The Research And Design Of A New Readout Circuit Of ECG Signal Detection

With the development of the technical science nowadays, ECG signal plays a veryimportant role in cardiovascular medical diagnosis. ECG signal is related to thephysiological function of the heart, which is produced by the electromagnetic activity inhuman heart. The cardiovascular diseases are often sudden, unforeseen, high mortalityand lead to disabilities. Continuous, accurate, real-time acquisition of ECG signal canprovide an important basis for clinical diagnosis and treatment of cardiovasculardiseases. Therefore, the research of portable ECG monitor has been given much moreattention.At present, the extraction of ECG signal is still the key technology for the researchof the portable ECG monitor. Based on the careful analysis and research, this paper usesa new detection method to extract ECG signal: The ECG signal determines theresonance frequency of the passive sensor circuit. The resonance frequency can bedirectly reflected in the phase signal of the read circuit by means of mutal coupling. Bymeasuring the phase change,the change information of ECG can be detected. And thenthe theory and the feasibility of simulation of the method are analysesed.Based on the theory of the new ECG signal detection method,a detection readoutcircuit system has been designed,and most of the modules are simulated,which mainlyincludes the following parts:First,the33MHz sine wave signal generator consisted ofOscillator,RLC frequency selection circuit and amplification circuit produce two highfrequency signals after phase shifting,one of which is used to be reference signal,andanother to be carrier signal to drive the sensor and detect the changes of the resonantfrequency of the sensor circuit.When the resonant frequency changes,the phase of thecarrier signal would change in proportion.Second, The phase shift circuit consisted ofresistance and capacitance accompulishes the stable90degree phase-shift, ensuring thestability of phase difference measurement.Third, the waveform transformation circuitcomposed of AD8611, transforms the sine wave into square wave by using a comparatorprinciple.Fourth,the phase-detector composed of AD9901detects the phase changebetween the reference signal and the modulated signal.Fifth, The RLC Butterworthlow-pass filter circuit, used for filtering phase detected signal, could obtain a level inaccordance with the variation of ECG signal.Last,the amplifier circuit composed of OP07,realizes the level high-pass filter and amplification, and the measured level signalis consistent with the variation of ECG signal.