ADRF6755 Baseband IQ Input signals are attenuating when connected to ADRF


We are generating the I,Q differential signals at the required level 540mv DC mean and 280mv P-P on each line.

But when we connect the these 4 lines(I+,I-, Q+, Q-) to ADRF, all these four signals are loading and changing values to 540mv  mean and 180mv P-P

We tried giving them to 450mv P-P also, still they are attenuating.

What could be the reason? How can I resolve this?