A low-power, reconfigurable, pipelined ADC for implantable bioimpedance measurement system with vertically aligned carbon nanofibers (VACNF) electrodes

Implantable bioimpedance monitoring has the potential to be an extremely powerful tool for biomedical research and healthcare. Currently, signal processing, specifically analog-to-digital conversion, does not allow for power-efficient conversion of bioimpedance data over a wide spectrum of frequency. In this paper, a reconfigurable pipelined analog-to-digital converter, for bioimpedance monitoring applications is presented. The converter can operate with a sampling rate between 100 kS/s to 20 MS/s and a resolution of 8 or 10 bits depending on the signal amplitude. Furthermore, the converter is self-configurable in terms of sampling rate and resolution based on the frequency and the amplitude of the input signal. A competitive FOM range (51.7–157 fJ/conv) is achieved by taking advantage of weak-inversion-biased transistors and utilizing an interference elimination technique in the 3rd pipeline stage to increase the power efficiency. The system is realized in a standard 130 nm CMOS process and consumes 16.1 μW and 1.06 mW in 8-bit and 10-bit mode, respectively. The core area of design is only 0.426 mm2. Test results show that the proposed ADC can successfully digitize the voltage drop across a bovine cell impedance model that is derived for an implantable bioimpedance measurement sensor application using the multi-electrode array of vertically aligned carbon nanofibers (VACNF).

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