Electronically Tuneable Low Power Cascaded OTAC Fifth Order Notch Filter for Front End ECG Processing System

Power line interference is a big issue in front end ECG processing system and its rejection is important to ensure signal accuracy. This article describes the design of electronically tuneable voltage-mode fifth-order operational transconductance amplifier-C (OTA-C) notch filter for front end ECG processing system. The proposed filter uses three cascaded blocks of OTA-C amplifiers with two feedback capacitors in Common Feedback (CMFB). This notch filter uses two feedback compensation capacitors of $C_{F}=1 \mu \mathrm{~F}$ for improving phase margin. The circuit is developed and simulated using Cadence Spectre tool in $0.18 \mu \mathrm{~m}$ CMOS process technology. The simulation results indicate that proposed filter produces - $\mathbf{~ d B}$ lower and upper cut-off frequencies of 48.87 Hz and 54.43 Hz respectively with a notch depth of 50 Hz frequency, 9.0041 Q value and 2.81° phase margin, and a consumption of only $229.1 \mu \mathrm{~W}$ power. The notch frequency of the filter can be electronically tuned by varying the bias voltage of the individual OTAs. Low standard deviation of output voltage with respect to its mean value and temperatures and DC supply voltage invariance shows robustness and insensitivity of the proposed design respectively. The proposed filter takes up a small area of $(20 \times 18.9) \mu \mathrm{m} 2$ with high degree of proximity between pre- and post-layout simulation results which validate the design at 180nm technology. This filter shows better results as compared to the similar filters reported in literature, with a smaller number of OTAs, lower power consumption, smaller value of load capacitance, higher Q value, and more specifically electronically tuneable characteristics of measured notch frequency with bias voltage.