The design of a chopped current-feedback instrumentation amplifier

This paper presents the design of a chopped fully-differential current-feedback instrumentation amplifier (CFIA). The current-feedback topology facilitates ground sensing and the use of independent input and output common- mode voltages. The amplifier is intended for the readout of a high-precision thermistor bridge. The required temperature sensing resolution is 1 muK (3sigma) in a 3 mHz - 50 mHz bandwidth, which translates to an input referred noise density of 31nV/VHz. Since these frequencies are very low, the input stages of the amplifier are chopped to suppress their 1/f noise. Moreover, to achieve optimum power efficiency at low noise, the first stage is designed to dissipate the most power (75%). Simulations show that the amplifier´s input-referred noise density is 17 nV/VHz at a supply current of 226 muA. The amplifier has been implemented in 0.7 mum CMOS technology.