AM Envelop Detector.

Cuthbert Nyack
The applet below illustrates the operation of an envelop detector used for AM demodulation. The circuit relies on having different time constants for charging and discharging. Typically the circuit consists of a diode rectifier feeding into a parallel RC combination.
When the capacitor is being charged, the time constant is determined by the dynamic diode resistance(small) and the source resistance(made small by step down transformer). When discharging, the time constant is determined by the resistor (large) in parallel with the capacitor.

In a real AM circuit, the ripples will be much less than that shown because the ratio of carrier frequency to modulating frequency is much larger than that shown.

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COPYRIGHT 2010 Cuthbert Nyack.