What is an Integrated Circuit?

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What is an Integrated Circuit? [Copy link]

What is an Integrated Circuit?

　　What is an integrated circuit? It is the small black block on the circuit board with many pins. It is not complicated inside. It is nothing more than some transistors combined together. That's all.

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The basic principle of triode

　　First of all, we need to understand the basic principle of the transistor. The transistor is a channel for current, and there is an electrode that controls the on and off of this channel. If the basic principle of the transistor is far-fetched with such a metaphor, it is very accurate when designing the layout of the transistor. We first draw a green line to represent the channel, and then draw a red line across the channel to represent the control gate, just like the green channel on the road and the red light controlled by the police. The on and off of the current in the green channel depends on the police's face. However, in integrated circuits, the channel is not called a channel, but an active area, a strange name, but it is easy to remember. We usually call semiconductor devices active devices, resistors and capacitors passive devices, and transistors are active devices. Therefore, just remember that the area related to the transistor is called the active area.

　　The source and drain are made of N-type or P-type semiconductor materials, and a layer of polysilicon is placed between the source and drain as the gate, which forms a MOS transistor. Make several more such transistors and connect them as required to form an integrated circuit. Putting many transistors together is an integrated circuit.
　　Integrated circuits are really that simple. Please don't ask questions such as why semiconductors conduct electricity, which are currently considered irrelevant. What we are discussing here is how to quickly learn to design integrated circuits, not semiconductor theory.

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Design an inverter

　　We know that a transistor is equivalent to a channel. The end where the current starts is called the source, and the end where the current arrives is called the drain. The electrode that controls the on and off of the current is called the gate. So what voltage does the gate need to carry to indicate that the channel is turned on? Generally speaking, when the voltage of the gate to the source is 0V, it means it is turned off, and when the voltage on the gate is above 0.7V, it means it is turned on. It should be noted that the gate voltage is relative to the source. The above-mentioned
　　MOS transistor is called an N-type MOS tube. Correspondingly, there is also a P-type MOS tube. The characteristics of the P-type MOS tube are exactly the opposite. The current starts from the drain and reaches the source. When the gate carries a voltage lower than 0.7V than the drain, the MOS tube is turned on.

　　If we can only use one type of MOS tube, we can also design integrated circuits. The semiconductor process at that time was only suitable for making N-type MOS tubes. Most of the integrated circuits at that time were NMOS integrated circuits. The early Z80 and 8048 we are familiar with were all manufactured using NMOS technology. Later, a process for making two different types of MOS tubes on the same chip was developed, called CMOS technology, which is now the mainstream process in the semiconductor industry.

　　There is no difference in the layout design of N tubes and P tubes. Just make a mark on their type. This mark is used to inform the people who manufacture integrated circuits to make these tubes into a certain type of tube. In the figure below, we circle the P tube with a dotted frame as a mark.

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Design a simple integrated circuit

　　Designing an integrated circuit is also very simple, it is just to connect those transistors, what to use to connect? You can't use a soldering iron and solder wire, right? In integrated circuits, this method is not used. A method similar to double-sided circuit boards is used. The vias on the double-sided circuit boards connect the two sides of the circuit boards. Vias are also used in integrated circuits. The two layers of conductive materials are aluminum and polysilicon. Aluminum can pass through various areas to any place without restrictions, but can polysilicon do the same? It seems that it can, but when polysilicon passes over the active area, the active area becomes a current path controlled by polysilicon: an extra transistor, which is not what we want, so we add a rule here: polysilicon cannot cross the active area. By connecting two transistors according to this rule, we have designed a simple integrated circuit containing an inverter.

　　There are four welding points around the chip, which are used to connect with the external circuit. However, they are not called welding points here, but pressure welding points, which may be named because of the process. If you call it welding points in the integrated circuit industry, it will make others stunned.

