Functionally, crystal oscillators can be divided into passive crystal oscillators and active crystal oscillators.

Passive crystal oscillators are quartz crystal resonators, while active crystal oscillators are positional quartz crystal oscillators. A passive crystal oscillator is just a quartz crystal chip that needs to be matched with corresponding peripheral circuits such as capacitors, inductors, and resistors to work. Its accuracy is lower than that of a crystal oscillator, but it does not require power supply. It can start with an oscillation circuit and usually has two pins, which is relatively low in price.

Active crystal oscillators contain external circuits such as quartz crystals and matching capacitors, which have high accuracy and stable output signals. They do not require peripheral circuit design and are convenient to use, but require power supply. Active crystal oscillators are generally four pin sealed, with a power supply, ground wire, oscillation output, and an empty terminal. When using an active crystal oscillator, special attention should be paid to ensuring that the power supply is stable and the power lead is as short as possible, and that it shares ground with the chip that uses the crystal oscillator signal in the system as much as possible.