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Technique for Accurate Measurement of Remote Signals Beyond Supply Rails

IP.com Disclosure Number: IPCOM000110109D
Original Publication Date: 1992-Oct-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Seastrand, NC: AUTHOR [+2]

Abstract

Disclosed is a mechanism for signal conditioning that allows for a very accurate, simple and calibration-free measurement of analog signals beyond the supply voltages.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 73% of the total text.

Technique for Accurate Measurement of Remote Signals Beyond Supply Rails

       Disclosed is a mechanism for signal conditioning that
allows for a very accurate, simple and calibration-free measurement
of analog signals beyond the supply voltages.

      Using a precision reference in shunt mode (see the figure) with
a series precision resistor, the A/D converter measures the voltage
drop across the resistor which is a result of subtracting a precise
voltage from the sense lines.  This results in a very accurate
shifting of the voltage in the area of interest down to a level
easily measured by the A/D converter.

      In the example shown, a 10 V precision reference is used for 12
V measurements.  This technique is easily extended to any voltage,
positive or negative.  The device used provides an A/D measurement
window of .8 V to 3.2 V.  The full 2.4 V range can now be
measured. Using a 10-bit A/D converter would result in a resolution
of 3.65 mV.  Given the accuracy of the A/D converter to be  one
half a least significant bit, the A/D converter would measure to
within 1.8 mV.  This error combined with the 10 V reference error of
10 mV (maximum) and .5 mV thermal drift results in a maximum of 12.3
mV error in the measurement.  With the excellent load regulation of
the 10 V reference and being connected in shunt mode with a precision
resistor, the effect of thermal/voltage changes associated with the
resistor are negligible.
ADVANTAGES:
1)   High Accu...