DS90UB948-Q1: Which function block does 1.2V supply for? If use 1.1V, what risk do we have?

Hello Jiawei,

Using a 1.1V on those pins is not a good idea, since the VDD12 pins requires a minimum voltage of 1.14V. 

The VDD12 supplies the OLDI/LVDS output drivers, Digital blocks, PLL which is Critical for LOCK detection block, and for the FPD-Link Receiver. So if you vaiolate this minimum spec you could have issue in any of the above blocks. I can't tell you what exactly will happend because we do not validate our devices outside our specs.