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Addition of Two PCM Coded Voltages

IP.com Disclosure Number: IPCOM000085254D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

Peard, M: AUTHOR

Abstract

In communication systems it is sometimes necessary to make the addition of two frequencies. When the signals are pulse code modulated (PCM signals) the direct addition of the PCM signals provides a solution, which avoids conversion to the analog voltage or occupancy of a larger bandwidth on the transmission link. Addition of digital signals through a simple adder can be made only if the PCM signals are linearized, i.e., converted into full-binary signals. When the sum is achieved in the adder, the resulting signal is then delinearized to obtain a PCM signal again.

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Addition of Two PCM Coded Voltages

In communication systems it is sometimes necessary to make the addition of two frequencies. When the signals are pulse code modulated (PCM signals) the direct addition of the PCM signals provides a solution, which avoids conversion to the analog voltage or occupancy of a larger bandwidth on the transmission link. Addition of digital signals through a simple adder can be made only if the PCM signals are linearized, i.e., converted into full-binary signals. When the sum is achieved in the adder, the resulting signal is then delinearized to obtain a PCM signal again.

The PCM code is generally composed of eight bits: the first bit is the sign bit, the following three bits characterize the segment and the last four bits indicate the number of sixteenths within the segment considered.

The rule of linearization is the following: if the segment number S is 000 or 001 no change is made; if the segment number S is greater than 001, S-1 zeros are placed on the right of the sixteenth four bits and the three bits of the segment value are replaced by a single bit "1".

Hereafter are given, by way of an example, a number of PCM sample values, on the left, and their corresponding binary values, on the right. The sign bit has been omitted because it is not involved in the conversion: 000 0101 0 0101

001 0100 1 0100

010 0110 1 0110 0

011 0001 1 0001 00

100 0010 1 0010 000

101 0011 1 0011 0000

110 0101 1 0101 00000

111 1001 1 1001 000000.

The figure shows a logical circuit designed to realize the conversion. This circuit is used only when the segment is greater that 001, since for se...