What Is PCM (Pulse Modulation Systems)?


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A series of regularly recurring pulses is made to vary in amplitude, duration, shape, or time as a function of the modulating signal

Used to transmit both analog and digital information, such as voice and data.The analog signal is sampled, digitized and encoded into a digital pulse stream.If the signal is already is in digital form, it may be encoded into a digital pulse train.

 Initially invented by A.H. Reeves in 1937
 Pulse Code Modulation is the representation of a signal by a series of digital pulses firstly by sampling the signal, quantizing it and then encoding it.
 The PCM signal itself is a succession of discrete, numerically encoded binary values derived from digitizing the analog signal.
PCM Steps
 Sampling
– Nyquist sampling rate theorem
 Quantizing
– Uniform and non uniform
– A- Law and m- Law
 Encoding
– Binary sequences.

Pulse Modulation Examples
 Pulse-amplitude modulation (PAM)
 Delta modulation (DM)
 Pulse-width modulation (PWM)
 Pulse-code modulation (PCM)
 Pulse-position modulation (PPM)
 Noise immunity
 Inexpensive digital circuitry
 Can be time-division multiplexed with other pulse modulated signals
 Transmission distance is increased through the use of regenerative repeaters
 Digital pulse streams can be stored.
 Error detection and correction is easily implemented
 Require a much greater bandwidth to transmit and receive than its analog counterpart
 Special encoding and decoding techniques may be necessary to increase transmission rates making the pulse stream more difficult to recover.
 May require precise synchronization of clocks between the transmitting and the receiving stations

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