Explain PCM in detail

Subject: Computer Engineering

Topic: Electronic Circuits and Communication Fundamentals

Difficulty: Medium / High


The transmitter converts the message sig x (t) into a series of coded pulses of coded pulses and sends it over the communication channel

The transmitter is also called as an encoder.

The receiver performs exactly in reverse way as compared to the transmitter, it will convert the received encoded PCM pulses back into the message signal.

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The analog signal x (t) is passed through a band limiting low pass filter, which has a cut-off frequency. fc = wHz. This will ensure that x (t) will not have any frequency. component higher than “w”. This will eliminate the possibility of aliasing.

The band limited analog signal is then applied to a sample and hold circuit where it is sampled at adequately high sampling rate. Output of Sample and hold block is a flat topped PAM signal

These samples are then subjected to operations called “quantization” in the “quantizer”, Quantization process is process of approximations.

The quantized PAM pulses are applied to an encoder which is basically an A to D converter. Each quantized level is converted into an N bit digital word by A to D converter. The value of N can be 8,16,32,64, etc

The encoder o/p is converted into a stream of pulses by the parallel to serial converter block.

A pulse generator produces a train of rectangular pulses with each pulse of duration “T” sec. The frequency of this signal is “fs” Hz. This signal acts as a sampling signal for sample and hold block. The same signal acts as “clock “signal for the parallel to serial converter. The frequency. “fs” is adjusted to satisfy the NY Quist criteria.


The waveforms at various points in PCM transmitter are shown

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