AD8055(opamp) - AD9240 (ADC ) - Change in Common mode voltage at ADC input terminals


We are using AD8055 op amp for a DC coupled application, to drive the AD9240 ADC.

We have to set the common mode of the inputs as 2.5V. We have implemented a recommended circuit as per the AD9240 recommedation as per below image.


As per above circuit VINA should have a common mode of 2.5 V and VINB commn mode as 2.5 V.

In the above scheme, before Rs resistor we have RC low pass filter, with resistance of 221 ohm and Rs = 24 ohm.

But we are measuring a drop of 0.7V between 6 pin of Op amp and VINA pin of ADC. This decrease the common mode to a Value of 2.28 V.

We dont understand the drop between these output terminals,Kindly request you to provide us from which path does this DC current flows to make a drop in the series resistors.

Awaiting your respose.