SEMICONDUCTOR INTEGRATED CIRCUITS

Demonstration of a fully differential VGA chip with small THD for ECG acquisition system

Gongli Xiao1, 2, Yuliang Qin1, Weilin Xu1, , Baolin Wei1, Jihai Duan1 and Xueming Wei1

+ Author Affiliations

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

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Abstract: We present both a theoretical and experimental demonstration of a fully differential variable gain amplifier (VGA) with small total harmonic distortion (THD) for an electrocardiogram (ECG) acquisition system.Capacitive feedback technology is adopted to reduce the nonlinearity of VGA.The fully differential VGA has been fabricated in SMIC 0.18-μm CMOS process, and it only occupies 0.11 mm2.The measurements are in good agreement with simulation results.Experimental results show that the gain of VGA changes from 6.17 to 43.75 dB with a gain step of 3 dB.The high-pass corner frequency and low-pass corner frequency are around 0.22 Hz and 7.9 kHz, respectively.For each gain configuration, a maximal THD of 0.13% is obtained.The fully differential VGA has a low THD and its key performance parameters are well satisfied with the demands of ECG acquisition system application in the UWB wireless body area network.

Key words: fully differential VGAtotal harmonic distortionECG acquisition systemcapacitive feedback



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s 1.  (a) Block diagram of the VGA system which including 4bit decoder,switched capacitor array $C_{1}$,and full differential OTA. (b) Microphotograph of the proposed VGA and test setup.

s 2.  (a) The corresponding equivalent small signal schematic. (b) The transmission model of the fully differential VGA.

s 3.  Simulation results including (a) the frequency response,(b) the maximal HD3 of all gain configurations,and (c) (color online) transient scan results with gain spans from 7 to 46 dB.

s 4.  Measurement of the frequency response.

s 5.  Measurement of the output power spectrum.

s 6.  The measurement of the ECG amplified by the VGA with (a) gain configuration of 6.18 dB and (b) gain configuration of 9.20 dB. The oscilloscope screenshot shows the VGA output voltage on CH2 and input voltage on CH1.

Table 1.   Measured performance summary in comparison with other works.

Parameter This work Reference [6] Reference [10] Reference [13] Reference [14]
CMOS process ($\mu$m) 0.18 0.35 0.35 0.35 0.18
Supply voltage (V) 1.8 $\pm$ 1.5 1 1 1
Power consumption ($\mu $W) 39 280 0.34 3.77 18
Gain range (dB) 6.18-43.55 10-62 45.6/49/53.5/60 45.7/49.3/53.7/60.5 8-58
Gain step (dB) 3 Continuous 3 3 6
High-pass corner (Hz) 0. 22 N/A 0.0045-3.6 0.23-217 0.015
Low-pass corner (kHz) 7.9 20 0.031-0.292 7.8 0.1-2
THD (%) 0.13
(at output $>$ 900 mV)
0.89
(at output< 900 mV)
0.55-0.1
(at output< 900 mV)
0.2-0.3
(at output< 900 mV)
0.65
Chip area (mm$^{2})$ 0.11 0.064 N/A 0.171 N/A
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    Received: 03 February 2015 Revised: Online: Published: 01 October 2015

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      Gongli Xiao, Yuliang Qin, Weilin Xu, Baolin Wei, Jihai Duan, Xueming Wei. Demonstration of a fully differential VGA chip with small THD for ECG acquisition system[J]. Journal of Semiconductors, 2015, 36(10): 105005. doi: 10.1088/1674-4926/36/10/105005 G L Xiao, Y L Qin, W L Xu, B L Wei, J H Duan, X M Wei. Demonstration of a fully differential VGA chip with small THD for ECG acquisition system[J]. J. Semicond., 2015, 36(10): 105005. doi: 10.1088/1674-4926/36/10/105005.Export: BibTex EndNote
      Citation:
      Gongli Xiao, Yuliang Qin, Weilin Xu, Baolin Wei, Jihai Duan, Xueming Wei. Demonstration of a fully differential VGA chip with small THD for ECG acquisition system[J]. Journal of Semiconductors, 2015, 36(10): 105005. doi: 10.1088/1674-4926/36/10/105005

      G L Xiao, Y L Qin, W L Xu, B L Wei, J H Duan, X M Wei. Demonstration of a fully differential VGA chip with small THD for ECG acquisition system[J]. J. Semicond., 2015, 36(10): 105005. doi: 10.1088/1674-4926/36/10/105005.
      Export: BibTex EndNote

      Demonstration of a fully differential VGA chip with small THD for ECG acquisition system

      doi: 10.1088/1674-4926/36/10/105005
      Funds:

      Project supported by the National Natural Science Foundation of China (Nos.61264001, 61465004, 61161003, 61166004), the Guangxi Natural Science Foundation (Nos.2013GXNSFAA019333, 2013GXNSFAA019338), the Science and Technology Research Key Project of Guangxi Department of Education (No.2013ZD026), and the Innovation Project of GUET Graduate Education (No.GDYCSZ201457).

      More Information
      • Corresponding author: xwl@guet.edu.cn
      • Received Date: 2015-02-03
      • Accepted Date: 2015-05-15
      • Published Date: 2015-01-25

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