Demodulation (communication engineering)

Demodulation (communication engineering) presentation

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 - V L  to + V L  . 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.

7. 7 Half-wave rectification and filtration of DSBTC AM signal.

8. 8 Circuit diagram of the low-pass filter .

9. 9 Block diagram of synchronous demodulator .

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