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.

Abstract: A transconductance amplifier for emitting an output current that is a replica of a input voltage has its accuracy enhanced by a current comparator having a first magnetic core, a second magnetic core, a pair of ratio windings electromagnetically coupled with both the cores, and a detection winding electromagnetically coupled with the first core but not with the second core. A first of the ratio windings is connected in series with the output current of the transconductance amplifier. A high value resistor is connected in series with the second of the ratio windings across the input voltage of the transconductance amplifier whereby the current in the second ratio winding accurately reproduces the waveform of the input voltage. A further amplifier has its input connected to the detection winding. The output of this amplifier is so connected as to add a correcting current to the output current of the transconductance amplifier and thus provide the necessary accuracy enhancement.

Abstract: A current ratio device for use in constructing a current transformer comprises a first magnetic core, a second magnetic core, a measuring winding electromagnetically coupled with the first core but not with the second core, and a compensating winding electromagnetically coupled with both cores. An externally powered amplifier has its input connected to receive the voltage waveform across the measuring winding. Its output provides a compensating current through the compensating winding equal to a magnetizing current required to magnetize the second core. The amplifier output also provides a measuring current through the measuring winding in the direction opposite that of the compensating current and equal to the compensating current multiplied by the ratio of turns in the compensating and measuring windings.