I need your help.
VREF is provided directly by AD5765. I set the common mode voltage of Vin to 0.5 V and the differential mode voltage to 1.0 V.
AD5765's output voltage is set to 0 V. Than I measure the voltage of AD8145's REF pin. However, it's not 0 V(Of course, AD5765 doesn't work exactly now). The voltage on REF pin has following features：
Its frequency is the same as Vin;
The following pictures show how its Vp-p varies with frequency:
My question is that why REF pin of AD8145 is not 0 V ?
Do you know the source impedance of the output that you're using from the AD5765? REF needs to be derived from a source with very low impedance, otherwise some of the output voltage will appear at the REF pin. If the source impedance is high, the best solution is to use a buffer with bypass capacitors to provide a broadband low-Z source. Can you connect REF to ground?