A Reconfigurable Mostly-Digital Delta-Sigma ADC With a Worst-Case FOM of 160 dB

This paper presents a second-generation mostly-digital background-calibrated oversampling ADC based on voltage- controlled ring oscillators (VCROs). Its performance is in line with the best $\Delta \Sigma$ modulator ADCs published to date, but it occupies much less circuit area, is reconfigurable, and consists mainly of digital circuitry. Enhancements relative to the first-generation version include digitally background-calibrated open-loop $V / I$ conversion in the VCRO to increase ADC bandwidth and enable operation from a single low-voltage power supply, quadrature coupled ring oscillators to reduce quantization noise, digital over-range correction to improve dynamic range and enable graceful overload behavior, and various circuit-level improvements. The ADC occupies 0.075 mm $^{2}$ in a 65 nm CMOS process and operates from a single 0.9–1.2 V supply. Its sample-rate is tunable from 1.3 to 2.4 GHz over which the SNDR spans 70–75 dB, the bandwidth spans 5–37.5 MHz, and the minimum SNDR+ 10log(bandwidth/power dissipation) figure of merit (FOM) is 160 dB.