In my design, I use ADA4930 to drive AD9257. When I give a DC=0.9V to VIN- of ADA4940 and a sine wave (100KHz Vpp=1.6V DC=0.9V) to VIN+，the VOCM=0.9V is from AD9257. But the results of AD9257 shows that the Vpp is 1.760V. Please tell me how to explain it or is this situation noamal? my schematic will be shown below.