Electronics > Beginners
how arbitray waveforms are generated
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AG6QR:

--- Quote from: ant17 on November 23, 2019, 02:17:27 am ---hi guys thanks for your reply i planned on using an fpga. With a external dac at 2Gs/s for an analog bandwidth of 400Mhz. I have seen that matlab has a function where you can make your own waveforms but something like a sawtooth. I don't understand how you know where each part of the waveform is suposed to go. Is there a formula or is it trigonometery can someone please explain

--- End quote ---

You generate the table of values however you want and put the parts wherever you want.  That's why they call it an arbitrary waveform generator.

If you have a particular purpose or set of requirements that you want the waveform to meet, of course you generate the table of values to meet those requirements.
ant17:
so if i want to generate a sawtooth of say 400Mhz with certain period how would that be generated thanks
james_s:
This is one of those things where if you have to ask, you're a long way from getting something workable. You generate a sawtooth like you generate any other waveform. You draw one cycle as a series of dots, the vertical position of each dot represents the value of that sample. If you want 400 MHz you have to clock the samples into the DAC at 400MHz times the number of samples, which is probably going to be 20-30 minimum. If you do the math you'll quickly see why AWGs are typically not anywhere near 400MHz.

Also frequency and period are inextricably linked, it makes no sense to specify both the frequency and the period, you can't change one without changing the other.
ant17:
ok thanks
oPossum:
Any periodic waveform can be created from a sum of sines. (Fourier synthesis).

Sawtooth for example... https://web.njit.edu/~matveev/Courses/M331_F17/html/FourierSawToothSine.html
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