Simple VHDL question

[pmuata]

I need to design a 3-switch controller in VHDL.

The input will be an 2.08 V AC signal. The output must be 3 PWM signals to contol 3 switches.

I need to write the code for the input. To synchronize the switches, when the first the input signal goes from negative to zero, that's when the switching must begin.

I have the basic code for the switchs' signals but I need the code for the input.