SEMICONDUCTOR INTEGRATED CIRCUITS

An OTA-C filter for ECG acquisition systems with highly linear range and less passband attenuation

Jihai Duan, Chuang Lan, Weilin Xu and Baolin Wei

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 Corresponding author: Weilin Xu, E-mail: xwl@guet.edu.cn

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Abstract: A fifth order operational transconductance amplifier-C (OTA-C) Butterworth type low-pass filter with highly linear range and less passband attenuation is presented for wearable bio-telemetry monitoring applications in a UWB wireless body area network. The source degeneration structure applied in typical small transconductance circuit is improved to provide a highly linear range for the OTA-C filter. Moreover, to reduce the passband attenuation of the filter, a cascode structure is employed as the output stage of the OTA. The OTA-based circuit is operated in weak inversion due to strict power limitation in the biomedical chip. The filter is fabricated in a SMIC 0.18-μ m CMOS process. The measured results for the filter have shown a passband gain of -6.2 dB, while the -3-dB frequency is around 276 Hz. For the 0.8 VPP sinusoidal input at 100 Hz, a total harmonic distortion (THD) of -56.8 dB is obtained. An electrocardiogram signal with noise interference is fed into this chip to validate the function of the designed filter.

Key words: ECG signalfully differential OTA-C filterhighly linear rangeless passband attenuation



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Fig. 1.  Analog frond-end circuit of ECG bio-telemetry monitoring system.

Fig. 2.  (a) OTA circuit with wide linearity. (b) Common-mode feedback of the OTA.

Fig. 3.  The small-signal equivalent circuit of the OTA.

Fig. 4.  (a) The ideal first-order fully differential filter. (b) Non-ideal first-order fully differential filter.

Fig. 5.  Tansconductance of the proposed OTA.

Fig. 6.  (a) The passive ladder type filter. (b) The fifth order OTA-C Butterworth LPF.

Fig. 7.  The HD3 of the filter with a sinusoidal wave of 100 Hz and 0.8 V$_{\rm PP}$.

Fig. 8.  Chip microphotograph of the proposed OTA-C filter.

Fig. 9.  The frequency response of the proposed OTA-C filter.

Fig. 10.  The output power spectrum of the proposed OTA-C filter.

Fig. 11.  The ECG signal with noise and the output ECG signal after being filtered out.

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Table 1.   Component values of the filter.

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Table 2.   Performance comparison of OTA-C filter.

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    Received: 05 October 2014 Revised: Online: Published: 01 May 2015

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      Jihai Duan, Chuang Lan, Weilin Xu, Baolin Wei. An OTA-C filter for ECG acquisition systems with highly linear range and less passband attenuation[J]. Journal of Semiconductors, 2015, 36(5): 055006. doi: 10.1088/1674-4926/36/5/055006 J H Duan, C Lan, W L Xu, B L Wei. An OTA-C filter for ECG acquisition systems with highly linear range and less passband attenuation[J]. J. Semicond., 2015, 36(5): 055006. doi: 10.1088/1674-4926/36/5/055006.Export: BibTex EndNote
      Citation:
      Jihai Duan, Chuang Lan, Weilin Xu, Baolin Wei. An OTA-C filter for ECG acquisition systems with highly linear range and less passband attenuation[J]. Journal of Semiconductors, 2015, 36(5): 055006. doi: 10.1088/1674-4926/36/5/055006

      J H Duan, C Lan, W L Xu, B L Wei. An OTA-C filter for ECG acquisition systems with highly linear range and less passband attenuation[J]. J. Semicond., 2015, 36(5): 055006. doi: 10.1088/1674-4926/36/5/055006.
      Export: BibTex EndNote

      An OTA-C filter for ECG acquisition systems with highly linear range and less passband attenuation

      doi: 10.1088/1674-4926/36/5/055006
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      Project supported by the National Natural Science Foundation of China (Nos.61161003, 61264001, 61166004) and the Guangxi Natural Science Foundation (No.2013GXNSFAA019333).

      More Information
      • Corresponding author: E-mail: xwl@guet.edu.cn
      • Received Date: 2014-10-05
      • Accepted Date: 2014-12-09
      • Published Date: 2015-01-25

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