Asynchronous Adaptive Threshold Level Crossing ADC for Wearable ECG Sensors

  • Anita AntonyEmail author
  • Shobha Rekh Paulson
  • D. Jackuline Moni
Image & Signal Processing
Part of the following topical collections:
  1. Wearable Computing Techniques for Smart Health


The level crossing ADC generates digitized samples consisting of the magnitude of input signal and time interval between two consecutive level crossings when the input signal crosses the threshold level. This paper presents a new architecture of low power asynchronous adaptive threshold level crossing (LC) ADC suitable for wearable ECG sensors based on a novel algorithm for determining adaptive threshold. The adaptive threshold was determined by calculating the mean of maximum and minimum values of signal in a predetermined window. Polynomial interpolation was used to reconstruct the signal. A signal to noise distortion ratio of 57.50 dB and a mean square error (MSE) measure of 1.368*10−8 V2 was achieved by the proposed algorithm for a 1 mV, 10 Hz input sinusoidal signal in MATLAB. The asynchronous adaptive threshold LC ADC operating from a supply voltage of 0.8 V occupied a layout area of 266.33*331.385 μm2 when implemented in CADENCE virtuoso using 180 nm technology. The designed circuit consumes an average power of 367.6 nW for a 1mVpp, 10 Hz input sinusoidal signal when simulated in Virtuoso.


Asynchronous Adaptive LC Level crossing ADC Analog to digital converter ECG Electrocardiogram Wearable Sensors Low power 



This research received no external funding.

Compliance with Ethical Standards

Conflicts of Interest

The authors declare no conflict of interest.


  1. 1.
    Sayiner, N., Sorensen, H. V., and Viswanathan, T. R., A level-crossing sampling scheme for A/D conversion. IEEE Transactions on Circuits and Systems II: Analog Digital Signal Processing 43(4):335–339, 1996. Scholar
  2. 2.
    Akopyan, F., Manohar, R., Apsel, A. B., A level-crossing flash asynchronous analog-to-digital converter. Proceedings of the IEEE International Symposium on Asynchronous Circuits and Systems, Berkeley, 11–22, 2006. doi:
  3. 3.
    Kozmin, K., Johansson, J., and Delsing, J., Level-crossing ADC performance evaluation toward ultrasound application. IEEE Transactions on Circuits and Systems I: Regular Papers 56(8):1708–1719, 2009. Scholar
  4. 4.
    Mark, J. W., and Todd, T. D., A nonuniform sampling approach to data compression. IEEE Transactions on Communications 29(1):24–32, 1981. Scholar
  5. 5.
    Wang, T., Wang, D., Hurst, P. J., Levy, B. C., and Lewis, S. H., A level crossing analog-to-digital converter with triangular dither. IEEE Transactions on Circuits System I, Regular Papers 56(9):2089–2099, 2009. Scholar
  6. 6.
    Allier, E., Sicard, G., Fesquet, L., and Renaudin, M., Asynchronous level crossing analog to digital converters. Elsevier Measurement Journal 37(4):296–309, 2005. Scholar
  7. 7.
    Guan, K. M., Kozat, S. S., and Singer, A. C., Adaptive reference levels in a level crossing analog-to-digital converter. EURASIP Journal on Advances in Signal Processing 2008(1):1–11, 2008. Scholar
  8. 8.
    Schell, B., and Tsividis, Y., A continuous-time ADC/DSP/DAC system with no clock and with activity-dependent power dissipation. IEEE Journal of Solid-State Circuits 43(4):2472–2481, 2008. Scholar
  9. 9.
    Li, Y., Zhao, D., and Serjdin, W. A., A sub-microwatt asynchronous level-crossing ADC for biomedical applications. IEEE Transaction on biomedical circuits and systems 7(2):149–157, 2013. Scholar
  10. 10.
    Inose, H., Aoki, T., and Watanabe, K., Asynchronous delta-modulation system. Electron Letters 2(3):95–96, 1966. Scholar
  11. 11.
    Kozat, S. S., Guan, K. M., and Singer, A. C., Tracking the best level set in a level-crossing analog-to-digital converter. Digital Signal Processing 23(1):478–487, 2012. Scholar
  12. 12.
    Canal, M. R., Comparison of wavelet and short time Fourier transform methods in the analysis of EMG signals. Journal of Medical Systems 34(1):91–94, 2010. Scholar
  13. 13.
    Ubeyli, E. D., Cvetkovic, D., and Cosic, I. J., AR spectral analysis technique for human PPG, ECG and EEG signals. Journal of Medical Systems 32(3):201–206, 2008. Scholar
  14. 14.
    Belkheiri, M., Douidi, Z., Belkheiri, A., ECG beats extraction and classification using radial basis function neural networks. In S M., Kumar, S., (Eds.), Proceedings of the Fourth International Conference on Signal and Image Processing 2012 (ICSIP 2012), Lecture Notes Electr. Eng. 2:127–136, 2012. doi:
  15. 15.
    Stamkopoulos, T., Maglaveras, N., Diamantaras, K., and Strintzis, M., ECG analysis using nonlinear PCA neural networks for ischemia detection. IEEE Transactions on Signal Processing 46(11):3058–3067, 1998. Scholar
  16. 16.
    Li, Y., Mansano, A. L., Yuan, Y., Zhao, D., and Serjdin, W. A., An ECG recording front end with continuous-time level-crossing sampling. IEEE Transaction on biomedical circuits and systems 8(5):1932–4545, 2014. Scholar
  17. 17.
    Mansano, A. L., Li, Y., Bagga, S., and Serjdin, W. A., An autonomous wireless sensor node with asynchronous ECG monitoring in 0.18μm CMOS. IEEE Transaction on biomedical circuits and systems 10(3):602–611, 2016. Scholar
  18. 18.
    Gneecchi, J. A. G., Magaña, R. M., Espinoza, D. L., Anguiano, A. D. C. T., Archundia, E. R., Patiño, A. M., and Miranda, R. C., DSP-based arrhythmia classification using wavelet transform and probabilistic neural network. Biomedical Signal Processing and Control 32:44–56, 2017. Scholar
  19. 19.
    Weltin-Wu, C., Tsividis, Y., An event-driven, alias-free ADC with signal-dependent resolution. Proceedings of IEEE Symposium on VLSI Technology and Circuits, Honolulu, HI, USA, 2012, 28–29, 2012. doi:
  20. 20.
    Li, Y., Serdijn, W. A., A continuous-time level-crossing ADC with 1-bit DAC and 3-input comparator. IEEE International Symposium on Circuits and Systems, Seoul, Korea, 1311–1314, 2012. doi:
  21. 21.
    Ushiyama, O., Okajima, H., Sasaki, Y., and Hasegawa, M., Noninvasive recording of his bundle activity with an analog delay device in normal subjects and patients with atrioventricular block. Hearts and Vessels 10(5):241–248, 1995. Scholar
  22. 22.
    Smith, S. W., Digital signal processors. The scientist and Engineer’s Guide to. Digital Signal Processing 28:506–509, 2002 Retrieved from Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of Electronics and Communication EngineeringKarunya Institute of Technology & SciencesCoimbatoreIndia

Personalised recommendations