Does a comparator's reference voltage have to be DC?

[Potaeto]

Does one input of a comparator always have to be a DC voltage?

Can I use AC voltages for both inputs?

 

[Nigel Goodwin]

You could, but what would be the point?, it would produce fairly random outputs - regardless of the inputs, it's comparing two DC voltages only.

 

[Hero999]

It depends on what you're doing, for example two create PWM with a comparator, the reference is an AC triangle wave and the input is a DC voltage or lower frequency AC signal.