Complete Description of Amplitude Demodulation

1. Amplitude Demodulation
Course No.: EEE 3218
Course Title: Communication Engineering
II Sessional

2.  Amplitude Demodulation
 Need of Amplitude Demodulation
 Application of Amplitude Demodulation
 Method of Amplitude Demodulation
 Theory of Envelope Detector
 Amplitude Demodulation Receiver Kit
 Experimental Input & Output
 Advantages & Disadvantages
Content

3. What is Amplitude Demodulation?
Amplitude Demodulation is a process of extracting the original
information bearing signal from a modulated signal.
Why is Amplitude Demodulation needed
 The diaphragm of a telephone receiver or a loud speaker cannot vibra
high frequency.Moreover, this frequency is beyond the audible range o
ear. So, it is necessary to separate the audio frequencies from radio- fr
carrier waves.
 To obtain the message or original modulating signal from the modulate

4. Method of Amplitude Demodulation
Envelope Detector
Square Law Detector
Synchronous Detector or Coherent Detection

5. Theory of Envelope
DetectorAn envelope detector is an electronic circuit that takes a high-
frequency signal as input and provides an output which is the
envelope of the original signal. The capacitor in the circuit stores
up charge on the rising edge, and releases it slowly through the
resistor when the signal falls. The diode in series rectifies the
incoming signal, allowing current flow only when the positive
input terminal is at a higher potential than the negative input
terminal.
Fig.: Envelope Detector

6. Capacitor discharges between positive peaks produces a ripple signal of
frequency ωc in the output. By increasing the time constant RC, ripple
can be reduced so that the capacitor discharges very little between the
positive peaks.
Theory of Envelope
Detector

7. Amplitude Demodulation Receiver
Kit
Fig.: Amplitude Demodulation Receiver Kit
Mixer
Circuit
IF Amplifier
Circuit
Envelope
Detector

8. Experimental Input & Output
Fig.: Modulated Signal Fig.: Demodulated Signal

9. Advantages
Disadvanta
ges A lot of functions and processes are involved with demodulation and all these are
 The overmodulated signal can not be recovered properly from this demodulation p
 The desired message signal is recovered through this process.

10. Thank You