Design Of Data Transfer System For Vep Signal Based On USB Interface

Visual Evoked Potentials (VEP) is the evoked response of specific visual stimulate, elicited by nerve centre system that occur at specific time and specific location. VEP has a feature which is called Non-stationary. In comparison with the background noises of environment, it has very low amplitude and always overlapped with noises, so it is hard to obtain the actual data of VEP. VEP is an important parameter for diagnosis of ophthalmology disease. It reflects integrity of client's Visual pathway, now it has been extensive and widely studied. By extract and analyze VEP data, It can detect ophthalmology disease in time which is helpful to patients. In view of all this, VEP is important in clinical medicine application, the design of VEP measurement and analyses system is of great significance to cure ophthalmology disease.Universal Serial Bus(USB) is a new-type computer bus which is widely used in data acquisition device. With the feature of high speed transmission, easily expanded and facility, USB interface becomes a developing trend of data acquisition and transmission system. In this paper, USB2.0 system and protocol is introduced, a system of data acquisition and transmission for VEP is designed. The system involves three parts: hardware circuit, firmware and software. Hardware circuit is composed of signal modulate circuit, A/D converter circuit, clock generation circuit, high speed FIFO cache and USB interface circuit. C program language is used in firmware development which is the key point of achieve USB communication protocols and configure USB device. VC++ is used in application development,the application can realize data transfer between USB device and host computer.Currently,the method of progressive average is widely used for VEP acquisition. It carries out stimulation time after time, and add all the results for removing noise jamming, then divide the number of stimulation to get the original VEP signal. Regard to this theory, a system of data acquisition and transmission is designed, the system adopt synchronize triggering to make sure the synchronization of VEP signal. And in addition,FIFO cache is used to save data which can improve the correctness of data transfer. In this paper, the major emphasis is data transfer via USB2.0, data transfer between USB device and host computer is realized. The A/D conversion accuracy is 12bit, sample frequency up to 20MHz. Bulk transfer rates can achieve to 7.3 MB/s .