Author Topic: Siglent SDS800X HD Review & Demonstration Thread  (Read 33818 times)

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Siglent SDS800X HD Review & Demonstration Thread
« on: January 23, 2024, 08:33:24 am »
A revised summary of this thread together with some new content in a PDF can be found here:

https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5422823/#msg5422823
----------

I have decided to evaluate the SDS824X HD and will post the results here.

Why the 800 and not the 1000X HD?

Well, I suppose the SDS800X HD to be the most popular offer for hobbyists and small businesses in Siglent’s lineup, eventually replacing the successful SDS1000X-E series.
Even though there are some differences, most of that are comfort features (except for the 50 ohm inputs), hence the SDS800X HD test results should be largely valid for the SDS1000X HD as well.

I’ve once listed the obvious differences between SDS800X HD and SDS1000X HD here (reply #45):

https://www.eevblog.com/forum/testgear/siglent-just-drop-its-mic-new-sds800hd-12bit-scope-crazy-price-leaked/msg5212773/#msg5212773

In the meantime I have a confirmed list of differences:

-SDS800X HD has no external trigger input.
-Only the 200 MHz SDS800X HD have 100 Mpts memory, the lower models have only 50 Mpts.
-SDS800X HD has no 50 ohm inputs.
-SDS800X HD doesn’t have the higher quality encoders with indents
-SDS800X HD has less serial protocols: CAN-FD and FlexRay are missing.
-SDS800X HD has only 2 USB host ports.
-SDS800X HD has only 7” capacitive touch screen, but at the same resolution 1024 x 600.
-SDS800X HD doesn’t support probe factor detection.
-SDS800X HD doesn’t support Tektronix Mode.
-SDS800X HD doesn’t support Advanced Measurements Display Mode M2.
-SDS800X HD doesn’t support Measurement Histograms Secondary Zoom.
-SDS800X HD has no RTC.

+SDS800X HD supports NTP.

The first impression was very positive. The instrument feels solid, the display appears a bit small, especially for someone used to the 10.1” screens of the 2000 series, yet the resolution is the same and it’s bright and crisp.

Operation feels snappy, it appears to be (at least) on par with the SDS2000X Plus/HD series in this regard.

The fan noise is about the same as in the SDS1104X-E, thus it can be slightly annoying and users will have something to optimize 😉

Boot time is less than 40 seconds.

And sorry, no, I haven’t tried to install a web browser or PDF reader or play doom on it, even though I know that these might be the most important features for some 😉

Now that these trivialities are out of the way, let’s have a look at the performance – and I have to state in advance that there is a lot of progress when compared to the trusty 1000X-E series – it’s almost a completely different world.


Table of Content

This posting
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/

1.   Bandwidth
2.   Pulse Response

Reply #1
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293744/#msg5293744

1.   Noise & Spurs
2.   Vertical Zoom Demo

Reply #2
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293747/#msg5293747

1.   History & Sequence Mode
2.   Counting Pulses
3.   Trigger Jitter

Reply #3
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293750/#msg5293750

1.   Measurements
2.   Measurement Histograms
3.   Vertical Axis Labels
4.   DC Check
5.   Counter

Reply #4
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293753/#msg5293753

1.   AC Trigger Coupling
2.   Triggering noisy signals

Reply #5
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293756/#msg5293756

1.   Deep Measurements
2.   Probe Bandwidth

Reply #6
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293759/#msg5293759

1.   Poor Men’s Differential Probing
2.   Distortion measurements

Reply #7
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293762/#msg5293762

1.   Digital Channels

Reply #8
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293765/#msg5293765

1.   Measurements 2 (Trend/Track)
2.   FFT Dynamic range

Reply #9
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293771/#msg5293771

1.   True Vertical Sensitivity
2.   Peak Detect
3.   Bode Plot at a glance

Reply #58
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5332358/#msg5332358

1.   Bode Plot Example

Reply #63
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5335604/#msg5335604

1.   SPI Speed Test

Reply #65
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5335802/#msg5335802

1.   The 200 Mbps SPI challenge

Reply #67
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5338655/#msg5338655

