However for FPGAs, they don't use the same definition for speed grade. Originally speed grades for FPGAs represented the time through a look up table but now the speed grade doesn't actually repesent a timing path. I am not sure if it is the same for other vendors, but for Xilinx FPGAs higher numbers are faster. Each speed grade increment is ~15% faster than the one before it. So a -5 is 10% faster than a -4 speed grade.
Determining the speed grade of Xilinx devices
Q:
I am having some trouble understanding the numbering system Xilinx uses for speed grade. Could someone explain what the numbers are and how to tell which speed grade is installed on my XS40. FWIW I have an XC4010XL FPGA. The available speed grade choices are -1, -2 -3, or -09.
A:
You usually see the speed grade imprinted on the chip on a line by itself. For an XC4000, you might see " 3C" printed on the chip. That means the chip has speed grade -3. (I think the "C" stands for commercial temperature range.)
For XC4000 devices, the number is roughly equivalent to the propagation delay through a CLB. So a -3 speed grade implies 3 ns of delay through a level of logic, -2 means 2 ns. Don't be mislead by -09, it actually means 0.9 ns of delay.
The situation changes with Spartan and Virtex devices. Now a larger number means the device is faster.
Reference : http://www.xess.com/faq/M0000236.HTMQuestion:
From: vlsigeek
Date Posted : 12/11/2004 4:42:49 AM Hi guys,
What is the speed grade in FPGA. What it tells actually.
Thanks in advance,
Soundar
Comments:
From: vlsi_giant欢迎光临 电子技术论坛_中国专业的电子工程师学习交流社区-中电网技术论坛 (http://bbs.eccn.com/) | Powered by Discuz! 7.0.0 |