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D D S S: University of Khartoum University of Khartoum

This document discusses the demodulation of signals in communication engineering, focusing on the use of nonlinear devices like multipliers and rectifiers. It compares synchronous detectors, which are more complex but sensitive, with simpler envelope detectors that are cost-effective but add distortion. The document emphasizes the importance of synchronous detectors for detecting DSB_SC signals, highlighting the popularity of AM signals in communication systems.

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Hassan Ahmed
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32 views9 pages

D D S S: University of Khartoum University of Khartoum

This document discusses the demodulation of signals in communication engineering, focusing on the use of nonlinear devices like multipliers and rectifiers. It compares synchronous detectors, which are more complex but sensitive, with simpler envelope detectors that are cost-effective but add distortion. The document emphasizes the importance of synchronous detectors for detecting DSB_SC signals, highlighting the popularity of AM signals in communication systems.

Uploaded by

Hassan Ahmed
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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‫ﺑﺴﻢ اﷲ اﻟﺮﺣﻤﻦ اﻟﺮﺣﻴﻢ‬

University of Khartoum
B.Sc. of Communication Engineering
4th Year Electrical Engineering

Communications Systems I
EEE 41201

LECTURE 5

DEMODULATION OF SIGNALS
Moutaman Mirghani
Institute of Space Research and Aerospace (ISRA)
INTRODUCTION
A modulated signal is to be demodulated at the receiver
side in order to extract the information signal sent.
A demodulator uses a nonlinear device such as a multiplier,
squarer or a rectifier to demodulate the received signal.
Note that; filtering is a linear process and hence it does not
extract the modulation signal used at the transmitter side.
Using a signal multiplier (or mixer) to multiply the received
signal with a locally generated carrier and then integrating,
is a sort of using a correlator as a demodulator.
11:03
11:03
11:03
SYNCHRONOUS DETECTOR

11:03
Why ?

rad/m
11:03
ENVELOPE DETECTOR
As mentioned earlier, the synchronous detector above can be
used to demodulate AM signals.
However, another but more simpler and asynchronous (non-
coherent) detector is normally used, which is the envelope
detector.
It applies a nonlinear device, such as a half-wave rectifier, in
order to demodulate the signal. It includes a simple LPF to
reconstruct the signal.
After rectification, the LPF which is typically an RC filter
smoothens the rectified signal by filling the empty portions.
The dc component is used in automatic gain
control (AGC) to provide a feedback control
signal to the pre-detection amplifiers.
Compared to synchronous detector, envelope
detector is simpler and of little cost, but it is
not so sensitive and adds distortion to the
demodulated signal.
Finally, synchronous detector should be used
to detect DSB_SC signal, as envelope detector
can’t do it. That is why AM is most popular.

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