DocumentCode :
84385
Title :
A High-Linearity Capacitance-to-Digital Converter Suppressing Charge Errors From Bottom-Plate Switches
Author :
Bing Li ; Lei Sun ; Chi-Tung Ko ; Wong, Alex Kak-Yeung ; Kong-Pang Pun
Author_Institution :
Dept. of Electron. Eng., Chinese Univ. of Hong Kong, Hong Kong, China
Volume :
61
Issue :
7
fYear :
2014
fDate :
Jul-14
Firstpage :
1928
Lastpage :
1941
Abstract :
A high-precision capacitance-to-digital converter (CDC) that is configurable to interface with unipolar or push-pull-type capacitive sensors is presented in this paper. In the conventional switched-capacitor CDC, it is well known that clock feedthroughs and charge injections from top-plate switches can be eliminated by a bottom-plate sampling scheme. However, those charge errors from the bottom-plate switches depend on the digital output and the varying value of the sensing capacitor itself. They will thus affect the overall CDC linearity. When the varying range of the sensing capacitor is wide, the nonlinearity becomes more pronounced. This paper proposes new switching and calibration schemes to reduce these non-idealities. A prototype of a second order CDC employing the proposed techniques in a 0.18 μm CMOS process achieves a 53.2 aF RMS resolution with a 1 ms conversion time. The proposed calibration technique improves the linearity of the CDC from 9.3 bits to 12.3 bits and from 10.1 bits to 13.3 bits in the unipolar and push-pull-type sensing modes, respectively, with a sensing capacitance varying from 0.5 to 3.5 pF. The CDC is also demonstrated with a real-life pressure sensor.
Keywords :
CMOS integrated circuits; analogue-digital conversion; capacitive sensors; insulation testing; pressure sensors; switched capacitor networks; CDC linearity; CMOS process; bottom-plate sampling scheme; bottom-plate switches; capacitance 0.5 pF to 3.5 pF; charge errors; charge injections; clock feedthroughs; high-linearity capacitance-to-digital converter; push-pull-type capacitive sensors; push-pull-type sensing mode; real-life pressure sensor; sensing capacitance; sensing capacitor; size 0.18 mum; switched-capacitor CDC; time 1 ms; top-plate switches; unipolar capacitive sensors; unipolar sensing mode; word length 10.1 bit; word length 12.3 bit; word length 13.3 bit; word length 9.3 bit; Capacitance; Capacitors; Clocks; Equations; Equivalent circuits; Sensors; Switches; Capacitance-to-digital converter; charge injection; clock feedthrough; unipolar and push-pull-type capacitive sensors;
fLanguage :
English
Journal_Title :
Circuits and Systems I: Regular Papers, IEEE Transactions on
Publisher :
ieee
ISSN :
1549-8328
Type :
jour
DOI :
10.1109/TCSI.2014.2298285
Filename :
6729125
Link To Document :
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