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Altera_Forum's avatar
Altera_Forum
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13 years ago

cyclone IV I/O standard

Hi,

I am using ep4ce30f29c6 (fbga780pin) with aproximately all IO in use. because of the need to use on chip termination, I use 3-volt as vccio. my main worry is that other parts in my design are 3.3volt. do I need to use pci-clamp diode for all inputs and also series termination on external drivers (feeding fpga)?

because of huge number of IO and considering clamping diode, will dissipation be critical and noticable? is it possible to interfacing with 3.3vot without clamping diode (disabling clamp diode)-it damage fpga or not? what is the value of forward voltage of clamp diodes?

thank you very much for your reply.

Ramin:confused:

2 Replies

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

    Clamp diodes are silicon diodes with respective forward voltage. Exact data can be e.g. derived from IBIS files. With 0.3 V forward voltage, diode current will be low. I think however, that reasonable source side impedance matching of fast digital signals to the FPGA can obviate the need for clamping diodes.