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Abdullah_2020
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Registered: ‎08-27-2020

10 dB drop in the ADC of the RFSoC ZCU111

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Hi All,

I am testing the amplitude response of the RFSoC's ADCs in the ZCU111. I used the following setup:

A signal generator generates an analog sinusoidal signal of 750 MHz and passes the signal into the RFSoC. On the RFSoC, ADC 0 (ADC224_T0_Ch0) is enabled with the following setup

Sampling rate = 737.280 MSamples/s

- Digital output data =  Real

- Decimation Mode = 1x

- Samples per AXI4-Stream Cycle = 8

- Mixer Type = Bypassed

- Mixer Mode = Real -> Real

- Nyquist Zone = Zone 1

- Calibration Mode = Mode 2

 

Then I capture the data after the ADC and display the frequency spectrum of the digital signal using Matlab. I noticed that there is around 10 dB power difference between the analog signal (at the ADC input) and the digital signal (after the ADC). Here is some measurements:

 

ADC input signal power (analog domain) [dBm]                      ADC output signal power (digital domain) [dBm] 

-49                                                                                            -59

-59                                                                                            -71

-69                                                                                            -81

-79                                                                                            -90.46

 

My questions are:

1- why is there around 10 dB power loss after the ADC? Is that expected? Or there is a problem in my setting? Is this loss frequency dependent? Note that I did some other measurements using different input signal frequency and sampling rate and the loss was also around 10 dB.

2- Is there a way to eliminate/ minimise the power loss?

I am looking forward for your support.

Many thanks

Abdullah

 

 

 

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zhendon
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Registered: ‎08-30-2011

Hi

Did you get the test result by using evaluation tools or your own project?

Insertion loss won't be more than 5dB for ADC and there almost no other loss if you don't enable mixer. So the expected power loss in your case should be around 5dB. 

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zhendon
Community Manager
Community Manager
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Registered: ‎08-30-2011

Hi

Did you get the test result by using evaluation tools or your own project?

Insertion loss won't be more than 5dB for ADC and there almost no other loss if you don't enable mixer. So the expected power loss in your case should be around 5dB. 

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-------------------------------------------------------------------------------------------------
如果提供的信息能解决您的问题,请标记为“接受为解决方案”。
如果您认为帖子有帮助,请点击“奖励”。谢谢!
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Abdullah_2020
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Registered: ‎08-27-2020

Hi @zhendon,

Thank you for your reply!

"Insertion loss won't be more than 5dB for ADC and there almost no other loss if you don't enable mixer

You are right! I think that I had an issue with the balun and also overlooked the meaning of dBFs. I retook different measurements with one of the differential ADCs and got around 5~6 dB loss.

I have another question if you do not mind. How much insertion loss will be added when I enable the mixer and x8 decimation please? Is there a way to reduce the insertion loss please? Many thanks!

 

Kind regards,

Abdullah

 

 

 

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zhendon
Community Manager
Community Manager
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Registered: ‎08-30-2011

Hi Abdullah,

You are welcome.

Good to hear you've gotten the expected result.

It will add extra 3dB loss when you enabled mixer because default mixer scale setting is -3dB. You can change that with API function XRFdc_SetMixerSettings.

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Abdullah_2020
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Registered: ‎08-27-2020

Thank you @zhendon  for the reply!

Kind regards,

Abdullah

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