TI中文支持网Part Number:LMX2581
我根据LMX2581评估板设计的电路板，所有参数包括环路滤波器参数与评估版一致，在低频段即500MHz以下输出不是正弦波，变成了方波，但是高频段仍是较为纯净的正弦波。I designed the board according to the LMX2581 evaluation board. All parameters including loop filter parameters are identical to the evaluation board. At the low frequency band that is 500MHZ below, the output is not a sine wave, changed into a square wave, but the high frequency band is still a pure sine wave
然后我又使用clock design tool修改了环路滤波器的参数，如图所示：Then I used the clock design tool to modify the parameters of the loop filter, as shown in the figure:
在低频段，以128MHZ为例，得到的波形如下图蓝色波形所示，相比之前的方波效果要好些了，但是还是存在谐波。In the low frequency band, take 128MHz as an example, the waveform obtained is shown in blue in the figure below, compared to the previous square wave effect is better, but there are still harmonics.
请问这个问题怎么解决？How to solve this problem?
Amy Luo：
您好，
是的，只要VCO信号被向下分频，波形就是方波。
是的，可以使用滤波器来衰减谐波，下面链接是clock design tool的用户指南，里面有Loop Filter 使用说明：
National’s Clock Design Tool v1.1 Instructions User's Guide
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?? ?：
谢谢！
