A Stable 24 A, 100 kHz Transconductance Amplifier

A transconductance amplifier was constructed as part of a trilateral South American project to develop a reference system for measuring electric power. The amplifier can convert a 4 V signal voltage applied to its input into a ground-referenced stable current up to 24 A rms (with ±7 V rms compliance voltage) over a frequency range from dc to 100 kHz. It is based on a design conceived in the 1990s where a number of precision bipolar voltage-to-current converters are paralleled. The present design version includes Vishay Z-Foil resistors (VTA) with low TCR in all critical circuit nodes to increase the output current stability. The amplifier short-term magnitude and phase stability are respectively a few parts in 10
⁶
from de to 100 kHz and less than one microradian at power frequencies.