　　We might as well boldly understand the integrated circuit design technology and manufacturing process with printing. When we want to print business cards, we must first design the layout, think hard about a trademark pattern, draw on the draft paper with colored pens, and even pay an artist to design this business card. The
　　designed business card may contain several colors and many fonts. When the design plan is sent to the business card shop, the printing plates will be made according to the color type, and then the various colors will be printed on the paper with these plates. Then a large piece of paper is cut into small business cards one by one, and finally these business cards are packed in a small box, waiting for users to pick up the goods.
　　The owner of a small business card printing shop only needs to know how to operate plate-making machines, quick-printing machines and the like. He basically does not need to know many words and only needs to have elementary school knowledge. It is unreasonable to require him to understand the principles of art before issuing an operator's license to work.
　　The biggest requirement for the artist who designs business cards is to be able to understand the customer's requirements and to be able to express the customer's intentions through the layout, font selection, and color matching. There is no need for us to require the artist to be able to make lead type in various fonts, read the large book "Principles of Photography", and be proficient in printing machinery. Accordingly, we
　　should have only one requirement for the customer: to simply and clearly state his intentions.
　　The same is true for integrated circuits. The user proposes the functions of his chip. The design process is to translate the functions into layouts, and the manufacturing process is to print the chip using the layouts.
　　The amazing similarity between printing and chips is that the artist only needs to use various fonts in the font library and does not need to make fonts one by one by himself; chip designers actually only need to use the cells in the cell library.
　　Another more surprising similarity between printing and chips is that when a specific symbol is not in the font library, such as an uncommon trademark, the artist has to make the symbol himself; chip designers sometimes encounter units that are not in the library, and they also need to draw the layout of the unit themselves.

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Designing a Layout for an Oscillator Chip

　　If you don't find it satisfying, you can design a more complex integrated circuit as shown below. It is an oscillator layout. You connect a resistor, a capacitor, and a light-emitting diode to it, and then connect it to a power source. You can see the light-emitting diode flashing.
　　This is pretty much it for integrated circuit layout design. There is no fancy tricks.

　　You may find that the inverter on the far right is a little bit bigger, which is to have a larger driving capability to make the light-emitting diode have a higher brightness. Another issue that should be paid attention to is to try to make a larger current flow in the aluminum conductive layer. The conductivity of aluminum is much better than that of polysilicon. This is a little different from the double-sided circuit board. The conductivity of both sides of the double-sided circuit board is equally good.

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Layout Design

Now, you know a little bit about layout design. If you know more, you will find that the layout design you are eager to learn is actually just a kind of jigsaw puzzle for adults, but it is not as fun as the jigsaw puzzle for children, nor as complicated and varied. Now
　　, everyone has their own aspirations. If you want to play with this jigsaw puzzle, you can, there are many friends here who are willing to play with you; or if you remember the original intention of coming here and want to make your circuit into an integrated circuit, then you should stop playing jigsaw puzzles for the time being and find a way to complete your chip design as soon as possible.
　　If you originally designed a circuit with discrete components and used many standard integrated circuits, including inverters, NAND gates, D flip-flops, counters, and even a liquid crystal display driver module, etc., it is reasonable that you have to design the layout of these units. This is not an easy job. Day after day, month after month, you will be stupid and dumbfounded. Your original enthusiasm for designing a high-performance circuit is useless here, and your spark-like circuit design inspiration is also of no help to layout design. Drawing a layout requires the skills of jigsaw puzzles.
　　After you have worked hard for three months, you find that the farmers who have started to plant the second crop of rice are not so hard. From this, it can be inferred that the workload of making a layout library is about the workload of planting two crops of rice. Being a chip designer is not as practical as farming.

　　But even if you are asked to do the work of drawing the layout, you don't have to be afraid. The most amazing feature of high technology on computers is that its labor can be reused. It takes two months to make a unit library for the first time. When you make the library for the second time, you can copy the first library and modify it in two weeks. This is the wonderful thing about COPY in computers. It's really strange why this computer technology is not promoted to agricultural technology. If farmers also use these technologies, they only need to concentrate on planting one acre of land, and then copy it to 108,000 acres. Then, standing at the endless golden field, watching the majestic and spectacular wheat waves rolling in the morning light, it is difficult to control the feeling of "being in the field, embracing the world".
　　Fortunately, farmers have not yet mastered this technology, otherwise we chip designers will be ashamed. But we should seize the time and make more contributions than farmers under the current advantage of chips being ahead of farming.

　　But now the situation is different. Here, there are ready-made cell layouts for you to use. These cell layouts are placed in a library with a wide variety of varieties, almost including all the varieties you may use. Don't think this is a "demo version". This is a working library that many chip designers are using. What you have to do now is no longer layout design, but something similar to what you used to do: wiring double-sided circuit boards.
　　With the cell library, you can carry out normal design work. You use the usual methods to draw circuit diagrams, and then connect them with corresponding components. In the past, an inexperienced circuit designer would often design circuits according to outdated textbooks. As a result, buyers often complained that they could not purchase components, and even had to go to Intel's company history showroom to see samples. Today's circuit designers are generally more concerned about the supply of original components. This experience also applies here. You should be familiar with the situation of the cell library before designing, so as not to draw a circuit diagram but have no cells to use.

