1. Pulse Amplitude Modulation and Pulse Code Modulation
oleh
Warsun Najib

2. Pulse Amplitude Modulation
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PAM-PCM

3. Demodulation of PAM Low Pass Band Pass *make sure that Sinc function
Low Pass
Band Pass
By using very narrow
*make sure that Sinc function
is big and flat by reduce time
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PAM-PCM

4. PAM-TDM before filtering
Multiplexing PAM-TDM
LPF
Clock
Pulse
generator
Sampler
switch
PAM1
PAM2
PAM-TDM before filtering
PAM-TDM to the
transmission line
Switch : determining the synchronization and sequence of the channels
Clock : determine the timing of the overall system
Pulse generator : produces narrow rectangular pulses to drive the sampler
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PAM-PCM

5. Nyquist Sampling For n channel Two signal are sampled equally
Tx=the time interval between adjacent channels or samples
For n channel
Nyquist interval
for one signal
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PAM-PCM

6. Bandwidth RequirementS1 S2 S3 S4 Tx BF
-BF
With condition of equal BW and sampling equally
therefore the Total BW Requirement is n x BW
If BW of each channel is not equal
Therefore the Total BW Requirement is n x largest BW
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PAM-PCM

7. Transmitting Analog signal in Digital format
Advantages
Immunity to noise : with some amount of noise digital can withstand while analog failed to provide virtually error free transmission.
Reduce signal to noise ratio
Error control coding ; parity check, Hamming code make more reliable
Signal can be completely regenerated at intermediate regenerator for long haul system.
More compatible with computer system for signal processing and digital memories for data storage.
More elaborate code can be used.
Ideal for integrated services digital network (ISDN)
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PAM-PCM

8. Pulse Code Modulation
m(t) is sampled, each sample value is rounded off to the nearest allowable value. This value is digitally encoded as a sequence of binary digits
There are three process of Digitization
1. Sampling
2. Quantization (devide into level of voltage)
The approximation of amplitude value of sinal m(t) into one of M discrete quantized values
3. Encoding
Each quantization level is encoded into N binary digits
Where N is the number of binary digit per code word
M is the number of quantization level
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PAM-PCM

9. Quantization V M Steps -V Sampling Signal Where M = no. of steps
= quantization step -V V t
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PAM-PCM

10. Encoding -V V t
000
001
010
011
100
101
110
111
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PAM-PCM

11. Quantization Error Quantization Noise Uniform distribution 29/12/61
Quantization Noise
Uniform distribution
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PAM-PCM

12. Signal to Noise Ratio The average power Time average Continuous RV
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PAM-PCM

13. Signal to Noise Ratio[1]
where
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14. Signal to Noise Ratio[2]
In dB
Encoding : each quantization level is encoded into N binary digit
No.of level
No.of binary digit
per code word
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PAM-PCM

15. TDM-PCM (E1 standard) voice (2x3.4k=6.8k) 300 3.4k 3.1k time 500 800
500
800
MAN
WOMAN
(2x3.4k=6.8k)
Nyquist
Each sample is quantized and encoded into 8 bits
Bit rate = x 8 = 64kbps ; with 32 channels
1channel = 8 bits therefore 8 x nsec = sec
Total bit length = 8 bit x 32 channels = 256 bits
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PAM-PCM