1.   Mask Test

Reply #68
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5341157/#msg5341157

1.   Zoom Expectations

Reply #72
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5343827/#msg5343827

1.   Serial Decoders

Reply #73
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5346977/#msg5346977

1.   Cursors

Reply #74
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5351024/#msg5351024

1.   System Performance with SP5050A Probe

Reply #80
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5354024/#msg5354024

1.   Custom Probe Factors

Reply #82
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5357321/#msg5357321

1.   Dots Mode

Reply #90
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5360858/#msg5360858

1.   X-Y

Reply #150
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5373095/#msg5373095

1.   Identity

Reply #155
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5373974/#msg5373974

1.   Noise Density

Reply #160
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5377403/#msg5377403

1.   Noise density 2

Reply #167
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5380811/#msg5380811

1.   Granular Noise

Reply #180
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5384846/#msg5384846

1.   HAM Test

Reply #199
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5389646/#msg5389646

1.   Fun with Square Waves

Reply #214
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5392730/#msg5392730

1.   Zoom Challenge

Reply #234
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5396741/#msg5396741

1.   FFT-Setup
2.   FFT Window Functions


Bandwidth

Let’s start with the bandwidth. We would like to get the specified bandwidth even with all channels active, yet we do not want to deal with excessive aliasing. 

At first, one single channel at 2 GSa/s:


SDS824X_HD_FR_2GSa_log

Amplitude drop at 200 MHz is less than 2 dB and actual -3 dB bandwidth is 244 MHz. Frequency response is even a tad better when two channels are in use at 1 GSa/s:


SDS824X_HD_FR_1GSa_log

Amplitude drop at 200 MHz is <1.8 dB and actual -3 dB bandwidth is 245 MHz. Finally we look at all four channels in use at only 500 MSa/s:


SDS824X_HD_FR_500MSa_log

Now the bandwidth is actually limited to the advertised 200 MHz.


Pulse Response

For all these tests, a 10 MHz square wave with 1 ns rise time has been fed into cannel 4.

Lets start with single channel mode and 2 GSa/s:


SDS824X_HD_PR_2GSa_Zoom_Stop

In stop mode, we get a clear picture of the imperfections of the pulse top even when zoomed in 20x (main window: 100 mV/div, zoom: 5 mV/div). The rise time measurements yield the expected result of ~1.8 ns, which corresponds to 1.5 ns rise time for the SDS824X HD. This is well below the specified 1.8 ns for the 200 MHz model.

In Run mode we can see some modulation because of noise, yet nothing that could not be cured by averaging using a math trace:


SDS824X_HD_PR_2GSa_Zoom_Avg16

In case you wonder why the imperfections of the pulse top are so pronounced in the previous screenshot, this is simply the price we pay for less than perfect impedance matching when using a scope that lacks 50 ohm inputs. External termination is always a compromise working reasonably well up to 70 MHz at best. Fast edges like the 1 ns rise time in this example occupy 600 MHz bandwidth. The output impedance of the pulse generator isn’t perfect 50 ohms either, and both phenomena combined lead to reflections showing up in the first ~16 ns of the pulse.

Of course it can be demonstrated, how better impedance matching improves things. For this I’ve used a quality 18 GHz cable with two 10 dB 18 GHz Narda in-line attenuators (one at each end) to ensure sufficient attenuation for any reflections between generator and DSO. Because of the 20 dB attenuation in total, I had to increase the generator output level by 20 dB as well. This would have been 6 V amplitude, but at that level, it’s rise time is limited to min. 1.2 ns, hence I made do with just 3 V and increased the DSO sensitivity to 50 mV/div, in order to still get the 1 ns rise time:


SDS824X_HD_PR_2GSa_Zoom_Avg16_Match

With two active channels, the sample rate drops to 1 GSa/s:


SDS824X_HD_PR_1GSa

The overshoot is more pronounced now (probably because of additional AA-filtering), yet rise time measurements haven’t changed.

With four active channels, the sample rate drops to only 500 MSa/s:


SDS824X_HD_PR_500MSa

We can see hints on slight reconstruction errors together with rather pronounced Gibbs ears. Rise time measurement is off by hefty 27%, so we can safely state that this configuration is not fit for characterizing pulses with <2 ns rise time.

