We propose a low-power impedance-to-frequency (I-to-F) converter for wearable transducers that change both its resistance and capacitance in response to mechanical deformation or changes in ambient pressure. At the core of the proposed I-to-F converter is a fixed-point circuit comprising of a voltage-controlled relaxation oscillator and a proportional-to-temperature (PTAT) current reference that locks the oscillation frequency according to the impedance of the transducer. Using both analytical and measurement results we show that the operation of the proposed I-to-F converter is well matched to a specific class of sponge mechanical transducer where the system can achieve higher sensitivity when compared to a simple resistance measurement techniques. Furthermore, the oscillation frequency of the converter can be programmed to ensure that multiple transducer and I-to-F converters can communicate simultaneously over a shared channel (physical wire or virtual wireless channel) using frequency-division multiplexing. Measured results from proof-of-concept prototypes show an impedance sensitivity of <inline-formula><tex-math notation="LaTeX">$19.66 \,\mathrm{Hz}$</tex-math></inline-formula>/<inline-formula><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> at <inline-formula><tex-math notation="LaTeX">$1.1 \,\mathrm{k}\Omega$</tex-math></inline-formula> load impedance magnitude and a current consumption of <inline-formula><tex-math notation="LaTeX">$128 \,\upmu\mathrm{A}$</tex-math></inline-formula>. As a demonstration we show the application of the I-to-F converter for human gesture recognition and for radial pulse sensing.

Original languageEnglish
Pages (from-to)1-12
Number of pages12
JournalIEEE Transactions on Biomedical Circuits and Systems
StateAccepted/In press - 2024


  • Capacitance
  • Frequency division multiplexing
  • Frequency measurement
  • Impedance
  • Impedance-to-frequency converter
  • Sensors
  • Transducers
  • Wearable sensors
  • frequency multiplexing
  • multi-modal sensors
  • strain gauge sensor
  • wearable sensor


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