GPS信号模拟器中sine存储表的设计和实现

结合Sunderland算法和泰勒多项式原理,给出了直接数字频率合成(DDS)中相位至幅度映射表的压缩算法的数学模型,分析了压缩效率.用快速傅里叶变换来分析杂散水平,利用matlab计算工具对整个算法进行了建模、优化和验证,仿真表明映射表采用该算法设计的DDS数字载波部分的最大杂散约为-90?dB,且有良好的压缩效率.该算法实现结构简单,没有乘法运算.在Xilinx公司的现场可编程门阵列(FPGA)中进行了实现,已成功地应用于一个实际GPS信号模拟器数字中频系统的设计.

Design of a algorithm of mapping from phase to sine amplitude in DDS of a GPS signal simulator system

Based on trigonometric identities, Sunderland technique is a effective compression algorithm for mapping from phase to sine amplitude in ROM-based direct digital frequency synthesizers(DDS)design. A modification based on Taylor-series linear interpolation method was proposed to provide additional improvements in compression efficiency. Their effect on distortion and trade-offs were investigated, and spurious were identified by using fast Fourier transform algorithm (FFT). A computer program was created to simulate and optimize the effects of the memory compression and algorithmic techniques on the output spectrum of the DDS with the help of matlab computing tool. The subjected multiplierless architecture was then implemented in a Xilinx’s field programmable gate array (FPGA). Simulation results show that the proposed techniques is effective, and the digital output of the designed DDS which using this compression technique has the worst case spurious about -90?dB. A 80?MHz DDS was developed and used successfully in a actual projects of a GPS signal simulator system.