Common impedance and suppression of PCB advanced design

In order to suppress the common impedance interference, the following measures can be taken:

(1) One point grounding

Make several grounding points of the same-level unit circuit as concentrated as possible to avoid the AC signal of other circuits from being in the current level, or the AC signal in this stage is thrown into other circuits. It is suitable for low-frequency circuits whose working frequency is less than 1MHZ. If the operating frequency is 1~10MHz and a little grounding is used, the grounding length should not exceed 1/20 of the wavelength. In short, one-point grounding is to eliminate ground-line common-impedance interference. The basic principle.

(2) Grounding near multiple points

A large number of common ground lines are distributed on the edge of the board, and a semi-closed loop (anti-magnetic field interference) is presented, and the circuits of all stages are grounded close to prevent the ground line from being too long. Suitable for high frequency circuits where the signal operates at a frequency greater than 10 MHz.

(3) Bus bar grounding

The bus bar is made of silver plated copper plate, and the ground wire of all integrated circuits on the PCB is connected to the bus bar. The bus bar has a low-impedance characteristic of a strip-shaped symmetric transmission line, and in a high-speed circuit, the signal transmission speed can be improved and interference can be reduced.

(4) Large area grounding

In the high-frequency circuit, all the unused areas on the PCB are uniformly grounded to reduce the inductive reactance in the ground line, thereby weakening the high-frequency signal generated on the ground line and shielding the electric field interference.

(5) Bold ground wire

If the grounding wire is very thin, the grounding potential changes with the change of the current, causing the timing signal level of the electronic device to be unstable, and the anti-noise performance is deteriorated, and the width should be at least greater than 3 mm.

(6) Ground separation of D/A (digital/analog) circuits

The ground lines of the two circuits are independent and then connected to the ground of the power supply to prevent them from interfering with each other.