Electronics > Beginners
how arbitray waveforms are generated
<< < (5/8) > >>
ant17:
ok thanks to all that have contributed i am going tohave to have a look at all the posts and think about it thanks agian
rstofer:

--- Quote from: gf on November 23, 2019, 09:34:45 pm ---
--- Quote from: rstofer on November 23, 2019, 06:28:26 pm ---Coming up with a highly variable sample clock is going to be a challenge. The alternative is to use a very fast sample clock but that implies a LOT of samples for slow signals.

--- End quote ---

"Classical" DDS generators are usually based on a fixed (fast) clock.
[ Some commercial AWGs use more sophisticated algorithms, though, than plain DDS, in order to overcome some limatations of DDS. ]


--- Quote ---A 1 Hz signal with a 1 GHz sample clock is going to need a billion samples.

--- End quote ---

Not really a problem, though. Just spend a sufficient number of bits for the DDS generator's accumulator and you can even generate sub-Hz signals. You don't need a waveform memory which can store a billion samples, but it can be much smaller (-> keyword "phase truncation").

gf

--- End quote ---

Are you thinking of periodic signals?  I'm not...  I'm thinking of arbitrary signals with weird patterns.  As a trivial example:  A car moving down the road with the normal bumps and bruises followed by a chuck-hole and perhaps a curb.  Periodic signals are easy, arbitrary maybe not so simple.
james_s:
AWGs produce periodic signals, at least the few I've played with did. The shape of a cycle is arbitrary but the cycle plays repeatedly as the selected frequency. I don't actually know what people typically use them for, other than playing around I never found a need for anything other than the usual sine, square and triangle waves.
gf:

--- Quote from: rstofer on November 23, 2019, 11:58:57 pm ---Are you thinking of periodic signals?  I'm not...

--- End quote ---

Well, the OP talked about 400MHz sawtooth, which is presumedly periodic (For a reasonable reproduction, this will require a pretty high sampling rate in the microwave range, though.)
rstofer:
It's common to think about repetitive waveforms but that doesn't have to be the case for an 'arbitrary' waveform.  The waveform will repeat but the experiment may be over before it does.
In the case of the Siglent SDG2082X, the device supports sample memory from 8 points up to 8 megapoints and sample rates from 1 uSa/s up to 75MSa/s in what they call TrueArb mode.  In DDS mode the sample rate is 300 MSa/s.  And then they claim a sample rate of 1.2GSa/s using 4x interpolation.
TrueArb mode is point by point, every output voltage comes from sample memory.

DDS will generate most common waveforms and most AWGs have a large menu of built-in waveforms.  TrueArb is different in that there are discrete samples for every time tick.

There is some very useful iinformation in the SDG2000 datasheet:
https://mediacdn.eu/mage/media/downloads/SDG2000X_DataSheet.pdf

About page 6, they talk about the EasyWave software which allows for manual drawing, line-drawing, equation-drawing, coordinate-drawing and so forth.

User Manual:
https://mediacdn.eu/mage/media/downloads/SDG2000X_UserManual.pdf

Starting on page 40, there is a list of built-in functions extending for 4 pages.  There are a LOT of built-ins.

Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod