LMX2595: problem with noises of LMX2595 PLL

Hi Yanni,

Instead of giving us the noise power, could you provide the screen shot of what you saw in the spectrum analyzer as per the configuration in Figure 2?

Hello! Fig4 is saved data from specrtum analizer. And data at Fig5 was made by hand, turning step by step LMX and measuring power at point 1.5 GHz.

Hi There,

I cannot understand the problem you are having from your excel plots, it will help me better if you could give us the screen shot of the spectrum analyzer.

Hello! I made a video that can help to understand my problem https://youtu.be/isqEOu3l61o

Hi Evgeniy,

Thank you for making the video, now I understand your problem.

We have seen this problem before, basically the problem is due to the output buffer. The problem gets worst at higher VCO frequency and output power. 

Please try if you can put a 3dB pad right after the buffer output, also use a smaller output power setting. These seem to be the only way to resolve this problem. 

Hello! I see srange thing. The level of noise decreases from 15 to 7.5 Ghz and at frequensy 7.5Ghz abruptly encreases and decreases to 3.75Ghz. At that points divider changes it's value and VCO goet to 15 Ghz (with max noise). So, i think, that that noise makes VCO. Am I right? And second question. 3dB pad will attenuate not onli noise? but signal too. SNR will be similar. Or pad will affect on LMX and SNR will be better?

Hi Evgeniy,

If the 3dB pad can fix the noise issue, I think a 3dB trade-off for output power is not a bad deal. After all, this is the only way we have ever found useful, I don't have other suggestion.