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Contributor
Contributor
315 Views
Registered: ‎05-10-2018

synchronization of clocks

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Hello sir, 

I am using zc706 boards. I have generated a clock of 10 MHz from OCXO board (which is perfect) and given it to the AD18 (user_clk_p) pin of the zc706. I want output of 320 MHz from AD19(user_clk_n) pin. This is for system suppose s1.

Same thing i have done for s1 system. I want both these generated clocks from those 2 zc706 boards (i.e AD19 => user_clk_n)  to be in sync but i am getting a shift of 50 degrees or some value every time. 

1. Cant i get those clocks in synchronization from 2 different boards.?

I have generated 6 ports from OCXO board which is giving fixed 10 MHz frequency and they are in synchronization.This output is given to AD18 pin.

Hope you have understood my problem.

thanks in advance.

 

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Moderator
Moderator
259 Views
Registered: ‎02-09-2017

Re: synchronization of clocks

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Hi @niranjan,

Please correct me if I didn't understand your question correctly.

I understand you have two different ZC706 boards, each one has a clock input of 10MHz, which passes by a MMCM and get increased to 320MHz, and finally leave at the port AD19.

What you need is that these two clock output, from the two different boards, are in sync, correct?

If that is the case, unfortunately it's not possible. The MMCM have a setup and lock time, which changes every time (every time you power off and on the board, that time will most likely change a bit). Even if the design programmed on both boards is exactly the same, there's no control to get both clocks in sync.

What is the application that you are developing? Maybe we can help you modify your design so you don't really need to synchronize those.

Thanks,

Andre Guerrero

Product Applications Engineer

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Moderator
Moderator
260 Views
Registered: ‎02-09-2017

Re: synchronization of clocks

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Hi @niranjan,

Please correct me if I didn't understand your question correctly.

I understand you have two different ZC706 boards, each one has a clock input of 10MHz, which passes by a MMCM and get increased to 320MHz, and finally leave at the port AD19.

What you need is that these two clock output, from the two different boards, are in sync, correct?

If that is the case, unfortunately it's not possible. The MMCM have a setup and lock time, which changes every time (every time you power off and on the board, that time will most likely change a bit). Even if the design programmed on both boards is exactly the same, there's no control to get both clocks in sync.

What is the application that you are developing? Maybe we can help you modify your design so you don't really need to synchronize those.

Thanks,

Andre Guerrero

Product Applications Engineer

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Voyager
Voyager
242 Views
Registered: ‎02-01-2013

Re: synchronization of clocks

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I guess it's important to agree on what it means to be "in sync(hronization)". Most of the time, synchronization means that two signals are frequency synchronized. If you look at two signals at the same time on an o-scope, using 1 signal as the timebase trigger for the scope, they should be in a fixed relationship to each other on the screen--neither one is walking across the screen with respect to the other. That's frequency synchronization.

If this is the case, and your outputs are 'walking', then there's a problem. Both boards should be producing the same frequency signal from the same-sourced references.

Beyond frequency synchronization, there's phase synchronization. That's the next level. In addition to being frequency synchronized, the signals maintain a fixed phase relationship with each other--often at a zero-degree phase, but not necessarily zero. Phase synchronization is much harder to maintain between two generators, even when the outputs of those generators are frequency synchronized. (In this case, each 706 board is a generator.)

In addition to the frequency reference to each generator, each generator needs a phase reference. The generator would then need a phase detector to determine the phase of its output with respect to the phase reference. When a phase error is detected, the generator would have to tweak the frequency of its output up (or down) temporarily, in order to advance or delay that output to drive the phase error to zero. When both generators have achieved zero phase error with the phase reference, they'll be in phase synchronization with each other.

This kind of behavior is easy for a single IC. It's pretty standard for a single board or module (built for such a purpose) to be able to do it. But for two separate units to do phase synchronization without specialized clocking circuitry will be extremely difficult. Depending on the required accuracy of the phase alignment, it might even be impossible.

-Joe G.

 

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