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pojotis
Observer
Observer
630 Views
Registered: ‎12-18-2018

ZCU111 ADC NCO Performance depends on mixing frequency

Hello,

There is another problem that we get in RF SOC ZCU111 eval board.

We use the NCO and the mixer in usp rf data converter IP afterADC sampling.

We input our modulated signal and an adjacent channel signal to the ADC.

By doing this, we want to perform adjacent channel rejection test.

When the input frequency is low (both the modulated and the adjacent channel), everything is fine.

However when we start increasing the input frequency, adjacent channel rejection performance decreases.

In our design, we use the NCO and the mixer, so we do all the signal processing in the baseband. So there must be no frequency dependence. 

For two different frequencies, we measure the ADC input SNR. They are also the same. So ADC dynamic range is the same.

So, we think that the NCO generates spurious signals, when the NCO is set to higher frequencies.

We could not find any info about the NCO performance on the datasheets.

Is it possible that NCO performance decreases by increasing the NCO frequency?

Thanks

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2 Replies
zhendon
Community Manager
Community Manager
511 Views
Registered: ‎08-30-2011

Hi

Sorry for the delayed response. 

I have not heard about that the performance would be affected by NCO set in different frequency. Are you using Evaluation tools or your own project?.

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pojotis
Observer
Observer
490 Views
Registered: ‎12-18-2018

Hello,

We are using our own project based on the eval. Board project.

I think xilinx should provide the spec.s about NCO output in the datasheet. So that we dont have to wait for weeks to get a technical answer.

I think, the spectral attacks of the NCO causes reciprocal mixing noise which degrades theperformance of RFSoC

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