16-Channel Analog-to-digital Converter Chip Design For EEG Measurement

With the development of science and technology and the growing desire of human beings to explore themselves,various bioelectrical signals have been discovered and utilized by scientific researchers.Among them,EEG signal is one of the important signals.It has a great role in many medical fields.If combined with computer technology,it is even possible to manipulate objects with consciousness,and EEG measurement is the first step and the most important step to application.However,because EEG measurement requires a large number of electrodes for detection,the traditional analog-to-digital converter is very cumbersome.In order to adapt to the development of the new era,it is necessary to design a multi-channel analog-to-digital converter to further improve the integration and reduce the weight and volume of the instrument.In this paper,by comparing the advantages and disadvantages of various multi-channel schemes,the structure of multi-channel and single analog-to-digital converter with time multiplexing is selected.A low-noise instrumentation amplifier is used to amplify the weak EEG signals,and finally a high-precision Sigma-Delta modulator is used for analog-to-digital conversion to achieve a high dynamic range.This paper designs a multiplexer for channel cyclic switching and designs a clock for cyclic switching.This paper designs a low-noise instrumentation amplifier with current feedback type and uses chopping technology to effectively suppresses low-frequency noise and uses a ripple suppression loop which greatly reduces the high-frequency ripple at the output.Dual path and resistor-capacitor feedback are used for frequency compensation,which broadens the bandwidth.A current attenuator is used to achieve a lower equivalent input noise.The modulator designed in this paper adopts a single-loop CIFF structure.In order to achieve higher conversion accuracy,the order is fourth-order,and the parameters of the integrators of each stage are designed by matlab.Choppers are used on the first stage op amp to reduce low frequency noise during circuit level design to further maintain pre-stage low noise performance.After designing all the circuits,the circuit is simulated.The pre-simulation results show that the equivalent input noise of the low-noise instrumentation amplifier at 1Hz is13.25 nV/sqrt(Hz),and the signal-to-noise ratio of the modulator can reach 120.9dB and the signal-to-noise distortion ratio can reach 116 dB.The simulation result of the whole analog part shows that the 250 Hz dynamic range(excluding harmonics)is about 132 dB.Then the layout design and post-simulation are carried out.The simulation results show that the single-channel output rate of the 16 channels reaches 600 SPS,and the equivalent input noise at 1Hz is 14.2 nV/sqrt(Hz).The signal-to-noise ratio is 119 dB,the signal-to-noise distortion ratio is 105 dB,and the 250 Hz dynamic range(excluding harmonics)reaches 132 dB.