General Envelope Detector Simulator
Envelope Detection and Amplitude-Based Modulations
Envelope detectors are fundamental for amplitude-based modulations because they exploit the fact that the instantaneous amplitude of the carrier encodes the message signal.
1. Why Envelope Detection Works
In amplitude modulation (AM), the modulated signal has the form:
s(t) = [A_c + m(t)] cos(2Ï€ f_c t)- A_c is the carrier amplitude
- m(t) is the message signal
- f_c is the carrier frequency
The envelope of this waveform is: Envelope = |A_c + m(t)|.
An envelope detector (e.g., a diode + RC circuit) follows the peaks of the carrier, reproducing A_c + m(t).
After removing the DC offset (carrier), the original message m(t) is recovered.
2. Envelope Detector Schematic
Below is a simple block diagram of a diode + RC envelope detector:
3. Amplitude-Based Modulations Suitable for Envelope Detection
- DSB-AM (Double Sideband AM with Carrier): Standard AM; envelope detection works perfectly.
- DSB-LC (Large Carrier): Strong carrier amplitude; envelope detection works easily.
- VSB (Vestigial Sideband): Partial sideband suppression; works if residual carrier exists.
- PAM (Pulse Amplitude Modulation): Pulses encode message amplitudes; envelope detection tracks pulse amplitudes.
- AM Stereo: Radio broadcasting; information is in amplitude envelope.
4. When Envelope Detection Fails
- Carrier fully suppressed signals (e.g., DSB-SC) – signal crosses zero; envelope cannot be detected directly.
- Phase or frequency modulations (e.g., PSK, FM) – amplitude carries no information.
- Very noisy channels – envelope may be distorted and unreliable.
Summary
Envelope detection works because AM signals encode the message in the instantaneous amplitude of the carrier. It is best suited for AM, DSB-LC, VSB, and PAM with a carrier. It does not work for carrierless AM (DSB-SC), FM, or PSK signals.