Key Points of Seven Common Interface Types in Circuit Design

by:A-TECH      2021-03-20
We know that there may be some problems in the data exchange between the various sub-modules of the circuit system, which may cause the signal to be unable to 'circulate' normally and with high quality. For example, sometimes the working timing of the circuit sub-modules is deviated (such as CPU and peripherals) or The respective signal types are inconsistent (such as the sensor detecting light signals), etc. At this time, we should consider handling this problem well through the corresponding interface method. Next, I will answer for you! The following is an explanation of the key points of the 7 commonly used interface types in circuit design: TTL level interface This interface type is basically a cliché, starting from studying analog circuits and digital circuits in college, for general circuit design, TTL electrical The flat interface basically cannot get rid of the 'related'! Its speed is generally limited to 30MHz, this is because there are several pF of input capacitance at the input of the BJT (constitute an LPF), if the input signal exceeds a certain frequency, the signal is Will be 'lost'. Its driving capacity is generally up to dozens of milliamps. The normal working signal voltage is generally higher, if it is close to an ECL circuit with a lower signal voltage, a more obvious crosstalk problem will occur. CMOS level interface is not unfamiliar to us, and we often deal with it. Some semiconductor characteristics of CMOS are not necessary here. What many people know is that the power consumption and anti-interference ability of CMOS is far superior to TTL under normal circumstances. But! What is less known is that the CMOS series actually consumes more power than TTL at high switching frequencies. As for why this is the case, please ask the theory of semiconductor physics. Since the operating voltage of CMOS can be very small at present, and some FPGA cores have operating voltages even close to 1.5V, this makes the noise tolerance between levels much smaller than that of TTL, which aggravates the voltage fluctuations. Signal judgment error. As we all know, the input impedance of CMOS circuit is very high, therefore, its coupling capacitance can be very small, without the need to use large electrolytic capacitors. Since CMOS circuits are generally weak in driving ability, it is necessary to perform TTL conversion before driving the ECL circuit. In addition, when designing CMOS interface circuits, care should be taken to avoid overloading the capacitive load, otherwise it will slow the rise time and the power consumption of the drive device will increase (because capacitive loads do not consume power). The ECL level interface is an old friend inside the computer system! Because it 'runs' fast enough, it can even run to hundreds of MHz! This is because the BJT inside the ECL is not in a saturated state when it is turned on. In this way, the turn-on and cut-off time of the BJT can be reduced, and the working speed can naturally be increased. But, this is a price! Its fatal injury: higher power consumption! The EMI problem it causes is also worth considering, and the anti-interference ability is not much better. If anyone can compromise the two points Factors, then he (she) should make a fortune. It should also be noted that the general ECL integrated circuit needs a negative power supply, which means that its output voltage is negative, and a special level shift circuit is needed at this time. The RS-232 level interface is basically no one who does not know about it anymore (unless he or she is just an electronic technology professional 'layman'). 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 a computer, a level conversion chip MAX232 is naturally indispensable. But we have to be soberly aware of some of its shortcomings, such as the data transmission speed is still relatively slow, the transmission distance is also short. Differential balanced level interface uses the relative output voltage (uA-uB) of a pair of terminals A and B to represent the signal. Under normal circumstances, this differential signal will pass through a complex noise environment during signal transmission, resulting in two Basically the same amount of noise is generated on the root line, and the energy of the noise will be canceled out at the receiving end, so it can achieve longer distance and higher rate transmission. The RS-485 interface commonly used in industry uses a differential transmission method, which has good resistance to common mode interference. Optical isolation interface Photoelectric coupling uses optical signals as a medium to realize the coupling and transmission of electrical signals. Its 'good' is that it can achieve electrical isolation, so it has excellent anti-interference ability. Under the condition that the circuit operating frequency is very high, basically only the high-speed photoelectric isolation interface circuit can meet the needs of data transmission. Sometimes in order to achieve high voltage and large current control, we must design and use optical isolation interface circuits to connect these low-level, low-current TTL or CMOS circuits as described above, because the input loop and output loop of the optical isolation interface It can withstand a high voltage of several thousand volts, which is sufficient for general applications. In addition, the input part and output part of the optically isolated interface must use independent power supplies, otherwise there is still an electrical connection, and it is not called isolation. The coil coupling interface has good electrical isolation characteristics, but the allowable signal bandwidth is limited. For example, transformer coupling, its power transmission efficiency is very high, 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 it can only give a lower output voltage. Current. In addition, the transformer's high-frequency and low-frequency characteristics are not optimistic, but its biggest feature is that it can realize impedance conversion. When matched properly, the load can obtain sufficient power. Therefore, the transformer coupling interface is used in the design of power amplifier circuits Very 'popular'. Here to enter the pricing page https://www./YA
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