With a signal rise time of 2ns we can measure 2.6 ns: assuming 1.5 ns rise time for the SDS824X HD, this measurement now is only ~5% off and should be acceptable already. Furthermore, we can use Dots mode to get rid of any reconstruction errors:


SDS824X_HD_PR_500MSa_2ns_Dots

« Last Edit: April 01, 2024, 10:10:24 am by Performa01 »
 

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Re: SDS800X HD Review & Demonstration Thread
« Reply #1 on: January 23, 2024, 08:34:33 am »
Noise & Spurs

This is a demonstration of the noise with all channels active, where the bandwidth is limited to true 200 MHz.

The noise is shown for various conditions:

Ch.1: input open, 200 MHz bandwidth;
Ch.2: input open, 20 MHz bandwidth;
Ch.3: input 50 ohm terminated, 200 MHz bandwidth;
Ch.4: input 50 ohm terminated, 20 MHz bandwidth;

Because of the pronounced 1/f characteristic of the frontend noise below about 300 kHz, the results strongly depend on the lower bandwidth limit. Let’s start with 100 kHz:


SDS824X_HD_Noise_100kHz-200MHz_4Ch

Compare this with 10 kHz lower bandwidth limit:


SDS824X_HD_Noise_10kHz-200MHz_4Ch

1 kHz lower bandwidth limit:


SDS824X_HD_Noise_1kHz-200MHz_4Ch

Finally 200 Hz lower bandwidth limit:


SDS824X_HD_Noise_200Hz-200MHz_4Ch

Here you can see the noise characteristic up to 25 MHz at a RBW of ~90 Hz. In order to prevent aliasing taking effect, the noise measurement has been done of a 20 MHz bandwidth limited input channel. Since this bandwidth limiter is only first order, a digital 30 MHz lowpass filter has been added.


SDS824X_HD_Noise_20Hz-25MHz_4Ch_F30M

The Noise characteristic is a combination of the 1/f noise of the MOSFET input buffer in the HF path and the FET OpAmp in the LF path, which is fed with a heavily attenuated signal that has to be amplified again before the recombination of both paths.

We can clearly see this in the previous screenshot:
At 300 kHz, the measured noise level is -150.894 dBV, this corresponds to a noise density of just 3 nV/√Hz at a RBW of 89 Hz. The following table shows the complete measurements:

300 kHz:   -150.894 dBV    3.0 nV/√Hz
100 kHz:   -144.227 dBV    6.5 nV/√Hz
 30 kHz:   -135.927 dBV   16.9 nV/√Hz
 10 kHz:   -125.303 dBV   57.5 nV/√Hz
  3 kHz:   -116.034 dBV  167.2 nV/√Hz
  1 kHz:   -111.083 dBV  295.6 nV/√Hz
300 Hz:    -111.665 dBV  276.5 nV/√Hz
100 Hz:    -108.281 dBV  408.2 nV/√Hz

At 10 MHz, the noise density has dropped to about 2.4 nV/√Hz.

Finally let’s have a look at the spurious signals (CH.4, 50 ohm termination, 20 MHz bandwidth limit):


SDS824X_HD_Spurs_200Hz-200MHz_4Ch

The Peaks List shows the 10 strongest spurious signals, where all are at or below 1 µVrms, except for a single spur at 1.14155 MHz, which is 3.85 µVrms. This is exceptionally good, especially in this class.


Vertical Zoom Demo

Vertical zoom can suffer from noise, if high zoom factors are used. Some demonstrations use bandwidth limits to reduce noise when zooming in. It is in the responsibility of the user then to make sure that no relevant high frequency detail gets lost by this.

In general, the question remains: what if we need to look at higher frequencies? A 200 MHz 12-bit DSO should be able to demonstrate a resolution advantage with 200 MHz bandwidth signals just as well…

Here is the signal mix: a 1 MHz 600 mVpp sine with a 200 MHz 10 mVpp sine riding on it:


SDS824X_HD_VZ10x_Run

I’ve chosen straight 10 mV/div for the zoom window, i.e. a ten times magnification. The superimposed waveform is a little noisy, yet clearly visible.

