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AD9523/PCBZ Evaluation Kit 40Mhz Clock

Question asked by cwshep on Jan 30, 2012
Latest reply on Feb 6, 2012 by cwshep

I recently purchased a couple AD9523/PCBZ clock evaluation kits (http://www.analog.com/static/imported-files/user_guides/UG-169.pdf) for simple 40Mhz clock generation/distribution.  Ideally I would like to have the signal generated onboard, but I can also use an external reference clock if necessary.  After playing with the kit for quite a while, the closest output I can get is 40.0977Mhz, and I haven't been able to get it to use the reference input.

 

To get the 40.0977Mhz I use the VCXO at 122.88Mhz, which is then fed to PLL2 where the doubler is off, and the N divider A = 3 and B = 7.  This gives a VCO of 3809.23, which I then divide by 5, then by 19 at the actual output. 

 

Is the frequency of the onboard VCXO fixed?

 

How do I get it to use the REF_A input rather than the VCXO?  Is it possible?  Typically I can see under PLL READBACK that it detects REF A as OK, but it says "PLL1 Output Lock Detect:  OFF (Clock Missing)".

 

So, in short, is there a way to use the AD9523 evaluation kit to generate 40Mhz outputs, either with or without an external reference clock?

 

Thanks!


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