28.4 A 400mVpp 92.3 dB-SNDR 1kHz-BW 2nd-Order VCO-Based ExG-to-Digital Front-End Using a Multiphase Gated-Inverted Ring-Oscillator Quantizer

Next-generation wearable devices will enable clinical-grade, continuous ExG (ECG, EEG, EMG, etc.) biopotential monitoring, providing medical professionals with valuable longitudinal data outside of hospital settings. These devices must be ultra-low power (<; 10μW) to enable long battery life while accurately digitizing sub-kHz, μV-level ExG signals in the presence of large motion and/or stimulation art ifacts (>100mV) with high input-impedance (Zin>10MΩ) to avoid signal attenuation. Achieving such performance with conventional PGA+ADC architectures is challenging due to the conflicting low-power and >90dB dynamic-range (DR) requirements [1]. To address this, several direct digitization analog front-ends (AFEs) have been reported [2-4]. While these offer wide DR, they typically have low input-impedance (<; 5MΩ) and/or low power-efficiency (FoM≤172dB). This paper presents a scalable 2nd-order voltage-controlled oscillator (VCO)-only ΔΣ ADC that achieves 92.3dB SNDR in a 1kHz bandwidth using a mismatch tolerant, multiphase gated-inverted ring-oscillator (GIRO) quantizer with dynamic powerscaling. The ADC uses an impedance-booster to maintain >50MΩ input-impedance over the entire bandwidth while consuming 4.25μW during nominal operation and 5.8μW in the presence of artifacts resulting in an FoM of 174.7dB.