33.11 A Hybrid Recording System with 10kHz-BW 630mVPP 84.6dB-SNDR 173.3dB-FOMSNDR and 5kHz-BW 114dB-DR for Simultaneous ExG and Biocurrent Acquisition

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 low-power 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>5 kHz, an input range (IR) >100 mV VPP is necessary to prevent saturation. Likewise, for biocurrent acquisition, a system has to meet BW>1 kHz, noise floor ~ 1 pAᵣₘₛ/√Hz, and DR>100 dB 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 >100 μ W 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 2 nd -order continuous-time Δ Σ modulator (CT-DSM). Such simultaneous recording is achieved by using a highly linear hybrid G <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> C integrator with a triplet VCO-based quantizer, where the differential voltage and single-ended current are combined into differential and common mode signals (Fig. 33.11.1 (c)).