Fully Digital, Low Energy Capacitive Sensor Interface with an Auto-calibration Unit

  • Chintanika Chothani
  • Biswajit MishraEmail author
Conference paper
Part of the Communications in Computer and Information Science book series (CCIS, volume 892)


This paper presents an all-digital Capacitive Sensor Interface (CSI) implemented in 0.18 \(\upmu \)m CMOS technology. The circuit consists of two blocks: a Capacitance to Time Converter (CTC) and a Time to Digital Converter (TDC). The CTC block uses a Capacitive Controlled Oscillator (CCO) in addition to a Calibration Unit with a dummy capacitor bank for estimating the capacitance value. The TDC consists of a ring delay line and an edge combiner. The CTC generates a pulse width according to the sensing capacitance (\(C_{sense}\)) and passes the generated pulse to the TDC that provides the coarse and fine counts according to the pulse width. The range of the \(C_{sense}\) is varied from 0.1 pF to 36 pF that can cover a wide range of applications. Energy efficiency of this circuit is 53.28 pJ and average power consumption is 28.08 nW with 5.72 bit accuracy at an operating voltage of 1.8 V at 10 Hz sampling frequency and can measure a minimum change in capacitance of 298.92 fF. At a lower voltage of 0.3 V, the CSI consumes 1.26 nW with 7.81 bit accuracy for the same sampling frequency.


Capacitive Sensor Interface Calibration CCO CTC TDC Low power 


  1. 1.
    Coosemans, J., Puers, R.: An autonomous bladder pressure monitoring system. Sens. Actuators, A 123, 155–161 (2005)CrossRefGoogle Scholar
  2. 2.
    Bracke, W., Merken, P., Puers, R., Hoof, C.V.: Ultra-low-power interface chip for autonomous capacitive sensor systems. IEEE Trans. Circuits Syst. I Regul. Pap. 54(1), 130–140 (2007)CrossRefGoogle Scholar
  3. 3.
    Danneels, H., Coddens, K., Gielen, G.: A fully-digital, 0.3 V, 270 nW capacitive sensor interface without external references. In: Proceedings of the ESSCIRC (ESSCIRC), pp. 287–290. IEEE (2011)Google Scholar
  4. 4.
    Jourand, P., Puers, R.: An autonomous, capacitive sensor based and battery powered internal bladder pressure monitoring system. Procedia Chem. 1(1), 1263–1266 (2009)CrossRefGoogle Scholar
  5. 5.
    Puers, R.: Capacitive sensors.: when and how to use them. Sens. Actuators, A 37, 93–105 (1993)CrossRefGoogle Scholar
  6. 6.
    Hou, Y., Watanabe, T., Miyahara, M., Matsuzawa, A.: An all-digital reconfigurable time-domain ADC for low-voltage sensor interface in 65 nm CMOS technology. IEICE Trans. Fundam. Electron. Commun. Comput. Sci. 98(2), 466–475 (2015)CrossRefGoogle Scholar
  7. 7.
    Savaliya, A., Mishra, B.: A 0.3 V, 12 nW, 47 fJ/conv, fully digital capacitive sensor interface in 0.18 \(\mu \)m CMOS. In: 2015 International Conference on VLSI Systems, Architecture, Technology and Applications (VLSI-SATA), pp. 1–6. IEEE (2015)Google Scholar
  8. 8.
    Pokhara, A., Agrawal, J., Mishra, B.: Design of an all-digital, low power time-to-digital converter in 0.18 \(\mu \)m CMOS. In: 2017 7th International Symposium on Embedded Computing and System Design (ISED), pp. 1–5. IEEE (2017)Google Scholar
  9. 9.
    Chapple, C.R.., Hillary, C.J., Patel, A., MacDiarmid, S.A.: Urodynamics Made Easy E-Book (2018)Google Scholar
  10. 10.
    Omran, H., Muhammad, A., Khaled, S.N.: 7.9 pJ/step energy-efficient multi-slope 13-bit capacitance-to-digital converter. IEEE Trans. Circuits Syst. II Express Briefs 61(8), 589–593 (2014)CrossRefGoogle Scholar

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© Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  1. 1.VLSI and Embedded System Research LabDA-IICTGandhinagarIndia

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