A Wearable Real-Time CMOS Dosimeter With Integrated Zero-Bias Floating Gate Sensor and an 861-nW 18-Bit Energy-Resolution Scalable Time-Based Radiation to Digital Converter

Abstract

Radiation, being invisible and odorless, has become a major concern in modern-day healthcare, mining, security, and nuclear applications that require professionals to work in environments involving radioactive materials, often with only elementary training. Furthermore, the scenario is worsened by the absence of a real-time, accumulative radiation dosimeter of small/wearable form factor that can provide direct digital output for long-term continuous monitoring. In this article, we present the first monolithically integrated CMOS wearable radiation dosimeter, consisting a floating-gate (FG) resistive sensor with a sensitivity of 14 $\Omega $ /rad, and a time-domain resistance-to-digital-converter (RDC) that functions as an 18-bit voltage-controlled oscillator (VCO)-based ADC, consuming 861 nJ for 10-ms active read time (which translates to 861-nW at 1 S/s), with 3.29-pJ/conversion step energy efficiency. The proposed time-based RDC exhibits programmable energy-resolution scalability by controlling the measurement time (unlike traditional voltage/current-mode ADCs) and achieves 6-bit better resolution than the state-of-the-art VCO-based ADCs at low frequency (conversion time ≈10 ms). The implemented integrated dosimeter achieves 8-bit better resolution, 7.5 $\times $ lower power, and 40 $\times $ better sensitivity (up to 10-mrad dose) than the current CMOS FG dosimeters.