CMOS Cascode Source-Drain Follower for Monolithically Integrated Biosensor Array

Abstract

Source-drain follower has been designed and implemented for monolithically integrated biosensor array. The circuit acts as a voltage follower, in which a sensing transistor is operated at fixed gatesource and gate-drain voltages. It operates at 10nW power dissipation. The wide-swing cascode configurations are investigated in constant and non-constant biasing methods. The constant biased cascode source-drain follower has the merit of small cell size. The chip was fabricated using 1.2μm standard CMOS technology, and a wide range of operation between 1nW and 100μW was demonstrated. The accuracy of the voltage follower was 30mV using minimum sized transistors, due to the variation of threshold voltage. The error in the output except for the threshold voltage mismatch was less than 10mV. The temperature dependence of the output was 0.11mV/°C. To improve the input voltage range and accuracy, non-constant biased cascode source-drain follower is examined. The sensor cell is designed for 10mV accuracy and the cell size is 105.3μm×81.4μm in 1.2μm CMOS design rules. The sensor cell was fabricated and showed that the error in the output except for the threshold voltage mismatch was less than 2mV in a range of total current between 3nA and 10μA and in a temperature range between 30°C and 100°C.