A Front-end Circuit Based On A Virtual Second-order Delta-sigma Modulator For EEG Application

In recent years,with the development of medical electronic equipment,braincomputer interfaces have been widely used in the diagnosis and treatment of epilepsy,stroke and other diseases.Among them,the implanted brain-computer interface directly embeds the electrodes inside the brain,which can obtain high-quality EEG signals and can better analyze the information contained.The EEG signal acquisition and conversion circuit is an important part of the implanted brain-computer interface,and its performance determines the acquired signal quality and processing accuracy.Therefore,the design of EEG signal acquisition and conversion circuit has gradually become an international research hotspot.Thesis according to the characteristics of cortical electroencephalogram(ECoG)and local field potential(LFP)processed by the implantable brain-computer interface,based on SMIC's 0.18?m CMOS(Complementary Metal Oxide Semiconductor)process,the EEG signal acquisition and conversion circuit design and simulation verification were completed.The overall circuit includes front-end amplifier,buffer stage circuit and delta-sigma modulator.The front-end amplifier circuit adopts capacitive coupling amplifier,and the influence of interference is reduced by using auxiliary circuits such as chopper modulation circuit,DC servo circuit and impedance boosting circuit.By adopting ClassAB amplifier in the buffer stage circuit,the driving capability is improved.The delta-sigma modulator is a second-order one-bit quantization modulator with a feedback structure,and through the use of amplifier multiplexing technology,a virtual second-order delta-sigma modulator is realized,which effectively reduces circuit power consumption and area.The simulation results show that the gain of the overall circuit in the bandwidth of 2.17 Hz to 5.73 kHz is 39.82 dB,and the low-frequency high-pass angle is 0.447 Hz,which can effectively suppress the DC electrode offset voltage.At the same time,the input impedance of the front-end amplifier circuit is 91 M?@200Hz,and the input reference noise in the 0.5 Hz?200 Hz frequency band is 5.73 ?Vrms.The deltasigma modulator achieves a signal-to-noise-distortion ratio(SNDR)of 76 dB in a 200 Hz bandwidth with 12 significant bits.With a supply voltage of 1.8 V,the total circuit power dissipation is 73.8 ?W.The EEG signal acquisition and conversion circuit designed in this paper basically meets the index requirements of the implantable brain-computer interface.