Analysis and implementation of a fourth- order bandpass filter for R- wave detection of an implantable cardiac microstimulator

作者：Lee Shuenn Yuh^*; Liang Ming Chun; Tsai Tsung Heng; Kao Wei Chun

来源：International Journal of Circuit Theory and Applications, 2013, 41(11): 1188-1202.

DOI：10.1002/cta.1828

• continuous-time filter
• analog filter
• operational transconductance amplifier
• intracardiac electrogram
• low power
• low frequency
• weak inversion

This paper presents an ultra-low-power fourth-order bandpass operational transconductance amplifier-C (OTA-C) filter for an implantable cardiac microstimulator used to detect the R-wave of intracardiac electrograms. The OTA-C filter fabricated by TSMC 0.35-mu m complementary metal-oxide-semiconductor (CMOS) technology is operated in the subthreshold region to save power under a supply voltage of 1V. The current cancellation technique is adopted to reduce the transconductance of the amplifier. Through this, the low-frequency OTA-C filter can be realized by ultra-low transconductance with on-chip capacitors. Direct comparison to conventional RLC ladders replaced by OTA-C circuits shows that the method of reducing the number of OTAs further diminishes power consumption. Design issues, including ultra-low transconductance, linearity, and noise, are also discussed. Measurement results show that the low-voltage, low-power filter has a bandwidth between 10 and 50Hz, third inter-modulation distortion of -40dB, dynamic range of 43dB, and power consumption of only 12 nW. The real electrocardiography signal is fed into the bandpass filter to verify the function of signal processing with the distribution of the R-wave.