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# What is the difference in the speed of FPGAs like Xilinx and Altera?

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#### pravi

##### Junior Member level 3
What is the difference in the speed grade of FPGA's like xilinx and altera.

Xilinx has V-5 devices with -1,-2,-3
and Altera also have -4.-5,-6.

Is it some thing relates with the propogatin delay or how does this affect timing

#### echo47

##### Advanced Member level 5

FPGA speed grade numbers usually don't mean anything like nanoseconds or megahertz.
They are simply code numbers that you refer to in the data sheet.

#### pravi

##### Junior Member level 3

No , You are wrong. They are not just mere code numbers printed on the FPGA.

You know if you buy -1 device for $5 then -2 will be around$8 . Just check with your FPGA vendor

#### echo47

##### Advanced Member level 5

No, you misunderstood my correct but unclear answer. I'll try to clarify.

In the old days, the speed grade of many PLD or GAL devices would directly tell you the performance. For example, -4 -5 or -7 would mean 4ns 5ns or 7ns.

Modern FPGAs speed grades usually don't have any intrinsic meaning like that. Now they are simply code numbers that you must look up in the AC Specifications section of the data sheet. The data sheet gives columns of timing parameters for each speed grade. Some FPGAs have hundreds of different parameter values for each speed grade.

#### pravi

##### Junior Member level 3

Sorry, Can you send me the data sheet for the same for better understanding

#### echo47

##### Advanced Member level 5

Here's the Virtex-5 info:
"Virtex-5 Data Sheet: DC and Switching Characteristics"

You didn't mention a particular Al.tera device, so here's a guess:
"Volume 2 - Stratix III Device Datasheet"

Those data sheets contain a lot of terms and abbreviations that won't make much sense unless you read additional user guides and manuals. If you'd like to browse for more device documentation: