Minimal readout scheme for ISFET sensing arrays based on pulse width modulation

Abstract

Proposed is an ISFET readout scheme with minimum analogue components to minimise parasitic and noise effects in large-scale chemical sensing arrays. For each array pixel, a pair of complementary ISFETs shares the same floating gate in an inverter configuration. An additional electrical input is capacitively coupled to the same floating gate with a periodic reference signal input. In this way, the conventional ISFET analogue output is replaced by a chemically controlled pulse width modulated signal. Theoretical analysis and experimental results show a pulse width pH sensitivity of around 6, of the input reference signal period, per pH. This is achieved along with ±1V offset suppressing capability. © 2012 The Institution of Engineering and Technology.