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Altera_Forum
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11 years ago

Cyclone lll emulated LVDS IO

Hi,

Currently, we are using Cyclone lll FPGA for our application. We plan to interface LVDS output signals with sensor chip. We had assigned LVDS related O/P signal in bank 7 and bank 8(top banks). As per the Cyclone lll handbook, top(bank 7 & 8) and bottom(bank 3 & 4) only support for Emulated LVDS signals while others banks supports for both LVDS and as well as Emulated LVDS signals.

For Emulated LVDS signal interface, is it compulsory to put external 3R resistor network? Presently we had not included any external 3R resistor network with emulated LVDS output signal but we had put only 100R resistor between differential signals. So, my concern is that whether FPGA provide proper signal interface with sensor chip or we need to redesign the board again.

Will appreciate comments.

Best Regards,

Mayur Akbari

6 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    For moderate speed, you can use RSDS scheme. Even at higher speeds, your sensor LVDS interface might tolerate non-standard (higher) differential signal levels. It's worth a try.

  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    To be more practical... guidelines are guidelines...

    best to use the scope to check out the signal at your interface chip.
  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    Hi,

    To ensure the Cyclone III emulated LVDS can perform as per the specification, it is recommended to follow the resistor network. If you are not able to comply to the required resistor network, you could try to run signal integrity simulation ie with IBIS model to tell if your setup can meet your target performance.
  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    Ultimate goal is your VOD VOCM of your signal meet the VID and VICM requirement of your RX

  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    You can refer to the Table 1–18. Cyclone III Devices Differential I/O Standard Specifications in the Cyclone III device datasheet for the LVDS VID, VCM and VOD specs. To ensure interface compatibility, you should make sure these specs are met.