A 99.8-nV/√Hz ΔΣ Modulator with an Input-Impedance-Boosted kT/C-Noise-Cancellation Integrator for Biopotential-Signal Acquisition

This paper presents a low input-referred-noise (IRN) discrete-time (DT) delta-sigma modulator (DSM) for precise biopotential-signal acquisition. The proposed structure utilizes a 1<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup>-order input-impedance-boosted kT/C-noise-cancellation integrator combined with a 2<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup>-order noise-shaping SAR (NS-SAR). The proposed integrator cancels the kT/C noise generated during the sampling and integrating phases by using feedback capacitors for the cancellation loop while boosting the input impedance. This novel integrator can utilize smaller capacitors for sampling and integration than the standard design without any performance degradation. A single amplifier in the integrator is reused for sampling, kT/C noise cancellation, and integration to reduce power consumption. The NS-SAR is utilized instead of an amplifier-based multistage integrator structure to attain high resolution while maintaining low power consumption. The prototype IC, simulated using a 65-nm CMOS process, achieves a 90.5-dB SNDR across a 1-Hz-to-1-kHz bandwidth with a 300-mV<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PP</inf> input, yielding a 99.8-nV/$\sqrt {{\text{Hz}}} $ IRN and a FoM<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SNDR</inf> of 173.4 dB. These results indicate that the proposed DSM can properly acquire biopotential signals from both muscular and cardiac sources.