CMOS pulse-width-modulation readout circuit with a wide modulation range for ion-sensitive FET-based sensors

摘要

A CMOS pulse-width-modulation readout circuit for sensors is presented. An input voltage, V-sen, which comes from a sensor, is converted into a current I-sen and then the I-sen is used to generate a single pulse by a procedure of constant-time charging and then constant-current discharging. With two signals RESET and SW, a control signal generator produces two signals MS1 and MS2 to control the charging and discharging of the capacitor C-p, and hence the sensitivity of the pulse width can be tuned by changing the period of the SW. The pulse width linearly depends on the V-sen with a linearity of at least 99.996%. The integration of the readout circuit with an ion-sensitive field effect transistor (ISFET) exhibits a measured transfer characteristic of pulse width versus pH value with a sensitivity of % 31.6 mu s/pH and a linearity of 99.35% after a charging time of 500 mu s at 25 degrees C. (C) 2015 The Japan Society of Applied Physics