Products > FMC150

Timing shift of FMC DAC output

<< < (2/4) > >>

arnaudNL:
Dear Sir,


Luis will be back to the office next Monday.


Best Regards,
Arnaud

lmunoz:

One guess that I have is that it is serialization. Are the shifts completely random or they always shifted a multiple of some number?

For example say the ADC takes a sampling clock of 250 MHz and you get a divided version to the FPGA at 62 MHz and you do 4-to-1 serialization. Because it takes 4 cycles of the 250 MHz the same time as 1 cycle of the 62 MHz, it might be randomly aligned in 1 out of 4 positions.

Is the clock you going directly from INPUT BUFFER to a BUFG to a SERDES? I would try an artificial delay on the digital data to see if moving fixes the alignment. For example have a MUX where you can change (while running) if the data going to SERDES gets a delay of 1,2,3,or 4 clocks.

fmcuser:
Dear lmunoz,


Thank you for your information.
As for the vhd files for DAC clock, data, and frame, I used the Xilinx component "OSERDES".
(the clock was input to an MMCM, converted to the single-ended scheme, and input to those OSERDES.)
Besides, I also tried self-made OSERDES.
The timing shift occurs for both of the above cases.
The time resolution of the timing shift is around 2 ns, and its dynamic range is around 150 ns.

lmunoz:
For FMC150 I believe the clock coming from U4P/N is 245.76. You can see that in the constraint file where it shows

NET "CLK_TO_FPGA_P_0" TNM_NET = CLK_TO_FPGA_P_0;
TIMESPEC TS_CLK_TO_FPGA_P_0 = PERIOD "CLK_TO_FPGA_P_0" 245.76 MHz HIGH 50%;


Why do you think it is 61.44 MHz, have you done modifications to slow the clock? That clock then should go to a PLL and from the PLL to the OSERDES. You should use the same clock going to OSERDES to go out the SMA connector. They should be in phase if you are generating the waveform correctly. Without looking at the code and knowing what modifications you have made it is difficult to say what can be causing random phase shifts.

ebarhorst:
Dear Chao,
do you have an update on this topic?


Best regards,
Erik

Navigation

[0] Message Index

[#] Next page

[*] Previous page