Linearity Measurements on Critical Noise Thermometer Components

A method for measuring the nonlinearity of noise thermometer components was developed that reduces the demands on the test signal generator. The method was applied to characterize the preamplifier and analog-to-digital converter (ADC) of PTB's new noise thermometer. For the complete signal path, gain nonlinearities below about one part in 10
⁵
were experimentally demonstrated at input rms noise levels between 71 μV and 284 μV. It was further demonstrated that dither can reduce the ADC nonlinearity by at least one order of magnitude.