With the development of modern science and technology, electrocardiograph (ECG) technology has gradually become one of the most important detection tools in modern medicine. This article introduces the characteristics of ECG including weak signal, strong noise, low frequency range and strong signal randomness, and it mainly includes P waves, QRS wave group and T wave. Also, the processing flow of ECG is introduced, and eliminate the effects of baseline drift, power-line interference, and electromyographic interference by denoising. Also introduces the characteristics of two-stage amplifier and the importance of frequency compensation. Then the electro cardio signal is simplified to classical differential signal, and a two-stage amplifier circuit is designed to amplify it. The simulation result is 80.31dB DC voltage gain, 3kHz -3dB bandwidth and 72 degrees phase margin. So, it can provide sufficient stability and allow the system to remain stable in the face of parameter changes, external disturbances, or any uncertainties. This study can better use of two-stage amplifier to obtain complete and accurate ECG.
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