Articles | Volume 6, issue 2
J. Sens. Sens. Syst., 6, 285–301, 2017
J. Sens. Sens. Syst., 6, 285–301, 2017

Regular research article 22 Aug 2017

Regular research article | 22 Aug 2017

An ultra-low noise capacitance to voltage converter for sensor applications in 0.35  µm CMOS

Alexander Utz1, Christian Walk1, Norbert Haas1, Tatjana Fedtschenko1, Alexander Stanitzki1, Mir Mokhtari2, Michael Görtz1, Michael Kraft3, and Rainer Kokozinski1,4 Alexander Utz et al.
  • 1Fraunhofer Institute for Microelectronic Circuits and Systems (IMS), Finkenstr. 61, 47057 Duisburg, Germany
  • 2Mir Enterprises Limited, 173c Goldhurst Terrace, Hampstead, London, NW6 3ES, UK
  • 3Montefiore Institute, University of Liege, Rue de la Decouverte, 4000 Liege, Belgium
  • 4Department of Electronic Components and Circuits, University of Duisburg-Essen, Bismarckstr. 81, 47057 Duisburg, Germany

Abstract. In this paper we present a readout circuit for capacitive micro-electro-mechanical system (MEMS) sensors such as accelerometers, gyroscopes or pressure sensors. A flexible interface allows connection of a wide range of types of sensing elements. The ASIC (application-specific integrated circuit) was designed with a focus on ultra-low noise operation and high analog measurement performance. Theoretical considerations on system noise are presented which lead to design requirements affecting the reachable overall measurement performance. Special emphasis is put on the design of the fully differential operational amplifiers, as these have the dominant influence on the achievable overall performance. The measured input referred noise is below 50 zF/Hz within a bandwidth of 10 Hz to 10 kHz. Four adjustable gain settings allow the adaption to measurement ranges from ±750 fF to ±3 pF. This ensures compatibility with a wide range of sensor applications. The full input signal bandwidth ranges from 0 Hz to more than 50 kHz. A high-precision accelerometer system was built from the described ASIC and a high-sensitivity, low-noise sensor MEMS. The design of the MEMS is outlined and the overall system performance, which yields a combined noise floor of 200 ng/Hz, is demonstrated. Finally, we show an application using the ASIC together with a CMOS integrated capacitive pressure sensor, which yields a measurement signal-to-noise ratio (SNR) of more than 100 dB.