6 Common Interface Types in Circuit Design

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6 Common Interface Types in Circuit Design [Copy link]

We know that when the submodules of the circuit system exchange data, there may be some problems that cause the signal to not "circulate" normally and with high quality. For example, sometimes the working timing of the circuit submodules is deviated (such as the CPU and peripherals) or the signal types are inconsistent (such as the sensor detecting the light signal), etc. At this time, we should consider using the corresponding interface method to handle this problem well.

The following is an explanation of the key points of 7 commonly used interface types in circuit design:

1.TTL level interface

This type of interface is basically a commonplace. Since I started studying analog circuits and digital circuits in college, the TTL level interface has 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 capacity 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.ECL level interface

This is an old friend inside the computer system! Because its speed is fast enough, it can even run up to several hundred MHz! This is because the BJT inside the ECL is not in a saturated state when it is turned on, so the turn-on and turn-off time of the BJT can be reduced, 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 the general ECL integrated circuit needs to be powered by a negative power supply, that is, its output voltage is negative, and then a special level shifting circuit is required.

3. RS-232 level interface

Almost everyone who is into electronic technology knows it (unless he or she is just a layman 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 a computer, a level conversion chip MAX232 is naturally indispensable. But we must be aware of some of its shortcomings, such as the relatively slow data transmission speed and short transmission distance.

4. 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 longer distance and higher rate transmission. The RS-485 interface commonly used in industry uses differential transmission, which has good resistance to common mode interference.

5. Optical isolation interface

Optocouplers use optical signals as a 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 optoisolation interface circuits 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 is still electrical connection, and it is not called isolation.

6. Coil coupling interface

Its electrical isolation characteristics are good, 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 provide a lower current. In addition, the high-frequency and low-frequency characteristics of the transformer are not optimistic, but its biggest 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.