External reference clock

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z9p

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External reference clock
« on: June 05, 2020, 02:27:27 PM »
Is there a way to drive and/or receive an external clock to synchronize multiple boards or with other equipment?  Typically this clock is 10MHz but doesn't have to be.  As far as I can see, this feature is not foreseen with a dedicated ref clk port, but I would imagine that it could be added using one of the digital channels, with appropriate firmware changes.  Is this possible?

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Dejan

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Re: External reference clock
« Reply #1 on: June 06, 2020, 07:40:30 PM »
This feature was not researched during development so unfortunately I can't tell you if it's possible or not. Digital interface can support 10 Mhz clock, but I don't know how the synchronization can be achieved if the sampling clock is running at 250 MSPS. If you find any information about how this could be implemented, It would be nice to know.

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z9p

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Re: External reference clock
« Reply #2 on: June 06, 2020, 07:56:18 PM »
One route to do this could be to use the 10MHz clock as the reference to the PLL/MMCM in the FPGA to synthesize the 250MHz clock, then send it to the ADC.  Would the current hardware support this?

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Dejan

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Re: External reference clock
« Reply #3 on: June 06, 2020, 09:01:39 PM »
The hardware is using onboard oscillator for ADC clock source. It's not possible to use the FPGA as a clock source for ADC. The clock generated by the FPGA would have a considerable amount of jitter which would degrade the ADC performance.