Products > Test Equipment
Siglent SDS2000 new V2 Firmware
Siglent America:
--- Quote from: Marchello on December 16, 2015, 02:53:10 pm ---
--- Quote from: Siglent America on December 16, 2015, 01:40:28 pm ---Hello, Performa01.
I just thought I would let you know that the Siglent SDS2000(X) product engineering people have been reading your posts on this thread. They are currently working on the issues you have noted.
Thanks for your help.
--- End quote ---
Hello!
When SDS2074X will be available for purchase?
Best regards!
Mark.
--- End quote ---
Hi Mark.
I can't speak for the areas outside North America but they are for sale here in N.A. now. The stock quantities will be small for awhile, however.
Regards
Performa01:
Digital Channels broken.
I’ve briefly reviewed the digital channels with firmware SDS2000-V2.0-1.02.01.01.27 a couple weeks ago and found them basically working.
Now I wanted to take a closer look and thought about sharing my experiences here.
Quite sadly I found the digital channel function broken again with firmware SDS2000-V2.0-1.02.01.28R1, see attached screenshot (Digital_Broken):
Yes, decoding basically works and all the signals appear to be there, but all channels are at the same vertical position. :(
Performa01:
Wave Gen.
I’ll start this review with some general thoughts.
As with most additional features that go beyond the core functionality of an instrument, we cannot expect them to replace dedicated gear, rather have to accept a bunch of limitations.
A DSO is just a DSO and just like the integrated trigger frequency measurement and the automatic measurements cannot replace (proper) frequency counter and multimeter, this is also true for the built-in waveform generator – but it could still be very useful when at a pinch.
The built-in Wave Gen of the SDS2000 is a single channel arbitrary waveform generator without sweep and modulation capabilities.
Many dual channel arbitrary waveform generators have been introduced during the last decade and these can be incredibly useful. Before that time, however, we had to make do with just one channel and this is still enough for the majority of applications today.
Even the old analog function generators provide internal/external sweep capabilities, i.e. frequency modulation. Nowadays we expect a complete set of modulation capabilities together with an internal universal modulation source, which means there must be essentially another DDS-generator per channel. The SDS2000 obviously doesn’t have a spare DDS generator to be used as modulation source and it doesn’t have the connectors usually associated with a fully-fledged waveform generator, like trigger/gate in, modulation in/out, sync out, which is no surprise, considering it is just a DSO after all.
However, a sweep function could have been easily implemented just in software.
According to the data sheet, it is a 125 MSa/s, 14 bits system with 1µHz of frequency resolution.
These specs sound good and would have been a big deal even just a decade ago. But the specs aren’t everything; what counts at the end of the day, is the actual signal quality.
The frequency range covers 25MHz for sine, 10MHz for square, 300kHz for ramps and 5MHz for arbitrary waveforms.
This is not too bad either. In the good old days, analog function generators were usually limited to 2MHz, and most early DDS function generators could not exceed 10MHz.
The output impedance is proper 50 ohms, but the maximum signal level is limited to 3Vpp into 50 ohms (6Vpp open circuit).
That’s a typical limitation of many built-in generators, as they lack a proper output amplifier that could provide 20Vpp open circuit and 10Vpp into 50 ohms. It should still be enough for a bunch of everyday tasks though.
Actual frequency resolution is just 2 or 4 digits
When reviewing the specs, the claimed frequency resolution of 1µHz is rather misleading. While the lowest frequency is indeed 1µHz, the default frequency resolution is exceptionally low at just 2 digits. This can be changed to ‘fine’ adjustment, where the resolution is 4 digits. That means that above 10MHz, the smallest frequency step is 1kHz, which might be too coarse for some measurements, such as determining the bandwidth of a 10.7MHz IF filter for instance. On the other hand, given the poor response characteristic of the select knob, this approach is still welcome as it would otherwise take hours to go through the entire frequency range.
The resolution for amplitude setting is 2 or 4 digits as well.
Waveforms
The Wave Gen provides all the standard waveforms including DC and noise, plus a few built-in arbitrary waveforms and 4 memories for user defined waveforms (AWG_Gauss)
I don’t know how well it works to create a user defined waveform and then transfer it into the scope memory. The manual suggests to use EasyWave, which didn’t come with the scope (there are just a couple PDFs on the CD). We should be able to download it from Siglent’s website, but since I wasn’t particularly interested in arbitrary waveforms right now I couldn’t be bothered.
