This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
We are using ADS61B29 at 50MSPS in our board. We are feeding a input of 32.5MHz at -6dBFS. When we capture the digital data and plot it in wavevision, we are seeing a unexpected degradation in SFDR and ENOB. We are seeing the harmonics with considerable amplitude as shown the FFT below:
The input signal fed to ADC is analyzed using spectrum analyzer and screenshot is shown below:
The following figure is the FFT of digital data when ADC input is terminated with 50ohms:
Please help us to proceed further. What could be the problem for this?
Edit 1: HSDC Pro screenshot also included. :
We were using on board oscillator generated clock. Changed to external clock and captured. The plot is :
Signal source is changed to R&S signal generator as suggested by Richard :
Running at 50MSPS, this device must be set in Low SPeed Mode. Has this been done?
Have you tried importing the data into HSDC Pro? There is a bug in the WaveVIsion 5 data import functions that incorrectly sets the resolution and therefore sets the scale wrong. It may be that you are clipping a little bit.
We are glad that we were able to resolve this issue, and will now proceed to close this thread.
If you have further questions related to this thread, you may click "Ask a related question" below. The newly created question will be automatically linked to this question.
In reply to Joshua Carnes:
Also, if you can write the SPI registers then make use of the test patterns that can be enabled in address 0x62. Two useful patterns are the ramp pattern (which is an arithmetic counting on the output sample - 0x000, then 0x001, then 0x002, etc.) and the custom pattern (which is a pattern that you set in a SPI register that then is output on the sample bus.) With custom pattern, you can put a single '1' with the rest '0' and see if you capture the '1' in the right spot in the sample. Then you can walk that '1' through all the bit positions in the sample. In this way you can verify that you don't have something like inverted DDR clock that swaps all you odd bit positions with even bit positions.
In reply to Richard Prentice:
In reply to Rakend R:
What is the source of your 50MHz sample clock? And are you using a narrow bandpass filter to remove as much phase noise from the clock as possible? It does appear that you are getting a lot of phase noise around your fundamental, enough to pull up the rms of your noise floor (red line at around -91 or -92 dBFS). With BlackmanHarris windowing function, the HSDCPro will notch out +/-25 FFT bins around the fundamental and replace that with the rms value, which is easy to see with only 4096 samples. if you use the pull-down menu options you can find a place to change that 25 bins of notching to zero and really see what is happening around the fundamental. I would start by looking at the clocking.
Hi Richard, Thanks for the reply. We were using on board clock and we changed to external clock by which the harmonics are vanished from the captured data. But still if we see the SNR,SFDR and ENOB there isn't much improvements. So what can we do next? Thanks a lot!!
Edit: Post has been edited and included that new plot.
I still don't know what you are using for clock, though. What is your signal source? If you want to see SNR, SINAD, ENOB near datasheet specifications then you will need a high quality low-jitter signal source, something like a Rohde&Schwartz SMA100 as one such example. And even with that you would need to use a narrow bandpass filter on the clock such as a TTE LC filter with 3% or 5% passband.
For on-board clock - you were using the CDCE72020? That is the only on-board clock that I know of and the VCXO and much of the surrounding components are not installed during manufacture as we don't know in advance what sample frequency the EVM might be used at.
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.