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Altera_Forum's avatar
Altera_Forum
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14 years ago

Emulated LVDS ?

Hi forum, this is my first post.

I'm trying to use a laptop lcd screen with the De0-nano board (fpga:EP4CE22F17C6), and i have some questions about lvds and emulated lvds:

What's the difference between LVDS and Emulated LVDS?

Why do i have to use a external resistor network? Is it necessary?

How could i damage the LVDS or the Emulated LVDS?, What cautions must i take?

My laptop's lcd datasheet says the LVDS signal must be between +100mv and -100mv,

why do i get +3.3 and -3.3 in the fpga's LVDS pins when i measure them?

Does it matter or LVDS just looks for the current direction?

thank you for your help,and time

sherneyko

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    --- Quote Start ---

    My laptop's lcd datasheet says the LVDS signal must be between +100mv and -100mv

    --- Quote End ---

    This sounds like a minimal specification. LVDS standards require a differential voltage of 200 or 250 to 450 mV. But in any case, LVDS spells low voltage differential signalling.

    --- Quote Start ---

    Why do i have to use a external resistor network? Is it necessary?

    --- Quote End ---

    It necessary to achieve the specified voltage range.

    --- Quote Start ---

    why do i get +3.3 and -3.3 in the fpga's LVDS pins when i measure them?

    --- Quote End ---

    LVDS signals are terminated with a 100 ohm resistor. You get the expected voltage with this termination.

    --- Quote Start ---

    What's the difference between LVDS and Emulated LVDS?

    --- Quote End ---

    Besides requiring the said resistor network, emulated LVDS is slower than dedicated LVDS drivers. Consult the FPGA device manual for the exact specification..