A Power Adaptive, 1.22-pW/Hz, 10-MHz Read-Out Front-End for Bio-Impedance Measurement

This paper presents a read-out front-end application-specific integrated circuit (ASIC) for the measurement of tissue impedances. The 10 mm(2) 2-channel front-end ASIC is fabricated in a 0.18 mu m CMOS technology. The measurement results show that the proposed ASIC operates over a frequency range of 100 Hz up to 10 MHz. The ASIC has 1.22 pW/Hz power performance, with an SNR over 72 dB for frequencies <= 1 MHz, and over 65 dB SNR for frequencies >= 1 MHz. The total measured power consumption of the read-out front-end is shown to range from 2.1 to 21.7 mW depending on the input frequency. To achieve a wide dynamic range, the instrumentation amplifier has an adaptive gain control feature, and it employs programmable bias currents and reconfigurable structure to save power while processing low-frequency signals. A dual digital-to-analog converter (DAC) hybrid SAR analog-to-digital converter (ADC) is presented that reduces the power consumption of the ADC driver by sevenfold for frequencies between 4 kHz and 1 MHz.