Demodulation is the process of extracting the original information signal from a modulated carrier wave. There are different types of demodulation depending on the modulation type used. The document discusses frequency modulation (FM) demodulation and amplitude modulation (AM) demodulation. For FM demodulation, it describes filtering, limiting, and differentiating the signal using methods like phase-locked loops or zero-crossing detection. AM demodulation is done using half-wave rectification and low-pass filtering of the modulated signal to recover the baseband signal. Diagrams of circuits and blocks used in FM and AM demodulation are also presented.

1. SUBJECT : COMMUNICATION ENGINEERING - I
Presentation
On Demodulation

2. CONTENTS
Introduction to Demodulation
Types of Demodulation
FM Demodulation
AM Demodulation

3. WHAT IS DEMODULATION?
Demodulation is the act of extracting the original information-
bearing signal from a modulated carrier wave. A demodulator is
an electronic circuit (or computer program in a software-defined
radio) that is used to recover the information content from the
modulated carrier wave. There are many types of modulation so
there are many types of demodulators. The signal output from a
demodulator may represent sound (an analog audio signal),
images (an analog video signal) or binary data (a digital signal).

4. FM SIGNAL DEMODULATION
 It is more resistant to noise than an AM signal.
 filtering and Limiting the transmitted signal.
 Differentiation to obtain the phase information in the
modulated signal.
 There are four ways to implement differentiation:
 Phase-Locked Loop
 Zero-Crossing Detection
 FM-to-AM Conversion
 Phase-Shift or Quadrature Detection

5. 5
DEMODULATION OF FM SIGNAL
1 - filter the signal in order to eliminate all
noise outside of the signal band. Broadcast
FM signals are filtered by a band-pass filter
prior to transmitting.
2 - Modulated FM signal is to pass it through a
limiter. This will restrict the signal amplitude
to the range -VL to +VL . The output is a
series of nearly rectangular pulses.
3 - low-pass filter eliminates the higher
frequency components from these pulses to
obtain a signal which very closely resembles
the transmitted FM signal:

6. 6
ENVELOPE DETECTION CIRCUIT.
Diode
C
R2
R1
RS( t ) Sf ( t )
Operational
Amplifier
Low-pass
filterHalf-wave
rectifier
Sr ( t )

7. 7
HALF-WAVE RECTIFICATION AND FILTRATION OF DSBTC
AM SIGNAL.
Baseband signal Sm ( t )
Modulated signal S ( t )
Rectified signal Sr ( t )
Filtered signal Sf ( t )

8. 8
CIRCUIT DIAGRAM OF THE LOW-PASS
FILTER.
86
10to10;   ggeeout
C
R2
R1
eout
Operational
Amplifierein RΣeΣ
-g
Σ

9. 9
BLOCK DIAGRAM OF SYNCHRONOUS
DEMODULATOR.
Sm ( t )
Sc ( t )
S ( t ) Multiplier
Low-pass
filter
Sdemod( t )

10. 10
DEMODULATION BY ZERO CROSSING
DETECTION
 Zero crossing detector
 Positive voltage.
 Negative voltage.
 Pulse generator.
 low-pass filter.
 The advantage of zero crossing detection
(and FM-to-AM conversion) is that no source
of the carrier frequency is required to
demodulate the signal. A digital signal can
easily be recovered from a FM signal in this
manner.
 Decoding an analog signal may be difficult by
this method, since the signal at the low-pass
filter output does not closely resemble the
baseband signal.

11. THANKS TO ALL
Presented by
Sadman-al-farabe(131-33-1234)
Md.Monir Hossain(131-33-1317)
A.M Jehadul Islam(131-33-1256)
Humayun kabir khan(131-33-1259)
Shahinuzzaman Rajon(131-33-1225)
DAFFODIL INTERNATIONAL UNIVERSITY
ELECTRICAL AND ELECTRONICS
ENGINEERING