　　After all, the contents of the cell library used in chip design are a little different from the contents of the CMOS 4000 series or TTL 74 series on the market. For example, the commonly used JK flip-flop cannot be found in the cell library (perhaps someone will add this unit later), because in ASIC design, there is no need to use the JK flip-flop, and using it will cause confusion when analyzing the circuit. You can quickly adapt to these differences, and even feel confident after reading the introduction of the cell library.

　　I remind you again: you come here to design integrated circuits, not to study layout design technology. If you are a beginner, the layout you design will probably not be better than the existing layout in the library, right? So for the time being, just understand a little about layout design, don't delve into it, use the ready-made cell library and double-sided wiring technology to complete your integrated circuit as soon as possible. If you encounter a unit that is not in the library, don't panic, please come here and ask, maybe there will be an old hand who will help you draw one, but it should be some more common units, don't ask about 16-bit A/D converters, camera control circuits and other units, if so, you might as well sleep and let others design it for you for free.
　　To be honest, the great and mysterious integrated circuit layout design is not much more complicated than the tangram puzzles played by children. The layout of the trigger below is almost the most complicated one in the layout library, but that's it, no big deal, I don't think you can't master it, I just think you don't need to master it for the time being.

　　Don't think this is a demonstration layout, this is a real layout in use, I call it DF06A, a design expert spent about a month to make a similar layout. I drew this layout based on his work, so it only took me about half a month, and there are some delay parameters that have not been calculated. After completing this layout, I have almost completed one-third of the workload of the entire standard cell library (more than 100 cells), because this is the most difficult layout in the library.

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Circuit Design

　　The most amazing and magical thing is that you can play many tricks with the circuit design you used to do. The unit I used to work in had a plastic machine as big as a locomotive. Suddenly one day it broke down. The output value of the machine was more than 500,000 yuan a day, and the profit was tens of thousands. This made the boss anxious like a bear, mobilizing all the elites of machinery and plastics. The technicians from Hong Kong also arrived the next day, but the result of the consultation was that there was nothing to be done. On the third day, a guy who knew a little about electronics appeared. He took a resistor from a broken radio and installed it on the machine. The huge plastic machine was revived. When the people present learned that the value of this magical component was only two cents, they were all stunned at the same time.
　　Those who came here are all experts in circuit design. I think there is no need to explain how a resistor can repair the plastic machine. It is too simple and common, but the greatest fun of circuit design lies in this: an extremely simple trick will trigger a big event in society. You should give full play to your intelligence in circuit design, and don't be bound by whether or not to use a public unit library.
　　Of course, integrated circuit design is a little different from your previous design. Here is one of its characteristics: there are a large number of transistors for you to use, while resistors and capacitors are very troublesome.
　　Or this way: you can treat it as an exam. The exam question is to design a circuit. Resistors and capacitors are not allowed, but unlimited transistors can be used. You may not be used to it at first and feel that a lot of transistors are wasted, but as long as you do it a few more times, you will get used to this wasteful design method. Don't feel guilty about your waste. In fact, even chip design experts do this.
　　Circuit design is to draw the circuit diagram you need, and then infer your circuit diagram to see if it is correct and whether it needs to be improved. Here, I suggest you use workview software and the circuit library provided here for design. If you use workview, it will help you do inference, which is called simulation here. It will show you the waveform of the circuit when it is working, which is very intuitive. Here we not only provide you with a layout library, but also provide a related circuit library. Using the circuit library here can simplify your design work. There are many practical unit circuits in the library, such as decimal counters and even dynamic LCD drive circuits. You just need to use them. If you design a dynamic LCD drive circuit by yourself, it doesn't mean that you can't do it, but there is no need to do these repetitive and tedious work. You should concentrate on completing your overall design, which is your specialty. You can make public some of the tricks and techniques you found in the design and add them to the library as free resources so that future designers can also enjoy the fruits of your labor. There
　　are two kinds of resources in the world. One is real resources, like oil, which is less and less as you use it; the other is virtual resources, like brainpower. The strange thing is that this virtual resource is actually a resource that is used more and more. The world is really wonderful and there are all kinds of wonders. If we mobilize all the people to develop virtual resources, it won't take long before we will become a resource-rich country. We can eliminate American imperialism and all reactionaries as easily as swatting flies. Just kidding, I don't want my worldview to be colored by nationalism. I am interested in the culture of any nation. What is "a rich country and a strong people"? To me, it feels like a farmer in a mountain valley hoping to have more sons so that he will not be bullied by his neighbors. It is a kind of consciousness that is closely related to ignorance. We develop virtual resources to welcome the arrival of the unknown tomorrow of mankind. We don't know what tomorrow will be like, but we know that tomorrow will not be as expected today.

