FPGA Powering PCB Guidelines??

You have to power the PLL pins (both digital and analog) whether you use the PLL's or not. That means that for most systems with 3.3V logic, you have three voltage rails. I suspect you *could* pull off a two-layer board, but you might end up with a "third" layer of wire jumpers. You do have to watch for inductance problems if you aren't using planes, so be sure that if you are using PLL's, you keep the traces or jumpers to the power supply short, and decouple them adequately. The bigger problem with a two-layer board is the lack of a proper ground plane. If you can manage to arrange your board so you can keep a large area under the FPGA clear for a "mini" ground plane and decoupling caps, that would help a lot. You can still leave the area under the pads free for vias, especially on a large QFP, like the 240, and stuff a fairly decent number of coupling caps in the center. I've even got a card that places the 1.2 and 2.5V regulators under the FPGA - but that's a four layer card with a ground plane. I will say, switching to a four-layer board will dramatically simplify your life, and make the odds of success much higher. At four layers, you can have an entire layer for ground (a huge bonus) and carve out voltage planes for the FPGA and other IC's. I've done several Cyclone 3 designs on 4-layer boards, and I've just about got the power plane design down pat. I'm not saying it can't be done, but I can't see how your power distribution will be anything better than marginal on a two-layer board.