Title: Design of ring oscillator-basedVCO for a pH-ISFET redout circuit ADC

Abstract

A VCO-based-ADC by using a ring oscillator for a pH-ISFET readout circuit is described in this paper. The goal is to enhance the performance of measuring a pH. The stability of the proposed readout circuit is ensured with a ring oscillator over a large range of pH changed from 1 to 12 and with a supply voltage of ±3V. The Caprio’s quad circuit is used as a pH-ISFET threshold voltage extractor. A schematic description, as well as Verilog-A were used to simulate the circuit using Cadence virtuoso software. The proposed readout circuit was designed in a 65- nm CMOS TSMC technology. For an oscillation frequency of 13 MHz, the sensors are expected to achieve a resolution less than 0.01.