External phase autozero loop to extend the voltage and/or current capabilities of a digital phase standard

Digital phase standards achieve their specified phase accuracy of ±0.005° by using an internal phase autozero circuit. It is shown how to increase the output current and/or output voltage capability of a phase standard by extending this phase autozero technique to include an external voltage amplifier and/or an external current amplifier within an external phase autozero loop. Voltages up to 1000 V and/or currents up to 1000 A are possible using available commercial equipment. The expanded output power capabilities of such a system can be used in the calibration or characterization of a number of different phase-sensitive devices. The authors review the problems involved in determining the phase errors in voltage and current phase-sampling circuits and provide illustrations of several uses of an external autozero loop for frequencies from 100 Hz to 100 kHz