02-11-2019 02:09 PM - edited 02-11-2019 02:10 PM
I'm a little bit confused when looking at the tdata stream from my ADC. Here's a quick dump:
So we have a 128bit data stream due to running at 4GHz sampling rate and 500MHz Axi Clk. So far so good.
According to the DS the 12Bits of the ADC are MSB aligned but instead I see how the 4 LSBs of every 16bit part of the 128 tdata toggles. Why is that? Furthermore the top 16bits of the tdata stream have the exact same value for every clk cycle. That doesn't seam right.
From the UG I would understand that I split the 128 bits in 16bit chunks and use the upper 12bits of each chunk as the ADC value. But looking at the above output this doesn't seam right.
Please correct my understanding of interpreting this data as it is obviously wrong.
02-12-2019 12:15 PM
Table 57 of pg269 shows the digital data format.
The axi stream is 16 bit 2s compliment. The table shows the shifted value to give the 12 bit accurate result
02-13-2019 07:47 AM
02-13-2019 08:39 AM
The ADC is always outputting 16 bit conversion results.
Accuracy is guaranteed to 12-bits.
This is the table detailing the data format
if the ADC is set up in Real in Real out mode like this:
If I take what you gave me and convert the 16 bit hex number i see to 2's comp I see this
Is this what you are sending in?
You always have the option to use RF analyzer to look at what is coming out of the ADC channel.
02-13-2019 01:06 PM
thanks for the detailed reply! We're currently using the ADC in I/Q Mode with the NCO running at 500MHz and no decimation (1x). The input is a 10MHz sine wave (not ideal, I know but all we can do at this moment). The samples I posted are from the real part only.
The wave you're plotting looks like what I've seen in Octave and is definitely not what we're sending in. What makes me most curious is that continuous 0x0d3b = 3387. I highly doubt that this is an actual sample, but what else could it be?
I probably should give the RF Analyzer a chance by now!
Last but not least: From what I'm seing in your Excel Spreadsheet, you're using the entire 16bit, while only the upper 12 should be valid right? For a rough plot it sure will be fine but for any kind of serious DSP I should through them away right?
02-13-2019 03:19 PM - edited 02-13-2019 03:25 PM
The sheet was something I used in the past for very quick validation of 16 bit ILA samples.
I didn't know it was iq data.
Perhaps RF analyzer would be a good idea here you could capture and do an fft of what you are receiving via the GUI. This would also give you a chance to drive the ADC with the DAC output.
I can't say what this fixed sample is just from the data you show.