Key Technologies Research On High Performance Analog Front-End Circuits For Bioelectricity Acquisition

The rapid development of wearable medical electronic devices promotes the growth of new medical models,such as remote medicine and smart hospital,and facilitates the development of advanced medical treatment and health industry in China.Wireless body area network?WBAN?,low-power integrated circuit and flexible sensor provide effective solutions for wearable medical devices with small size and low power.The analog front-end circuit for bioelectrical signal acquisition is an important part of the wearable medical device.Its performance determines the quality of signals,the processing accuracy and the interference suppression ability,etc.The analog front-end circuit with low power consumption,small volume and high performance has become an important development direction of advanced electronics in the future.The amplitude of bioelectric signals is generally in the range of microvolts to millivolts,and the frequency is about tens of Hertz.In addition,the contact between biological electrodes and human body is unstable,hence the acquisition of biological electrical signal is easily interfered by low-frequency noise in circuit,power line interference,motion artifact and electrode dc-offset.This bring great challenges to the design of high performance signal acquisition circuit.This thesis studies the key technologies about biological signal acquisition and processing,mainly introduces the technology on low power consumption,low noise,high input impedance,and interference elimination.The technical bottleneck of analog front-end integrated circuit on high performance,low power consumption and small volume is break through,which effectively improves the overall performance of the bioelectrical signal monitoring system.This thesis firstly describes the characteristics of bio-potential signals and introduces the system structure of analog front-end circuit.Secondly,we expound the key technical problems and the design requirements of the analog front-end circuits.The noise optimization method had been studied both on circuit system level and transistor level.Then,The implementation scheme of low power analog front-end circuit is studied.Methods to improve the input impedance of the front-end circuit is proposed.The mechanism and elimination methods of bio-potential signal interferences are illustrated,and several interferences,such as electrode DC offset,50/60Hz power line interference and motion artifact had been well eliminated.This thesis presents a pseudo-differential chopper analog front-end circuit with low noise,low power and high input impedance,which can be used for ECG signal acquisition and processing.In order to make the circuit suitable for use in WBAN,this thesis proposes a new low-power front-end circuit architecture,which integrates a pseudo-differential chopper instrumentation amplifier,a switched capacitor filter and a continuous time sigma-delta modulator.The pseudo-differential structure and negative-capacitor circuit are introduced to boost the input impedance.The chopper modulation technology is used to eliminate the 1/f noise and input offset voltage,and a DC-Servo circuit and a RRL circuit are added to eliminate the electrode DC offset and amplifier output ripple.The right leg drive circuit is implemented to suppress power frequency interference.This bio-signal monitoring front-end IC has been fabricated using SMIC 0.18?m standard CMOS process.The test results show that the power consumption of the front-end circuit is only 84?W,the input impedance is 2.5G?,the input-referred noise is 0.7?V_rms,the CMRR is 87.3dB,PSRR is 81.8dB,and it achieves 12.7-bit ENOB.The circuit performance can meet the design requirements of wearable applications very well.This thesis also presents a low power current-reused analog front-end IC for wearable ECG monitoring.This IC mainly includes three parts,namely,current-reused chopper instrumentation amplifier?CCIA?,switched capacitor filter?SCF?and 10-bit LSB-first SAR ADC.In addition,the right leg drive circuit is added to eliminate the interference of the 50/60Hz power line.The current-reused amplifier is introduced to reduce the power consumption.The input impedance is boosted by a new type of chopper coupling method which combins resistance and capacitance.Then,due to the low frequency and low activity of ECG signals,a novel LSB-first algorithm is proposed in the SAR ADC to greatly reduce the power consumption.Fabricated in TSMC 65nm CMOS process,this front-end IC occupies 0.52mm² active area and consumes 7.9?W from a 1.2V supply.It achieves 93dB CMRR,85dB PSRR,9.4-bit ENOB,input-referred noise lower than 1.6?V_rms,input impedance higher than 2.4G?and DC suppression as large as±300mV.