ADS5560: ADS5560

What ADC output Is the spectrum plot showing above? Is it all three you mention? What is the frequency of the analog input? 

This plot is for ADS4149. And input frequency 328MHz and Fs = 24 MHz. For other ADC's also we see the clock harmonics present in input signal.

What does the output look like with no input? Do you still see the clock harmonics? Is there a chance the clock from the FPGA could be causing this?

What is the amplitude of the clock at the input pins? Do you have a way to insert an external clock source to isolate this issue?

Please send your register settings.

Hi Jim,

Q: What does the output look like with no input? Do you still see the clock harmonics? Is there a chance the clock from the FPGA could be causing this?

Response: Without input the output looks noisy. Yes, we saw the clock harmonics in analog input of ADC while input is not given. To verify that we erase the FPGA code, and the clock harmonics is not present in ADC input.

Q: What is the amplitude of the clock at the input pins?

Response: For ADS4149 and ADS4128 the amplitude is 1.8V and for ADS5560 is 3.3V

Q: Do you have a way to insert an external clock source to isolate this issue?

Response: We tried with on-board PLL and external Function generator. But the response is same.

The clock harmonics were still present in ADC analog input.

Register settings for your information,

x"41C0", x"3D80", x"4208", x"DF30", x"2503", x"2500"

Hariprasanth,

This issue may be related to your board layout. Can you send your pcb design files for us to look at?

Regards,

Jim 

Hi Jim,

Can I send the layout document to mail instead of forum.

I sent you my email info.

Hi Jim,

I already sent layout file for your review.