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Browse Prior Art Database

EXTENSION OF A/D CONVERTER RESOLUTION

IP.com Disclosure Number: IPCOM000006247D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2001-Dec-18
Document File: 2 page(s) / 95K

Publishing Venue

Motorola

Related People

Jeff Wright: AUTHOR [+2]

Abstract

The invention uses a digital to analog (D/A con- verter in conjunction with some simple circuitry in order to increase the resolution of a multi channel sin- gle analog to digital (A/D) converter. The invention is especially, but not exclusively, applicable to microcon- trollers where A/D and D/A (in the form of a PWM) elements are common but where the A/D often does not have enough resolution for the end application. High resolution A/D converters are of course avail- able, but they are expensive and so this idea may pro- vide a more cost effective solution for many applica- tions.

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MOTOROLA INC. Technical Developments Volume 13 July 1991

EXTENSION OF A/D CONVERTER RESOLUTION

by Jeff Wright and Jean-Claude Hamelain

INTRODUCTION

  The invention uses a digital to analog (D/A con- verter in conjunction with some simple circuitry in order to increase the resolution of a multi channel sin- gle analog to digital (A/D) converter. The invention is especially, but not exclusively, applicable to microcon- trollers where A/D and D/A (in the form of a PWM) elements are common but where the A/D often does not have enough resolution for the end application. High resolution A/D converters are of course avail- able, but they are expensive and so this idea may pro- vide a more cost effective solution for many applica- tions.

DESCRIPTION

  Fig. 1 shows a schematic of the invention. On a microcontroller the A/D and D/A would normally be on-chip peripherals, resulting in a minimum of exter- nal hardware. The idea is to use the D/A converter in conjunction with the amplifier to isolate and then amplify the error from the A/D converter so that it can then be measured on another channel of the A/D.

The source signal is first measured using A/D

channel 1. This will give a result with the resolution of the AiD converter (e.g. 8 bits). The limitation of the resolution of the AiD converter means that an error will have been introduced into this result. If this result is then used as the data for a D/A converter, the resul- tant analog signal can be subtracted from the original signal and the difference amplified into AiD channel
2. The signal reaching channel 2 is therefore the amplified error that resulted from the first conversion. This error signal can then be converted using the A/D and the result manipulated digitally with the first result in order to obtain a higher resolution representa- tion of the original signal (this could simply mean sub- tracting the error result from the original result). With two 8 bit converters and an amplifier gain of 256 this would result in a theoretical resolution of 16 bits. In practice however, limitations (in the amplifier linearity

0 Motorola. 1°C. ,991

or filtering of the D/A) may cost 1 or 2 bits of resolu- tion and it m...