A 95.9-dB SNDR 10-kHz BW 3rd-Order VCO-Based CT ΔΣ Modulator Using a Phase-Time Two-Step Quantizer

Capacitively-coupled continuous-time ΔΣ modulators (CC-CTDSMs) are widely used in precision bio-sensing applications such as ExG readout and neuromodulation for their low-noise and intrinsic anti-aliasing capabilities [1]–[7]. Growing demands in wearable and implantable bioelectronics drive CC-CTdSM designs to achieve better energy and hardware efficiency. Classic CC-CTDSMs employing SAR quantizers have demonstrated excellent performance [1]–[3], but they require a dedicated reference buffer for the SAR, which adds overhead on the system level. Time-domain architectures exploiting VCO-based quantizers are gaining popularity for several attractive merits, such as low-voltage compatibility, high-gain integration, intrinsic quantization, and intrinsic dynamic element matching (DEM). However, existing designs exhibit a few drawbacks. Firstly, achieving high quantizer resolution is challenging, as it requires exponential growth of hardware complexity (e.g., VCO tap numbers or free-running frequency), similar to flash/slope ADCs. Moreover, the intrinsic DEM is often forfeited if counting quantizer is used [4]–[7]. Secondly, when employing multiple VCOs, it requires back-and-forth time-to-voltage mapping, causing extra power and errors. While MASH can alleviate these issues [8], it introduces the problem of noise-leakage due to analog-digital filter mismatch.