find some more enlightening ideas. You have clearly known the circuit specifications and performance you need to achieve, and you also know that circuit design essentially requires many reasonable compromises. But you can't figure out how this "reasonable" is determined, and how to choose the compromise between different indicators. You think it’s really too difficult to design a proper circuit that can work normally. You don’t believe that someone in this world can do as good as they claim, because you are as smart as you feel helpless in the face of such a variety of choices. How can they do it? At this stage, you feel that the spice function is still too limited, and you are often in a daze at the error message of "time step too small". Occasionally, you will create huge simulation files to crash everyone and the computer.

In the fifth paragraph, you think that many competitors' things are nothing more than that. You start to have a more familiar design method. But you don’t know how to optimize the tools you have. You have used some scripting languages compiled by others, but when you often encounter a lot of problems, you can't remember to use awk or perl to do it. You start to take up a lot of simulation time on the server, and you believe that after a lot of simulation, you can clearly adjust the module you designed to a suitable look. Sometimes you feel that doing circuit design is simply too boring. If it doesn't work, you are thinking about whether you should give up. At this stage, you think the spice is good or not, but it is still far behind the fast spice series of emulators; you don't believe in AC emulation at first, and replaced by a lot of transient emulation.

In the sixth paragraph, you begin to understand that there is only the most suitable design in this world, and there is no best design. You start to have a set of design methods that really belong to you. You will tend to one or two simulation tools and be able to use them proficiently. They evaluate your design. You start to consider PVT changes in your design. You know the evolution of a circuit from the beginning to the present, and you can tailor them for different applications. You start to pay attention to power consumption and area, and the chips you tape out have begun to meet product requirements. But sometimes you still cannot fully understand the design methods of some complex systems, and make some stupid mistakes and lead to disastrous consequences. When you start to read JSSC, you should not just pick one or two articles to read. Perhaps using JSSC as a toilet reading is a good choice for you. At this stage, you think that spice is a great tool. You know how to make reasonable simulations of accuracy and speed in spice, and make the most appropriate choice at any time.

In the seventh segment, you begin to truly understand the nature of analog circuit design, and you have your own unique views and experience in both high-precision systems and high-speed systems. You can trade off different module indicators at the system level in exchange for the best performance. You will understand a potential market and start your own product definition, and you know that as long as you are right, the product you design will be very competitive. You can easily divide the functions and indicators of the entire circuit from head to toe. You understand how every technical detail and 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 like Monte Carlo simulation, but you still often complain that the server is too slow, although you often run the simulation in the middle of the night.

At this time, it is common for you to successfully make a chip for Ba Duan. It is like a veteran driving a car, stopping at a red light and just a green light. The design of a product is almost unconscious to you. You no longer need to constantly adjust parameters and optimizations based on the simulation results. More often, you can end the design of a module with a small amount of simulation. You can clearly feel whether the circuit module of a certain indicator is technically possible or impossible. You don't need to care about the noise figure or signal-to-noise ratio or distortion of the specific module at all. You only need to know that it can be designed, and more detailed technical indicators are meaningless to you. You start to think that everything on JSSC is actually making up the numbers. Sometimes you think that JSSC is unqualified even as toilet paper (too thin and too brittle). You think that spice is good for occasional use, but it is really unreliable. In many cases, it is almost enough to look at the working point.

At this time in Jiudan, you already know many circuits well, and you can predict the next round of development of many technologies in advance. You only run the simulation a few times a year, or it may last for a few years. You rarely draw circuit diagrams, most of the time you are playing golf or fishing on a small island in the Pacific Ocean. Except occasionally joining in the fun on ISSCC, you never talk to others about circuits, because you know no one can understand.

The above is an introduction to the nine stages of analog integrated circuit design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.