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High order intermod products from ADL5375/5380

Question asked by DJ01 on May 23, 2012
Latest reply on Jun 1, 2012 by THA

Hi there,

I am building a frequency translator with ADL5380/5375. I first demod the input to baseband with ADL5380 in ~2.5GHz(f1), then filter the BB signals with active lowpass filters (a few MHz passband). The the baseband signals drive ADL5375 to ~700MHz(f2). The output is amplified by the PA.


I am seeing this annoying high order intermod spurs that fall in my output band. they are exactly as 4Xf2-13f1 and 15Xf1-4f2. The spur level is about -85dBm at the output of ADL5375, so after the amplification it got quite high (~50dBm).


I first thought that it was my LO's harmonics problem even I filter them with LPF. But even when I replace the LO signal with the one from agilent SigGen, it still shows exactly the same spurs. Putting on the metal shielding can (has individual chambers for 5380/filter/5375/PA) doesn't change the spurs at all, so they look conductive.


The whole chain is powered by the same 5V rail with only ferrite beads for some isolation.


I would appreciate any suggestions on where to attack the issue.