Main clock voltage levels for Cyclone III

Thanks Csrana. VCCIO is 3.3V in my case. I have a reference design here that works well with a clock that oscillates between 1V and 2.2V. However, it is possible that such a clock is considered marginal, and moving the low end up to 1.2V could be a problem. Or perhaps it is not a problem. I'm trying to remove the uncertainty.

Other circuit constraints have made it very difficult to improve the clock further and I'm working under time pressure, which is why I am seeking guidance on whether I should invest the time in strengthening the clock signal or if I should look to other causes for being unable to communicate with the Cyclone.