Amplifiers – Modulator-demodulator-type amplifier
Patent
1993-07-07
1994-10-18
Mullins, James B.
Amplifiers
Modulator-demodulator-type amplifier
330196, 330197, H03F 126
Patent
active
053572106
ABSTRACT:
A transconductance amplifier circuit employs the known combination of a transconductance amplifier and a current comparator (with or without a ratio extender, preferably in the form of a two-stage current transformer) to compare the output current from the transconductance amplifier with that flowing through a reference resistor, both these currents having been derived from the same alternating input voltage. A current corresponding to the unbalanced ampere-turns in the current comparator is used to produce a feed-forward error signal that is used to modify the output of the transconductance amplifier. The invention is characterized by an output transformer that has coaxial inner and outer toroidal magnetic cores, and primary and correction windings outside the outer core. This primary winding receives the output current from the transconductance amplifier and the correction winding receives the error signal. A winding located between the cores detects the error current in the output transformer (its magnetizing current), and injects this error current into the current comparator. The secondary of the output transformer can be a single turn conductor extending through the hole formed by its toroidal cores. The result of this circuit arrangement is that the output current in the secondary of the output transformer follows the amplitude and phase of the input voltage with a very high level of accuracy.
REFERENCES:
patent: 3656831 (1972-04-01), Seidel
patent: 3810256 (1974-05-01), Van Doorn
patent: 4795969 (1989-01-01), So
patent: 4884038 (1989-11-01), Miljanic
So, "A Current-Comparator-Based Load Loss Standard For In-Situ Calibration of Transformer Loss Measuring Systems", IEEE Transactions on Power Delivery, vol. 3, No. 4, Oct. 1988.
Miljanic, "Calibrator for Alternating Voltage, Current and Power", IEEE Transactions on Instrumentation and Measurement, vol. 38, No. 2, Apr. 1989.
Miljanic et al., "High Precision Range Extenders for an AC Calibrator up to 600 V and 100 A", IEEE Transactions on Instrumentation and Measurement, vol. 40, No. 2, Apr. 1991.
Miljanic Petar N.
So Eddy
Anderson J. Wayne
Mullins James B.
National Research Council of Canada
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