I am an amateur and I don't have experience with logic circuits so please forgive me if this is very simple.

I have a 5V TTL crystal oscillator (4-pin). I need to create a second square wave from it that is 180 degrees out of phase with the first wave. It would be optimal to be able to adjust the duty cycle of the waves. (Just to note - this will operate at up to 20MHz)

I know I can probably use an inverter, but I have never made 'logic' circuitry before.