Siglent SDG1000x possible to get better DC Acccuracy? And a few other issues - Page 1
Forum section: electronics / testgear

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: May 03, 2020, 07:56:25 pm
content: I got an SDG1000x awg a month ago and am pretty pleased with it, but there are some things that I wish I could upgrade.#1 is the dc accuracy, for example with dc waveform selected when i output 1mv i get 1.8mv out, verified with a few SMS, scopes and reference. And at 1v i get 1.02v. I'm not looking for dead nuts accuracy here but in the MV range it would be nice to get 1.08mv instead and 1.002V. So my question is what's the deal here, is this due to a voltage reference (which no one points out in teardowns) or is it a problem with dac resolution? If it's a vRef can I just replace with a better one as long as its pin/voltage compatible? I would like to do this in my sdm3045x too (using the maxim ref in the 5 digit model) but I'm afraid that maybe siglent is burning in the chips and calibrating them in software which would mean a better vref would give less accuracy?#2 The phase deviation between channels gets worse the higher the frequency, I think 15 degrees at 60mhz, there are options to shift the channels phases but that's no good for sweeps, is there some way to manually store a phase correction table that's always in effect?#3 lastly I would like to get higher voltages out of the thing using a separate diy amp. The 200ma current output is more than fine and if more is needed plenty of current feedback maps cascaded should do the trick. But I cant find any opamps that will give 40+ volts out pk to pk all the way to 60mhz, can this be done?

author: tautech
author_rank: Super Contributor
timestamp: May 03, 2020, 11:12:22 pm
content: Quote from: rwgast_lowlevellogicdesin on May 03, 2020, 07:56:25 pmIt meets spec and is not a precision PSU.QuoteIn the UI search for Phase locking for both channels.QuoteIf it could be done easily all SDG models would have it.The challenge of fast slew rates at high voltages put this in the 'hard' basket.

author: Someone
author_rank: Super Contributor
timestamp: May 03, 2020, 11:37:07 pm
content: Quote from: tautech on May 03, 2020, 11:12:22 pm$400 function generator has less precision than $10,000 SMU....STOP THE PRESSES!

author: Someone
author_rank: Super Contributor
timestamp: May 03, 2020, 11:39:31 pm
content: Quote from: rwgast_lowlevellogicdesin on May 03, 2020, 07:56:25 pmIts unlikely a reference issue if the error isn't a constant ratio (multiplicative). You'd likely get more improvement from "rolling" opamps (in the absence of understanding the problem and reverse engineering the circuitry).

author: tautech
author_rank: Super Contributor
timestamp: May 03, 2020, 11:40:03 pm
content: Quote from: Someone on May 03, 2020, 11:37:07 pm$319 !

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: May 04, 2020, 05:30:52 am
content: The phase deviation of 15 degrees is with phase lock on, it scales from 0 to 15 degrees as the frequency rises.I'm not sure why everyone is so sarcastic about the precision, no it's not a kiethly smu and I dont need 6 digit precision either.. but my decades old power designs has better accuracy, i knew the specs when i purchased it and I'm not dumping on siglent or the web, just wondering if I can improve things a bit.

author: klausES
author_rank: Regular Contributor
timestamp: May 04, 2020, 09:32:41 am
content: I have never tried it with 60 MHz (my ranges are mostly up to just over 4 MHz, rarely around 8 MHz)but I could not find such a phase shift between channels a and b on my 1062X.Also none that would increase with increasing frequency.I have not yet measured DC waveform voltage, but more often with sine, and the deviations were very small.As far as the output voltages are concerned, you could try out what effects it could have on starting the self-calibrationwhen the device has become as warm as it gets during operation by you.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: May 04, 2020, 06:42:50 pm
content: Thank you I will try the self cal when run for an hour didnt think of that.As far as phase deviation I am talking about ac signals. I first noticed when running bode plots with 60 mhz sweep (phase lock on) that at higher frequencys my phase plot looked funky, next I tried sweeping from a single channel using a BNC T and saw the expected flat plot. So next I just phase locked the AWG and viewed multiple frequencys from 0 to 60 on my scope and the waves shifted farther apart the higher i went, at 60mhz I took me adjusting 15 degrees of phase deviance to line the waves up. No such problem using a signal channel and T so I know it's not the scope channels.

author: klausES
author_rank: Regular Contributor
timestamp: May 04, 2020, 07:59:01 pm
content: Quote from: rwgast_lowlevellogicdesin on May 04, 2020, 06:42:50 pmI will try it on mine afterwards.

author: klausES
author_rank: Regular Contributor
timestamp: May 04, 2020, 11:31:46 pm
content: With mine at 60 MHz actually also 15°Up to 10 MHz it is still negligibly small (that's why I never noticed it), from 20 MHz it becomes more.Since it is not linear, the possibility of compensation (e.g. in the channel coupling menu) is not practical.If you don't have to change constantly, for a longer measurement at the same frequency,you could only compensate for it in the respective channel 1 or 2 menu over phase.However, the voltage at Waveform DC (measured at 1V) for both channels (channel 1 = 1.00114V, channel 2 = 1,00092V) is quite accurate.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: May 05, 2020, 07:59:33 pm
content: The phase issue is kind of suck, not only do I want to do synced sweeps but I've been collecting parts to build a 2-4 channel coherent SDR with 50-100mhz bandwidth on each channel and I was hoping to use this thing to help me generate quadrature signals (with phases locked 90 apart). I have no idea where to start looking to find out why the deviation does this.As far as DC goes I think I figured out the issue, first off I got much better accuracy when using 50ohm out instead of hi-z, next I got dead on dc accuracy of 1.0000 to 4.9998 using a 100ohm 10 turn port as the load when adjusted to 50.2ohms instead of 50. The load needed to get 500uv or better accuracy in the mv range ranges from 25 to 50ohm for each decade of the mv range. So there's some creative ways to fix the problem using an external box talking through the USB port to the generator.