Why 4*LO has problems in AD8333

Really thank you for your help.

I am struggling with the application of AD8333.

I am confused that when I input 4*LO sine wave to Din of DS90C401, its output (Dout-, Dout+) was not a sine wave. Even though I adjust the amplitude of the input. It still could not work.

I don't how to solve this issue. 

The purple trace with a sine wave is the input to Din of DS90C401,but the other two traces were Dout(+, -). I don't know why they were not sinewave.

Thanks for your kind help