A 22.9µW 87.5dB-SNDR 20kHz-BW Capacitive Input CT Zoom ADC with 100.2dB SFDR
Student Contest:
No
Affiliation Type:
Academia
Keywords:
Continuous-Time ADC, Zoom ADC, Noise-Shaping SAR ADC, Delta-Sigma ADC, Capacitive Input, Direct-Sensing Interface, Low-Power ADC, High Input Impedance
Abstract:
This paper presents a 22.9μW fully continuous-time (CT) Zoom ADC for direct-sensing interfaces requiring high input impedance, wide input range, and inherent anti-aliasing. The proposed architecture combines a capacitive input network, a coarse CT noise-shaping SAR ADC, and a fine Gm-C-based CT ΔΣ ADC. The capacitive input interface provides high input impedance while supporting a 2.4Vpp differential full-scale input. The coarse noise-shaping SAR ADC suppresses coarse quantization-noise leakage and shapes the interstage gain error arising from physically separated coarse and fine DAC paths. A duty-cycled Gm-C integrator with an input/DAC tracking-and-reset network is employed in the coarse path, while the fine path utilizes a source-degenerated Gm-C integrator with inverter-based Gm boosting. Fabricated in a 65nm CMOS process, the prototype achieves 87.5dB SNDR, 89.8dB dynamic range, and 100.2dB SFDR over a 20kHz bandwidth while consuming only 22.9μW from a 1.2V supply. The ADC exhibits more than 58dB alias rejection and an input impedance exceeding 5.6MΩ, demonstrating a power-efficient direct-sensing ADC with high input impedance and rail-to-rail input capability.
