In the crystal oscillator (SMD), the ordinary active oscillator has 4 pins, and the differential crystal oscillator has 6 pins. It is a complete oscillator, in addition to the quartz crystal, there are transistors and resistance-capacitance components. Crystal oscillators are also called active crystal oscillators. Active crystal oscillators are divided into DIP in-line crystal oscillators and SMD patch crystal oscillators. The active crystal oscillator is composed of quartz crystal, and the reason why it can be used as an oscillator is based on its piezoelectric effect. The active crystal oscillator does not require the internal oscillator of the digital signal processing DSP, and the signal quality is good and stable. Differential crystal oscillator, as the name suggests, is a crystal oscillator whose output is a differential signal. The output differential signal uses two signals with completely opposite phases to each other, thereby eliminating common mode noise and creating a higher-performance system.