How to learn analog circuit design

Since the 1980s, digital signal processing algorithms and integrated circuits have developed rapidly. Although many types of signal processing have been converted from analog circuits to digital circuits, analog circuits are indispensable in a single chip. As a rookie in an analog circuit designer, talk about some of your own experiences in learning and working.

I have been in contact with analog integrated circuits for four years since I graduated. I have read the article "The Four Realms of Analog Chip Design". I should be in the realm of rookie now.

Analog circuit design and digital circuit design are very different. The most basic is that analog circuits process analog signals and digital signals processed by digital circuits. Analog signals are continuous in time and value, and digital signals are discrete in time and value. Based on this feature, analog circuit design is somewhat more difficult than digital circuit design. The specific reasons for the difficulty in designing analog circuits are as follows:

1. Analog design requires a compromise between speed, power, gain, accuracy, supply voltage, noise, area, etc., while digital design requires only a balance between power, speed, and area.

2. Analog circuits are much more sensitive to noise, crosstalk, and other interference than digital circuits.

3. As the process size continues to decrease, the reduction in supply voltage and the secondary effects of the device have a much more severe impact on analog circuits than on digital circuits, presenting new challenges for analog design.

4. The layout affects the analog circuit much more than the digital circuit. The same layout of the line difference will cause the chip to fail.

My analog integrated circuit design learning path begins with Lazard's analog CMOS integrated circuit design book. This book will still be viewed in the current work, and is one of the classic textbooks for analog integrated circuit design. The first thing I want to talk about is the relevant courses and textbook suggestions for analog circuit design. Analog circuit design is like other things. First, we must learn some basic guidelines, methods, and knowledge points. The classic analog circuit design textbook is a fusion of these things. razavi's design of analog CMOS integrated circuits, sansen's analog design essentials Allen's CMOS Analog Circuit Design, paul gray's Analysis and Design of Analog Integrated Circuits, and baker's CMOS Circuit Design, Layout, and Simulation are all classic textbooks for analog circuit design, and are books that need to be read even if they are already working.

Razavi's design of analog CMOS integrated circuits is ideal for introductory learning. As for the teaching sequence of several other textbooks, it is up to you. I feel that reading textbooks is to analyze the circuit with the help of the author, and the post-class exercises are to exercise the ability to analyze the circuit and design the circuit independently, and to analyze each formula of each circuit in the book. It is very necessary to master single-stage amplifiers, current mirrors, and bandgap references. Rail-to-rail input, class AB. Op amp. Basic circuits such as comparators are of great help and can lay a good foundation for future development. Signals and systems and matlab are skills that must be learned during the undergraduate period and are often used in postgraduate studies and later work.

Analog circuit design focuses on learning and accumulating experience

Learning analog circuit design begins with analyzing the analog circuit. The analog circuit analysis should follow the following steps: first determine the purpose of the analysis, clarify the circuit problem; second, break the complex circuit into the basic circuit module that you are familiar with; third, use the basic The model of the circuit module models the system; fourth, the system model is manually calculated; fifth, the manual calculation results are verified by simulation. If they are inconsistent, the cause must be carefully searched, and the simulation result cannot be blindly believed.

In addition, when designing the circuit, pay special attention to the signal flow in the circuit, including the power, ground, clock, input signal to the output signal path, etc., to clearly understand the key signal flow of the whole system, and find the circuit faster. The problem in the effective reduction of circuit bugs and the time it takes to shorten the debug.

For example, in the Miller capacitance compensation circuit shown in FIG. 1, the signal at point A reaches point B in two ways, one is that signal stream 1 is fed through capacitor to point B, and the other is signal stream 2 is passed through MOS tube. Arrive at point B. The A and B points in the signal stream 1 have the same polarity, and the points A and B in the signal stream 2 have opposite polarities, so the transfer function from A to B has a zero point in the right half plane. The zero point of the right half plane reduces the phase margin of the system loop, which will reduce the stability of the system. Therefore, after discovering this problem, it can be compensated in time to prevent the chip from working properly and reduce the risk and cost of product development.

The layout design of the analog circuit mentioned above is not only related to the performance and area of ​​the chip, but also affects the function of the chip and completely disables the chip. Therefore, I would like to talk about the layout design in the analog circuit design. Now SOC has become the mainstream trend of chip design, integrating analog circuits and digital circuits on one chip, which raises the layout design of analog circuits to a new level of difficulty.

The key to analog circuit layout design

One is the match; the other is the trace of the power, ground and key signals.

Some predecessors say that analog integrated circuits do match, especially in high-performance analog integrated circuits. Matching is to reduce offset, reduce nonlinear distortion, improve common-mode rejection ratio, and power supply rejection ratio. Important measures to reduce the effect of process temperature and supply voltage on the performance of the chip, such as the ratio of two bipolar tubes of the bandgap circuit is usually 1:8, which is a better match for layout design. power supply. The ground and key signal trace design is mainly to reduce the interference of the digital circuit to the analog circuit and the sensitive module in the analog circuit is interfered by other modules of the analog circuit. The specific learning method is to first learn the art of simulation layout, master the basic rules of simulation layout design, and deeper learning can only rely on the accumulation of experience in learning and work.

Become an excellent analog circuit designer

All in all, analog integrated circuit design is a combination of art and science. It requires both the analog circuit designer to have the divergent innovation ability of the artist, and the analog circuit designer to have the rigorous attitude and method of the scientist, because the analog circuit design is the details to determine success or failure. As a rookie, there are still many things I have to learn. To be a good analog circuit designer is the goal I have been striving for. More exciting can enter the group exchange.