The application of varactor diodes

A varactor diode is an electronic variable capacitor. In other words, the capacitance exhibited by a varactor diode is a function of the reverse bias potential. This phenomenon has led to several common applications of varactor diodes in situations where capacitance factors need to be considered. Figure 1 shows a typical LC oscillator circuit tuned with a varactor diode. The function of the circuit coupling inductor l2 is to input the RF signal into the oscillation circuit when it is used as an RF amplifier. The main LC oscillation circuit includes a main inductor l1 and a series capacitor c1 and cr1.diode In addition, it is also necessary to consider the stray capacitance CS widely present in electronic circuits. The functions of DC blocking capacitors and series resistors have been introduced earlier. The function of capacitor c2 is to filter the tuning voltage vin.  diode

The tuning circuit of the variable capacitance diode in the diagram

Because the resonant frequency of the LC tuned oscillating circuit is a function of LC, we found that the ratio of the maximum to minimum resonant frequencies of the oscillating circuit varies with the square root of the capacitance ratio. The capacitance ratio here refers to the ratio of the capacitance at the minimum reverse bias voltage to the capacitance at the maximum reverse bias voltage. Therefore, the tuning characteristic curve of the circuit (bias voltage resonant frequency) is basically a parabola.diode