Compensated high input impedance stage for the measurements of four terminals resistors up to 20 kHz

This paper describes the design of a high input impedance stage intended for the calibration, at LNE, of AC four terminals resistors up to 1 M Ω and for frequencies up to 20 kHz. The stage has been compensated in order to minimize the phase shift to less than a few μrad up to 10 kHz and less than 15 μrad up to 20 kHz. The phase shift and the gain errors have been determined with an uncertainty less than 2 μrad and 2 μV/V respectively.