Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – With auxiliary means to condition stimulus/response signals
Patent
1989-11-01
1991-07-02
Wieder, Kenneth A.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
With auxiliary means to condition stimulus/response signals
324607, G01R 2506
Patent
active
050288741
ABSTRACT:
A noise rejection circuit improves the signal-to-noise ratio of a ratiometric measurement circuit. A first operational amplifier produces a scaled-up voltage proportional to a low reference voltage. The scaled-up voltage is applied to a series connected reference resistance, whose value is known, and a resistance whose value is unknown and is to be measured. A parameter voltage formed across the resistance is applied to second operational amplifier acting as a buffer. A buffered parameter voltage is scaled down by a voltage divider. The scaled-down voltage is applied to a ratiometric converter, that produces an output representative of the unknown resistance value. The ratio of a first pair of resistors that determines the gain of the first operational amplifier is the same as the ratio of a second pair of resistors that form the voltage divider, such that the low reference voltage is scaled up and the parameter voltage is scaled down by the same factor. The ratiometric converter operates from a low power supply voltage and consumes low amounts of power. The first and second amplifiers are CMOS operational amplifiers that, despite operating from a relatively high power supply voltage, consume low amounts of power.
REFERENCES:
patent: 3895376 (1975-07-01), Uchida
patent: 4187459 (1980-02-01), Wolfendale
patent: 4263653 (1981-04-01), Mecklenburg
patent: 4608553 (1986-08-01), Ormond
patent: 4748399 (1988-05-01), Caldwell et al.
patent: 4816745 (1989-03-01), Schneider
John Fluke Mfg. Co. Inc.
Koske Richard A.
Mueller Robert W.
Wieder Kenneth A.
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