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Elimination of Offset During Analog to Digital Conversion

IP.com Disclosure Number: IPCOM000087648D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Holloway, BL: AUTHOR

Abstract

If an analog quantity is converted to a digital value by means of a timing pulse variation, the resulting digital value may consist of the required signal variation superimposed on an offset value.

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Elimination of Offset During Analog to Digital Conversion

If an analog quantity is converted to a digital value by means of a timing pulse variation, the resulting digital value may consist of the required signal variation superimposed on an offset value.

The drawing shows a variable resistor 1 connected in the timing circuit of a single-shot 2. Single-shot 2 always produces an output pulse of some fixed duration (Y), and it is an additional duration (X) that is under control of variable resistor 1. The output pulse from single-shot 2 gates pulses of frequency (f) from oscillator 3 through AND gate 4 to counter 5. The resulting digital value in counter 5 is therefore the offset value (f.Y) plus signal variation value (f.X).

If Y is large compared with X, precision of the signal variation may be lost unless the offset is eliminated. The technique involves choosing a counting frequency such that the offset part of the single-shot pulse (Y) will overflow the counter by an exact multiple of the counter's length. Provided the counter will wrap around, it will be at zero at the start of the signal variation part of the pulse stream, and hence the digital value of the signal variation alone will appear in the counter. The following equations apply: f x Y = n x 1 f x m less than or equal to 1 where f is the frequency, Y is the offset portion of single-shot pulse, n is an integer, 1 is the counter length, and m is the maximum signal portion of single shot pulse.

For maxim...