ADC non-linear errors correction in thermal diagnostics for the LISA mission

Low-noise temperature measurements at frequencies in the milli-Hertz range are needed in the LISA and LISA PathFinder (LPF). The required temperature stability for LISA is around 10 uK/sqrt(Hz) at frequencies down to 0.1 mHz. In this paper we focus on the identification and reduction of a source of excess noise detected when measuring time-varying temperature signals. This is shown to be due to non-idealities in the ADC transfer curve, and degrades the measurement by about one order of magnitude in the measurement bandwidth when the measured temperature exhibits drifts of uK/s. In a suitable measuring system for the LISA mission, this noise needs to be reduced. Two different methods based on the same technique have been implemented, both consisting in the addition of dither signals out of band to mitigate the ADC non-ideality errors. Excess noise of this nature has been satisfactorily reduced by using these methods when measuring temperature ramps up to 10 uK/s .