Btw, the datasheet claims a maximum of 16k for the arbitrary waveform length.
Now let’s take a closer look at some waveforms:
Sine
Amplitude accuracy appears quite good. At 1kHz, a 2.8Vpp signal measures 1.00864Vrms, which is not too far from the expected value of 0.99Vrms, indicating an error of +1.8%. This really is not bad at all, given the fact that the actual resistance of my pass-through terminator is a bit high at 50.259 ohms.
The same experiment without pass-through terminator results in an output of 1.00596Vrms and the error is +1.6%.
No matter how many bits and what the sample rate is, what really counts is the signal quality. I don’t have a proper spectrum analyser right now, but I can make accurate THD measurements up to 20kHz and will use a properly implemented FFT on another scope to look at the frequency range above.
At 2.8Vpp into 50 ohms, the measured distortion levels from 20Hz to 20kHz are generally below 0.01%, thus would be well suited for quality audio measurements (AWG_THD)
As already mentioned, for higher frequencies I have to use the FFT on another scope, which doesn’t provide the dynamic range to measure distortion figures below 0.1%. In order to check the limits of my test setup, I measured 10kHz once again (AWG_Spectrum_10kHz)
THD is measured as 0.066% now, whereas the true figure is an order of magnitude lower. This test setup will still be useful, as the distortion figure inevitably rises at higher frequencies, hence will eventually enter the dynamic range available.
The sinewave remains nice and clean up to 5MHz, where distortion is still below 0.1%, but non-harmonic spurs touch the -60dBc mark (AWG_Spectrum_5MHz)
Distortion and spurs keep rising with increasing frequency and at 10MHz, THD starts exceeding 0.1% (AWG_Spectrum_10MHz)
At 25MHz, the signal shows all kinds of harmonic and non-harmonic content and THD is measured as 0.355% (AWG_Spectrum_25MHz)
All in all these results aren’t bad at all – at least the real thing appears a lot better in terms of spectral purity than what the rather unexciting specs in the datasheet would suggest.
Square
I’ve checked the square wave across the entire frequency range and could not find any flaws. Overshoot is next to non-existent and there particularly is no ringing, provided the scope input is properly terminated at 50 ohms. Rise- and fall times are both 24ns, which is still fast enough to produce a nice looking squarewave at 1MHz (AWG_Square_1MHz_2800mVpp)
At the maximum frequency of 10MHz the output doesn’t looks very square anymore, but that’s to be expected (AWG_Square_10MHz_2800mVpp)
So no complaints here either. The rise- and fall times are exactly as specified, and overshoot is actually much better.
Pulse
Minimum pulse width is 48ns, rise- and fall times are the same as with square. Again, the pulse looks nice and clean (AWG_Pulse_48ns_2800mVpp)
Ramp
Ramps are limited to a maximum frequency of 300kHz but the linearity looks still pretty perfect at that frequency in exchange. I chose a symmetry of 0% and as a big surprise, the leading edge has a risetime of only 12ns. So ramp can do twice as good as square and pulse (AWG_Ramp_300kHz_2800mVpp)
Noise
Noise at the maximum standard deviation of 225mV provides a reasonable flat spectrum up to 10MHz and submerges in the noise floor of my test setup (some -98dBV) at about 115MHz (AWG_Noise_225mV_2800mVpp)
Conclusion
The Wave Gen option on the SDS2000 is actually quite a useful signal source. Without any bells and whistles, particularly no sweep capability and limited output level, it still does the job for many applications and performs significantly better than specified in terms of signal purity.
Performa01:
Noise Reduction
Just a few experiments with an extremely noisy signal.
Ch. 4 input: 1kHz, 500mVpp sinewave with 250mVpp white noise superimposed.
CH. 4 settings: DC coupling, full bandwidth, Probe 1x, Impedance 50 ohms.
Rising edge trigger on Ch. 4, HF-reject, Noise Reject on.
Display type dots.
With the above settings, I get a rock stable triggering despite the strong noise.
