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MinzhiWang's avatar
MinzhiWang
Icon for Occasional Contributor rankOccasional Contributor
2 years ago
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Why do i get this error when I use lvds?

Hello guys, My device is 10CX220YF780E5G and the Quartus is QPP23.4. I implemented one channel LVDS receiver in my project. External PLL was checked. After full complilation, I found LVDS module was...
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  • AqidAyman_Altera's avatar
    AqidAyman_Altera
    1 year ago

    Hi,


    Yes, I found it in Volume 2, pages 4-18, from the link I provided earlier.

    Let me know if you can't find it.


    Regards,

    Aqid


AqidAyman_Altera's avatar
AqidAyman_Altera
Icon for Regular Contributor rankRegular Contributor
1 year ago

Hello,


Okay, if it’s AC coupled, then it will need DC restoration resistors on the board. The GPIO and dedicated clock pins in our devices do not have DC biasing capability and require external circuitry when AC coupling. The transceivers have the required termination and biasing circuits to support AC coupling.


Here is an example from the Cyclone 10 GX Handbook that shows AC coupling with the DC restoration circuit. VICM can be set with a voltage divider or power supply, typical values used by customers is 1.2V or 1.25V. Then the two 50 Ohm resistors serve as the DC bias connection and 100 Ohm differential termination:

https://www.intel.com/content/www/us/en/docs/programmable/683775/current/lvpecl-termination.html


Thanks.


  • MinzhiWang's avatar
    MinzhiWang
    Icon for Occasional Contributor rankOccasional Contributor
    1 year ago

    Hi Aqid,

    Thanks for you info above. There are two things which need to confirm with you.

    1. Your provided example is of external LVPECL drives FPGA LVPECL I/O. You know, our case is of external CML drives FPGA LVDS I/O. Can we use the same structure of the example in our case?

    2. If item 1's answer is "Yes". According to your comments "Then the two 50 Ohm resistors serve as the DC bias connection and 100 Ohm differential termination", after using this structure, the LVDS receiver's inside differential OCT should not need to be used any more?

    Thanks