Continuous-Time Hybrid ΔΣ Modulators for Sub-μW Power Multichannel Biomedical Applications

The design of $\Delta \Sigma $ modulators for multichannel biomedical applications introduces challenges with high density and very low power consumption. While possible solutions in the form of VCO and passive integrator-based $\Delta \Sigma $ modulators have been reported, these modulators suffer from limited resolution. Hybrid $\Delta \Sigma $ modulators provide an excellent tradeoff between area, power, and achievable resolution compared to the counterpart active and passive integrator $\Delta \Sigma $ modulators. This work explores hybrid continuous-time delta–sigma modulator (CTDSM) architectures for multichannel biomedical applications, operating with a single clock phase. To alleviate the high power consumption of the active integrators in the CTDSM, an auxiliary digital-to-analog converter (DAC)-based and a passive $RC$ front-end-based hybrid CTDSMs are proposed. Through a detailed analysis and performance comparison, we demonstrate that the two proposed hybrid architectures exhibit the classical area–power tradeoff for a target resolution. We demonstrate the designs in standard 180-nm mixed-mode CMOS technology for biomedical bandwidth. Measurement results show that the auxiliary DAC and the PRC-FE-based hybrid CTDSMs achieve an SNDR and DR of 65.18 and 68.3 dB and 66.85 and 71.1 dB while consuming 845- and 730-nW power and achieving an FoM of 28.48 and 20.3 fJ/conv, respectively, ideal for multichannel biomedical applications. In vitro and in vivo measurements are also performed to validate the proposed hybrid CTDSM designs.