An Auto-Zero Stabilized Voltage Buffer with a Quiet Chopping Scheme and Constant Input Current

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The readout of high-impedance sensors and sampled voltage references [1] requires amplifiers that can achieve both low offset and low input current. Recently, it has been shown that this unique combination can be achieved by an auto-zero (AZ) stabilized buffer [2]. However, its low-frequency noise density is surd 5 times higher than the buffer's own white-noise voltage spectral density e n . Furthermore, its input current is not constant, but varies significantly with the input voltage. To overcome the first issue, a chopped AZ stabilization loop with an optimized duty-cycle is proposed to bring the low-frequency noise density close to surd 2cdot {e}-{n}, the fundamental limit of an AZ stabilized amplifier. The second issue is solved by replacing the transmission-gate input switches used in [2] with NMOS switches and a constant Vgs drive. This keeps their charge injection constant over a wide input voltage range, and results in a constant input current.

Original languageEnglish
Title of host publication2019 IEEE International Solid-State Circuits Conference, ISSCC 2019
EditorsJan van der Spiegel
Place of PublicationPiscataway, NJ
Number of pages3
ISBN (Electronic)978-1-5386-8531-0
ISBN (Print)978-1-5386-8532-7
Publication statusPublished - 2019
EventISSCC 2019: IEEE International Solid-State Circuits Conference - San Francisco, CA, United States
Duration: 17 Feb 201921 Feb 2019


ConferenceISSCC 2019
Country/TerritoryUnited States
CitySan Francisco, CA

Bibliographical note

Session 18.3
Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project
Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.


  • Low-frequency noise
  • Current measurement
  • Voltage measurement
  • MOS devices
  • Capacitors
  • Chopper (circuits)
  • Switches


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