Write short note on PCM ( Pulse Code Modulation).
Figure shows the basic block diagram of pulse code modulation scheme. The main elements of the PCM systems is
Transmitter:
The transmitter of the circuit consists of incoming analog message signal, Low Pass Filter (LPF), Sampler, Quantizer and Encode. The base band signal first of all passes through the low pass filter to avoid aliasing effect and converted to the band limited signal. The sampling is the operation in which an analog signal is sampled according to the sampling theorem resulting in a discrete – time signal. The quantizing and encoding operations are usually performed in the same circuit which is known as an analog to digital converter (ADC).
Transmission path (Channel):
Transmission channel is contained only regenerative repeater circuit which performs important operation. The signal amplification, noise elimination and regenerate the original signal all are performed by the regenerative repeater circuit.
Fig.12 Basic Pulse Code Modulation (PCM) technique
Receiver:
The essential operations in receiver are regeneration of impaired signals, decoding and demodulation of the train of quantized samples. These operations are usually performed in the same circuit which is known as a digital to analog converter (DAC). The PCM allows the use of regenerative repeaters. This improves its noise performance. PCM allows the transmission of analog signals in the form of digital signal.
What is Carson’s rule? Explain it.
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