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AD9548 eval. board OCXO

Question asked by Jaime on May 14, 2014
Latest reply on Jun 19, 2017 by igorfreire

Hello, I have a simple question about the OCXO used in the evaluation board. I am interested just because we use a very similar OCXO model in 1pps synchronization applications.


The external supply for the VCXO is specified to be 3.3V, nevertheless the OCXO model OX-220-1-DAJ-1080-20M seems to be a 5V supply model that needs at least 4.5V supply to guarantee specification.


The OCXO reference corresponds also to a LVCMOS (not sinewave) output waveform, so I wonder if the model reference is wrong concerning the 3.3/5V supply, as far as 3.3V supply seems to be the useful option as far as even if the eval. board admits many system clock options, the onchip OCXO one seems to be foreseen to drive in high impedance LVCMOS 3.3V OCXO output to the AD9548 and this admits only, I guess, a maximum of 3.3Vpp.


And by the way assumming the OCXO is a LVCMOS output one (no slew rate issues), can you advice on using a 20 MHz one instead a 10 MHz, in both cases with or without use of the frequency doubler, for phase noise improvement (of the internal system clock VCO), assumming the equivalent noise of the OCXO is the same? I mean without assumming a benefit in OCXO phase noise relative to its frequency (as if the 20 Mhz OCXO phase noise would be 6dB worst than the 10's). I am intereted in the possible difference of effect of the use of 10/20/40 MHz system clock (10x1 or 10x2 and 20x1 or 20x2) reference (for the DDS be driven at 1Gs/s, for instance) due to the onchip PLL and also to the dobler itself. Is data sheet fig. 8 got with or without the doubler?


Finally the evaluation board user guide refer to a OCXO named OX-221, instead 220, but this is not published in vectron. Is it different in something?


Thanks in advance


Jaime Martin