On Mon, 4 Feb 2008, Larry Doolittle wrote: > On Sun, Feb 03, 2008 at 01:26:40PM +0000, ST de Feber wrote: > > The device in mind is an Altera Cyclone-3 FPGA. > > Most probably the ep3c5. > > FPGAs are the easiest chips to lay out, as long as you keep > an open mind about pin assignments until you're halfway > through the layout. Unless there is some other complex > part of the board, four layers is probably enough. > One for power, one for ground, and the top layer has > most of the routing away from the FPGA to its peripherals. > That leaves one layer for anything that doesn't quite > fit on the other three. A little while ago I laid out a QFP144 Spartan 3 on a 2 layer board without too much difficulty. The bypass network underneath was a bit of a hassle but it didn't take that long. Recently it got redesigned so that the top and bottom layers were covered with ground polys, again not too difficulty. I imagine 4 layers would be "better" but if you're on a budget 2 layers might be worth it :) -- Daniel O'Connor software and network engineer for Genesis Software - http://www.gsoft.com.au "The nice thing about standards is that there are so many of them to choose from." -- Andrew Tanenbaum GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C
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