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Explain PCM encoder and PCM decoder with block diagram.

PCM stands for pulse code modulation, which is a digital modulation technique as against PAM, PWM, PPM which are analog.

PCM wave has digital pulses with constant amplitude width and position.

The information is transmitted in form of ‘code words’

The analog s/g x(t) is passed through a band-limiting LPF which has a cutoff frequency Fc = w(Hz)

The band limited s/g is applied to a sample and hold ckt to give sampled o/p

These samples are then quantized through the quantizer.

The quntized PAM pulses are applied to an encoder which is basically an A to D converter.

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

A PCM noise contaminated s/g is available at the $Rx^r$ i/p

The re-generator ckt at $Rx^r$ separates the PCM pulses from noise and reconstructs the original s/g

The pulse generator operates in sync with the $Tx^r$ to get a clean PCM

Re construction is possible sue to digital nature of PCM.

o/p of serial to parallel converter is applied to the decoder which is a D/A converter.

The quantized PAM s/g is passed through low pass filter to recover the analog s/g

The LPF is called as the reconstruction filter and its cut off frequency is equal to the band width ‘W’

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