Development of in-situ calibration method for current-to-voltage converters for high-accuracy SI-traceable low-DC-current measurements
George P. Eppeldauer, Howard W. Yoon, Dean G. Jarrett, Thomas C. Larason
For photocurrent measurements with low uncertainties, wide-dynamic range reference current-to-voltage converters and a new converter calibration method have been developed at the National Institute of Standards and Technology (NIST). The high feedback resistors of a reference converter were in-situ calibrated on high-resistivity, printed-circuit-board placed in an electrically shielded box electrically isolated from the operational amplifier using jumpers. The feedback resistors, prior to their installation, were characterized, selected, and heat treated. The circuit board was cleaned with solvents, and the in-situ resistors were calibrated using measurement systems for 10 kohm to 10 Gohm standard resistors. We demonstrate that DC currents from 1 nA to 100 microA can be measured with uncertainties of 40 x 10^-6 (k=2) or lower which are lower in uncertainties than any commercial device by factors of 10 to 30 at the same current setting. The internal (NIST) validations of the reference converter are described.