Peak and envelope detector
An AM signal is a fast carrier whose amplitude follows the audio. A diode passes the positive peaks and an RC holds them: fast enough to follow the audio, slow enough to ignore the carrier. What is left is the original 500 Hz tone.
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How it works
R·C = 470 µs: much longer than one carrier cycle (50 µs) and shorter than one audio cycle (2 ms).
To follow the troughs without clipping, R·C < √(1 − m²) ÷ (2π·f_audio·m) = 551 µs.
The output carries the 500 Hz tone.
Try it on the bench
- Change C to 100 nF and watch the troughs.
- Change the modulation tone to 1 kHz: the output follows.
Parts on the bench
In the course
Electronics Engineering, module “Op-amps and feedback”.