Design Of Interface Special Integrated Circuit For EEG Signal Measurement

With the continuous progress and development of science and engineering technology,the accuracy of all kinds of sensors and the ability of information data processing are also developing rapidly.It provides a more convenient and comfortable and efficient way of life.All kinds of consumer electronics,medical electronic products,etc.are developing and updating rapidly.At the same time,it integrates a variety of sensors,with more comprehensive functions and realizes the interaction of multiple ways.As an important medium for the exchange of information between human civilization and nature,sensors are constantly improving as technology continues to improve,and the accuracy requirements are also increasing,and the matching interface circuits are also constantly improving.As the most abundant signal of bioelectric signal,EEG signal has a wide application prospect in the fields of medical treatment,EEG control and so on.At the same time,as the weakest bioelectric signal,its precise measurement also puts forward more stringent requirements for the corresponding interface circuit.In this paper,the design scheme of EEG measurement interface circuit at home and abroad is investigated and compared.At the same time,the characteristics of EEG signal and the electrical models of various kinds of measurement electrodes are investigated and analyzed.A four channel EEG signal measurement scheme is proposed,which works with AE chip and BE chip,for non-contact dry electrode.The input of AE chip adopts current balance structure instrumentation amplifier,realizes AC coupling through low frequency suppression feedback loop,effectively suppresses the impact of electrode offset,and effectively ensures sufficient input impedance.The input chopper adopts low voltage input bootstrap structure,effectively reduces the conversion impact of injection current noise caused by high electrode impedance.The variable feedback loop of gain controlled amplifier in AE chip adopts bidirectional variable feedback network,which can achieve a wide gain range of 1-128 times of 8 gears and reduce the occupied area of feedback network as much as possible.At the same time,AE chip provides data for the following motion artifacts suppression by measuring the electrode impedance ETI signal.The BE chip is designed with multichannel structure.The output signals of four AE chips is processed at the same time to realize the conversion of EEG signals from analog to digital.The input of BE chip is a current feedback instrumentation amplifier,which can sample and hold current to realize multichannel sigma delta modulator.According to the application and overall system design,the circuit structure and parameter design of the module are completed.The simulation results show that the input instrument amplifier in the AE chip realizes the AC coupling of the low-frequency cutoff frequency 0.22Hz;and within the signal bandwidth 1-1k Hz,the equivalent input reference noise of the input instrumentation amplifier is 22 n V/sqrt(Hz).In BE chip,input reference noise is less than 35 n V/sqrt(Hz)within 1 ? 1k Hz,and the structure design of the multichannel modulator is realized through the sample and hold circuit.Finally,the circuit level simulation verifies that the signal-to-noise ratio of the modulator is 112.29 d B,and the conversion accuracy is more than 18 bits.