Signal tap II list files

Question

I am using an ADC to measure the current of my inverter. It is coming from a rogowski coil. When I hook the rogowski coil output to the oscilloscope I get a sine wave with some jitter on the falling side of max values and the rising side of min values. Now, I hook the rogowski coil to the ADC which goes to the fpga through lvds and look at the signal tap file which is taking the values directly from the register coming out of the lvds megafunction. I capture the waveform by making a list file and then I copy the data to excel.

The problem I'm having is when I graph the data based on the sample number and the register value from the lvds megafunction I get a waveform that looks different than the oscilloscope. I get noise on the opposite sides of the maxima then what I was seeing on the scope. The only thing I can think of is that the output list file is giving me the data from last to first. Is this a correct assumption or is there something I'm missing.

altera_forum · Answer

Before you start to work with list files, you may want to inspect the data in Signal Tap using a "line chart" display format. The data aren't inverted in the list file, but I can imagine many reasons why the ADC output looks different from the oscilloscope display. Generally, it's more suitable to start with a signal generator that has a simple known waveform.

altera_forum · Answer

I have a rogowski coil rated for a high current device so I'm only getting about 10% of the range of my adc which is giving me a very small waveform to look at in the line chart. I could recompile throwing in some logic to convert the 12 bit number to a 8 bit number to make the line chart more readable but if it displays the same problem or not I still don't understand how the waveform is shifted across the vertical axis when I graph the data in the list file.

The problem I have is that in the oscilloscope there is clear noise on these certain areas of the waveform and very nice in the other. Large enough that there is no way you would get a nice waveform. You would see the values oscillate by a decent amount in this area of the waveform. Now with the values that signal tap gives me, it shows these areas reversed. I don't see how this is happening other then a vertical axis shifting.

altera_forum · Answer

I've been looking at some help files for signal tap and I see they talk about different triggering conditions. I have samples from -512 to 3584 this seems to correspond with post-trigger, but under setup I have pre-trigger. Does this have something to do with my issue or is it unrelated?

altera_forum · Answer

The trigger condition has no influence on the sample sequence. I didn't yet notice reversal of signal tap data sequences. But you can record a counter value with thze data. if you're not sure about.

altera_forum · Answer

Well here is a picture of what I get graphing the data and then what the waveform actually looks like from the oscilloscope. I don't understand how you can get one from the other unless their timings were inverted. The other option could be that they're completely unrelated, but I find that hard to believe because all the min/max timings come out almost perfect when I invert the timings.

I have counters running with the waveforms and they're going up so it doesn't seem like the list file is inverted, just the values coming from the lvds receiver megafunction.

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Signal tap II list files

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