Q.Draw the schematic diagram of a diode detector and describe its operation.

A diode (envelope) detector recovers the modulating signal from an AM wave. The diode rectifies the AM signal and an RC low-pass filter follows the envelope, whose time constant is chosen to smooth the carrier ripple but still track the audio. …

[!TLDR]

A series diode rectifies the AM wave and a parallel RC filter follows its envelope, recovering the audio; RC is set so $1/f_c \ll RC \ll 1/f_m$.

Schematic arrangement: The AM signal is coupled from the tuned secondary of the last IF transformer to a diode connected in series. The diode is followed by a parallel combination of a resistor $R$ and a capacitor $C$ connected to ground (the load and filter). The output audio is taken across this RC combination through a coupling capacitor, which blocks the dc and passes the audio to the next (AF) amplifier.

Operation:

1. During each positive half-cycle of the AM wave the diode is forward biased and conducts, quickly charging the capacitor $C$ up to the peak value of that cycle.
2. During the following negative half-cycle the diode is reverse biased and stops conducting; the capacitor now discharges slowly through the resistor $R$.
3. The time constant $RC$ is chosen so that it is long compared with the period of the carrier, $1/f_c$, but short compared with the period of the highest modulating frequency, $1/f_m$; that is $1/f_c \ll RC \ll 1/f_m$.
4. With this choice the capacitor cannot follow the rapid carrier oscillations (so the carrier ripple is smoothed out) but can follow the slower variation of the envelope. The voltage across $RC$ therefore reproduces the envelope, which is the original modulating signal plus a dc level.
5. The coupling capacitor at the output removes the dc component, leaving the recovered audio signal. …