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ADL5375-05 vs -ADL5375-15

Question asked by DRS-des on Oct 5, 2012
Latest reply on Oct 10, 2012 by THA

Which is the better for lowest spurs -the 0.5V biased ADL5365-05 vs. the  1.5V biased ADL5375-15?


I am driving the ADL5375 IQ mod with ADF9788 DAC,  fixed LO freq =900M, with internal DAC DDS set  to 150Mz. The data rate is 225M for Instantaneous BWidth (IBW) > 180MHz, hence I &Q baseand range 150+/-90MHz. The fixed 900M LO means the carrier and image leakage at the ADL5375 o/put can be removed by an analog filter centered at 1050MHz.


Currently I use the -05 becuse the DC biasing interface to the AD9788 DAC is easier than ADL5375-15. But I note from the data sheet for 2nd &3rd harmonics (Flo+2*Fbb) & (Flo+3*Fbb) , the the -15 is better than the -05.Eg if Fbb=70M, the signal is 970M with a spur at 1040M, inside the analog filter passband.


If lowest spurs is main criterion, which version is best? Are there two different bias types because of spur perfromance or is it because DACs have either 0.5 or 1.5V DC common-mode interface? If the -ADL537515 has better spurs nominally, how difficult is level shifting with a wide baseband from 60M to 240MHz?


Going forward, I am investigating the AD9122 DAC for IBW up to 500MHz, with the IQ mod in zero-IF mode (DAC DDS= 0Hz); RF out from 500M to 6G. The IQ baseband filter is a low -pass > 250MHz. Now, I will need carrier and image cancellation., and there is no filtering after the ADL5375. Which is best for optimum spurs?