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Bulletin of the Polish Academy of Sciences Technical Sciences

The Journal of Polish Academy of Sciences

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Volume 61, Issue 3


Technique to improve CMRR at high frequencies in CMOS OTA-C filters

G. Blakiewicz
  • Corresponding author
  • Department of Microelectronic Systems, Gdansk University of Technology, 11/12 Narutowicza St., 80-952 Gdansk, Poland
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Published Online: 2013-10-15 | DOI: https://doi.org/10.2478/bpasts-2013-0074


In this paper a technique to improve the common-mode rejection ratio (CMRR) at high frequencies in the OTA-C filters is proposed. The technique is applicable to most OTA-C filters using CMOS operational transconductance amplifiers (OTA) based on differential pairs. The presented analysis shows that a significant broadening of CMRR bandwidth can be achieved by using a differential pair with the bodies of transistors connected to AC ground, instead of using a pair with the bodies connected to the sources. The key advantages of the technique are: no increase in power consumption (except for an optional tuning circuit), a small increase of a chip area, a slight modification of the original filter. The simulation results for exemplary OTAs and a low-pass filter, designed in a 0.35 μm CMOS process, show the possibility of broadening the CMRR bandwidth several times.

Keywords : common-mode rejection ratio; CMRR; CMOS; OTA; differential pair; OTA-C filters; component mismatch

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About the article

Published Online: 2013-10-15

Published in Print: 2013-09-01

Citation Information: Bulletin of the Polish Academy of Sciences: Technical Sciences, Volume 61, Issue 3, Pages 697–703, ISSN (Print) 0239-7528, DOI: https://doi.org/10.2478/bpasts-2013-0074.

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