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The Siglent SDG2042X Thread

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billfernandez:
I just got a Siglent SDG2042X Function & Arbitrary Waveform Generator.  I searched to see if there was a thread already started that focuses on this device and didn't find one, so am creating one.

Here's a thread on this forum announcing the new line of which this is a part:
https://www.eevblog.com/forum/testgear/siglent-sdg2000x-new-arbitary-generator/msg774407/#msg774407

And here's the thread for EEVBLOG #805, where Dave tears down the SDG2122X -- the 120MHz model in the SDG2xxxX line:
https://www.eevblog.com/forum/blog/eevblog-805-siglent-sdg2122x-arb-generator-teardown/msg776709/#msg776709

billfernandez:
OUTPUT LEVEL VS DC OFFSETS

By default (0V DC offset) the output always swings symmetrically above and below ground.

Into 50 Ohms it can at most output a maximum voltage of +5V and a minimum voltage of -5V.  How you use that range is up to you.

For example, if you output a 10Vpp waveform, it will take up the whole range, and the device will not allow you to add a DC offset.

On the other hand, if you have a 1Vpp waveform, it will allow you to add an offset of up to +/- 4.5V. (remember that the 1Vpp swings from +1/2V to -1/2V.)


OUTPUT LEVEL VS FREQUENCY

When outputting sinewaves into a 50 Ohm load: For frequencies of up to 20MHz the unit lets you specify (and it will deliver) up to 10Vpp.  But above 20MHz (up to 40MHz for this model) the unit will only let you specify up to 5Vpp.

Same for squarewaves except that squarewave generation tops out at 25MHz.

Pulses have the same limits as squarewaves.

Ramps (triangle and sawtooth waves) have a maximum frequency of 1MHz, and a maximum output of 10Vpp into 50 Ohms.

The DC Offset output can only go to +/-5V.

Haven't figured out the limits for arbitrary waveforms.  All the ones I've tried have allowed me to specify up to 10Vpp, but I haven't generated a waveform faster than 10MHz (max frequency depends upon # of samples, etc.).


ABOVE 50 OHM LOAD

The documentation says that into a "high impedance" load the output can swing up to 20Vpp (-/+10V), but I haven't explored the limits thereof.

billfernandez:
The arbitrary waveform generator can play samples at a maximum rate of 75 megasamples/second.  But the minimum length of a sample set is 8 samples.  So the fastest rate at which you can play an 8-sample set is 9.375MHz.

In the EasyWave program I created a new wave:
   9 points
   40MHz
   20Vpp
I used 9 points so that I could create a symmetrical waveform with no discontinuities where the sample set repeats.

Then I edited the waveform to create a sawtooth waveform with 4 peaks, from 0V to +10V.

Then ran it on the unit in DDS mode at 20MHz, 10Vpp, into 50 Ohms.

What I saw on my scope was an 80MHz softened sawtooth at about 4Vpp, with, that seemed to be amplitude modulated with a 960mVpp, 20MHz sinewave.

Also, the entire waveform seemed to be offset about 400-400mV above 0V.

Then I switched the arbitrary waveform generator from "DDS" (Direct Digital Synthesise) mode to "TrueArb" mode.  The result on the scope was a 3MHz squarewave, with no offset above 0V, with amplitude of 5.2V, and a discontinuity where the sample set repeats. 

I've noticed that TrueArb seems to add a short 0V segment at each sample-set repeat point.  I've also noticed that DDS and TruArb produce distinctly different waveforms, and I'm still trying to figure out what's going on.

I've attached a few files showing screen shots.

alank2:

--- Quote from: billfernandez on November 06, 2015, 10:37:06 pm ---But the minimum length of a sample set is 8 samples.  So the fastest rate at which you can play an 8-sample set is 9.375MHz.
--- End quote ---

It will go down to 2 even though the documentation says 8.  I didn't test this with loading a CSV file, but a BIN file.

It will also autoscale a CSV file, so if the maximum value given is -1 to +1, it will scale those to the lowest value to the highest value.  The amplitude will actually be driven by the amplitude setting.


--- Quote from: billfernandez on November 06, 2015, 10:37:06 pm ---I used 9 points so that I could create a symmetrical waveform with no discontinuities where the sample set repeats.

--- End quote ---

This is necessary for the DDS mode because the final sample does not get a time slot like the TrueArb mode does.

In TrueArb mode if you have 4 samples, sample 0, 1, 2, and 3 will have the same amount of time each is "played" at the sample rate.

In DDS mode, if you have 4 samples, sample 0 is the left edge and sample 3 is the right edge of the waveform.  DDS mode interpolates between samples.  What you have then is a time slot assigned to sample 0-1, 1-2, and finally 2-3.  This is why you want sample 3 to be the same as sample 0.  Otherwise it will end at 3 and then instantly SNAP to sample 0.  There is no time slot assigned to sample 3-0.


--- Quote from: billfernandez on November 06, 2015, 10:37:06 pm ---I've noticed that TrueArb seems to add a short 0V segment at each sample-set repeat point.  I've also noticed that DDS and TruArb produce distinctly different waveforms, and I'm still trying to figure out what's going on.

--- End quote ---

They are completely different, one interpolates a waveform and the other plays samples.

By the way, you can load CSV files of your own samples without having to use or make them with EasyWave.  Just use this format:

data length,8
xpos,value
,1
,-1
,1
,-1
,1
,-1
,1
,-1

In this case 1 being the highest value will be scaled to the maximum and -1 being the lowest value will be scaled to the minimum.

What the generator does with this file is turns it into this binary file (see picture)

It is a simple 2 byte signed integer array.  FF 7F 00 80 --> 0x7FFF (highest value from the "1") followed by 0x8000 (lowest value from the -1).  0x0000 would be the center.

You can load binary files directly from a USB stick though they will not be copied to the internal drive.

I was very impressed with the arbitrary wave testing I did on the Siglent.  It excels at generating waveforms with its interpolating DDS mode, and you can use its TrueArb mode with deep memory to deliver 8M samples at the sample rate you choose.  That means you could send 8M/10=838860 8-bit UART frames (1 start, 8 data, 1 stop) using TrueArb!

billfernandez:
@AlanK2 thanks for your comments.  I'll do some experiments.

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