Explain the operation of a varactor diode in generation of FM?

Varactor diodes are constructed in the same way as a capacitor and operate under reverse bias conditions, which gives rise to three current-conducting regions. Currents conduct through positive (P) and negative (N) regions, located at either end of the diode. Near the junction of the P and N regions, a depletion region ensures that no current carriers are available, thus acting as an insulator. Due to this arrangement, a varactor diode's conductive plates are separated by an insulatorlike dielectric, much like a capacitor

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