This document discusses digital communication systems and pulse code modulation (PCM). It outlines the key elements of a digital communication system including sampling, quantization, and coding techniques. The main advantages of digital communication systems are that they are less affected by noise, more reliable, and easier to design than analog systems. PCM is described as a method to convert analog signals to digital for transmission. The main elements of PCM are low-pass filtering, sampling, quantization, encoding, decoding, and reconstruction filtering to convert the digital signal back to analog.

1. DIGITAL
COMMUNICATIONS
K.NAGAHANUMACHARI
ASST.PROFESSOR
RISE KRISHNA SAI GANDHI GROUP OF INSTITUTIONS

2. Outlines
• WHAT IS COMMUNICATION?
• ELEMENTS OF DIGITAL COMMUNICATION
SYSTEM
• ADVANTEGES OF DIGITAL COMMUNICATION
• ELEMENTS OF PCM
• SAMPLING,QUANTIZATION,CODING
TECHNIQUES.
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3. COMMUNICATION: The exchange/interchange of
information(data) between one point and another
point is simply called as communication.
Data could be: voice,video,text,codes etc..
The electronic equipments used for the
purpose of communication are called
communication equipments,when assembled
together forms a system called as
communication system
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4. Communication system
Examples:
• Line telephony
• Telegraphy
• Radio broadcasting
• Mobile communication
• Radar communication
• Satellite communication etc.
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5. ELEMENTS OF DIGITAL COMMUNICATION
SYSTEM
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6. 6
Techniques
NOISE

7. ADVANTAGES OF DIGITAL
COMMUNICATION SYSTEM
• The effect of distortion, noise, and
interference is much less in digital signals as
they are less affected.
• Digital circuits are more reliable( good in
quality or performance)
• Digital circuits are easy to design and cheaper
than analog circuits.
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8. • Digital communication gives facilities like
video conferencing which save a lot of time,
money and effort. It is easy to mix signals and
data using digital techniques. The digital
communication is fast, easier and cheaper.
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9. PULSE CODE MODULATION(PCM)
• Introduction:Pulse code modulation is a
method that is used to convert an analog
signal into a digital signal so that a modified
analog signal can be transmitted through the
digital communication network. PCM is in
binary form, so there will be only two
possible states high and low(0 and 1).
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10. PCM INPUT & OUTPUT
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11. • ELEMENTS 0F PCM/BLOCK DIGRAM OF PCM
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12. • Low Pass Filter
This filter eliminates the high frequency
components present in the input analog signal
which is greater than the highest frequency of
the message signal, to avoid aliasing of the
message signal.
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13. • Sampler
This is the technique which helps to collect the sample data at
instantaneous values of message signal, so as to reconstruct
the original signal. The sampling rate must be greater than
twice the highest frequency component W of the message
signal, in accordance with the sampling theorem.
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14. • Quantizer
Quantizing is a process of reducing the excessive bits
and confining the data. The sampled output when
given to Quantizer, reduces the redundant bits and
compresses the value.
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15. • Encoder
The digitization of analog signal is done by
the encoder. It designates each quantized
level by a binary code(The process of
assigning digital code to the quantized
sample is called as “encoding”). The sampling
done here is the sample-and-hold process.
These three sections LPF,Sampler,and
Quantizer will act as an analog to digital
converter.
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16. • Example for sampling,quantization and
encoding fig:1
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17. • Example for samplig,quantization and
encoding fig:2
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18. • SAMPLING,QUANTIZATION AND ENCODING
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19. • Regenerative Repeater
This section increases the signal strength. The output
of the channel also has one regenerative repeater
circuit, to compensate the signal loss and reconstruct
the signal, and also to increase its strength.
• Decoder
The decoder circuit decodes the pulse coded
waveform to reproduce the original signal. This circuit
acts as the demodulator.
• Reconstruction Filter
After the digital-to-analog conversion is done by the
regenerative circuit and the decoder, a low-pass filter
is employed, called as the reconstruction filter to get
back the original signal.
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20. • Reconstruction of input signal
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