Discussion on the Influence of Electrostatic Capacitance C0 on Crystal Oscillator

In electronic devices, quartz crystal oscillators play a crucial role in providing a stable clock signal to the circuit. The performance parameters of crystal oscillator have a direct influence on the stability and accuracy of its output signal. Among these parameters, the electrostatic capacity C0 is a very important index, which has a significant effect on the performance of the crystal oscillator.

Electrostatic capacitance C0, also known as the shunt capacitance of a quartz resonator, refers to the capacitance formed by two electrodes in a quartz crystal oscillator. This capacitor is not a separate component, but a capacitor formed by the quartz crystal sheet itself as a medium, and the two electrodes connected to it. More specifically, the electrostatic capacitance C0 is equivalent to the capacitance of a plate capacitor with a quartz wafer as the medium and two electrodes as the electrode plate, plus the sum of the stand capacitance and lead capacitance.

The influence of electrostatic capacitance C0 on crystal oscillator is mainly reflected in the following aspects:

1. Resonant frequency

The resonant frequency of the crystal oscillator is inversely proportional to the capacitance value, that is to say, the higher the electrostatic capacity C0, the lower the resonant frequency of the crystal oscillator; Conversely, the smaller the electrostatic capacitance C0, the higher the resonant frequency of the crystal oscillator. Therefore, when designing the circuit, it is necessary to adjust the size of the electrostatic capacitance C0 according to the actual demand in order to obtain the appropriate resonant frequency.

2. Stability and Precision

The stability of crystal oscillator refers to the stability of the output signal of crystal oscillator, and the electrostatic capacity C0 has an important influence on the stability of crystal oscillator. The larger the electrostatic capacity C0 is, the better the stability of crystal oscillator is. On the contrary, the smaller the electrostatic capacitance C0, the worse the stability of the crystal oscillator. In addition, the electrostatic capacitance C0 also affects the precision of crystal oscillator. The smaller the electrostatic capacitance C0 is, the higher the precision of crystal oscillator is. On the contrary, the higher the electrostatic capacity C0, the worse the precision of crystal oscillator.

3. Q value

Q value of crystal oscillator refers to the quality factor of the resonant circuit of crystal oscillator, which reflects the frequency selection performance of crystal oscillator. The higher the C0 is, the higher the Q is. On the contrary, the smaller the electrostatic capacity C0, the lower the Q value of the crystal oscillator.

4. Temperature compensation

Since the temperature coefficient of the quartz crystal is not zero, its resonant frequency will change with the change of temperature. By designing the appropriate C0 value of the electrostatic capacitance, the frequency change of the crystal oscillator can show the opposite trend to the temperature change, so as to achieve the purpose of temperature compensation and improve the temperature stability of the crystal oscillator.

In summary, the electrostatic capacitance C0 has an important effect on the performance of crystal oscillator. In the design and application of crystal oscillator, it is necessary to fully consider the size of the electrostatic capacitance C0 to obtain the ideal resonant frequency, stability and precision. At the same time, it is also necessary to pay attention to the influence of the change of electrostatic capacitance C0 on other performance parameters of crystal oscillator to ensure the performance of crystal oscillator in practical applications.