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I'm working on a ADC-AD9266 which gives output at a reference of Data Clock Output (DCO) whose frequency is same as that of ADC conversion rate which also the frequency of Clock. f(clock) = f(DCO) = ADC conversion rate.

I have used FXO Oscillator to clock the ADC. before I was using FXO-16MHz & I was getting DCO (16 MHz) which was correct. But due to some reason I needed to move down to lower data collection rate. So I used FXO-10 MHz IC but now the DCO signal has disappeared.

This was happening even before when I was using FXO-25 & FXO-16 but slightly change(7V-8V) in power supply gave me proper DCO signal.

The problem is, I'm not not getting DCO signal with FXO-10 IC (which was there when I used FXO-16). I'm not able to figure out the problem. connection are proper & no pins are short. I'm having doubt in current that is supplied to FXO or ADC. could there be any other reason because I have just replaced FXO-16 by FXO-10 IC.

ADC-AD9266 Datasheet

BLM21PG221SN1D Datasheet

FXO Oscillator Datasheet

ADC FXO Power Supply

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Step one is getting rid of your 1N4148 diodes to "make 3.3V", because that's not even likely going to be 3.3V.

And look at your datasheets:

Your Oscillator needs 3.3V +/-5%. The 3.5V to 3.7V made by those diodes doesn't fit the bill, so could one be working and another not? Possibly.

But much more importantly, you say that it is your "3.3V_AVDD", I do not see you convert that to the actual net AVDD, so you may have paid attention to it, but it worries me none the less. Did you look at page 4 of your AD converter?

AVDD: min: 1.7V; max: 1.9V DRVDD: min 1.7V; max: 3.6V (again the diodes? will they? won't they?)

Are you taking care of that with an actual regulator?

If not, be aware you may just be in the process of just destroying your ADC and this could be the first step in its downfall.

Things with this level of internal complexity aren't joking around when they say they have a maximum voltage to think about.

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  • \$\begingroup\$ I have used 1.8V regulator for the AVDD supply to ADC. I too had doubt of diodes I have used here for generating 3.3V which I will avoid. But I still couldn't find the reason when I just replaced FXO-16 by FXO-10 DCo signal disappered. could there be any other reason? \$\endgroup\$ – nkg2743 Jun 22 '15 at 4:00
  • \$\begingroup\$ @nkg2743 It's still possible that the different voltage affects one more than the other. It's also possible you accidentally got a type that's not got the same outputs, check that. It's also possible the biasing of your signal changes and is wrong, see ADC datasheet page 20 about uncoupling with capacitors and if you use capacitors, go back to the FXO advised connection scheme. \$\endgroup\$ – Asmyldof Jun 22 '15 at 9:09

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