IEEE Access (Jan 2019)

A Low-Power Delta-Sigma Capacitance-to-Digital Converter for Capacitive Sensors

  • Rongshan Wei,
  • Wanjin Wang,
  • Xiaoxia Xiao,
  • Qunchao Chen

DOI
https://doi.org/10.1109/ACCESS.2019.2922840
Journal volume & issue
Vol. 7
pp. 78281 – 78288

Abstract

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This paper proposes a low-power delta-sigma capacitance-to-digital converter (CDC) for a capacitive sensor. The input of the capacitive sensor employs a zoomed-in technique with the offset capacitor to extend the input capacitance range. The proposed CDC uses a third-order switched capacitor delta-sigma modulator to provide a digital output, based on a cascade of integrators with a feed forward (CIFF) structure. The current-starved operational transconductance amplifiers (OTAs) are applied in the delta-sigma modulator's first integrator to improve the current efficiency and reduce the power consumption. An auto-zeroing technique is used in the OTAs to reduce their offset and noise. The circuit was implemented in a 0.18-μm CMOS technology and occupies an area of 0.496 mm2. The measurable capacitance range of the CDC can be varied from 0 to 8 pF. In a measurement time of 0.8 ms, the delta-sigma CDC achieved a 12.7 effective number of bits while consuming 18.6-μA current from a 2-V supply voltage.

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