OR
Block diagram of PCM transmitter
The analog signal x (t) is passes through band limiting / low pass filter, which has a cutoff frequency fc=W Hz. This will ensure x (t) will not have any frequency component higher than “W”. In other words, suppresses high frequency components and passes only low frequency signal to avoid „aliasing error‟.
The band limited analog signal is then applied to sample and circuit where this circuit acts as modulator and both modulating input signal and sampling signal with adequately high sampling rate are inputs to this circuit. Output sample and hold block is a flat topped PAM signal.
These samples are subjected to operation “quantization” in the “quantizer”. The quantizer is used to reduce effect of noise. Quantization is a process of approximation of the value of respective sample in to a finite number that will reduce data bits. The combined effect of sample and quantization produces is „Quantized PAM‟ at the quantizer output.
The Quantized PAM output is analog in nature. So to transmit it through digital communication system the quantized PAM pulses are applied to an encoder which is basically A to D convertor. Each quantized level is converted into N bit digital word by A to D converter.
The communication system is normally connected to each other using a single cable i.e. serial communication. But the output of ADC is parallel which cannot be transmitted through serial communicating links. So this block will convert the parallel data into serial stream of data bits.
A pulse generator produces train of rectangular pulses of duration “t” seconds. This signals acts as sampling signals for the sample and hold block. The same signal acts as “clock” signals for parallel to converter .the frequency “f” is adjusted to satisfy the criteria.