A 0.2 pJ/step open loop VCO-based ADC with inverse R-2R preweighted linearization

摘要

An open loop analog-to-digital converter based on ring voltage-controlled oscillator (VCO-based ADC) is presented. By introducing the inverse R-2R pre-weighted front-end technique, the nonlinearities of the voltage to frequency conversion of the proposed VCO is kept less than 1% over rail-to-rail input swing. Unlike prior approaches, this proposed method does not suffer from any stability issues or feedback imperfections. A prototype was fabricated using TSMC 65 nm process. It occupies an actives area of 0.03 mm(2) and consumes as little as 3.1 mA from 1 V power supply. Measurement results of linearity indicate SFDR and SNDR of 77 and 66.7 dB, respectively, over 5 MHz passband bandwidth. This reveals energy less than 0.2 pJ/step.