Studies Of AD9910-based High-Speed Digital Frequency Source

Over the last decades,significant improvements in magnetic resonance imaging(MRI) have been made.Nevertheless,the implementation of more and more complicated scanning protocols requires higher and higher performance of MRI equipments,As the core,the spectrometer controls other parts in the MRI system.Thus,the capability and the flexibility of the spectrometer sub-system is one important factor in the MRI system design.Digital frequency source is an essential unit of the spectrometer system.It is used to generate RF pulse,and excite nuclear spins in samples for obtaining physiological information. In order to overcome the shortcoming of the earlier frequence source in our home-built MRI scanner,a high-speed digital frequence source based on integerated direct digital synthesis(DDS) chip is designed and implemented.The design and implementation is described in detail in this thesis,and the performance of the frequence source is verified and demonstrated in the home-built MRI scanner.The main contents of this thesis are as follows:The first part introduces three types of frequency synthesis technology and the principle of DDS.And then the discussion is focused on the analysis of requirements of an MRI frequency source.The second part presents the hardware design and realization of the frequency source which is based on a fully integerated DDS chip(AD9910).Specifically,the details include the control logic in field programmerable gate array(FPGA),the configuration of the DDS chip internal registers,the access control of synchronous dynamic random access memory (SDRAM),and so on.In addition,the coherence maintenance between transmit and receive channels are taken into account.The third part shows experimental results and performance analysis,Finally the proposed frequence source is integrated into the home-built scanner,and MR experiments are carried out to demonstrate the performance of the frequency source.