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lmx2594 跳频
上图所示：是LMX2594输出后接固定四分频器到相噪仪的结果。SPI时钟频率为25MHz，每200us切换一次频率，在图中可以看到正常情况下在全辅助模式可以得到极短的跳频时间，但是偶尔会出现图中一些不正常的现在，跳频时会出现一个大过冲，然后需要大概100us才能稳定到目标频点。这种现象在同一个VCO段内出现的概率小，跨段的时候出现的概率大一些。下面是初始化的代码。初始化完成以后置位VCO_SEL_FORCE, VCO_CAPCTRL_FORCE, and VCO_DACISET_FORCE进入全辅助状态。
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
跳频时寄存器的写入顺序如下，其中R20,R19和R16是通过回读以后记录下来的值，然后用FPGA采用读表的方式写入频率对应的寄存器值。
1. change R36(0x24) (note:PLL_N)
2. change R43(0x2b) (note:PLL_NUM)
3. change R20(0x14) (note:VCO_SEL)
4. change R19(0x13) (note:VCO_CAPCTRL)
5. change R16(0x10) (note:VCO_DACISET)
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