[Repost] 7 commonly used interface types in circuit design, how much do you know?
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We know that when the submodules of the circuit system exchange data, there may be some problems that cause the signal to not flow normally and with high quality. For example, sometimes the working timing of the submodules of the circuit is deviated (such as the CPU and peripherals) or the signal types of each submodule are inconsistent (such as the sensor detecting light signals). At this time, we should consider using the corresponding interface to handle this problem well. 25)]The following are the key points of 7 commonly used interface types in circuit design: (1) TTL level interface: This interface type is basically a commonplace. Since I started studying analog circuits and digital circuits in college, TTL level interfaces have basically been "involved" in general circuit design! Its speed is generally limited to 30MHz. This is because there are several pF input capacitors at the input end of the BJT (forming an LPF). If the input signal exceeds a certain frequency, the signal will be "lost". Its driving capability is generally a maximum of tens of milliamperes. The signal voltage for normal operation is generally high. If it is close to the ECL circuit with a lower signal voltage, it will cause obvious crosstalk problems. (2) CMOS level interface: We are familiar with it and often deal with it. There is no need to elaborate on the semiconductor characteristics of CMOS. Many people know that under normal circumstances, the power consumption and anti-interference ability of CMOS are much better than TTL. However, what is less known is that at high switching frequencies, the CMOS series actually consumes more power than TTL. Since the operating voltage of CMOS can be very small, the operating voltage of some FPGA cores is even close to 1.5V, which makes the noise margin between levels much smaller than TTL, thus further aggravating the signal judgment errors caused by voltage fluctuations. As we all know, the input impedance of CMOS circuits is very high, so its coupling capacitor capacity can be very small, and there is no need to use large electrolytic capacitors. Since CMOS circuits usually have weak driving capabilities, they must be converted to TTL before driving the ECL circuit. In addition, when designing CMOS interface circuits, care should be taken to avoid excessive capacitive loads, otherwise the rise time will be slowed down and the power consumption of the driver device will increase (because capacitive loads do not consume power). (3) ECL level interface: This is an old friend inside the computer system! Because its speed is "fast" enough, it can even run up to hundreds of MHz! This is because the BJT inside the ECL is not in a saturated state when it is turned on, which can reduce the turn-on and turn-off time of the BJT, and the working speed can naturally be increased. But, this comes at a price! Its fatal flaw: high power consumption! The EMI problem it causes is also worth considering, and the anti-interference ability is not much better. If someone can compromise these two factors, then he (she) should make a fortune. It should also be noted that ECL integrated circuits generally require negative power supply, that is, their output voltage is negative, and then a special level shifting circuit is required. (4) RS-232 level interface: Almost no one who plays with electronic technology does not know it (unless he or she is just an "outsider" in the field of electronic technology). It is a low-speed serial communication interface standard. It should be noted that its level standard is a bit "abnormal": the high level is -12V, and the low level is +12V. So, when we try to communicate with peripherals through computers, a level conversion chip MAX232 is naturally indispensable. But we must be aware of some of its shortcomings, such as the data transmission speed is still relatively slow and the transmission distance is also short. (5) Differential balanced level interface: It uses the relative output voltage (uA-uB) of a pair of terminals A and B to represent the signal. Generally, this differential signal will pass through a complex noise environment during signal transmission, resulting in basically the same amount of noise on both lines, and the noise energy will be offset at the receiving end, so it can achieve long-distance and high-speed transmission. The RS-485 interface commonly used in industry adopts differential transmission, which has good common-mode interference resistance. (6) Optical isolation interface: Optical coupling uses optical signals as the medium to achieve the coupling and transmission of electrical signals. Its "advantage" is that it can achieve electrical isolation, so it has excellent anti-interference ability. Under the condition of high circuit operating frequency, basically only high-speed optical isolation interface circuit can meet the needs of data transmission. Sometimes, in order to achieve high voltage and high current control, we must design and use optical isolation interface circuits to connect these low-level, low-current TTL or CMOS circuits as mentioned above, because the input and output circuits of the optical isolation interface can withstand a high voltage of several thousand volts, which is enough to meet general applications. In addition, the input and output parts of the optical isolation interface must use independent power supplies, otherwise there will still be electrical connection, which is not called isolation. (7) Coil coupling interface: It has good electrical isolation characteristics, but the allowed signal bandwidth is limited. For example, transformer coupling has a very high power transmission efficiency, and the output power is basically close to its input power. Therefore, for a step-up transformer, it can have a higher output voltage, but can only give a lower current.25)]In addition, the high-frequency and low-frequency characteristics of the transformer are not optimistic, but its greatest feature is that it can achieve impedance transformation. When matched properly, the load can obtain sufficient power. Therefore, the transformer coupling interface is very popular in the design of power amplifier circuits. Source: Internet, if infringed, please delete
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