Hi everyone ı am working on my final project and I faced problem while getting square waves with 90 degrees of phase apart. Can you help me??

 

You probably need to start with a circuit called an "astable multivibrator".

 

Think two flip flop circuits, toggle them right and you have your answer.

 

Think two flip flop circuits, toggle them right and you have your answer.

That's two steps and I think you have your answer

 

Look up "Johnson counter".

 

A two stage Johnson Counter has a state sequence that goes
00 -> 01 -> 11 -> 10
which is just the thing you need, and can be built as a shift register. If the FFs have inverted outputs, then you don't even need an external inverter, but you still need a clock to make it work. That is where the multivibrator comes in.