Q.What is an Envelope Detector?

Demodulation, also called detection, is the process of recovering the original modulating (baseband) signal from a modulated carrier — exactly the reverse of modulation. The circuit that does this is a detector or demodulator. It is necessary because the received wave carries audio riding on a radio-frequency carrier that a loudspeaker cannot follow (its diaphragm has too much inertia) and that lies far above the audible range, so the audio must first be separated out.

An AM detector performs two jobs: (1) it rectifies the modulated wave — an AM wave has equal positive and negative peaks and so a zero average, which a speaker cannot respond to, so a diode keeps only one half of each cycle; and (2) it separates the audio from the carrier — a capacitor filter bypasses the residual RF, leaving the low-frequency message. …