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A Charge-Based Low-Power High-SNR Capacitive Sensing Interface Circuit

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5 Author(s)
Sheng-Yu Peng ; Georgia Inst. of Technol., Atlanta, GA ; Qureshi, M.S. ; Hasler, P.E. ; Basu, A.
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This paper describes a low-power approach to capacitive sensing that achieves a high signal-to-noise ratio (SNR). The circuit is composed of a capacitive feedback charge amplifier and a charge adaptation circuit. Without the adaptation circuit, the charge amplifier only consumes 1 muW to achieve the audio band SNR of 69.34 dB. An adaptation scheme using Fowler-Nordheim tunneling and channel hot-electron injection mechanisms to stabilize the dc output voltage is demonstrated. This scheme provides a very low frequency pole at 0.2 Hz. The measured noise spectrums show that this slow-time scale adaptation does not degrade the circuit performance. The dc path can also be provided by a large feedback resistance without causing extra power consumption. A charge amplifier with a MOS-bipolar pseudo-resistor feedback scheme is interfaced with a capacitive micromachined ultrasonic transducer to demonstrate the feasibility of this approach for ultrasound applications.

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Circuits and Systems I: Regular Papers, IEEE Transactions on  (Volume:55 ,  Issue: 7 )