Design Of Low Noise Analog Front-end For Bioelectric Signal Detection

The development of lightweight,portable wearable sensor devices has benefited from the continued growth of semiconductor technology.Compared to traditional medical devices,it is smaller in size and lower in power consumption,providing remote monitoring for patients.Therefore,the system suitable for bioelectrical signal monitoring has a broad development prospect and application market.The front-end circuit(AFE)of the bioelectric signal acquisition system is a critical module in the monitoring system because it determines the quality of the acquired signal and directly affects system performance.Therefore,it is necessary to design an analog front end circuit with good performance.Based on the analysis of the amplitude-frequency characteristics and main interference characteristics of bioelectrical signals,an analog front-end circuit with adjustable bandwidth gain,low noise,high common-mode rejection ratio and various bioelectrical signal acquisitions is designed.The collected bioelectrical signals need to be amplified and filtered,so the analog front-end system designed in this paper is mainly composed of low-noise preamplifier,programmable gain amplifier(PGA)and low-pass filter(LPF).The low-noise preamplifier has a large prevention of bioelectrical signals.A capacitively coupled negative feedback structure is used to generate a low high-pass cutoff frequency using a pseudo resistor and a capacitor to filter out the DC offset of the electrode.Symmetrical OTAs have a good compromise between power consumption,noise,and output swing.The programmable gain amplifier makes the analog front end circuit gain configurable.The capacitive input structure reduces the thermal noise introduced by the resistor and the nonlinearity introduced by the MOS switch.The low-pass filter filters out the out-of-band interference of the signal.The introduction of the current-rudder module allows the low-pass filter to achieve a lower cut-off frequency without using large resistors and large capacitors,saving chip area.The proposed bioelectric signal simulation front-end system was designed and simulated using a standard 130nm CMOS process with a single 1.2V supply voltage.The simulation results show that the analog front-end circuit gain can be adjusted in two steps,34dB and 48dB respectively;the bandwidth can be adjusted in three steps,434.3 mHz-1.057KHz,434.3mHz-124.2Hz,461.3mHz-57.97Hz,which can be used for EMG signals.,ECG signals and the extraction of EEG signals.The analog front-end circuit has a common-mode rejection ratio of up to 148dB,the input impedance is as high as 28.9G?at 0.5Hz,and the input impedance is 289.6M?at 50Hz,which is much higher than the design requirements.The analog front-end circuit consumes 42 watts,integrates in the0.5-100 Hz band,has an equivalent input noise of,and has a layout area of approximately0.18mm~2 to meet design requirements.