Ultralow-Power Bioimpedance IC With Intermediate Frequency Shifting Chopper

A bioelectrical impedance IC with an intermediate frequency shifting chopper (IFSC) technique driven by a merged clock is presented. The proposed technique enables high-frequency impedance measurements with a narrow bandwidth low-power instrumentation amplifier (IA). The conventional series-connected double choppers required for the frequency shifting operation are replaced with a single chopper driven by a XNOR-merged clock. The proposed IC can measure bioelectrical impedance at a maximum excitation frequency of 1.24 MHz in an IA bandwidth of only 30 kHz. A DC trimming technique that uses a dummy impedance and anti-phase current source can adjust the output offset and prevent output saturation. This DC trimming technique also enables shifting of the impedance measurement scope. The proposed IC is fabricated using 0.13-μm CMOS process, and is shown to achieve a dynamic range of 97.1 dB, and 52 μW of power consumption.