Design of an ECG Sensor Circuitry for Cardiovascular Disease Diagnosis

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.