1. Main points of circuit design of active crystal oscillator EMC:

(1) The decoupling of the crystal oscillator power supply is very important. It is recommended to add magnetic beads, choose two or three decoupling capacitors, and decrease the capacitance value.

(2) The clock output pin is matched, and the specific matching resistance value can be determined according to the test result.

(3) The reserved capacitor C1 should have a small capacitance value, which constitutes a first-level low-pass filter. The selection of resistors and capacitors depends on the specific test results.

2.Circuit design points of PCB board:

(1) In the PCB design, the shell of the crystal oscillator must be grounded, which can prevent the longing radiation of the crystal oscillator and shield external interference.

(2) The ground should be laid under the crystal oscillator to prevent interference with other layers. Because some people do not lay the ground on the top and bottom layers when laying multi-layer boards, but it is recommended to lay the ground on the one where the crystal oscillator is located.

(3) Do not wire under the crystal oscillator, and do not wire and other components within a range of 5mm (some books recommend a range of 300mil, you can refer to it), mainly to prevent the crystal oscillator from interfering with other wiring and devices.

(4) Do not place the crystal oscillator on the edge of the board, because for safety reasons, the ground of the board is often connected to the metal shell or mechanical structure. This ground is called the reference ground plate for the time being. If the crystal oscillator is placed on the board At the edge, the crystal oscillator and the reference ground plane will form an electric field distribution, and there are often many cables on the edge of the board. When the cable passes through the electric field between the crystal oscillator and the reference ground plane, the cable is disturbed. The crystal oscillator is placed far away from the edge, and the electric field distribution between the crystal oscillator and the reference ground plate is divided by the GND of the PCB board, and the electric field distributed to the reference ground plate is greatly reduced.

(5) Of course, the clock line should be as short as possible. If you don‘t want the clock line to go all the way and interfere all the way, just make it short. Another point, regarding the choice of crystal oscillator, if your system can work at 25M, try not to choose 50M crystal oscillator. The high clock frequency is a high-speed circuit, and the steep rising edge of the clock is also a high-speed circuit, and signal integrity needs to be considered.

The above is the sharing of "Main Points of Circuit Design of Active Crystal Oscillator EMC and PCB Board". Hope to help everyone.