Balanced transconductance amplifier for precision comparison of AC/DC thermal current convertors

A supplying system for precision comparison of AC/DC thermal convertors is described, which produces an AC or DC current proportional to an input voltage and drives the electrical potential at the conjunction point of the series of the two convertors under comparison to the ground potential. A first implementation of the system for currents up to 3 A and frequencies up to 100 kHz, with two sections acting as a differential wideband, low-distortion instrumentation amplifiers and a suitable feedback circuit, has been tested. Experimental results on the device show that the fundamental component of the voltage at the conjunction point of the two convertors can be easily kept within 10 mu V with respect to the ground potential.