A 172.5dB-FoM Hybrid CT/DT Incremental Σ∆Modulator for Direct Current-to-Digital Conversion

This paper presents a high area and power efficiency incremental hybrid Continuous-Time/Discrete-Time Sigma-Delta Modulator (CT/DT SDM) based Current-to-Digital Converter (CDC). The system utilizes a resistor-free continuous-time integrator as the first stage and a Switched-Capacitor (SC) integrator as the second stage to achieve second order noise shaping, leading to significant reduction in the overall area and power consumption when current signal is served as sensor output. The integration of a recycling folded-cascode (RFC) op-amp further contributes to power reduction, while the enhanced charge injection cancellation switch further improve the harmonic and noise characteristics of the system. The proposed CDC achieves 102.5dB Signal-to-Noise and Distortion Ratio (SNDR) with total current consumption of only 54.8µA and an area of 0.08 mm
²
. The calculated Figure of Merit (FoM) for the system is 172.5dB, indicating an outstanding trade-off between system resolution and power consumption.