Envelope Detector LPF calculator
The above calculator helps to calculate the source voltage internal impedance Rs and the resistor RL for the low pass filter, provided the carrier frequency, the signal bandwidth and the capacitor values are given.
Amplitude Modulation (AM) is a method of transmitting information by varying the amplitude of a carrier wave in proportion to the message signal. However, in order to recover the original information from the received AM signal, we need to demodulate it. One of the most common methods of demodulating an AM signal is through the use of an single diode based envelope detector circuit.
Envelope Detector Circuit
A simple demodulator for AM signals. Extracts the original information by detecting the peak amplitude of the modulated wave. Utilizes a diode for rectification and a low-pass filter to remove noise and recover the original signal.
Circuit Diagram and Operation
The following shows circuit diagram of envelope detector circuit diagram for AM demodulation.
This circuit demonstrates an efficient and simple envelope detector for demodulating narrowband AM signals, where the carrier frequency significantly exceeds the message bandwidth. The detector comprises a diode (D1) and a low-pass RC filter (C1, R1).
Working Principle:
During positive input cycles, the diode conducts, charging capacitor C1 to the signal peak. In negative cycles, the diode blocks, and C1 discharges through resistor R1. This charge-discharge cycle reconstructs the original message signal.
Component Selection:
Optimal component values depend on the modulating signal frequency. For audio signals (max. 22kHz), consider these criteria:
- Fast Charging: \(R_SC << \frac{1}{f_c}\) ensures rapid capacitor charging within the carrier signal period.
- Controlled Discharging: \( \frac{1}{f_c} << R_LC << \frac{1}{B.W}\) allows slow discharge between carrier peaks while maintaining responsiveness to the modulating signal.
Video Demonstration
See the following video which demonstrates demodulation of AM signal using the envelope detector circuit.
If you are interested in learning more about designing AM modulator circuits or other communication circuit the following online calculator might be useful to you.- Air Core Inductor Calculator