　　In my opinion, circuit design is really suspected of being opportunistic. I have no intention of belittling my colleagues, but in many cases I have seen, an electronics enthusiast who can repair semiconductors is often more popular than a mechanical undergraduate. The developers of a home appliance project are composed of electronics and mechanics. If you have participated in several such development teams, you will understand the following conclusions: the workload of electronics is small, and they always make tricks on some local problems, ignoring the overall situation, and often rework and cause trouble, but they are easy to get the boss's favor; the workload of mechanics is large, and they need to consider the coordination of the whole machine comprehensively and comprehensively, but sadly they are always unpopular. In the boss's eyes, it seems that working in mechanics is not a big deal. It's just a matter of drawing with a pencil. But working in electronics is different. That thing is mysterious. Two cents can make a machine as big as a locomotive move.
　　If you have friends who study mechanics, you will understand that mechanics is not so simple that everyone can draw. Just looking at the courses of mechanics, you can understand that mechanical knowledge is much more complicated and rigorous than electronic knowledge. In a household appliance such as a refrigerator or a washing machine, mechanics account for most of the work, and electronics are just some tricks based on mechanics, such as timing, alarms, etc., all tricks. Mechanical design involves rigorous and extensive knowledge, and electronic knowledge may be obtained from miscellaneous books such as "200 Examples of Small Electronic Production".
　　The idea of many bosses to focus on electronics and neglect mechanics is actually wrong. Maybe you can draw a drawing of a part with a pencil, but can you calculate how much pressure this part can withstand? Do you know under what circumstances will the part you draw resonate? How much damage will it cause to the whole machine after resonance occurs? If you want to understand these situations, you have to spend several years reading several books such as "Principles of Mechanics", "Mechanics of Materials", etc. However, the mysterious electronic technology can be learned by buying a few miscellaneous books on the street. Don't think it's a joke. In fact, we guys who are engaged in electronics know the details of electronics best.
　　Have you ever heard of amateur mechanical enthusiasts? Or amateur material mechanics enthusiasts? It should be said that there are, but very few, so it is difficult to give an example.

　　There are a lot of amateur radio enthusiasts and amateur electronics enthusiasts around us. Why is this? This shows that electronic circuits have several characteristics: it is easy to get started, and another greater characteristic is that as long as you learn a little, you can use your intelligence and carry out fruitful circuit design. From this
　　, we can't help but ask: Are there any amateur integrated circuit design enthusiasts?

　　I have been paying attention for a long time and want to know if there are any amateur integrated circuit design enthusiasts, but I haven't found any so far. This makes me very puzzled, and I can't help but mutter in my heart: Am I the first amateur integrated circuit design enthusiast in China?

　　In the past, being an amateur integrated circuit design enthusiast may be a fantasy, and people feel like hearing about amateur intercontinental missile enthusiasts. But times have changed. The external conditions for amateur integrated circuit designers are already in place, but these conditions came too quickly for us to react. The integrated circuits we heard about seemed to require an investment of tens of millions of US dollars, but when we woke up from our dreams this morning, we could have the chip factory make the integrated circuits we designed ourselves for just a few thousand RMB.

