Abstract
This paper presents an electrical impedance-based cytometer for cell anaylsis applications. By adopting a 3-electrode layout and using a source-differential sensing scheme, baseline current is cancelled prior to the sensor front-end measurement circuit to achieve high sensitivity. To leverage the source-differential sensing scheme, a high-gain closed-loop impedance sensing circuit was designed to sense the difference current which corresponds to the difference impedance between the electrodes. The impedance sensor was fabricated in a general purpose 180nm CMOS process and consumes 9.7mW at 1.8V supply with an excitation operating frequency from 50 kHz to 40 MHz. Measurements demonstrates that the impedance sensor achieves 6pA <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</inf> input-referred noise over 200 Hz bandwidth at 0.5 MHz modulation frequency. Combined with a microfluidic flow cell, measured experimental results demonstrate single-cell resolution detecting down to 3µm diameter microbeads in solution with 22dB SNR.
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