This is run mode. In stop mode, we can see that all the noise is just modulation and lowering the bandwidth wouldn’t help anyway:


SDS824X_HD_VZ10x_Stop

In stop mode we basically get a clean waveform with some distortion. Yet this is just 12 bits without any additional tricks.

We can use the average math function to get rid of the modulation:


SDS824X_HD_VZ10x_Avg16

16 times average (Math trace F1) is enough to get the waveform pretty clean even in run mode. The implicit resolution enhancement of this measure is 4 bits, so that the DSO is effectively working with 16 bit data now.

« Last Edit: January 25, 2024, 06:37:56 am by Performa01 »
 
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Re: SDS800X HD Review & Demonstration Thread
« Reply #2 on: January 23, 2024, 08:35:34 am »
History & Sequence Mode

Inspired by the complaint here:

https://www.eevblog.com/forum/testgear/rigol-hdo1000-and-hdo4000-12bit-oscilloscopes-launched-in-china/msg5269170/#msg5269170

I’ve tried to replicate the test scenario described by forum member Egonotto, which is a fairly moderate one. For this, the SDS800X HD doesn’t need any special mode; the always active background history can handle that:


SDS824X_HD_5ms_Hist

The test signal is a burst packet, 20 µs long, consisting of 100 pulses. The repetition interval (burst period) was 5 ms for this test.

At 5 µs/div, the SDS824X HD takes an average of 650 µs/frame and a maximum of <2 ms/frame. The screenshot shows the History List displaying the time delta between the packets. It is 5 ms throughout, with the occasional 4.999 ms because of the not so accurate timebase of the SDS800 (25 ppm vs. 1 ppm in the SDS2000X Plus/HD series).

For event recording, we’d rather use the dedicated Sequence mode. This provides a constant 52 µs/trigger @ 5 µs/div, hence can capture a burst period of 100 µs without a single missing frame:


SDS824X_HD_100us_Seq

The screenshot shows the History List displaying the time delta between the packets. It is 100 µs throughout, with the occasional 99 µs because of the not so accurate timebase of the SDS800.

For complete information, here are my measurements for the trigger rates during normal use with vector and dots display mode as well as sequence recording from the fastest timebase of 1 ns/div up to 100 µs/div.


SDS824X HD Trigger rate


Counting Pulses

This is a demonstration of the pulse count function. As further refinement, gated measurements can be used in order to ignore unwanted portions of the record.

First the basic pulse measurement without any bells and whistles; a 100 MHz pulse packet with 1 ns rise time and 1000000 pulses is fed into Ch.4


SDS824X_HD_Pulsecount

The scope registers the correct number of one million positive pulses. The negative pulse count naturally delivers the same number minus one. Together with the peak to peak deviation of zero over >100 acquisitions it is obvious that the pulse count is spot on.

Let’s add a measurement gate. We define it to start 1.0 ms after the trigger point and to be 5 ms wide:


SDS824X_HD_Pulsecnt_Gate

We now get a count of ~500k (100 MHz x 0.005 sec.) as expected. The count is a little higher because of the limited accuracy of the timebase in the SDS800.

We can engage the zoom view for a closer inspection of the waveform:


SDS824X_HD_Pulsecnt_Gate_Zoom

We can still see the gating cursors in the main window, but the detailed view with time data is in the zoom window now. Since the “B” cursor exceeds the size of the zoom window, it is drawn at the right border and the time specification of 6.00 ms is another hint that it is outside the zoom window, which is only 100 ns wide.

The gating cursors are fully independent, consequently we can still add regular cursors (manual/tracking/measurement):


SDS824X_HD_Pulsecnt_Gate_Zoom_Cursors

With all these information, screen gets a bit busy, but we could also use the traditional info block for the regular cursors and place it at the least disturbing spot:


SDS824X_HD_Pulsecnt_Gate_Zoom_Cursors2


Trigger Jitter

The datasheet specifies the trigger jitter as <100 ps. This doesn’t sound great, considering the SDS2000X HD, where the specification is <10 ps RMS (and it has been measured as 2.02 ps actually).

