EMC design strategy - clock

There are generally two kinds of clock crystal circuits ： Passive crystal circuit and active oscillator circuit . Clock crystal circuit is generally the interference source of radiation emission .

1  Passive crystal

The standard circuit of passive crystal is as follows ：

In actual design ,R3 Resistance and C3 The capacitor is reserved .R3 Resistance can help start the shock ;C3 Capacitance can improve the quality of oscillating signal .

 

2  Active oscillator

The standard circuit is as follows ：

In actual design ,C1 It's a reserved design .C1 Capacitance can improve the output signal quality of the oscillator .

 

Generally, the power supply magnetic beads cannot be defaulted , Its function is to prevent the high-frequency signal of the oscillator from polluting the external circuit through the power supply .

Clock chip power pin adopts LC Filter circuit or PI Filter circuit ; The crystal shell should be grounded ; When the clock signal forks, the matching resistance is set in each channel after the forking , The matching resistor is close to the clock chip ;T Type network , Or use end matching .

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