To Jerry

[afd-2000]

We posted earlier about errors in the NI examples, and these have been fixed, so thanks a lot.  We next have to learn how to generate a noisy signal inside the FPGA and do some trivial things to get used to the board, such as implementing a simple FIR filter.  Is their any further reading that could help us perform tasks such as the generation of an internal signal?  Thanks.  And your previous comments were very helpful in fixing our problem.

[Mauricio Capistran-Garza]

You might already know this, but the first thing to notice is that you must generate IQ signals for the IF-RIO to generate them. You also have to feed the signals to the board inside a Single Cycle Timed Loop, so you probably want to generate the signals inside one too.

Having said that, let me add a possbile way to generate the signals. I would advise generating two differnt signals:

1) Sine tone. This can be generated using a couple lookup tables and a phase accumulator (similar to a DDS implementation; see DDS.bmp)

2) Noise. For this you can use another lookup table.

Then you only have to add both signals. This will also let you very easily change the frequency of the sine tone or the level of the noise.

- Mauricio

[afd-2000]

I've looked at the DDS screenshot that you attached and I've been reading about the process, which seems to rely on a Sine Look-up table, which seems to be a built in tool.  How can I use the sine-lookup table?  I searched it in LabView and could not find it.  I would like to first implement this type of system by LabView on my own.  My other question is about the block in the middle of your screenshot, which had an input labeled "impairments."  What exactly did this block do in your system?  Thanks.

[Mauricio Capistran-Garza]

The lookup table can be found under the "FPGA Math and Analysis" palette (you must have the VI targeted to run on FPGA to get this palette). You can search in LabVIEW's help for "Look-Up Table 1D" for more information on how to use them.

The "Add impairments" VI that is shown in the picture basically scales and adds an offset to the sine. By default it scales by "1" and adds "0" offset, so you can ignore it for practical purposes. Having said that, it's useful to have it in there because then you can play with the scaling and offset and see how it affects the output.

The other VI that you see in the screenshot translates the phase accumulator to an index for the sine and cosine tables. I'm attaching screenshots of those two VIs so you can see how simple they really are.

Good luck

- Mauricio