Now let’s measure this using a 200 MHz sine signal from an OCXO-driven AWG (SDG7102A), fed into channels 2 and 4 of the SDS824X HD via a 12.4 GHz resistive power splitter. This way we can observe the jitter in the trigger channel as well as a not triggered channel.

The high quality 200 MHz sine signal has been chosen for its fast edges and low inherent jitter – after all we want to characterize the DSO and not the signal source.

We need to utilize a measurement gate, because for some unknown reason the T@M measurement considers all rising edges in the record, whereas we only want to measure the first one.


SDS824X_HD_Trigger Jitter

At a timebase of 1 ns/div, we cannot see any jitter in the triggered as well as the non-triggered channel after more than 10 minutes at infinite persistence.

The jitter measurements are as follows:
Triggered channel: 28.6 ps pk-pk, 4.852 ps rms;
Un-triggered channel: 28.9 ps pk-pk, 4.652 ps rms;
Skew Ch.2-Ch.4: 20.9 ps pk-pk, 3.39 ps rms;

While this is about twice as much as the SDS2000X HD, it is still very respectable and miles ahead of older designs with analog trigger system (none of Siglent’s X and A series).

« Last Edit: January 24, 2024, 06:19:14 am by Performa01 »
 
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Re: SDS800X HD Review & Demonstration Thread
« Reply #3 on: January 23, 2024, 08:36:11 am »
Measurements

There are the simple measurements, where we can define an arbitrary set of up to all 52 measurements that are related to a single channel. This set can subsequently be applied to any Input-, Zoom-, Math- or Reference-Channel. That’s also one disadvantage of the simple measurements – it’s restricted to a single channel. The other drawback is the total lack of statistics in this mode.


SDS824X_HD_Measure_Simple_Embedded

A high number of measurements might be desirable at times, yet it takes up a lot of screen space. Siglent has now introduced a new display option for measurements; “Floating”:


SDS824X_HD_Measure_Simple_Floating

This is a transparent overlay which might help to better utilize the screen space in certain situations.

We also got the Advanced Measurements., but unfortunately only mode A; mode B is available only in its bigger (and more expensive) siblings:


SDS824X_HD_Measure_Advanced_Embedded

We can have statistics and also enable the little Histicons (History Icons) as in the screenshot above, we can also mix various channels, yet we are restricted to only 5 measurements at a time.

We can have floating measurements in this mode as well, yet it might be a good idea to turn the axis labels off to avoid text collisions:


SDS824X_HD_Measure_Advanced_Floating


Measurement Histograms

The small Histicons in the advanced measurements statistics can be enlarged by simply clicking or tapping on them. This opens a separate window with a more detailed version of the histogram. The last measurement result is marked by a small red dot in the histogram, so one can watch the build up of the histogram even when there is already a lot of data collected and histogram bars don’t visibly change anymore.


SDS824X_HD_Measure_Advanced_Histogram


Vertical axis labels

The new kids in town like the SDS800X HD also bring new features: apart from the logarithmic frequency axis for the FFT, as demonstrated in the noise measurements, we also got a selectable vertical label position.


SDS824X_HD_VLabel_left


SDS824X_HD_VLabel_right


SDS824X_HD_VLabel_center


DC Check

One of the advantages of a 12 bit DSO should be not only high resolution, but also good accuracy. The SDS800X HD has a typical error of 0.5% at vertical gain settings from 5 mV/div up to 10 V/div, thus entering 3.5 digit DMM territory.

Here is a quick check with a 300 mV DC “signal”:


SDS824X_HD_DC_300mV

The error in this measurement is <0.13%. Mean and RMS measurements show pretty much the same result, as expected.


Counter

The SDS800X HD does not provide a DMM, but it has at least the Counter application. It can be used as a frequency counter or totalizer. I don’t see much use in the frequency counting function, chiefly because the automatic measurements can do exactly the same – and even on more than one channel at a time – and then we have the always visible 7 digit trigger frequency counter on top of that (I wouldn’t ever want a scope without that feature!).

