Mumbai University > Information Technology > Sem 3 > Principles of analog and digital communication

Marks:- 5M

Year:- Dec 2015

PCM

• The short form of the Pulse Code Modulation is PCM. In PCM, the analog speech waveform is sampled and converted directly into a multibit digital code by an Analog to Digital converter. The digital code is stored in the memory and which is later re-called for the playback.

• In this type of modulation, analog data is sampled and quantized before being represented to digital binary form. Hence using PCM, continuous amplitude and continuous time signal waveform is converted into discrete amplitude and discrete time waveform.

DPCM

• The short form of Delta Pulse Code Modulation is DPCM. In DPCM, a multi-bit difference value is stored. A bipolar D/A converter is used for playback to convert the successive difference values to an analog waveform.

• Only a single bit is stored for each sample. This bit 1 or 0, represents a greater than or less than condition, respectively as compared to the previous sample. An integrator is then used on the output to convert the stored nit stream to an analog signal.

• Delta modulation refers to the procedure of encoding and thereby transmitting only the difference between consecutive samples instead of sending each of the samples themselves.

• This method is useful only when the variation in the amplitude of the signal is small, otherwise, it leads to a phenomenon called "slope overload".

• Pulse code modulation is the procedure where each of the levels of an analog signal is assigned a value closest to a quantizer level used to quantize the signal.

• Another method of PCM that can be confused with Delta Modulation is the D (differential) PCM. Here, the difference between the signals is encoded based on its magnitude