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PCM Encoder

IP.com Disclosure Number: IPCOM000084270D
Original Publication Date: 1975-Oct-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 68K

Publishing Venue

IBM

Related People

Vautier, R: AUTHOR

Abstract

As long as comparators were expensive, it was preferable to use serial encoders with a single comparator to convert a voltage level Vx into a digital PCM code. Such a way was not expensive but sacrificed the coding speed. Now, integrated comparators which discriminate a voltage level from the ground allow a cost reduction.

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PCM Encoder

As long as comparators were expensive, it was preferable to use serial encoders with a single comparator to convert a voltage level Vx into a digital PCM code. Such a way was not expensive but sacrificed the coding speed. Now, integrated comparators which discriminate a voltage level from the ground allow a cost reduction.

The present PCM encoder ensures the conversion of voltage Vx into the PCM code in three steps. The sign is first determined by one comparator, not shown, during the first step. According to the sign of Vx, switches 10 and 11 are set in a high or a low position depending on whether Vx is negative or positive.

In the second step, the characteristic is determined by a nonlinear ladder voltage divider 12 having an input end connected to a constant-current source I and the other input end connected to a constant-current sink I, the two connections being switched according to whether the sign is positive or negative.

Voltage level Vx is connected to the ladder input end without resistors. The current flows through resistors R of the ladder 12, thus causing potential drops between the nodes. Therefore, the nodes of the ladder 12 are at different voltage levels, geometrically decreasing from the node connected to the current source to the one connected to the current sink, some of them being at a positive voltage and the other ones being at a negative voltage. With each node being connected to a comparator which discriminates voltage levels from the ground, only certain comparators have their output up. The outputs of the comparators are delivered to decode unit 13, which provides the three bits of the characteristic corresponding to the segment number.

The four bits of the mantissa are provided bg a linear ladder voltage divider
14. The latter has its input ends, respectively, connected to a constant-current source and to a constant-...