But the Counter is still not totally useless, as it can also be configured as gated totalizer:


SDS824X_HD_Totalizer_Gated

Channel 3 is fed with a 1 ms wide pulse as a gating signal, channel 4 is connected to a 10 MHz sine source. Consequently, a single shot acquisition results in 10000 hits = 10 khits. This is deadly accurate because both signals come from the same AWG, hence both signals are derived from the same OCXO (whose accuracy is irrelevant in this application, yet is specified <100 ppb)

Other than the pulse counts in the measurements, the counting process can be controlled by an external signal.

EDIT: Section "Measurement Histograms" added.
« Last Edit: January 31, 2024, 10:42:45 am by Performa01 »
 
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Re: SDS800X HD Review & Demonstration Thread
« Reply #4 on: January 23, 2024, 08:36:51 am »
AC Trigger Coupling

Most of us use DC coupling for the trigger almost all the time, and there is not much to talk about it, other than that it works just as it should. We rather want to examine AC trigger coupling now.

Why and when would we need AC coupling for the trigger at all? Usually, we make that choice for the channel input and if we select AC coupling there, the trigger will inevitably be AC coupled as well. So there we already have the answer – we have the opportunity to force the trigger into AC coupling, even when the corresponding input channel is DC coupled. This can be useful for AC signals that have a DC offset that we want to watch on the screen. The offset might change with time and we still don’t want to lose triggering.

AC trigger coupling does not display a trigger level indicator, simply because it would need to closely follow even a fast-changing signal offset, thus might be rather distracting instead of beneficial.

The following test uses a 200 mVpp 100 ns wide pulse at 1 MHz repetition frequency that is superimposed on a 600mVpp sine wave at 100mHz, which acts as a variable DC offset here. As if this weren’t enough, this signal has a fixed DC offset of -6V on top of that, which needs to be removed by means of the vertical position control and the trigger level adjusted accordingly. Infinite persistence is used to give a hint what is going on.


With DC trigger coupling, triggering would only occur about 1/3 of the total time in this scenario and even then, the horizontal position would only be reasonably stable because of the short 1 ns rise time of the pulse edges. A signal with slower edges would move horizontally as well, because of the permanently changing trigger level (relative to the AC portion of the input signal). 


SDS824X_HD_Trigger_DC_VarOffset

It’s totally different if we use AC trigger coupling. When using Auto-Set by pushing the trigger level control, the trigger level is set to 50% of the signal amplitude. With this, triggering occurs always at the same point on the X-axis, no matter what the DC offset or low frequency instantaneous signal level is. The waveform constantly changes its vertical position on the screen, but remains stable on the time axis – and even more important, the signal is triggered continuously.


SDS824X_HD_Trigger_AC_VarOffset

We’ve heard complaints about DSOs that prove unable to maintain an AC- or LFRJ-trigger without some additional jitter. So here’s a test with AC trigger coupling and a 6 ns wide pulse with 1 MHz repetition frequency. The screenshot has been taken after several minutes with infinite persistence.


SDS824X_HD_Trigger_AC_Jitter

Jitter can be measured as 36.0 ps peak to peak and 6.84 ps RMS; not quite as good as the former test with the 200 MHz sine signal, yet certainly not bad either – and also reveals that my pulse generator (SDG7102A) produces quite stable signals, even when fast edges are involved.


Triggering noisy signals

Of course, for serious measurements our goal should be to find a reliable, stable and noise-free trigger source with sufficient amplitude. Sometimes this is not available and we need to try the next best thing by getting a stable triggering also from less ideal sources.

Let’s assume a low frequency signal with high frequency spikes (maybe from fast logic cicuits nearby) superimposed. To simulate this, a 600 mVpp 1 kHz sine wave has a 10 mVpp 3.254 MHz pulse train (10 ns wide pulses) riding on it. Standard DC trigger doesn’t work with such a signal, but HF-reject coupling does:


SDS824X_HD_Trig_Spikes_HFRJ

Just for fun, we can do the opposite thing and use LF-reject trigger coupling. This triggers stably on the pulses, yet because of the high waveform update rate the screen is full of traces from the 1 kHz sine.


