OP 741 Modeling of ECG Amplification and Active Filtering Circuit Design

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This paper establishes a design of an integrated amplification and filtering circuit for the analog front end (AFE) of the electrocardiogram (ECG) signals with the modeling of the representative 741 operational amplifiers (op-amps). The instrument amplifier in the first stage utilizes the popular topology with three op-amps. The voltage gain of the input noninverting amplifiers are designed with a factor of 10. The difference amplifier behind the noninverting amplifiers provides the voltage gain of 10. ECG signals are amplified through an instrumentation amplifier with high common-mode rejection ratio at the voltage gain of 40dB. The cascaded low-pass filter is designed at the cut-off frequency of 100Hz to suppress the interferences at higher frequencies with the voltage gain of 10. The Instrumentation amplifier accompanying with the low pass filter totally supply the voltage gain of 60dB. The notch filter at the final stage is designed to reject the 60Hz noise from the power supply system. This notch filter applies active equivalent inductance to avoid the requirement of conventional inductive component. Simulations between frequency response and time domain response of ECG AFE circuits are achieved with the Hspice modeling of 741 op-amps.