Design of an ECG Sensor Circuitry for Cardiovascular Disease Diagnosis

Abstract

ECG biosignal conditioning (BC) is critical because it directly affects measurement accuracy, reliability, and repeatability. It also presents a great challenge due to the small amplitude of ECG raw signals and their ease of corruption with noise and other disturbances. This paper describes how an ECG biosignal conditioning circuitry was designed, built, and tested. The circuit consists of an instrument amplifier (AD8220), a 1st-order active high-pass filter (containing a MCP6271 op-amp and a RC filter in Sallen-Key configuration), a 5th-order active Bessel low-pass filter (consisting of a 1st-order LPF and two 2nd-order Sallen-Key filters), and a Twin-T active notch filter (combining two "T" shape RC filters with a MCP6271 op-amp). A right leg drive circuit was added in order to cancel the common-mode signal between the left and right arm electrodes. A power supply circuit provides a ±5V DC source for the system using two 9V batteries and two voltage regulators (NTE977 regulates +9V power supply to +5V; NTE1917 regulates -9V supply to -5V). Data acquisition and sampling were performed using a USB6009 module with a built-in A/D converter. Testing of a real electrocardiogram from a human subject was performed on the designed BC circuit, which has indicated that the developed BC circuitry can preserve useful ECG information while removing unwanted noise and interference components. with a cutoff frequency of 0.05Hz, and a low-pass filter with a cutoff frequency of nearly 100Hz. The sampling rate in the ADC (analog to digital conversion) for the ECG signal is 500Hz. Fulford-Jones et al. 4 designed a portable, low-power ECG system. 4 An operational amplifier (op-amp) embedded in a single INA321 chip was used due to its low noise and low power consumption. This op-am has a CMRR of 94dB. A high-pass feedback filter corrects any DC shift occurring over time. Their ADC sampling rate is 120Hz. Matviyenko 5 used a CY8C27443 microcontroller for ECG signal acquisition and processing. The IA embedded in the controller has a CMRR of 60dB. According to the author, this low CMRR was acceptable due to the unique design which placed a differential low-pass filter before the IA to reduce radio frequency interference (RFI), because RFI error cannot be filtered out after the ECG signal has been rectified by the IA. A 2kHz cutoff frequency high-pass filter was placed at the output of the IA. A buffer amplifier and an inverting amplifier were also used to cancel the RFI interference. The ADC sampling rate is 240Hz. Two industry leaders, Texas Instruments (TI) 6 and Analog Devices Inc. (AD), 7 also developed the ECG conditioning circuits. TI's circuitry features an INA321 IA with several unique features: a power down mode that shuts down the circuit when the supplied current is less than 1 mA (for power saving), embedded op-amps in the microcontroller, a feedback loop that maintains a constant DC level, and a 512Hz sampling rate. Further filtering was digitally implemented to remove power line noise and to provide a pass band o...

An Embedded System Based on Raspberry Pi for Effective Electrocardiogram Monitoring

“…The ECG signal is represented as a waveform with peaks and valleys that form the PQRST pattern [6,[8][9][10]. The deflections of the sinus rhythm represent the events of the atria and the ventricles of the heart in the normal rhythm.…”

“…The deflections of the sinus rhythm represent the events of the atria and the ventricles of the heart in the normal rhythm. The morphological characteristics of the heartbeat vary from person to person and for the same person under different circumstances [8][9][10]. The amplitudes of the P wave, QRS complex, S wave, T wave, and the intervals namely RR, PR, QT, and QRS complex are used to measure the health condition of the heart [6].…”

“…The variations in the morphological pattern of the heartbeat can be used by experienced doctors to detect any abnormal heart conditions. The changes of these measures are compared to the normal values to predict the cardiac arrhythmia which is referred to any irregular cardiac cycle patterns [10][11][12][13][14].…”

“…Continuous monitoring and analysis of ECG signals provide better diagnoses, assessment, and control of many of the cardiovascular diseases (CVDs) [10,11]. The risk of heart diseases could be prevented by early and fast monitoring using advance systems [4,5,[7][8][9][10][11][12].…”

“…Continuous monitoring and analysis of ECG signals provide better diagnoses, assessment, and control of many of the cardiovascular diseases (CVDs) [10,11]. The risk of heart diseases could be prevented by early and fast monitoring using advance systems [4,5,[7][8][9][10][11][12]. Nowadays, there is a real suffering due to the lack of availability of important medical resources for the treatment of heart diseases especially in developing countries; where there is not enough number of medical experts and clinical equipment [4,5,7,10,11].…”