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Chip Design

　　After completing the circuit design, you can start to consider the entire chip design. If your chip is not big, you can design your chip using the double-sided circuit board wiring method, using some special software such as LEDIT for design. First, put the units used on the board, and then use aluminum and polysilicon for wiring. If your chip is slightly larger, this will be a hard job.
　　If the chip is larger, we can use a computer for automatic wiring. In fact, the means we mainly consider to achieve layout and wiring should be automatic wiring.
　　There are many software that can perform excellent automatic wiring, such as cadence, mento graph, but the software is expensive, and there are many people who spend 200,000 US dollars. There are
　　also many software with lower prices and good performance,
　　and even free software. Here in the free software library, there is a set of Alliance, which has very good wiring performance. In fact, using it for wiring is really a bit of a waste of talent. It is a set of integrated circuit design tools with more powerful functions. Let's talk about the matter for the time being and discuss its wiring tool. Its wiring tool is very good and has good optimization capabilities. The description method of the library it uses is a little different, but it is similar to the description method of other software. We can write a small program to convert it. Compared with other software, the description format of the circuit diagram it receives is actually in the format of C language source program. Fortunately, it is in the source program format, which provides certain convenience for writing conversion programs. There is a special database operation program viewdate in workview, which should be able to complete this work.
　　We can imagine remote wiring. Mr. Gong Min once gave an example that a chip designer in Xinjiang can run the precious design software installed on the host in Shanghai through the Internet. This is what he meant. Going
　　further, we can even write some automatic functions for the system. It automatically receives the circuit board files sent by the user in the form of email, and after the wiring software completes the wiring, it sends the results back to the user via email. In this way, the efficiency of high-end software can be fully utilized without infringing copyright. Units that have these high-end software and email servers can provide this free or paid service.

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Design Check

　　The design of integrated circuits does not seem to be complicated, but it is not so easy to check the designed layout. I bet that you can't check a layout of 10,000 tubes in 10 years. But the world is really wonderful. The more difficult things are, the easier they become. Now there are many software that can help you check. You just need to learn to use these software. What I mean is that I advise you not to try to use manual methods to check a slightly larger layout. The human brain is used for creation. Using it to do some repetitive and tedious work is not only inefficient, but also more troublesome. It will cause many unexpected errors.
　　There are still relatively few truly practical layout checking software. Dracula is one of the best. Before finding a cheap and practical checking software, we can consider entrusting the inspection through email and let the unit with Dracula software help with the inspection work. If the format of the file is standardized, perhaps I can convince some units to use their machine's idle time to serve you.

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External Support

　　The most effective and traditional support comes from books. You should collect books on this subject.
　　Newsgroups, mailing lists, and email can all provide you with technical support from the outside world cheaply and quickly, which is also one of the benefits of the Internet. The support obtained through the Internet is very effective most of the time, but it is not certain and clear, because no one has the obligation to help you. The minimum condition for them to help you enthusiastically is that they must be free.
　　You must learn to use the support from the outside world. This support is not out of obligation, but out of enthusiasm. Don't abuse this enthusiasm. Before asking a question, please spend a little more time to study your problem and then ask your question accurately. When other people ask similar questions in the future, you should also answer enthusiastically and introduce your experience in solving problems.
　　The way to get certain and clear help is that you can find an integrated circuit design company near you and get this help at a certain price. When I first learned to design integrated circuits, the method I adopted was to entrust the project to a design company and asked them to tell me the design process so that I would have someone to imitate.

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Introduction to ASIC and PGP Mailing Lists

　　Mailing lists are a form of communication similar to newsgroups. They are composed of a group of like-minded people. They are cheaper and more targeted than newsgroups. After joining a mailing list, you can often receive various messages sent to this mailing list by others. You can express your views on various issues, or put forward new suggestions, new ideas, or put forward the difficulties you encounter to get help from others. The most valuable thing is that all operations can be performed through email on a free email account.
　　Soon after sending a subscription application letter, you will receive a confirmation letter. Reply to this letter directly and you will join the mailing list. In the future, you can post manuscripts to these two mailing lists, participate in discussions, seek help, or express any insights you want to express. You only need to try to focus on the topic to take care of the interests of other members.
　　You can post, join or leave the mailing list through the form below. Please note that you should use the same email account to operate. If you encounter any trouble during the operation, please write to me and let me help you complete it from the server. You need to go online to view archived files.

bryan213

I am a candidate of the 2007 class. I really want to apply for science and technology, including integrated circuit design and application. After reading your article, I have many questions to ask you. I hope you have time to add me on QQ 610718849. My name is Zhang Lei. E-MAIL: bryanking911@163.com

awnuaw

Very detailed introduction

huchuan987

Haha, please introduce more~~~~~

mbb

Very good!! Thumbs up!

imbaby335

Thank you very much. I have also drawn the layout of several devices, just copying them.

smart-pcb

I learned a lot! Thank you!

路尽隐香处

Very detailed