ADRV9009 Anti-aliasing Filter not working

Can you please share the spectrum plot where you see the aliasing issue ? 

Are you testing with a default profile Tx/Rx/ORx 245.76MHz as shown below   ?

imBilal said:

What is the role of rxAdcProfile in the adrv9009 configuration?

This tunes the bandwidth of the passband and noise transfer functions of the ADC

imBilal said:

Is there any way to change the rxAdcProfile values to achieve the desired response? How?

ADI recommends to use filter wizard to generate filter coefficients as it compensates FIR response for analog filter roll off to make pass band flat.

Thanks vanitha  for the response.

I have tried multiple profiles. The one that you have mention, I have also tried this one but with both observation receivers. And even with all the profiles I am seeing the same response.

Attached below are the responses that I have received. 

Setup: ADRV LO 1 GHz, Input tone 1.010GHz (10 MHz tone)

Observations: We can clearly see the original tone at 10 MHz (-42db) but also we can see 30 MHz (-85db) and 50 MHz (-90db). 

Comments: It is clear that these are 3rd and 5th harmonics because when original tone is moved 1Mhz these other signal move 3MH and 5MHz respectively. 

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Now I have a bandpass filter that I can connect at the adrv9009 Rx input to show that these are actually harmonics. 

Setup: ADRV LO 1 GHz, Input tone 1.010GHz (10 MHz tone). External filter: 1 GHz bandpass filter (500MHz - 1500MHz). 

Observations: There is only one signal that is at 10MHz(-45db).

Comments: This shows that there were actual harmonics that were affecting the baseband.

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I have also capture the signal to capture the harmonics only by setting the LO to the 3rd and 5th harmonics of the actual signal.

Setup: LO 3 GHz, 1.010GHz (10 MHz tone). No external filter.

Observations: There is a signal that is at 30MHz(-65db).

Comments: This is the 3rd harmonic.

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I have also capture the signal to capture the harmonics only by setting the LO to the 3rd and 5th harmonics of the actual signal.

Setup: LO 5 GHz, 1.010GHz (10 MHz tone). No external filter.

Observations: There is a signal that is at 50MHz(-80db).

Comments: This is the 5rd harmonic.

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Conclusion: All these observations show that there are harmonics (3rd and 5th) that are appearing in the baseband signal. This points to the situation that adrv9009 inherent antialiasing filtering mechanism is not working. (Either it is not being configured properly or may be something else that I don't know).

Discussion:

vanitha said:

Are you testing with a default profile Tx/Rx/ORx 245.76MHz as shown below   ?

I have tried many profiles and I am still working on trying more profiles but I am getting the same response.

About that:

vanitha said:

ADI recommends to use filter wizard to generate filter coefficients as it compensates FIR response for analog filter roll off to make pass band flat.

Using the ADI filter wizard to generate the rxAdcProfile gives the worst response when visualized in the TES tool. You can try it for yourself. So I mostly generate the profiles that are already built in the TES tool. I believe that profiles that are built in the TES tools have been carefully crafted by ADI so that a user is not require to go with the ADI filter wizard for the first stage.

But nonetheless, I have tried building profiles from ADI filter wizard tool and then used those profiles in the TES to generate the talise_config.c file. But still I am getting the same response. 

Big Question:

What is the way forward now?

Thanks

vanitha 

Is there any update on this issue?

buha  Can you please comment on it if possible?

The third order harmonics and its levels at 80-90dBC are expected as per datasheet specs. There is no way to reduce the levels further, you need to use external filters in order to completely eliminate them. 

Test the harmonics at the below conditions with a reduced tone power level of -20dBm .

as per the image:

The composite response shows that the output will be around suppressed by roughly 150dbm. I am assuming the response of this filer. Even when I am giving the input power of -20dBm, the 3rd harmonic peak is 40dbm below the original peak. But as per your argument:

srimoyi said:

The third order harmonics and its levels at 80-90dBC are expected as per datasheet specs. There is no way to reduce the levels further, you need to use external filters in order to completely eliminate them. 

the 3rd harmonic peak should be 80dbm below. So I am again back in the same boat, what should I must do to reduce the 3rd harmonic peak?

Thanks

what is the level are you getting for the 3rd harmonic, you need to use external filtering to suppress them.