Calibration of the Absolute Linearity of Lock-In Amplifiers

This paper describes the development of a system capable to calibrate the absolute linearity of lock-in amplifiers in their 1-μV range for frequencies between 20 Hz and 1 kHz. The system is based on cascaded inductive voltage dividers that have been especially designed to maximize their input impedance and to have minimal influence on the previous stage. The cascaded topology reduces the uncertainty for very large ratios (>1000:1) and reaches measurement uncertainties below 1 nV at 10 μV.