@User: Generally speaking, those buffers called "clkbuf" will be better balanced than regular buffers, as the purpose of the clock buffer is to avoid messing with the clock duty cycle. In the HVL library, there is a true schmitt trigger buffer (3.3V), and there is a symmetric level shifter (lsbuflv2hv_symmetric) that appears to have the rise and fall balanced, although it's likely that neither of those is what you're looking for.