Common Interface Types in Circuits 2

Common interface types in circuits

(3) ECL level interface:

This is an old friend inside the computer system! Because its speed "runs" fast enough, even reaching hundreds of MHz! This is because the BJT inside ECL is not in a saturated state during conduction, which can reduce the conduction and cut-off time of BJT, and naturally improve the working speed.

But, this comes at a cost! Its fatal injury: high power consumption! The EMI problem it causes is worth considering, and the anti-interference ability is also insufficient. It should be noted that generally, ECL integrated circuits require a negative power supply, which means that their output voltage is negative, and then a specialized level shifting circuit is needed.

(4) RS-232 level interface:

Many people know that this is the foundation of electronic technology. It is a low-speed serial communication interface standard. It should be noted that its level standard is somewhat "abnormal": the high level is -12V, while 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 need to be aware of some of its drawbacks, such as slow data transmission speed and short transmission distance.

(5) Differential balanced level interface:

It represents the signal using the relative output voltage (uA uB) of a pair of terminals A and B. Generally, this differential signal will pass through a complex noise environment during signal transmission, resulting in essentially the same amount of noise on both wires. At the receiving end, the energy of the noise will be offset, so it can achieve long-distance and higher rate transmission. The commonly used RS-485 interface in industry adopts differential transmission method, which has good resistance to common mode interference.

(6) Optical isolation interface:

Optoelectronic coupling uses 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 high operating frequency conditions, only high-speed optoelectronic isolation 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 described above, because the input and output circuits of the optical isolation interface can withstand high voltage of several thousand volts, which is sufficient to meet general applications.

In addition, the input and output parts of the optical isolation interface must use independent power sources, otherwise there will still be electrical connections, 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 provide a lower current.

In addition, the high-frequency and low-frequency characteristics of transformers are not optimistic, but their biggest feature is that they can achieve impedance transformation. When matched properly, the load can obtain sufficient power. Therefore, the transformer coupling interface is very suitable for power amplification circuit design.

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