Research And Design Of High-preformance Analog Front-end Circuit For ECG Signal Acquisition Module

In recent years,the development of the integrated circuit industry is facing a bottleneck.People need to explore new research directions.Recently,the integration of Bio-Medical and integrated circuits has become a popular research topic.With the combination and rapid development of biotechnology,cardio cerebral vascular and microelectronic technology,electrocardiograph signal acquisition and recording technologies are playing an important role in the prevention and treatment of cardiovascular diseases increasingly.The analog front-end circuit,which constitutes the Electrocardiograph signal acquisition module,has also got more and more attention.Electrocardiograph signals usually range from dozens of microvolts to several millivolts,and the frequency is within 300Hz.Besides,electrocardiograph signals are easy to be disturbed.To address this problem,this paper selects the appropriate circuit structure,and designs an analog front-end circuit chip which is applied to the electrocardiograph signal acquisition module.The analog front-end circuit consists of the Instrumentation Amplifier and the Sigma-Delta modulator.According to the application in the front-end circuit in biomedicine,the main research work in this paper includes the following aspects:high Common-Mode-Rejection-Ratio,low noise,high input impedance of the Instrumentation Amplifier,and high precision design of Sigma-Delta modulator,and low power consumption of the overall circuit.Firstly,this paper theoretically analyzes and manually calculates the noise factors that cause by the circuit.Then,the design indexes of Instrumentation Amplifier and Sigma-Delta modulators are determined by the calculated results,and the suitable whole circuit architecture is selected.The entire circuit uses SMIC 0.18μm CMOS process.The whole circuit design process adopts gm/Id method,which effectively reduces the iteration times of circuit parameter calculation,shortens the circuit design cycle and improves the work efficiency.In this paper,capacitive coupling structure is selected for the Instrumentation Amplifier circuit,chopping modulation method is used to reduce the op amp's offset voltage and 1/f noise,the ripple suppression loop is used to suppress the chopped ripple,and the constant transconductance technology is adopted to reduce the nonlinearity of Instrumentation Amplifier.The results of Instrumentation Amplifier simulation show that the gain is 40dB and Common-Mode-Rejection-Ratio is close to 163dB.The Sigma-Delta modulator uses a cascade integrator feedback structure.Firstly,modeling system for Sigma-Delta modulator with the help of MATLAB SDtoolbox.Then the stability of the system,signal-to-noise ratio and the final modulator coefficient are determined through behavioral simulation.Under the simulation of non-ideal behavior level model,the Signal-to-Noise ratio of the behavior model of the modulator is 112.5dB,the effective number of bits is 18.39 bits.The power consumption is 1.26mW,and the the effective number of bits is 18.03bits in the circuit level modulator.Then begin to the design of the overall analog front-end circuit.Finally,the layout of the analog front-end circuit is designed,and the layout is verified by DRC,LVS and post simulation.The post simulation result of the analog front-end circuit shows that the Signal-to-Noise ratio is 99dB,the effective number is 16.15bits,and the power consumption is about 1.78mW.The area of the entire circuit layout is 1.677×0.898mm~2.