In normal acquisition mode, the trace (or should I rather say ‘track’ or even ‘field’?) looks like this (Noise_Norm)
In peak detect mode, we get the extremes only – because display type is dots! – so we effectively could call this ‘Envelope Mode’ – another reason why dots mode is a good default setting. Noise amplitude level now appears even higher a bit higher than it was set on the generator (Noise_Peak)
The same situation with display type vectors doesn’t look much different to normal acquisition mode – yet the envelope is still visible to some extent (Noise_Peak_Vectors)
But now we want to see the noise reduction of average mode. With just 4 averages, the effect is quite noticeable already. The original noise level of 250mVpp has been reduced to 125mVpp. The screen capture looks like there is even less noise, but this is only because now the waveform update rate is slow at about 5/s (one of the limitations in average mode), not showing all the scattered dots at once (Noise_Avg_4)
With 16 averages, the noise level halves again and is now 62.5mVpp (Noise_Avg_16)
With 64 averages, the noise level halves again to 31.25mVpp (Noise_Avg_64)
64 averages is about the sensible maximum; Not much can be gained with further increasing the averages. For instance, 256 averages do not halve the noise (as would be expected) – probably because we’re now in the realm of numerical noise introduced after the averaging process. Noise is now down to some 20mVpp (Noise_Avg_256)
For the reasons mentioned before, I did not test the 512 and 1024 averages settings, as they need very long to settle and still don’t reduce visual noise any further.
In this context, it would be interesting to see how strong the effect of the 20MHz input bandwidth limit is in this scenario. Yes, it does indeed affect the noise level, that is now down to 190mVpp (Noise_Peak_Limit)
The noise source for this experiment has a bandwidth of just 60MHz, so the reduction could be expected to be much stronger if the noise bandwidth were >300MHz.
Performa01:
I thought it was a good time to provide a new list of all the bugs and flaws found so far for the SDS2000-V2.0-1.02.01.28R1 firmware, including all the bugs found in previous firmware versions, that have not yet been confirmed to be solved.
Bugs:
1. Traces sometimes disappear when switching from Average or Eres acquisition modes back to Normal/Peak Detect and only can be brought back by toggling modes once again.
2. Automatic measurements disappear in roll mode.
3. Residual trace garbage on the screen and in the ‘Averages’ and ‘Enhance by bits’ menus after switching from Average/Eres to Normal/Peak Detect modes and using less channels.
4. Clear Screen does not work.
5. No memory available in Average acquisition mode.
6. No memory available in Eres acquisition mode.
7. Resolution enhancement in Eres acquisition mode doesn’t make it to the screen display.
8. Memory depth selection is not restored when changing back from a restricted mode (Average, Eres) to Normal/Peak Detect.
9. Sometimes a state is reached, where automatic measurements actually displayed on the screen don’t match the selection in the ‘Type’ menu.
10. Automatic measurement for Vmax (and probably also Vtop and some others) gives nonsense readings for FFT trace.
11. Strong spurious signals visible on FFT analysis with 70Mpts of memory.
12. Trigger state ‘Arm’ and no automatic measurements update even though the scope is actually triggered, when Average/Eres acquisition modes are used and FFT analysis is active.
13. Self Cal hangs and scope has to be restarted.
14. Automatic trigger level for AC trigger coupling behaves the same as with DC coupling, instead it should reset the trigger level to zero.
15. Display persistence doesn’t show on screenshots for small signal variations.
16. History mode freezes during playback (probably only when trigger channel is 3 or 4).
17. Digital channel display broken.
Flaws:
1. Unexpected strong ghosting with peak detect in roll mode.
2. Fast Mode has no effect on Average acquisition mode.
3. Fast Mode has no effect on Eres acquisition mode.
4. No resolution enhancement in Average acquisition mode.
5. Low frequency resolution for FFT, apparently only 1024 points.
6. Very slow update speed for FFT math.
7. Offset error changes sign at 1mV/div vertical gain setting.
8. Trigger Frequency Counter not reciprocal, thus very low resolution at frequencies <1MHz.
9. Frequency counter accuracy considerably worse than competition.
10. Automatic measurements very inaccurate for signals with pk-pk amplitude less than 2 divisions.
Bugs should be fixed at any rate.
For the flaws, some improvement would be appreciated, but it is also clear that for some (or even many) of them there might not be any reasonable improvement possible with the existing hardware.
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