Doppler frequency shift simulation is a key technique in high dynamic satellite navigation signal simulator.Considering the features of field programmable gate array,a mixed-clk third-order direct digital synthesizer (DDS )simulation model was built,and its output phase expression was derived.The calculation method for initial control word for each stage DDS was given and it was pointed out that the same-clk third-order DDS simulation model is only a special case of mixed-clk simulation model.After analyzing the signal phase error caused by mixed-clk,the word length design method for each stage DDS was discussed.Comparison between the same-clk third-order DDS and the mixed-clk third-order DDS can reduce both resource and power consumption.Simulation results indicate that the proposed method can be used to simulate signal Doppler is of high precision.%在高动态卫星导航信号模拟器中，信号多普勒频移模拟是一项关键技术。结合现场可编程门阵列的特点，建立了分析混合时钟三阶直接数字频率综合（DDS ）输出相位的仿真模型，推导了其输出相位表达式，给出了各阶DDS初始累加控制字的计算方法，并指出等时钟三阶DDS仿真模型仅为混合时钟仿真模型的特例。在分析了混合时钟速率对信号相位模拟造成的误差后，讨论了各阶DDS的字长设计方法，并与等时钟三阶DDS进行比较，说明了采用混合时钟三阶DDS可以降低实现资源消耗和功耗。仿真分析表明，所提方法可以实现对信号多普勒特性的高精度模拟。
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