A Multi-Step Incremental Analog-to-Digital Converter With a Single Opamp and Two- Capacitor SAR Extended Counting

This work describes a hybrid incremental ADC (IADC) with two-capacitor (2-C) successive-approximation registers (SAR) extended counting in two-step operation to achieve high resolution data conversion. The circuits in the first step is acting as a first-order incremental analog-to-digital converter (IADC). Finite impulse response (FIR) DAC is incorporated in the loop filter to reduce the transient voltage step. It is reconfigured as a 2-C SAR to perform extended counting technique in the second step. Only one opamp is re-used in both steps. The hardware is prototyped in 0.18 μm CMOS technology, and the hybrid ADC accomplishes a measured DR / SNR / SNDR of 100.2 / 97.1 / 96.6 dB and an input signal bandwidth of 1.2 kHz. Operated at 1.5-V, it consumes 33.2 μW, and this achieves a Walden figure-of-merit (FoM) of 0.25 pJ/conversion-step and Schreier FoM of 175.8 dB.