555 chip is used to form a closed-loop three-phase multivibrator

Crystal oscillator

Quartz Oscillator 3225 20M OSC

A multivibrator is a self-excited oscillator that produces a rectangular wave, also called a rectangular wave generator. Composition: 1, discrete components; 2, op amp composition; 3, integrated gate circuit composition; 4, integrated Schmitt trigger; 5, transistor frequency stabilization; 6, 555 integrated circuit.