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AN ANALOG TO DIGITAL CONVERTER WITH VARIABLE THRESHOLD DETECTION

IP.com Disclosure Number: IPCOM000007173D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2002-Mar-01
Document File: 4 page(s) / 200K

Publishing Venue

Motorola

Related People

Jaswinder S. Jandu: AUTHOR

Abstract

This article deals with a modified A/D converter (30) which is used to determine whether an analog input signal has exceeded a programmable thresh- old voltage. The A/D converter (30) can be used to check an input voltage against an upper bound or against a lower bound without the aid of a central processing unit (CPU) (12). As a result, the CPU (12) does not need to service the A/D converter (30) after every conversion. Instead, the CPU (12) only needs to service the A/D converter (30) after the A/D converter (30) has detected that a threshold has been exceeded.

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Technical Developments Volume 22 June 1994

AN ANALOG TO DIGITAL CONVERTER WITH VARIABLE THRESHOLD DETECTION

by Jaswinder S. Jandu

This article deals with a modified A/D converter
(30) which is used to determine whether an analog input signal has exceeded a programmable thresh- old voltage. The A/D converter (30) can be used to check an input voltage against an upper bound or against a lower bound without the aid of a central processing unit (CPU) (12). As a result, the CPU
(12) does not need to service the A/D converter (30) after every conversion. Instead, the CPU (12) only needs to service the A/D converter (30) after the A/D converter (30) has detected that a threshold has been exceeded.

  In most existing data processing systems utiliz- ing an A/D converter, the central processing unit (CPU) must perform any required boundary checking. The CPU performs this boundary checking by retrieving the converted digital value from the A/D converter and by comparing the converted dig- ital value to a binary number representing the upper bound or to a binary number representing the lower bound.

  On the other hand, a modified A/D converter itself, without the aid of a CPU, can be used to deter- mine whether an analog input signal has exceeded a specified threshold. Thus a modified A/D con- verter can be used to check an analog input voltage against an upper bound or against a lower bound without the aid ofa CPU. As a result, the CPU does not need to service the A/D converter after every conversion. Instead, the CPU only needs to service the A/D converter after the A/D converter has detected that a threshold has been exceeded. Thus, in many applications using an A/D converter, the "threshold detection" performed by the modified A/D converter replaces the need for a CPU to perform a "boundary check" on the converted digital values the CPU retrieves from the A/D converter.

  Instead of merely adding considerable circuitry to the A/D converter in order to perform a bound- ary check, the modified A/D converter allows the

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boundary check to be performed utilizing the preexisting A/D converter circuitry, with only minor modifications and additions.

  The user of the modified A/D converter is able to program the value of the threshold voltage. In addition, the user of the modified A/D converter is able to change the value of the threshold voltage. The threshold voltage is selected from a set of dis- crete voltages within a predefined range. The predefined range of values of the threshold voltage is dependent upon the number of binary bits in the converted digital value, and is also dependent upon the voltage references VREM (voltage reference high) and VREFL (voltage reference low).

Figure 1 illustrates a digital data processing system
10. Figure 2 illustrates an analog to digital converter (A/D converter) 30 of Figure 1. Figure 3 illustrates the bit fields of the control and result register 44 of Figure 2. Note that bits O...