AD9251 Common Mode Voltage

Hello,

AD9251 VCM voltage in my circuit is set to the 1.2V instead of 0.9V. In datasheet it is advised to set VCM to AVDD/2 which is 1.8V/2 in my case. I used "differential double balun input configuration" (Figure 44 in AD9251 datasheet rev.B) in my circuit as the common mode voltage input. Sometimes when I probe the digital data output pins (DCO pin for example) VCM became 0.9V and it starts working fine but usually it stays at 1.2V. I used ADT1-1+ from mini circuits as the voltage transformes in the differential double balun configuration.

Can you give any advice about this issue?

Thanks in advance.