A temperature insensitive continuous time ΔpH to digital converter

Abstract

This paper presents a novel scalable readout-converter operating in weak inversion with a least significant bit resolution of 0.015pH change. The readout-converter eliminates the effect of temperature on measurements and suppresses the influence of sensing membrane buffer capacity as well as the transistor slope factor variation when in weak inversion. With the ISFET floating-gate resetting, there is no limit on dynamic range while maintaining its linearity. The system is scalable for higher resolutions and ranges without any compromise on performance. While the readout-converter can be used separately, a reference pixel is used here to eliminate the effect of any possible common mode signals in measurements with a common mode rejection ratio of 83.5dB. The system operates in continuous time and does not require any clock signal.