DAC38RF82: DAC38RF82EVM + TSW14J56 bundle to generate sub-nanosecond pulses.
Part Number: DAC38RF82
We followed the "Quick Start" section in the manual to set up both boards and were able to observe the NCO frequencies (2140 MHz) with DAC board in on-chip PLL mode.
Now, we would like to have the boards generate a short pulse. Thus I put together another waveform .csv file that contains a single Gaussian wave (see attached + screencap) and uploaded it to HSDC Pro. Since our oscilloscope could only see up to 25 MHz, we set the NCO frequency to somewhere less than 25 MHz. Nevertheless, we are not able to observe the Gaussian pulse from our oscilloscope, but some sort of wavepackets (see image). The number of peaks within the wavepacket positively correlates with the NCO frequency. This is undesired as we were hoping to see the waveform in .csv file appear in our oscilloscope. Pardon my ignorance, but the more knowledgeable members in our group suggested that it's the .csv waveform mixing with the NCO?
single_pulse.csvand this is what we get
Suspecting that NCO is doing something that we don't want, we turned it off and fed different waveforms and observed the result using the same oscilloscope.
I am not sure how to proceed. Please advise or request additional information. Most settings should be the same listed in the "Quick Start" section in the manual (except NCO frequency and the wave pattern generation).
Thanks a bunch!
Try making the pulse frequency an integer divide of the NCO frequency. How are you syncing the NCO? Can you use SYSREF to synchronize both the pulse and the NCO?
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In reply to jim s:
I am unsure what the pulse frequency? I've set the data rate to be 384M SPS. Would that be the pulse frequency you are referring to? Would the pulse width (in samples) that I feed into HSDCPRO matter? I am also unsure how to sync the NCO and the pulse.
Apologies for my ignorance.
In reply to Jiawei Qiu:
The DAC38RF82 NCO is doing exactly the function of your amplitude/phase modulation pulse. Therefore it has such behavior.
“The number of peaks within the wavepacket positively correlates with the NCO frequency.” (Note: this is due to the amplitude phase modulation with the NCO)
Regarding your comments:
“This is undesired as we were hoping to see the waveform in .csv file appear in our oscilloscope.”
This is the expected behavior of using an NCO + complex mixer. If it is undesired, then you need to turn off the NCO like you did before.
Thanks for your patience and replies so far!
Alright, we won't use NCO + complex mixer. But with NCO + mixer turned off, how come we are not seeing what we feed into HSDCPRO? Since your first reply to this post suggest that we can play with the NCO and pulse frequency and we don't want to use NCO anymore, what else could we do to match the input and output waveform?
Please continue to bear with us! Thanks a bunch!
After some investigation, I have found the reason behind the waveform mismatch. I have been generating the wavefroms with the greatest absolute peak value as 32768. But due to 2's compliment arithmetic it wraps around to be -32768, I think? I am not familiar with that. But once I change the absolute peak value to 32767, I saw the correct waveforms.
Also the "glitch" also disappeared.
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