Pulse Code Modulation (PCM)

Objective of Pulse Code Modulation
Block Diagram of PCM
Process of PCM
Sampling
Quantization
Encoding
PCM Standards
Bit Rate and Bandwidth in PCM
Advantages and Disadvantages of PCM
Applications of PCM

1. Pulse Code Modulation (PCM)
Dr.ArunChokkalingam
Professor
Department of Electronics and Communication
RMK College of Engineering and Technology
Chennai.
1
Digital Communication

2. Learning Outcome
At the End of this session youwill be able to
Understand the importance and operation of PCM
2

3. Outline
•Objective of Pulse Code Modulation
•Block Diagram of PCM
•Process of PCM
Sampling
Quantization
Encoding
•PCM Standards
•Bit Rate and Bandwidth in PCM
•Advantages and Disadvantages of PCM
•Applications of PCM
3Dr.C.Arun, Professor, ECE, RMKCET, Chennai

4. Objective of PCM
•Pulse-code modulation(PCM) is a method used to covert analog
signal into digital data.
4Dr.C.Arun, Professor, ECE, RMKCET, Chennai

5. PCM Block Diagram
5
Audio signal 20-20kHz
fc = 20kHzSampling Rate fs=2x20kHZ=40KHz
Aliasing filter
Dr.C.Arun, Professor, ECE, RMKCET, Chennai

6. PROCESS of PCM
6
Continuous time
continuousamplitude
Discrete time
continuousamplitude
CommunicationSystems
6 PulseModulation
Discretetime
discreteamplitude
Max freqof Audio Signal in
Telephone line fm=4kHz
Sampling rate for telephone voice communication
Fs=2x4kHz=8KHz (8000 samples/ Sec)
No. of quantization levels for
Telephone voice communication is
256 levels
Dr.C.Arun, Professor, ECE, RMKCET, Chennai

7. 0000
1111
1110
1101
1100
1011
1010
1001
0001
0010
0011
0100
0101
0110
0111
A brief about ADCs or PCM
0000 0110 0111 0011 1100 1001 1011
Numbers passed from ADC to computer to represent analogue voltage
Resolution=
1 part in 2
n
7V
6V
7.4V
Quantization Error=7.4-7=0.4
Dr.C.Arun, Professor, ECE, RMKCET, Chennai
7

8. PCM Standards
8Dr.C.Arun, Professor, ECE, RMKCET, Chennai

9. BIT RATE AND BANDWIDTH
REQUIREMENTS OF PCM
Dr.C.Arun, Professor, ECE, RMKCET, Chennai 9

10. Dr.C.Arun, Professor, ECE, RMKCET, Chennai 10
We want to digitize the human voice. What is the bit
rate, assuming 8 bits per sample?
Solution
Thehumanvoicenormallycontainsfrequenciesfrom0
to4000Hz.Sothesamplingrateandbitrateare
calculatedasfollows:
Bandwidth B= ½ ( bit rate) = 32kbps
Example

11. To Improve quality of Message Signal at
Rx
•Increasing Sampling rate
•Increasing no. of quantization levels will reduce
quantization error
•Increasing sampling rate and quantization levels will
demands more bit rate and Bandwidth.
Dr.C.Arun, Professor, ECE, RMKCET, Chennai 11
f
s> 2f
m

12. Advantages of PCM
1.It is robust against noise and interference.
2.Uniform transmission Quality.
3.Efficient SNR and bandwidth trade off.
4.It provides Secure Data Transmission.
5.It offers efficient re-generation.
6.It is easy to add or drop channels.
12Dr.C.Arun, Professor, ECE, RMKCET, Chennai

13. Disadvantages of PCM
1.Large bandwidth is required for transmission.
2.More attenuation.
3.The difference between original analog signal and translated
digital signal is called quantizing error.
4.Encoding, decoding and quantizing circuit of PCM is very
complex.
13Dr.C.Arun, Professor, ECE, RMKCET, Chennai

14. Applications of PCM
1.It is used in Telephone Voice Communication.
2.It is used in Compact Disc (CD)
3.PCM is used in the satellite transmission system.
etc..
14Dr.C.Arun, Professor, ECE, RMKCET, Chennai

15. Thank you
Dr.C.Arun, Professor, ECE, RMKCET, Chennai 15