An Energy Efficient Period-modulation-based Current-to-digital Converter for FET-type Sensors

This paper presents an energy-efficient current-to-digital converter with period modulation (PM) to support gas sensors based on a field-effect transistor (FET). A frequency-locked loop (FLL) converts sensor current signals into a periodic signal, which is then quantized by applying a low-noise on-chip RC oscillator. The RC oscillator with an edge combiner and a digital filter is applied to reduce quantization noise. In addition, a current digital-to-analog converter (I-DAC) at the FLL input is employed to reduce conversion time and energy. This work is implemented standalone to minimize the system costs. The proposed work is implemented in 180-nm CMOS process, achieving a fast conversion time of 4.1 μs and a superior FoM<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</inf> of 208.4 fJ/c-s.