J. Semicond. > Volume 34 > Issue 5 > Article Number: 055002

A low-power portable ECG sensor interface with dry electrodes

Xiaofei Pu , , Lei Wan , Hui Zhang , Yajie Qin , and Zhiliang Hong

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Abstract: This paper describes a low-power portable sensor interface dedicated to sensing and processing electrocardiogram (ECG) signals. Dry electrodes were employed in this ECG sensor, which eliminates the need of conductive gel and avoids complicated and mandatory skin preparation before electrode attachment. This ECG sensor system consists of two ICs, an analog front-end (AFE) and a successive approximation register analog-to-digital converter (SAR ADC) containing a relaxation oscillator. This proposed design was fabricated in a 0.18 μm 1P6M standard CMOS process. The AFE for extracting the biopotential signals is essential in this ECG sensor. In measurements, the AFE obtains a mid-band gain of 45 dB, a bandwidth from 0.6 to 160 Hz, and a total input referred noise of 2.8 μV rms while consuming 1 μW from the 1.8 V supply. The noise efficiency factor (NEF) of our design is 3.4. After conditioning, the amplified ECG signal is digitized by a 12-bit SAR ADC with 61.8 dB SNDR and 220 fJ/conversion-step. Finally, a complete ECG sensor interface with three dry copper electrodes is demonstrated in real-word setting, showing successful recordings of a capture ECG waveform.

Key words: ECGsensor interfacedry electrodeanalog front-endSAR ADC

Abstract: This paper describes a low-power portable sensor interface dedicated to sensing and processing electrocardiogram (ECG) signals. Dry electrodes were employed in this ECG sensor, which eliminates the need of conductive gel and avoids complicated and mandatory skin preparation before electrode attachment. This ECG sensor system consists of two ICs, an analog front-end (AFE) and a successive approximation register analog-to-digital converter (SAR ADC) containing a relaxation oscillator. This proposed design was fabricated in a 0.18 μm 1P6M standard CMOS process. The AFE for extracting the biopotential signals is essential in this ECG sensor. In measurements, the AFE obtains a mid-band gain of 45 dB, a bandwidth from 0.6 to 160 Hz, and a total input referred noise of 2.8 μV rms while consuming 1 μW from the 1.8 V supply. The noise efficiency factor (NEF) of our design is 3.4. After conditioning, the amplified ECG signal is digitized by a 12-bit SAR ADC with 61.8 dB SNDR and 220 fJ/conversion-step. Finally, a complete ECG sensor interface with three dry copper electrodes is demonstrated in real-word setting, showing successful recordings of a capture ECG waveform.

Key words: ECGsensor interfacedry electrodeanalog front-endSAR ADC



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[1]

Pu X, Wan L, Sheng Y. A wireless 8-channel ECG biopotential acquisition system for dry electrodes[J]. IEEE Radio-Frequency Integration Technology Conference, 2012.

[2]

Park S, Jayraman S. Enhancing the quality of life through wearable technology[J]. IEEE Eng Med Bio Mag, 2003, 22(3): 41. doi: 10.1109/MEMB.2003.1213625

[3]

Waterhouse E. New horizons in ambulatory electroencephalog-raphy[J]. IEEE Eng Med Bio Mag, 2003, 22(3): 74. doi: 10.1109/MEMB.2003.1213629

[4]

Xu X, Zou X, Yao L. A 1-V 450 nW fully integrated biomedical sensor interface system[J]. IEEE Symp VLSI Circuits Dig Tech Papers, 2008: 78.

[5]

Yazicioglu R F, Merken P, Puers R. A 200μ W eight-channel EEG acquisition ASIC for ambulatory EEG systems[J]. IEEE J Solid-State Circuits, 2008, 43(12): 3025. doi: 10.1109/JSSC.2008.2010844

[6]

Nemati E, Deen M J, Mondal T. A wireless wearable ECG sensor for long-term applications[J]. IEEE Commun Mag, 2012: 36.

[7]

Yan L, Yoo J, Yoo H J. A 0.5-μ Vrms 12-μ W wirelessly powered patch-type healthcare sensor for wearable body sensor network[J]. IEEE J Solid-state Circuits, 2010, 45(11): 2356.

[8]

Hoffmann K P, Ruff R. Flexible dry surface-electrodes for ECG long-term monitoring[J]. IEEE Eng Med Bio Soc Conference, 2007.

[9]

Harrison R R, Charles C. A low-power low-noise CMOS amplifier for neural recording applications[J]. IEEE J Solid-State Circuits, 2003, 38(6): 958. doi: 10.1109/JSSC.2003.811979

[10]

Wattanapanitch W, Fee M, Sarpeshkar R. An energy-efficient micropower neural recording amplifier[J]. IEEE Trans Biomed Circuits Syst, 2007, 1: 136. doi: 10.1109/TBCAS.2007.907868

[11]

Shahrokhi F, Abdelhalim K, Serletis D. The 128-channel fully differential digital integrated neural recording and stimulation interface[J]. IEEE Trans Biomed Circuits Syst, 2010, 4(3): 149. doi: 10.1109/TBCAS.2010.2041350

[12]

Zou X, Liew W S, Yao L. A 1 V 22μ W 32-channel implantable EEG recording IC[J]. IEEE ISSCC Dig Tech Papers, 2010.

[13]

Qian C, Parramon J, Sanchez-Sinencio E. A mircropower low-noise neural recording front-end circuit for epileptic seizure detection[J]. IEEE J Solid-State Circuits, 2011, 46(6): 1392. doi: 10.1109/JSSC.2011.2126370

[14]

Wattanapanitch W, Sarpeshkar R. A low-power 32-channel digitally programmable neural recording integrated circuit[J]. IEEE Trans Biomed Circuits Syst, 2011, 5(6): 592. doi: 10.1109/TBCAS.2011.2163404

[15]

Verma N, Chandrakasan A P. An ultra-low energy 12-bit rate-resolution scalable SAR ADC for wireless sensor nodes[J]. IEEE J Solid-State Circuits, 2007, 42(6): 1196. doi: 10.1109/JSSC.2007.897157

[16]

Van der Plas G, Decoutere S, Donnay S. A 0.16 pJ/conversion-step 2.5 mW 1.25 GS/s 4 b ADC in a 90 nm digital CMOS process[J]. IEEE ISSCC Dig Tech Papers, 2006: 566.

[17]

Zhang Hui, Qin Yajie, Yang Siyu. A 455 nW 220 fJ/Conversion-step 12 bits 2 kS/s SAR ADC for portable biopotential acquisition systems[J]. Journal of Semiconductors, 2011, 32(1): 015001. doi: 10.1088/1674-4926/32/1/015001

[18]

Wakayama M, Abidi A. A 30-MHz low-jitter high-linearity CMOS voltage-controlled oscillator[J]. IEEE J Solid-State Circuits, 1987, 22(6): 1074. doi: 10.1109/JSSC.1987.1052857

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X F Pu, L Wan, H Zhang, Y J Qin, Z L Hong. A low-power portable ECG sensor interface with dry electrodes[J]. J. Semicond., 2013, 34(5): 055002. doi: 10.1088/1674-4926/34/5/055002.

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Manuscript received: 27 August 2012 Manuscript revised: 26 November 2012 Online: Published: 01 May 2013

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