Windowed Sliding DFT Structure for Integrated Resistance and Capacitance Sensing With Wider Sensing Range
Ranjan Tiwari, P. Sumathi · IEEE Transactions on Instrumentation and Measurement · 2025
This article presents an integrated frequency domain measurement system for resistance (R) and capacitance (C) sensing. The proposed software and hardware combination achieves one of the largest R and C measurement ranges in the literature. A simple analog front-end circuit with a relaxation oscillator is designed to toggle between resistive and capacitive sensing. This oscillator accommodates the sensing variable (R or C) and converts this parameter change into the corresponding change in frequency of square wave output. A novel 2-in-1 Hanning and Blackman window-based FLL is designed to track the input square wave signal frequency. The proposed integrated measurement system contains two measuring units in a single system-on-chip, designed and implemented on an FPGA. Therefore, two types of measurements such as humidity measurement (C) and temperature measurement (R) are possible with a single instrument. Further, the windowed SDFT incorporation in a frequency-locked loop offers a wide capacitive and resistive measurement range. The range of R measurement is found to be ($150~\Omega $–21.5 M$\Omega $)$\pm ~0.2\%$with an error of 0.023%$\pm ~0.53\%$while the same for C measurement is (3.4 pF–507.8 nF)$\pm ~0.5\%$and 0.038%$\pm ~0.53\%$. The proposed measurement system is also validated through the measurement of temperature from (30 °C to 90 °C)$\pm ~0.1\%$and humidity in the range of (40%RH–90%RH)$\pm ~4\%$separately.