The precise measurement of a capacitance difference or ratio in a digital form is
very important for capacitive sensors, for CMOS process characterization as well as for the
realization of precise switched-capacitor data converters, amplifiers and other circuits
utilizing ratioed capacitors. This thesis introduces design techniques for on-chip capacitor
ratio testing and sensor readout that utilize sigma-delta modulation and integrate the sensor
capacitors into the modulator. Several single-ended circuits are introduced, and the
correlated-double-sampling (CDS) technique is used in the circuits to reduce the non-ideal
effects of opamps. Several simple calibration schemes for clock-feedthrough cancellation
are also introduced and discussed. A fully-differential implementation is also described and
various common-mode feedback schemes are discussed and analyzed. Simulation and
experimental results show that these circuits can provide extremely accurate results even in
the presence of non-ideal circuit effects such as finite opamp gain, opamp input offset and
noise, and clock-feedthrough effect from the switches.
To verify the effectiveness of the circuits and simulations, two prototype chips containing
a single-ended realization and a fully-differential one were designed and fabricated
in a 1.2 ��m CMOS technology. Two off-chip mica capacitors were used in the test circuits,
and the measured results show that very accurate results can be obtained using these circuit
techniques even with off-chip noise coupling and large parasitic capacitances. / Graduation date: 1999
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33343 |
| Date | 06 November 1998 |
| Creators | Wang, Bo, 1970- |
| Contributors | Temes, Gabor C. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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