Calculation of external matching capacitance of crystal load capacitance and experience of crystal oscillation circuit design (II)

The relationship between crystal load capacitance and frequency offset:

The load capacitance mainly affects the load resonance frequency and the equivalent load resonance resistance. Together with the quartz resonator, it determines the operating frequency of the oscillator. By adjusting the load capacitance, the operating frequency of the oscillator can generally be adjusted to the nominal value. When applying, we generally use external capacitors, so that the equivalent capacitance at both ends of the crystal oscillator is equal to or close to the load capacitance. For high requirements, the capacitance of the ic input terminal should be considered, so that the frequency of the crystal oscillator can reach the nominal frequency. .

The standard values commonly used for load capacitors are 12.5 pF, 16 pF, 20 pF, 30 pF. The relationship between load capacitance and resonant frequency is not linear. When the load capacitance becomes small, the frequency deviation becomes larger. When the load capacitance increases, the frequency deviation decreases.