Design Of Analog Front-end Circuit For ECG Signal Acquisition

With the development of economic level,people's quality of life is constantly improving and improving,and the real-time monitoring of health status has gradually become one of the daily needs of everyone.In our country,every year hundreds of thousands of people die from heart disease,while tens of millions more suffer from cardiovascular disease.Traditional medical electrocardiographic testing equipment,the measurement process is cumbersome and expensive.With the continuous development of semiconductor industry,intelligent hardware has opened up a new market to meet the needs of ordinary people for real-time heart monitoring.For heart monitoring equipment,it is important to provide high-quality monitoring modules,the higher the quality of ECG signals,the more reliable the health information.As a result,the analog front-end circuit(AFE),which plays the role of signal acquisition and amplification,is undoubtedly the most critical module.A low-noise analog front-end acquisition circuit is designed based on the system performance,noise,area and other factors,and based on the analysis of ECG characteristics and bio-electrode equivalent circuit model.The circuit is mainly composed of preamplifier,gain amplifier and filter module.The low-noise preamplifier(LNA)is designed based on AC coupling-capacitor feedback mechanism,the amplifier uses the pseudo-resistance formed by capacitance and PMOS tube to produce low-frequency high-pass cutoff frequency to filter out the misalignment interference introduced by electrode.The folded two-stage operational amplifier structure uses PMOS tube to realize differential signal input,which has a good compromise between output voltage swing,noise and gain.Furthermore,the gain configurable amplifier(VGA)circuit is constructed to widen the range of signal detection and to solve the difference of input signal amplitude.The gain is adjustable by changing the input capacitance therein.To filter out signal band interference,a low pass filter(LPF)with-20 d B/Dec attenuation is designed,the frequency response curve of the filter is smooth and good linearity and low frequency performance.Based on the above circuit design,the verification ECG signal acquisition analog frontend circuit is completed by using standard 180 nm CMOS technology.The simulation results show that the common-mode rejection ratio is 118.5 d B,the power supply rejection ratio is 124.6 d B,the input impedance is 57.6GΩ@0.5Hz.the gain is 47.6 d B/59.8d B adjustable;and the high pass cutoff frequency is 0.52 Hz,the low pass cutoff frequency is 108.6 Hz,and the equivalent input noise integral in the band is 3.5 μ Vrms,the performance of the signal acquisition analog front-end circuit meets the design requirements.