The voltage-controlled crystal oscillator (VCXO) adjusts the crystal oscillation frequency by applying an external voltage. The process of controlling the frequency mainly involves the following key steps and principles:
1、Oscillation circuit: The oscillation circuit of the voltage-controlled crystal oscillator consists of a crystal, a capacitor and a transistor. The crystal is the core component of the oscillation circuit and has the characteristics of mechanical oscillation and electrical oscillation.
2、Mechanical oscillation and electrical oscillation: The crystal generates mechanical oscillation under the action of mechanical vibration. This physical oscillation in turn triggers electrical oscillation, that is, the charge inside the crystal is displaced under the action of the electric field, generating electrical oscillation.
3、Feedback effect: After the crystal oscillation signal is amplified by the feedback loop, it returns to the crystal through the piezoelectric effect of the crystal, so that the crystal continues to oscillate and output signals.
4、Application of varactor diodes: In voltage-controlled crystal oscillators, varactor diodes are often used as adjustable elements. The capacitance value of the varactor diode changes with the change of the applied voltage. By changing the voltage applied to the varactor diode, the load capacitance of the quartz resonator can be adjusted, thereby changing the resonant frequency of the resonant circuit and achieving frequency control.
5、Relationship between voltage and frequency: There is a certain relationship between the output frequency of the voltage-controlled crystal oscillator and the input voltage. Generally, as the input voltage increases, the output frequency also increases, and vice versa. This relationship allows the oscillation frequency to be precisely controlled by adjusting the voltage.
6、Tuning circuit: During the production process, the voltage-controlled crystal oscillator needs to be electrically tuned through a tuning circuit to ensure that its output frequency reaches the required range.
In summary, the voltage-controlled crystal oscillator controls the capacitance value of the varactor diode through an external voltage, thereby adjusting the resonant frequency of the resonant circuit to achieve precise frequency control.
