There are two essential components in the crystal oscillator circuit, namely resistance and capacitance. However, what are the roles of these two components in the crystal oscillator circuit?Here is a brief description of their role in the circuit.
The four main functions of the parallel resistor:
1, with the IC internal circuit composed of negative feedback, phase shift, so that the amplifier works in the linear region;
2. Current limiting prevents the resonator from being overdriven;
3, parallel reduction of resonance impedance, so that the resonator easy to start;
4, the value of resistance affects the pulse width of the waveform.
Functions of capacitance at both ends:
This is the matching capacitance of the crystal. Only in the case that the external connected capacitance is the matching capacitor, the oscillation frequency can be guaranteed within the error range near the nominal frequency.It is best to follow the data provided. If not, it is generally about 30pF.Too small for easy vibration.In some cases, it is possible to fine-tune the oscillation frequency by adjusting the size of the two capacitors, usually within the 10ppm range.