Hybrid Buffer Amplifier for AC-DC Difference Measurement Applications

This paper describes the design and testing of a hybrid buffer amplifier (HBA) with a theoretical gain error of less than 1 μV/V gain error and 60 μdeg phase error up to 20 kHz. The application of this amplifier is for use in ac-dc difference measurements such as unloading low amperage ac-dc current shunts and Josephson Arbitrary Waveform Synthesizers. Preliminary experimental results show the ac-dc difference errors less than (3±2) μV/V (k=2) for 200 Ω and 400 Ω impedances at a rms amplitude of 1 V, and less than (4±2) μV/V (k=2) for 50 Ω impedance at a rms amplitude of 2 V.