A 0.12-V 200-Hz-BW 10-Bit ADC Using Quad-Channel VCO and Interpolation Linearization

Wireless IoT devices operating remotely benefit from energy harvesting to ensure continuous operation. Energy harvesters typically generate output voltages in the range of a few 10's mV to 100's mV, thus requiring a voltage booster to power the CMOS circuits that operate at a nominal supply of 1 V. However, this voltage conversion incurs loss and its efficiency decreases as the voltage differential increases. Therefore, from a systems perspective, there is a need for CMOS circuits that can operate close to the native energy harvester output voltage. Most IoT devices require low-power ADCs to digitize signals and the data rate may be low in many applications. Several previous works have demonstrated deep-subthreshold ADCs. VCO-based quantizers [1]-[3], and a low-supply comparator [4] are used in 0.2-V ADCs. The delta-sigma ADC [5] operates under a 0.15-V supply but can support only sub-Hz bandwidth. In this work, we propose a 0.12-V 10-bit 200-Hz-BW ADC based on a quad-channel VCO architecture. This work represents the lowest supply reported for an ADC to the best of our knowledge.