Electronic Design - The key points of seven commonly used interface types in circuit board design

The key points of seven commonly used interface types in circuit board design

Circuit board factory: 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. Peripherals) or their respective signal types are inconsistent (such as sensors detecting light signals), etc. At this time, we should consider handling this problem well through corresponding interface methods. Next, the editor will answer for you!

The key points of 7 commonly used interface types in circuit board design are explained below:

TTL level interface

This interface type is basically a cliché. Starting from studying analog circuits and digital circuits in college, for general circuit design, the TTL level interface is basically indispensable! Its speed is generally limited to 30MHz. This is because Because there are several pF of input capacitance at the input of the BJT (which constitutes an LPF), if the input signal exceeds a certain frequency, the signal will be "lost". Its driving capacity is generally up to dozens of milliamps. The normal working signal voltage is generally higher, and if it is close to an ECL circuit with a lower signal voltage, a more obvious crosstalk problem will occur.

CMOS level interface

We are no stranger to it, and we often deal with it. Some semiconductor characteristics about CMOS don't need to be long-winded 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 now be very small, 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 capacitor capacity can be very small, without the need to use a large electrolytic capacitor. Since CMOS circuits generally have weak drive capability, 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).

ECL level interface

This 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, so it can be reduced. The turn-on and cut-off time of BJT can naturally increase the working speed. 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.

RS-232 level interface

Basically no one who plays electronic technology doesn't know it (unless he or she is just a "layman" in 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 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

It 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, causing both wires to be generated Basically the same amount of noise, and the energy of the noise will be canceled out at the receiving end, so it can achieve longer-distance, higher-speed transmission. The RS-485 interface commonly used in the industry uses a differential transmission method, which has a good ability to resist 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.

Coil coupling interface

Its electrical isolation characteristics are good, 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". ipcb is a high-precision, high-quality PCB manufacturer, such as: isola 370hr PCB, high-frequency PCB, high-speed PCB, ic substrate, ic test board, impedance PCB, HDI PCB, Rigid-Flex PCB, buried blind PCB, advanced PCB, microwave PCB, telfon PCB and other ipcb are good at PCB manufacturing.