AFE58JD48EVM: Reasons to have a high second harmonics peak when I am giving a clean sine wave as input to ADC

Nitin Yadav

Part Number: AFE58JD48EVM
Other Parts Discussed in Thread: AFE58JD48

Tool/software:

I am working with AFE58JD48EVM eval board to send the ADC data over JESD204B interface to FPGA and then plotting the extracted data on the JESD204B RX on wavevision.
I am sending a 1MHz 400mVpp sine at the ADC input from signal generator.
The plotted waveform from JESD204B RX is a sine wave with correct peak at 1MHz frequency but there are harmonics as well with high peaks. I am not sure what could be the reason for the same, so can someone help me with this.

5 days ago

0 Sachin H K 5 days ago

TI__Expert 5085 points

Hi,

What is the gain for AFE58JD48? Adc input might be saturating . Either try to reduce the input amplitude or reduce gain .

0 Nitin Yadav 2 days ago in reply to Sachin H K

Prodigy 70 points

Hi Sachin

The VCA gain is set at minimum and input swing is 400mVpp
I tried with further reducing the input swing but still the same obeservation.

0 Sachin H K 2 days ago in reply to Nitin Yadav

TI__Expert 5085 points

Nitin ,

Can you please specify the LNA Gain and PGA gain and attenuator settings you used?

If you reduce the signal swing to 200mVpp do you see similar hd2 ?

Which is the signal source you have used ? What is the hd2 spec of that ?

0 Nitin Yadav 2 days ago in reply to Sachin H K

Prodigy 70 points

Hi Sachin

I have attached the analog front end setting which I am using in my application

We are using JDS6600 -60M as signal generator
Its harmonic suppression specs are 45dBc (<1MHz) and 40dBc(1MHz ~20MHz).

0 Sachin H K 1 day ago in reply to Nitin Yadav

TI__Expert 5085 points

Nitin,

Your gain setting looks fine and it is not saturating signal chain.

But if the source hd2 is 40dBc you will see that in AFE output . You need to give cleaner signal to actually see the AFE hd2 .

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AFE58JD48EVM: Reasons to have a high second harmonics peak when I am giving a clean sine wave as input to ADC