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A low power multi-frequency current mode lock-in amplifier for impedance sensing

We show the design of a low-power, multi-frequency on-chip current-mode lock-in amplifier for biomedical impedance sensing. This lock-in amplifier obtains the phase and magnitude of the input signals in analog domain and therefore does not require a digital signal processing module.

It is composed of translinear bandpass filters, 4-quadrant subthreshold multipliers, translinear low pass filters, translinear pythagorators and dividers. Monte Carlo results show that 80% of the devices will perform according to specifications with a power consumption of 207.7 μW. Experimental results of the bandpass modules show the impedance spectrum can be determined at the 100 Hz, 1 kHz, 10 kHz and 100 kHz frequency points.