Research And Design Of Low Power ECG Signal Acquisition Circuit

The rise of wireless body area network promotes the development of wearable health monitoring system.As the first stage of wearable health monitoring system,the bioelectrical signal acquisition circuit is directly connected with bioelectrical signal.It is the most critical and core part of wearable health monitoring system,and its performance determines the quality of bioelectrical signal.As a common bioelectrical signal,electrocardiogram(ECG)is has great significance in the prevention and diagnosis of cardiovascular diseases.Therefore,through analyzing the characteristics of ECG signal and the circuit model of collecting electrode,this paper designs a low-power,low-noise,gain adjustable ECG signal acquisition circuit for wearable health monitoring system.The designed ECG signal acquisition circuit in this paper includes a low-noise instrumentation amplifier,a low-pass filter,a programmable gain amplifier and a reference current source.In order to reduce the power consumption,the MOS transistors of all analog modules in the circuit are biased in the subthreshold region to reduce the current,and a design method based on g_m/I_d is adopted.The low-noise instrumentation amplifier combines the capacitive coupling instrumentation amplifier with the chopping technology to realize the low-noise amplification of the ECG signal.In order to suppress the DC offset introduced by collecting electrodes,a DC offset cancellation loop is added to the instrumentation amplifier.A duty cycle resistor is used in the loop to solve the problems of poor accuracy of traditional pseudo-resistance and high noise of switched capacitor resistance.The low-pass filter adopts Gm-C structure to achieve ultra-low cut-off frequency on the premise of low power consumption and small area,which can filter out the out-of-band noise and interference.The programmable gain amplifier changes the input capacitance or feedback capacitance by switching the flip capacitor array to change the gain.The schematic and layout of the proposed low-power ECG signal acquisition circuit are designed in 0.18?m CMOS process.The post simulation results show that the designed circuit consumes 1?A quiescent current under 1.2 V supply voltage and achieves a adjustable gain between 46 and 60.8 d B in the band from 0.17 Hz to 4.3 k Hz,with the input referred noise of 2.3?Vrms(from 0.5 to 150 Hz).The circuit can suppress the electrode offset voltage of 50 m V,and the layout area is 0.87×0.67 mm~2.All aspects of circuit performance basically meet the requirements of ECG signal acquisition.