基于FPGA的磁共振接收机数字下变频设计

Digital down conversion design of magnetic resonance receiver based on FPGA

介绍了变带宽数字下变频(Reconfigurable Digital Down Conversion,RDDC)的原理,针对磁共振成像接收机数字下变频的特点,提出了一种抽取率可在线编程的数字下变频器设计方法。对主要功能单元(变级数CIC滤波器、串并混合式FIR滤波器)的设计与FPGA实现进行了具体分析,同时针对ALTERA公司的5CGXFC9器件与1.5T磁共振成像系统数字下变频需求,利用Verilog语言设计了输出量化位数为16bit、抽取率为180~11520的RDDC实例,基于ModelSim与MATLAB进行了功能仿真。通过仿真结果分析可知,该实例在给定器件资源约束下,实现了100MHz采样率、2kHz^200kHz带宽信号的RDDC功能,在单片FPGA内完成了对不同带宽信号的数字正交检波与抽取滤波操作,为磁共振成像接收系统提供了一种高通用性与高灵活性的变带宽DDC解决方案。

The principle of reconfigurable digital down conversion(RDDC)is introduced,and a design method of digital down converter with decimation rate can be programmed online is proposed,which aiming at the requirement of digital down conversion in magnetic resonance imaging receiver.The design and FPGA implementation of the main functional units(variable series CIC filter,serials-parallel FIR filter)are analyzed.For 1.5T magnetic resonance imaging system design a quantized 16bit,decimation rate is 180~11520 reconfigurable RDDC instance based on Verilog language use ALTERA’s 5CGXFC9 device.Through the analysis of the simulation results of ModelSim by MATLAB,the system realizes the RDDC function with 2kHz^200kHz reconfigurable bandwidth under the 100MHz sampling rate with the constraints of device resources.It provides a versatile and flexible reconfigurable bandwidth DDC solution for magnetic resonance imaging receiver systems.