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 0.35μm 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.