Mumbai University > Computer Engineering > Sem 3 > Electronic Circuits and Communication Fundamentals

Marks: 10 Marks

Year: Dec 2015

1. The TDM-PCM system uses many codecs as shown in figure (a). the code is basically a PCM encoder (transmitter) and decoder (receiver).
2. Codec generates serial stream of PCM data.
3. At the receiver side, codec receivers serial PCM data and generates anolog signals.
4. The sampling frequency of PCM can be selected by external clock given to the codec. One codec per channel is used.
5. The outputs from various codec are combined by the multiplexer into a single bit stream.
6. This bit stream is converted to baseband waveform by line waveform generator.
7. The low pass filter band limits the baseband signal. The waveform generator to clear digital signal.
8. The Demux then detects individual channel signals and separates them. The codec then recover the required analog signal.
9. The multiple channel alignment is very important in TD/PCM system.
10. Figure (b) shows the TDM frame format of most widely used T1 system.
11. As shown in the figure (b), this system contains a multiframe of 12 frames. The duration of the multiframe is 15 msec. Each frame consists of samples from 24 channels.
12. Thus the samples of 24 channels are Time Division multiplexed.
13. Each channel sample is encoded into 8 bits.
14. Thus the total bits of 24 channels will be 24 x 8=192 bits.
15. This indicates the start of the next frame, the frame sync bit or ‘S’ bit is transmitted at the beginning of each frame. Thus the total bits in one frame are (24 x 8)+1=193 bits.