Dear All, Problem. I've just been let down by a oscillator manufacturer. They can only make the ordered 3.3V differential LVPECL oscillator parts work at 5V. Some excuse about their quartz supplier. So, I can't stick
5V PECL into my 3.3V Virtex-E differential input, it's outside the common mode range. So, I could AC couple it with a couple of caps after the PECL driver's emitter resistors. I then need to bias the signal into the common mode range of the VirtexE diff input. Question. Anybody know if I could somehow activate the internal pullup resistor on one input and the pulldown on the other to bias the signal in the middle of the supply? There's already a 100 ohm termination resistor between the pins. Or, any better ideas? cheers all, Syms.p.s. I know I could use more resistors to do this biasing, but the board layout makes this awkward. The VirtexE is, of course, a BGA.