Demodulation or discrimination, or detection is the process of extracting the original data signal from a modulated signal.
In general, demodulation has to be phase sensitive in the sense that, algebraic sign of the data signal should be preserved and determined by the demodulation process.
In full-wave demodulation an output is generated continuously.
In half wave demodulation no output is generated for every alternate half-period of the A simple and straightforword forward method of demodulation is by detection of the envelope of the modulated signal.
For this method to be feasible, the carrier signal must be quite powerful (i.e., signal level has to be high) and the carrier frequency also should be very high.
An alternative method of demodulation, which generally provides more reliable results, involves a further step of modulation performed on the already-modulated signal followed by low-pass filtering.
Consider the amplitude-modulated signal xa (t) shown in Figure (b). If this signal is multiplied by the sinusoidal carrier signal 2/ac cos2pƒct, we get
We can conveniently low-pass filter the signal using a filter with cutoff at fb to recover the original data signal.
A schematic representation of this method of amplitude demodulation is shown in Figure (b).