Design Of Analog Front-end Of Implantable Neural Signal Detection System

The detection of neural signals plays a vital role in the study of the nervous system,the treatment of tissue damage to the nervous system,and the emerging brain-computer interface,which has developed rapidly in industry and academic in recent years.With the rapid development of integrated circuits(IC),the use of IC technology to complete the detection of neural signals has become a popular research direction.The electrical characteristics of neural signals are low frequency and low amplitude.And during detected signals many interference signals are introduced.When designing implantable systems,in order to avoid damage to tissues,it is necessary to take into account factors such as power consumption and area of the system,which makes the design of the system have many difficulties.In this paper,the design of an analog front end of an implant neural signal detection system is proposed,the main modules include the pre-amplifier,the band-pass filter and the analog-to-digital converter(ADC).The pre-amplifier will amplify the detected weak neural signals to produce a pair of differential analog signals,and then the differential signals are sent into ADC and converted into digital signals for subsequent digital signal processing.The system also includes a band-pass filter that filters clutter outside the neural signal and a buffer that connects between different modules.After the proposed system architecture verifies the function through the ideal device,the schematic design and layout design are completed by using the 0.18-μm 1.8-V CMOS process,and the correctness of the system is verified by pre-circuit simulation and post-layout simulation.The system uses±0.9 V dual power supply,input impedance is 37.41 GΩ,overall power consumption is 237.99μW,bandwidth covers the effective band of neural signals,from 0.1 Hz to 40 k Hz,the gain within the system bandwidth is 45 d B,the number of digits of the converted digital signal is 12 bits,the overall area of the system is about 0.5 mm~2.The common mode rejection ratio(CMRR)of the system is improved by using a fully differential structure,CMRR in the passband exceeds 90 d B,which can meet the requirements of implantable neural signal detection systems.