A reconfigurable time-to-digital converter based on time stretcher and chain-delay-line for electrical bioimpedance spectroscopy

Time Stamp – A Novel Time-to-Digital Demodulation Method for Bioimpedance Implant Applications

“…0.5T and 0.75T of the signal (where T is the signal period) using different capacitor discharge rates posing challenges due to possible process mismatches. The time window selected is narrow which leads to a complex circuit implementation [25]. Both [24] and [25] are simulation results and excluded from Table I.…”

“…The time window selected is narrow which leads to a complex circuit implementation [25]. Both [24] and [25] are simulation results and excluded from Table I. Lastly, the time stamp method is able to demodulate with less demands on the second-stage gain amplifier, which often requires additional calibration to accommodate different gains/phase delays at different frequencies.…”

“…For such small implantable devices including, for example, implantable impedimetric biosensors for monitoring blood biomarkers, an optimal design for demodulation will require minimal power consumption and an output signal that can be easily transmitted by a simple inductive link, for example, using impedance modulation. Several time-to-digital demodulation methods have been proposed but have limitations such as a narrow bandwidth [23] or rather complex circuitry [24], [25].…”

Fundamentals, Recent Advances, and Future Challenges in Bioimpedance Devices for Healthcare Applications

“…(ii) Phase measurement: if a square current signal is generated, the comparison of the original signal and the measured signal can be used to detect the phase of bioimpedance [115]. XOR or SR latch schemes have also been employed to generate clock signals with pulse width dependent on the phase shift [116].…”

“…The complexity of the bioimpedance systems is usually quite high (current injection, voltage measurement, demodulation, processing, etc.) [351] and the use of high frequency signals (from tens to hundreds of kHz) generally requires a high energy consumption [351], so this new horizon involves a hardware optimization in size, robustness, and precision, but also in energy consumption, to maximize the autonomy of the devices, fundamental in the case of implants [116,352]. A key point of bioimpedance systems is the improvement of the current source.…”