The computer-aided design method of integrated circuits was developed in the late 1960s. At that time, large-scale integrated circuits had just begun to develop. Because the number of transistors on each chip is increasing and the circuit is becoming more and more complex, it is becoming more and more difficult to analyze, calculate the circuit performance and design the layout manually. Not only the design cycle is long and consumes a lot of manpower, but also the correctness of the layout is difficult to guarantee. Therefore, a method of using computer to assist people in designing integrated circuit layout and analyzing integrated circuit performance is proposed. Using the ability of computer to calculate and process a large amount of data quickly, as long as the design principles and methods are summarized, these design principles and methods can be realized by writing computer programs. In computer-aided design, as long as simple raw data are input in a certain format, the computer can design the correct layout. However, integrated circuits cannot be designed automatically, and designers need to be constantly involved in the whole design process. It is necessary to repeatedly analyze and compare the design results, select a better scheme, and then carry out the next design. Computer-aided design can not only shorten the design cycle, but also easily find out the mistakes and reduce the design cost, which has become an important part of large-scale integration technology.
There are many contents in computer-aided design of integrated circuits, and computer-aided design methods have been developed in almost every stage of the design process. Its main contents include system division and simulation, logic simulation, circuit analysis and simulation, process simulation, device performance simulation, layout design, layout verification, and auxiliary plate making. , and there are corresponding description languages and databases, such as cell layout database and device parameter database.
System partition and simulation are the design of the whole system. Due to the development of VLSI, a complete electronic system often needs only a few integrated circuits to realize all functions. Therefore, based on the analysis of the whole system, the most reasonable and economical chip partition scheme is determined according to the function, and there is computer simulation. Logic simulation is to determine the logic circuit of the chip and check whether it meets the requirements of the original function. Logic simulation includes gate level simulation, register level simulation and function level simulation. Circuit analysis and simulation is to analyze and simulate the electrical performance of the selected circuit, including static, dynamic and tolerance analysis, and design with the best center value. Circuit analysis needs the electrical characteristic parameters of the device, which can be provided by process simulation, device performance simulation and other programs. In this way, the technological conditions of chip processing in the future can be determined. Another method to provide the electrical characteristic parameters of the device is the program to automatically extract the device parameters, that is, the electrical characteristic parameters of the device actually measured and analyzed by the program extraction circuit. Generally speaking, the latter method is more reasonable and practical.
Layout design is to select the correct circuit diagram according to the results of circuit analysis, and then to pattern the device according to the requirements of device performance. Each device is placed somewhere in the layout and interconnected according to the circuit diagram. This is the most time-consuming work in the design of integrated circuits, especially large-scale and ultra-large-scale integrated circuits, and it is also the most important link in the computer-aided design of integrated circuits. There are two methods of layout design: man-machine interaction design and automatic design, which are combined in general design. However, in order to improve the efficiency of layout design, it is necessary to establish a cell layout database.
There may be errors in the layout of the design, and it is time-consuming and laborious to check the errors manually. Computer-aided error detection has a good effect, that is, the layout verification program. This verification program can not only find out the geometric errors, but also consider the parasitic effects such as connection and isolation, and correct the unreasonable parts in the original design. After proofreading the correct layout data, it is sent to a drawing (engraving) machine or a pattern generator through a computer-aided plate-making program, or a mask required by an integrated circuit is made by electron beam exposure.
The completed integrated circuit still needs to be tested, which is arduous and complicated. In modern times, computer-aided testing is also used to improve work efficiency. In the circuit design stage, the improvement of test efficiency has been considered, which is testability design. Therefore, computer-aided testing is also a part of generalized computer-aided design.