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Question asked by tneagoe on Nov 17, 2011
Latest reply on Nov 23, 2016 by rbrennan

I need to understand the difference between the new ADF4351 and the older ADF3250. From the preliminary datasheet they look identical except for improvements in the VCO. I presume that the ADF4351 is intended to solve the temperature sensitivity of its predecessor, which under temperature variations may cause loss-of-lock. May application is an airborne VHF radio navigation receiver tunned at fixed-frequesncies, with the VCO operating close to 2.9GHz. Offcourse a loss-of-lock when landing is hardly acceptable. If this is true then ASDF4351 woudl be suitable for this application.


The VCO phase-noise performance is critical, it shouldbe better than -146dBc/Hz at 185MHz (nominal) and for a 400KHz offset after division-by-16.

It looks like the ADF4350.4351 can do this, albeit with a small margin, but I no longer expect wide margins. I intend to use two PLLs per receiver, the first one for LO synthesys proper, the 2nd one as LO tracking filtersimplicity, less EMI/shielding issues, cost/size savings and easier and easier field trouble-shooting/repairs. Remains to see if these promises hold true using the brassboard I am building.