Low-Noise Low-Pass Filter for ECG Portable Detection Systems with Digitally Programmable Range
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Low-Noise Low-Pass Filter for ECG Portable Detection Systems with Digitally Programmable Range Soliman A. Mahmoud · Ahmed Bamakhramah · Saeed A. Al-Tunaiji
Received: 6 November 2012 / Revised: 30 January 2013 © Springer Science+Business Media New York 2013
Abstract This paper presents the design of an operational transconductance amplifier-C (OTA-C) low-pass filter for a portable Electrocardiogram (ECG) detection system. A fifth-order Butterworth filter using ladder topology is utilized to reduce the effect of component tolerance and to provide a maximally flat response. The proposed filter is based on a novel class AB digitally programmable fully differential OTA circuit. Based on this, PSPICE simulation results for the filter using 0.25-µm technology and operating under ±0.8 V voltage supply are also given. The filter provides a third harmonic distortion (HD3) of 53.5 dB for 100 mV p-p @50 Hz sinusoidal input, in√ put referred noise spectral density of 120 µVrms/ Hz, total power consumption of 30 µW, and a bandwidth of 243 Hz. These results demonstrate the ability of the filter to be used for ECG signal filtering that is located within 150 Hz. Keywords ECG · OTA-C filters · Low-voltage low-power CMOS circuits · Low-frequency filters 1 Introduction The world of biomedical electronics is rapidly changing with high future potential [12]. New designs with new technologies are emerging in which more features S.A. Mahmoud () · A. Bamakhramah · S.A. Al-Tunaiji Electrical and Computer Engineering Department, Sharjah University, Sharjah, United Arab Emirates e-mail: [email protected] A. Bamakhramah e-mail: [email protected] S.A. Al-Tunaiji e-mail: [email protected] S.A. Mahmoud Electrical Engineering Department, Fayoum University, Fayoum, Egypt e-mail: [email protected]
Circuits Syst Signal Process
Fig. 1 A block diagram illustrating the typical input stage of an ECG detection system
are placed into the biomedical devices. Biomedical devices need to be accurate, precise, and comfortable in usage as well as condensed in size. In case of portable devices, issues related to power consumption become also important. The designs for these portable devices must be capable enough to provide different tradeoffs between power and noise depending on the biomedical signal characteristics. For preprocessing the Electrocardiogram (ECG) signal (also called cardiac signal), a typical system shown in Fig. 1 is used [4]. Since the cardiac signals are weak amplitude signals, typically in the range of 400 µV–2.5 mV, a preamplifier is used to amplify the signal with a gain of 10–100 [3, 13]. After this amplifier, a low-pass filter (LPF) with low cut-off frequency (around 250 Hz) is used to eliminate the unwanted noise [3, 13]. This LPF is the key part in the whole system since the accuracy of the overall system depends on it. The major critical issues in designing such LPF are the linearity, input referred noise, and power consumption. The need of high linearity is to achieve low THD and acceptable IM3; also a high inp
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