Frequency Modulation CircuitThe varactor diode is a semiconductor diode whose junction capacitance changes appreciably with d.c. bias voltage. This diode is shunted with the tuned circuit (tank circuit) of the carrier oscillator as shown in the figure:
Phase Modulation vs Frequency Modulation
|Sl. no||Frequency Modulation||Phase Modulation|
|1||Here the angular frequency of the signal is modified.||Here the Phase angle of the signal is modified.|
|2||The amplitude is kept constant||The Phase deviation is proportional to the amplitude of the modulating signal|
|3||The modulating index is proportional to amplitude of modulating voltage||The modulation Index is proportional to the modulating voltage only.|
The detector performs the extraction in two steps:
- It converts the frequency modulated signal (FM) signal into a corresponding amplitude modulated signal (AM) signal by using frequency-dependent circuits, i.e. circuits whose output voltage depends on input frequency. Such circuits are called as frequency discriminators.
- The original modulating signal f (t) is recovered from this AM signal by using a linear diode envelope detector.