ADS5562EVM: Low SFDR continued: unable to reproduce >80 SNR measurement using the same apparatus

ALB,

It appears from the capture the data is saturated. Can you back off the input power of the tone? What frequency is the input tone? Please send a screen shot of the codes from HSDC Pro GUI.

The ADS5562 needs to output data as unsigned binary. Is there a chance this was set to 2's compliment?

Regards,

Jim 

Jim,

Thank you for the suggestion. I backed off the input power to 8dBm from 15dBm and by checking on the code it spans from 00000 to 53000 after reduction. The input frequency of 16.13MHz and  clock input signal of 80MHz 1.5Vpp sine wave are applied to ADS5562EVM. The screenshot of the codes and real FFT is attached. Both ADS5562EVM and TSW1400 are set to factory defaults and hence, ADS5562 J2 2's complement jumper is not present. 

Regards,ADS5562EVM_TSW1400_datacapture_reducedInPwr.pdf

Codes zoomed in.pptxALB,

Can you use the zoom tool and try to capture a screen shot in cods mode so it looks something like the file attached?

Regards,

Jim

Jim,

Please find attached codes zoomed plot.The input tone is close to the FSR, but does not saturate the max code of 65535. Would you be available for a live run/call to resolve this quickly? This postings back and forth is not very time efficient resolving technical issue like this.

Regards,

ADS5562EVM_TSW1400_datacapture_Codes_zoomed in.pptx

ALB,

You are to close to full scale. Back off on the input power by another 1 or 2dB. When we capture data for the data sheet, you will notice most plots have a fundamental of -1dBFs. Switch to FFT mode and back off until your fundamental is at -1dBFs.

Regards,

Jim  

Jim,

Please find attached plot with input amplitude set so that the fundamental is -1dBFs. As you can see, SNR/SFDR is nowhere near expected 80dB. Can you advise why? I need to resolve this today as this has been dragging us a long time.

Regards,

ADS5562EVM_TSW1400_datacapture_reducedInPwr_v2.pdf

ALB,

Is your EVM a Rev C board? If so I have attached the schematic. Please make sure all jumpers are set per the board photo I am sending. Take a scope probe (diff probe would be better) and monitor the ADC input across R21 and R26. You should see a clean sine wave with the correct DC offset. It appears to me you have a bad input signal source. Did you try without the filter or a different one and using a different IF frequency?

If you have an older board, this may be the problem.

Regards,

Jim

ADS55xxEVM-SCH_C.pdf