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Pulse Code Modulation to Delta Converter

IP.com Disclosure Number: IPCOM000078475D
Original Publication Date: 1973-Jan-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Beraud, JP: AUTHOR

Abstract

Pulse Code Modulation (PCM) is a coding method which provides at each sampling instant, a binary word describing the amplitude of the signal sampled at the sampling instant. Delta Modulation, rather than providing the signal amplitude at each sampling instant, provides a bit describing the change in signal amplitude in the interval between the sampling instant at which the bit is transmitted and the previous one.

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Pulse Code Modulation to Delta Converter

Pulse Code Modulation (PCM) is a coding method which provides at each sampling instant, a binary word describing the amplitude of the signal sampled at the sampling instant. Delta Modulation, rather than providing the signal amplitude at each sampling instant, provides a bit describing the change in signal amplitude in the interval between the sampling instant at which the bit is transmitted and the previous one.

In order to perform PCM to delta conversion, the converter shown in Fig. 1 subtracts two adjacent PCM words yielding a difference word, which is converted into a delta bit pattern.

The difference word is provided by a binary subtractor S, the input (-) of which is connected to a delay element T introducing a delay equal to the time interval between two consecutive PCM words. The difference word is stored in a shift register 1, which comprises as many delay elements t (t is one difference word bit delay) as there are bits in the difference word. In the shown example, the difference word comprises four bits, allowing the coding of fifteen different values -7 to +7. In a conventional manner, these four bits comprise one Sign bit and three bits describing the absolute value of this difference.

At READ time the difference word stored in shift register 1 is decoded by a set of six AND gates, in order to generate the corresponding delta bit pattern, as shown in Fig. 2.

A difference equal to zero is coded into an alternat...