33.11 A Hybrid Recording System with 10kHz-BW 630mVPP84.6dB-SNDR 173.3dB-FOMSNDRand 5kHz-BW 114dB-DR for Simultaneous ExG and Biocurrent Acquisition

Abstract

As the precise acquisition of continuous ExG (ENG, ECG, etc.) and biocurrent (chemical, PPG, etc.) signals provides further insights into chronic health conditions [1,2], a lowpower readout system capable of simultaneously recording ExG and biocurrent signals with high precision is beneficial (Fig. 33.11.1(a)). Such a system requires BW>5kHz, noise floor ~100nV/√Hz, and FOMSNDR>170dB to cover the entire ExG spectrum. Also, an input range (IR)>100mVPP is necessary to prevent saturation. Likewise, for biocurrent acquisition, a system has to meet BW>1kHz, noise floor ~1pArms/√Hz, and DR>100dB to detect small charge perturbations without saturation from large baseline currents. Extensive effort has been conducted to design a simultaneous V & I monitoring system (Fig. 33.11.1(b)). For instance, [1] allows the design of a simultaneous V & I monitoring system based on simple integration of individual readout schemes. However, this system consumes power >100μW and is unsuitable for simultaneous ExG and biocurrent signals due to the limited BW. Although [2] achieves wide BW for both signals, it cannot record V & I simultaneously due to the time-division manner and also has narrow IRs. On the other hand, [3] employing frequency division, achieves simultaneous readout while consuming low power. However, it is vulnerable to artifacts, while the BW of each V & I readout limits the other. This paper presents a simultaneous V & I recording system using a single 2nd-order continuous-time ΔΣ modulator (CT-DSM). Such simultaneous recording is achieved by using a highly linear hybrid GmC integrator with a triplet VCObased quantizer, where the differential voltage and single-ended current are combined into differential and common mode signals (Fig. 33.11.1 (c)).