AD9783 ACLR degration for pi/4 DQPSK signal over temperature

Hi,

We are using AD9783 for our TETRA base station Transmitter.

The baseband I/Q data from FPGA is fed to AD9783 in DCI/DATA parallel LVDS at a clock speed of 5.76MSPS.

When the temperature changes there is a significant degradation in the ACLR performance.

We tested this in the thermal chamber. 

When the temperature reaches +50 DegC the ACPR degrades. When we keep the temperature constant at +50DegC, in about 5 minutes the distortion reduces  and the ACLR readings comes back to normal performance.

The same behavior is observed when we reduce the temperature also. When the temperature reaches about +30 DegC (while coming down from +50DegC), the ACLR performance degrades.

This seems to be a thermal behavior.

I suspect whether the calibration procedure mentioned in the datasheet need to be done for the digital interface.

But I'm using only 5.76MHz clock. Or will I have an advantage if I use the DCO for latching the data.

Regards,

Vishnu R.