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Altera_Forum's avatar
Altera_Forum
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18 years ago

Ris/fall time?

Hello, I am developing a simple test board for a cyclone FPGA (EP2C8T144). It is my very first FPGA project, and I want to build my own FPGA board. Now, my question is: Which rise and fall...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
18 years ago

Some suggestions haven't been clear to me, so I like to mention, what I would do.

Basically I use a series resistor a the driver, that means at both end for a bidrectional signal. On chip series termination respectively selecting a low current strength (another name for the same thing) with FPGA can save external resistors in most cases.

A typical single ended trace impedance on a multilayer PCB is in the 50 to 90 ohms range. You can use calculation tools to determine the nominal impedance for your board. So if you have a digital output with high current strength (e. g. a logic device with 10 to 20 ohm output impedance) a series resistor of 33 to 68 ohm would be a suitable choice.