Examples of systems composed of MOS integrated circuits and their characteristics and problems

Now take the desktop computer composed of MOS integrated circuits designed based on the above analysis as an example to illustrate its characteristics and existing problems.

The specification list of the computer based on the four arithmetic operations is as follows.

The block diagram is roughly the same as the structure in Figure 3.1. At this time, the calculation methods are all serial control, and one calculation cycle requires (T1~T13)×2 time. T is a digital timing signal, take the time from T1 to T13 as P, thenOne operation can be processed within time. Integrated circuit system. inThe judging device determines the calculation content within P within the cycle, and specifies the next calculation content when P ends.

The components constituting each block diagram use MOS integrated circuits. Its varieties include 4D flip-flops, dual 8-bit shift registers, dual 2-input AND -2 input OR gates, and dual 4-input AND gates , 5 inverters, 4MOS field effect transistors and other six types. Table 3.4 shows the required number of MOS integrated circuits, transistors, diodes, resistors, capacitors and other components.

The characteristics and problems of computers using MOS integrated circuits are listed below.

(A) Strive to reduce the variety of integrated circuits and reduce the number of varieties used (reduced to 50), and put the design focus on economic aspects. The advantage of integrated circuit is that it can improve the efficiency of production and maintenance.

(B) In terms of gates, since there are only two input terminals "AND" gates and 4 input terminals "AND" gates, if 3 input terminals "AND" gates and 5 input terminals "AND" gates are required, they must be used together Diode gate. Integrated circuit system. Therefore, considering the waveform distortion caused by stray capacitance, for fan-out margin, level shift, etc., you should consider adding emitter followers and paying attention to the wiring method on the printed circuit board.

(C) Compared with bipolar integrated circuits, MOS integrated circuits have a large load resistance and stray capacitance cannot be ignored. Therefore, the control signal conversion time (T1t1) input by the program device to each gate circuit is longer than other timing pulses. So as not to affect the rise time of the waveform.

(D) The remaining unusable circuits in the integrated circuit shall be divided logically.

(E) In the diode gate, in addition to the forward voltage drop and reverse current of G and Si in opposite directions, the number of levels, the threshold voltage of the MOS integrated circuit, the number of input terminals, and the noise tolerance should also be considered. , Current and voltage changes, cost, etc.

(F) The structure of the power supply part of this system is extremely simple, composed of Zener diodes and power transistors, and the operating tolerance can be limited to ±0.5% in the range of 0-40°C.

In the initial stage of the development of MOS integrated circuits, due to the unstable phenomenon of the semiconductor surface and reliability problems, the process of practical application was delayed. However, the reliability of MOS integrated circuits is not lower than that of the bipolar type. The current failure rate data of MOS integrated circuits is about 500 non-special. Integrated circuit system. If the average time between failures of the system is calculated on this basis, as shown in Table 3.5, it is approximately 2500 hours. If a system of the same scale uses discrete components, the average time between failures is about 1400 hours, which shows that the reliability of MOS integrated circuits has been greatly improved.

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