Passive network as a complex-voltage generator in four quadrants

Abstract

In single-channel and multichannel measurement systems, operating at an audio or low radio frequency, it is often necessary to adjust either the polar or cartesian components of the voltage in one or more of the channels to establish an initial set of conditions. A passive network is described that provides independent and precise control of the real and imaginary components of its output voltage. It can also be used as a generator of a complex voltage in any of the four quadrants with similar control of the cartesian components from a zero condition. Alternatively, if the real and imaginary components of the network's output are fed to a suitable sine/cosine potentiometer, the output voltage can be adjusted continuously in phase with constant modulus, and the latter parameter can be controlled independently by means of an attenuator. A brief description is given of the results obtained with an experimental network that was constructed to prove the theory at 1 MHz. A modified Kelvin-Varley voltage divider is also described that provides equal voltage increments with a constant voltage overlap between adjacent steps. If three capacitors in the network are switched, then it can be made to cover at least three decades in frequency. It is suggested that, for the frequency range from 50 Hz to about 50 kHz, when operating in the complex-voltage-generator mode, it could replace the mutual inductance of the conventional quadrant potentiometer. Also, in the case of multiport network analysers, operating at a fixed intermediate frequency, it could be used as an analogue vector voltmeter, in which the generated voltage is nulled against the network's response voltages. A further possible application is to precision inductance voltage dividers for either error-signal cancellation or the intercomparison of dividers of this type.