Excess current noise in amplifiers with switched input

A basic model for excess current noise in amplifiers with switched input is presented. Thermal noise in the input switches causes charge fluctuations in the amplifier input capacitance with a bandwidth much higher than the switching frequency. This wideband charge noise is undersampled by the switching process, leading to excess current noise with a spectral density proportional to temperature, capacitance and switching frequency. The model was verified using a test chopper operated at room temperature and liquid Nitrogen (77 K). Good agreement between theory and experiment was found.