A 0.36-V 5-MS/s Time-Mode Flash ADC With Dickson-Charge-Pump-Based Comparators in 28-nm CMOS

Dickson charge-pump (CP) is proposed here to realize a voltage-to-time converter (VTC) within an array of time-domain comparators of a 54-level time-mode subthreshold flash ADC operating at 0.36V. Two identical CPs in each of the 54 ADC slices convert the input and reference voltages into variable-slope ramp signals fed into comparators for `flash' quantization. Considering the fact that the comparator's evaluation time gets severely degraded at subthreshold input voltages, the proposed ADC delivers the maximum bandwidth by means of the inherent input voltage boosting by the Dickson CPs. The proposed architecture quantizes the analog input signal into time with CPs and then into digital domain with latches and simple logic, without using any analog-intensive circuits such as amplifiers and current sources, thus yielding a digitally friendly implementation. Measurement results show peak ENOB of 5.04-bit, SNDR of 32.1dB at the peak, power consumption of $88~\mu \text{W}$ . The conversion rate of 5 MS/s is the highest among near- and subthreshold ADCs.