How to reduce the noise of PCB board

- Jan 10, 2017-

A good performance of the board, we can see the general distribution of electronic engineers can be seen (the premise is to know what the function of the board), which is what we often say that the functional module separation principle. Function module, is a combination of some electronic components to complete a certain function of the circuit set. In the actual design, we need to close these electronic components, reducing the length of wiring between electronic components in order to increase the role of circuit modules. In fact, it is not difficult to understand, our common development board or mobile phone is to do so, especially if you will open the mobile phone, mobile phone, you will find that the separation between each module and each module are very obvious, with Faraday electric shielding cage.

Secondly, it should be noted that when a PCB circuit board with analog and digital circuits, the need to separate the two, if you have to buckle a hat, there is silence. The so-called silent zone, is the analog circuit and digital circuit or the isolation of the functional modules of the region. In this way, we can prevent the interference of other modules to the module. In the mobile phone circuit board above, the silence is clear. Note that the silent area is not connected to the circuit board.

In the actual circuit design, not every PCB board is enough space for us to do silent area, then, in the space is not allowed, how should we design?

A, the use of transformers or signal isolation components design. We often use CMOS or transistor transistor components such as circuit separation is the meaning of.

B, signal into the module before the filter circuit. This method is a common method to prevent ESD, put it here, but also take into account this method can play a role in eliminating noise (ESD, high frequency and high voltage noise) role.

C, the use of common mode inductance signal protection. If we do not know the role of common mode inductance, we will find in the schematic is only two coils, and no effect. In fact, it is very important for the stability of the signal and the elimination of the noise interference. On the other hand, it also reveals that it takes a long time for electronic engineers to grow.

One of the approaches to the quiet area of the circuit board design is the trench protection technology. This technique is to remove the partition of the quiet area of copper skin, forming a bare circuit board material technology. The concept of the bridge is also derived from this: will be divided into different areas of the power supply, ground and signal line called bridge. The protection technology has the function of resisting the peak voltage and the endurance of the classical discharge protection. In the design of the circuit board, and the isolated area independent of the wiring through the trench, will produce RF loop current, but more influence on the performance of the circuit board, this need to pay attention to.

Now, a lot of analog to digital and digital to analog components in the component itself has two parts connected together, typically ADC and DAC devices, these devices are separated, there must be a standard reference, if digital signal current cannot be effectively back to the source, it will cause noise EMI in principle, we found that when the drawing pins are AGND and DGND, is a superior performance of the device, we can reduce the design difficulty.

In general, the circuit is divided into blocks according to the module, and the quiet zone is set in order to minimize the influence of the power supply and ground to the signal.

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