Varactor diode frequency modulation oscillation circuit

①The figure below shows a capacitor three-point oscillation circuit, which achieves frequency modulation through the capacitance change of the varactor diode. 　

②The special point of this circuit is that two varactor diodes are used and connected to the oscillation circuit in the same polarity. Since two diodes replace one diode in the circuit, the high-frequency voltage across each varactor diode is reduced. This reduces the influence of the high-frequency voltage on the total capacitance of the varactor diode. 　　 　　

③ The high-frequency choke is short-circuited to the DC and modulation signals, but open-circuited to the carrier frequency. Therefore, the reverse voltage applied to the two varactor diodes is the same.