Programmable Ion-Sensing Using Oscillator-Based ISFET Architectures

Abstract

This paper presents two novel oscillator-based architectures for scalable, programmable, and robust ion sensing using CMOS-based ISFETs. These architectures encode the measured ion concentration in the time domain, generating a pulse width modulated (PWM) signal with a chemically controlled duty cycle. Each architecture is developed for different scenarios and applications. First, the Sawtooth Oscillator front-end addresses the need for robustness and compensation on safety-critical diagnostic platforms. On the other hand, the chemically controlled ring oscillation (CCRO) is ideal for portable point-of-care (PoC) devices, where low power and node scalability are key factors on the system’s feasibility, consuming 655 nW during operation. Fabricated in standard CMOS AMS $0.35~\mu m$ process, these architectures leverage on the benefits of differential measurements to remain insensitive to temperature, obtaining a relative thermal sensitivity error of $0.0021\%/K$ and $0.0022\%/K$ , respectively, becoming ideal front-ends for the next generation of Lab-on-Chip platforms.