Can PERST, CLKREQ, WAKE#, and SMBUS operate at 1.8 V? What I am designing is a mini-PCIe slot compatible with a WWAN card, but this WWAN card can only operate at 1.8 V.
Per the mini-PCIe electromechanical specification, the sideband signals use the 3.3Vaux supply as there power source, and are therefore intended to be used with 3.3V signalling levels.
Indeed oer the DC specifications for these signals, the minimum high voltage is 2V for an input.
So simply, no they will not work correctly with a 1.8V device. Fortunately there are many simple level shifting ICs which will allow interfacing between a 1.8V device and a 3.3V interface.