Many sensors demand energy-efficient precision voltage sensing interfaces with low noise performance down to very low frequencies. Examples include micro Kelvin resolution temperature sensors for wafer stepper temperature stabilization [1] and others [2]. In many such applications, analog-to-digital conversion is inevitable, which mandates sampling. So far, sensor interfaces have demonstrated low offset drift using chopping/auto-zeroing while preserving the intrinsic SNR of the transducer by anti-aliasing filtering before sampling. Integration with a boxcar window, or boxcar sampling, is a particularly convenient way to realize anti-aliasing filtering in the sampling process [3]. However, implementations of the technique, due to their use of just a voltage-to-current converter whose output current is integrated over a time window, e.g. in a sigma-delta modulator [2], remain susceptible to gain drift resulting from either transcon-ductance or time window drift. Meanwhile, related work suggests that embedding the boxcar sampler in a feedback loop effectively removes this limitation [4]. Whereas the loop in [4] is closed electromechanically, the design presented here overcomes the same limitations by using a purely electrical feedback loop to establish a well-defined gain that is insensitive to boxcar sampler parameter drift.
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