AC-DC transfer control loop of the PTB highly accurate AC power source

A multijunction thermal converter (MJTC) being used as the AC-DC transfer device within the control loop of a highly accurate AC power source is considered. A fast buffer amplifier for driving the low input impedance of the MJTC and a very-high-gain differential amplifier for comparing the MJTC output voltage to a DC reference voltage have been specially designed. The special requirements imposed on these amplifiers and how they are solved are described. The input buffer can operate from DC to several kilohertz with a transfer error of less than 1 p.p.m. and an input voltage of up to 10 V r.m.s. A fast-reversed, highly accurate DC signal with a period of about 100 ms can be used to eliminate the DC reversal difference without disturbing the regulation process. The MJTC output voltage can be measured with a sensitivity of about 5 nV (0.05 p.p.m.).<>