KCC's Quizzes AQQ294 about a digital phase splitter design

1. Quote of the month: "I've learned that people will forget what you said, people will forget what you did, but people will never forget how you made them roll their eyes" - Robin Williams

2. New quiz of the month: AQQ294 about a digital phase splitter circuit

One has to build a digital 90 degrees phase splitter circuit giving an in-phase (LO_I) and a quadrature phase (LO_Q) square LO signals phased out 90° one to each other. Among the following 4 circuits, there is one which is not performing that role.

Question: can you localize it and tell why?

Good luck and try to be among the first ones!