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AD9548 Phase Noise @ Free run mode

Question asked by bacelestica on Apr 29, 2016
Latest reply on May 5, 2016 by bacelestica

Hi,

We are using AD9548 in our design and we are experiencing phase noise issues on its output. Below are the details of the AD9548 configuration.

 

Sysclock: 12.8MHz, OCXO (attach is the phase noise plot of the OCXO vs 40MHz output)

Internal System clock: 998.2MHz

DAC out: 200MHz

AD9548 Mode: Freerun

Output frequency: 40MHz (attach is the phase noise plot of the OCXO vs 40MHz output)

doubler: disabled

reference clk in: powered down.

unused output: powered down.

 

Question:

1. I assume the best phase noise that we can get when we are on free run mode is close to the system clock phase noise. Is this assumption correct? I attached the phase noise plot of the system clock 12.8MHz and the 40MHz output and looks like I am seeing spur and high phase noise issue @ free run mode.

2. I attached our AD9548 configuration (*.stp), can you please take a look at the configuration and let me know if you see issues contributing to the observation above?

 

Thanks.

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