AD9783 Thermal Problem


We need your support for an issue with one of the DAC used in our design - AD9783.
While evaluating AD9783 for our new TETRA Base Station Transmitter, we are experiencing certain thermal issues.
The DAC is being driven by an FPGA in 16 bit parallel mode with interleaved I and Q
Other configuration parameters are as follows:
DCI & DAC CLK = 5.76MHz
DCO not used.
50E termination at 4 DAC analog outputs.
Internal REFIO

We are observing the DAC output in spectrum analyser. The DAC works fine till about 35
DegC, but when the temperature increases to 40DegC, the noise floor of
the DAC increases.
This is visible as a degradation in the signal to noise performance for continuous wave signal and degradation in the intermodulation distortion performance with modulated signal.
When the temperature is reduced to less than 35 DegC, it will start working normally.
The above said temperatures are the ambient temperatures recorded from a environment chamber used for this experiment.

Attaching a spectrum analyzer screen shot at DAC output, captured during one of the experiments with DAC to study the thermal effect.
The Yellow trace is the reading at 27 Degree C, The blue trace is the reading with the same setup at 60 Degree C. The green trace is recorded at 65 Degree C.

I expect a reply at the earliest.

Vishnu R,
Principal Engineer,
C-DAC Trivandrum.

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