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Altera_Forum
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15 years ago

How to receive LVDS signals from ADC?

Hello everyone,

I'm going to design my first FPGA board(EP2C50) with 14bits ADC(AD9445). There are 14 groups of two differential traces going to FPGA I/O ports with 100-Ohm termination resistor between the two signals at the FPGA's input buffer. Or we can say there are two groups of 14bits digital signals. But I'm now puzzling that how can I get the 14bits digital signals in the FPGA?

One of my colleagues suggests that I can substract Dx- from Dx+ to get Dx( x from 0 to 13) with HDL code. I wonder if there are better ways to figure out this problem? Thanks a lot!

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

    --- Quote Start ---

    Hello everyone,

    I'm going to design my first FPGA board(EP2C50) with 14bits ADC(AD9445). There are 14 groups of two differential traces going to FPGA I/O ports with 100-Ohm termination resistor between the two signals at the FPGA's input buffer. Or we can say there are two groups of 14bits digital signals. But I'm now puzzling that how can I get the 14bits digital signals in the FPGA?

    One of my colleagues suggests that I can substract Dx- from Dx+ to get Dx( x from 0 to 13) with HDL code. I wonder if there are better ways to figure out this problem? Thanks a lot!

    --- Quote End ---

    See ALTLVDS megafunction.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    Open your project, then open the Pin Planner. In the cell containing <new node> enter a new group name for your differential signals, say D[13..0]. Pin Planner will add the 14 signals for you in a separate row each. Then in the IO standard column set it to LVDS. The Pin Planner will now create the complement pin for that signal -> D[*](n). If you later place the positive pin on a (valid) location in the pin diagram it will nicely take the complement signal along and place that as well. In your logic you just connect the D[*] pins in your entity.