Optimised Preamplifier for LF-Noise MOSFET Characterization

A modular design of preamplifier for low frequency noise measurements with interchangeable first stage was chosen to improve reliability and to reduce the influence of connection cables on measurement results. In this communication we present the optimised preamplifier modules as the first stages for MOSFETs gate leakage and drain current noise measurements with input impedance 50 Ω – 108 Ω in the frequency range 1.0 Hz — 105 Hz. The best available commercial operational amplifiers (OPA’s) AD549, OPA637 and LT1028A were used for the first stage module at each of the three chosen impedance ranges. The noise characteristics of different OPA’s, which have been tested, are also presented.