Q. Explain Demodulation of DSB?

Demodulation of DSB SC AM signals requires a synchronous demodulator, which is also known as coherent or synchronous detector. That is, the demodulator must use a coherent phase reference. This is usually generated by means of a phase-locked loop (PLL), which forces the phase of the voltage-controlled oscillator to followthe phase of the reference signal, to demodulate the received signal. The need for such a device is a chief disadvantage of the DSB SC scheme.

Figure shows the general configuration. A PLL is utilized to generate a phase-coherent carrier signal that is mixed with the received signal in a balanced modulator. The output of the balanced modulator is fed into a low-pass filter of bandwidth W, which passes the desired signal and rejects all signal (and noise) components above W Hz.