# Analog circuit design: The myth of Theory and the reality of cruelty

Source: Internet
Author: User

This article combined with my personal experience, through a simple example, to illustrate some of the characteristics of analog circuit design, I hope to engage in analog circuit design related direction of the students have some help.

Theoretical knowledge

Analog circuit needs more theoretical knowledge, need to use a lot of mathematical calculation, circuit Foundation, signal and system and other disciplines, and these disciplines need to use higher mathematics, linear algebra, complex variable functions and other mathematical basis. Of course, the mathematical knowledge used is not very complicated, it is generally a relatively basic mathematical knowledge, calculus in the high number, the matrix in the linear algebra, complex functions in complex operations. Many calculations and physical electricity calculations are a bit like, mathematically not very complex, but the principle behind each formula is many, but also to consider a lot of realistic factors. The reason why analog circuit learning is difficult, there is a factor is a lot of people during the university's Mathematical Foundation did not learn, the theoretical calculation of a kind of fear (learning when do not know what to do, when using the time only to find not learning).

Scientists and engineers

Transistor is a very basic and important knowledge in analog circuits.

On the one hand, scientists (physicists, chemists, etc.) from the microscopic point of view of theoretical analysis, hypothesis and experiment, the development of transistors this device, with amplification, but the amplification effect is not ideal. Transistor magnification, by the temperature, supply voltage, input voltage and other factors, it is too unsatisfactory. Scientists have done their best, perhaps one day, to find a more perfect amplification device, better than the three-pole tube.

On the other hand, the ideal amplifier magnification should be constant, otherwise the output will be large and small. We can not lack the ideal amplifier in our life, because we need to use amplifiers to make telephones, loudspeakers and other devices.

Coordination of these two aspects of the conflict, to solve this problem is the task of engineers, analog circuit is the core of engineering ideas. Engineers are not concerned about how transistors were invented, only about what the transistor has, and what kind of circuits people need in real life. Then try to use imperfect devices to create the equipment that meets the needs of people as much as possible. Using imperfect things to create perfection, engineering is doing it very often.

Transistor characteristics: Learning transistors generally start with the basic principle of PN knot, involving a little knowledge of chemical molecules. In analog circuits, the characteristics of PN Junction are mainly concerned, but not further in depth.

Solution to the problem: transistor magnification is not stable, we can use negative feedback form, sacrifice magnification, to achieve the stability of magnification.

Signal and System

Signal and system is a very important basic theory course. Signaling system This course is very abstract, basically is learning mathematics. And it is because of its abstraction that it can be applied to many disciplines. The signal system can be used not only in the circuit, but also in the mechanical system, but also can be used in acoustic systems (such as the acoustic design of the speaker). Signaling System This theory lesson is a bit difficult to understand, because do not know how it is applied. What we can do is not too early to ask why, first of all the theoretical knowledge to remember, back to practice (theory and practice of the combination of learning is better, but the knowledge is difficult to arrange).

What is negative feedback, and how to achieve the amplifier magnification stability, can refer to "My understanding of analog circuit course" http://www.hainter.com/analog-circuit

The myth of theory and the cruel reality

Analog circuits, especially high-frequency/RF, are often very difficult, in addition to the need for more theoretical knowledge, but also need a lot of experience accumulation. When doing the electric race, the depth of experience, analog circuit design is not easy, even the simplest op amp integrator. Ideally, the integrator circuit, such as theoretical analysis is also relatively simple (learn the signal system and the mode of the person should be able to understand, do not do analysis here).

In fact, such circuits often do not work because of the non-ideal characteristics of op amp and other devices. Even the most basic wires have resistors, and theoretical analysis makes it difficult to consider so many non-ideal factors. In fact, it is generally necessary to add a few more devices, such as.

Even if the circuit is perfected, each device parameter can not be arbitrary value, even power, wiring is also fastidious. Especially in the HF/RF, the components will be disturbed by electromagnetic waves, to solve these problems and need to use some of the theoretical knowledge of similar signaling systems. Finally, the intended integrator effect can be achieved, and can only work under given conditions (imagine the radio, or the television that used to be an antenna, which could affect the work of the TV).

Theoretical analysis/software simulation/actual circuit

In analog circuit design, the usual design process is to analyze the theory first, design the circuit, then verify through the simulation software, finally make the actual circuit, and modify and Debug. For simple and low-demand circuits, you can try to build a bread plate before welding, for some of the higher requirements of the circuit, such as the demand for large current, high frequency, etc., the bread board is difficult to achieve, and even the welding plate welded can not be used, but also to design a PCB to try, the process is more troublesome.

The overall situation is that the theoretical analysis and simulation circuit is far from the same, and the simulation circuit and the actual circuit is far from the difference. Like the example above, a lot of seemingly simple circuits, completely in accordance with the original design of the circuit to build, it is likely not to work. This time, we need to pass the instrument test and other auxiliary means, analysis and circuit improvement.

Chip Manuals

Chip manuals in the circuit design process is often used in reference materials, especially integrated chip manuals, of course, many of the basic components include transistors, MOS tubes, etc. also have a chip manual.

Modern circuit designs tend to be built with chips, not entirely from discrete components. Once the chip is designed, batch manufacturing can greatly save costs and improve the efficiency of circuit design. Many times an op amp is used to design an amplifier, which is much easier than using discrete transistors and other devices, and instead saves a lot of cost.

Chip manuals will have the device packaging, pin and other basic information, as well as the use of voltage, temperature, humidity range requirements, chips often have internal structure of the block diagram and so on, and even some chips, especially high-frequency and high-power chip, will also give reference to PCB design drawings.

Learning to read chip manuals is an essential skill for analog circuit design. Many of the chip manuals are in English, then have to be familiar with a variety of English professional terminology. This topic is discussed in more detail below:

Don't be afraid of English-the role and importance of English Http://www.hainter.com/english

A wealth of experience

Solving a lot of problems in analog circuits requires a lot of experience, and many times it is difficult to use theory to explain some problems, because it is too complicated. Experienced hardware engineers are rare (for example, decades of experience) and millions of dollars are not a problem. So if the hardware is very interested, can continue to do, often the older the more popular.

This knowledge is very miscellaneous, it is difficult to be organized (many of the engineers are not very good at expressing, and not so much energy), even if the collation of a book, it is difficult to quickly learn from others, and in some cases, the knowledge is often very high value, not necessarily open (such as many foreign high-tech secrecy). From the point of view of all mankind, the dissemination of these knowledge is a difficult problem to be solved urgently.

Learning conditions

Learning hardware is not only difficult, but also very money-burning. It is best to learn through competitions, because often the laboratory can provide a variety of expensive instruments, the competition will be funded to buy a variety of devices, so that there is sufficient learning conditions. Many school conditions are not enough, even few oscilloscopes, only to do single-chip control of the direction of the class. But in the west, high-frequency, switching power supply, instrumentation and other directions have sufficient conditions (the school to the electric game attaches great importance to provide more funds, but want to participate in the request is also relatively high). Better schools are well funded, and libraries, especially labs, can provide more valuable learning opportunities.

The electric race process of the West can refer to the "2013 Electric Race Summary" Http://www.hainter.com/nuedc

Analog circuit design: The myth of Theory and the reality of cruelty

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