question_answer

Given below is a circuit diagram of an AM demodulator. For good demodulation of AM signal of carrier frequency f, the value of RC should be:

A) \[RC=\frac{1}{f}\]

B)                       \[RC<\frac{1}{f}\]           

C)       \[RC\ge \frac{1}{f}\]      

D)       \[RC>>\frac{1}{f}\]

Correct Answer: D

Solution :

From the modulated signal, we can demodulate or detect the modulating or message signal by using a diode and a suitable capacitor filter. The AM signal given to the input of the circuit appears at the output of the diode as a rectified wave as shown. For good demodulation of AM signal the value of RC (which is a time-constant) is chosen such that \[\frac{1}{f}<<RC\]   or     \[RC>>\frac{1}{f}\] where f is the frequency of the carrier signal.