SDS824X_HD_Trig_Spikes_LFRJ

After stopping the acquisition, we can closely inspect the last record. Even better, we can look up all the previous acquisitions in the history:


SDS824X_HD_Trig_Spikes_LFRJ_Hist1


SDS824X_HD_Trig_Spikes_LFRJ_Hist2

Another common situation is just a noisy signal like this:


SDS824X_HD_Trig_Noise_DC

Infinite persistence has been used to visualize the unstable signal phase.

We can still trigger on such a signal by simply lowering the trigger bandwidth, i.e. using HFRJ:


SDS824X_HD_Trig_Noise_HFRJ

Alternatively, the Noise Reject switch in the trigger settings will increase the trigger hysteresis, thus making it immune to noise (within reason).


SDS824X_HD_Trig_Noise_DC_NRJ
 
« Last Edit: February 17, 2024, 08:38:33 am by Performa01 »
 
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Re: SDS800X HD Review & Demonstration Thread
« Reply #5 on: January 23, 2024, 08:37:25 am »
Deep Measurements

Here's some demonstration of a common exercise which cannot be solved without deep measurements.

Imagine a 16 bit PWM based on 20 MHz clock frequency. This results in a rather slow 304 Hz PWM signal that can resolve 65536 different levels of duty cycle. To analyze this, we should be able to have accurate time measurements with at least 0.001525878 % (15 ppm) resolution

A very similar demonstration has been published for the 8-bit SDS2354X Plus a while ago already (reply #4336):

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg5183499/#msg5183499

Let’s see how the SDS800X HD fares.

Timebase is set to 500 µs/div, so that we can capture at least one full PWM period.

At 2 GSa/s, this results in 10 Mpts record length.

The PWM signal for this test has 1 ns rise time and 0.001% resolution for the duty cycle.

First the lowest at 0.001 %:


SDS824X_HD_Duty_0.001

Near full scale at 99.999 %:


SDS824X_HD_Duty_99.999

Half scale at 50.000 %:


SDS824X_HD_Duty_50.000

Finally, one step higher at 50.001 %:


SDS824X_HD_Duty_50.001

The duty cycle measurement is spot on and stable, even though not quite as impressive as the SDS2000X Plus (look at the peak-peak and standard deviation).

The period measurement is fairly stable too, with a standard deviation of only 9.2 ps. Peak deviation can only be measured in 100 ps steps, which is ten times more than the SDS2000X Plus. Quite obviously the peak deviation was well below 100 ps, hence gets reported as 0 s.

The Cycle Mean measurements gives an approximation of the resulting voltage level. It is far less precise than the duty cycle measurement though. No wonder – an even 12 bit DSO is still no precision bench DMM, hence measurement resolutions of ~15 µV are not going to be stable – this also shows in the standard deviation of ~324 µV – which is about ten times as much as with the SDS2000X Plus, but that’s only because the amplitude was ten times lower for the test back then (and the required resolution there would have been ~1.5 µV).

Finally, the rise and fall times are about as (in)accurate as can be realistically expected at 2 GSa/s. The rather high peak deviation of ~1.4 ns already hints on the averaging of many individual measurements to get the final result. Once again, we see an advantage of the SDS2000X Plus, even though the sample rate is the same. Yet this is not only about the physical sample rate, but also interpolation strategies, which require massive HW support and might be a bit simpler in the SDS800X HD. The higher bandwidth of the SDS2000X plus is helpful in this case as well.

Of course we can always get full accuracy for one local detail like the rise time by using zoom trace measurements:


SDS824X_HD_Duty_50.001_Rise

Now the rise time measurement result is much closer to the truth. The key for this is to use a timebase faster than 50 ns/div in the zoom window. Now the Sinc reconstruction generates additional data points, thus increasing time resolution and reducing the standard deviation of the measurement to just ~6 ps, which is in turn even better than the SDS2000X Plus.


Probe Bandwidth

The frequency response plots in the “Bandwidth” section have been made with a properly terminated coax connection. A proper review should also test the associated probes – unfortunately, I don’t have one, as my test unit didn’t include any accessories. I suspect that the standard probes delivered with the SDS824X HD will be the well known PP215. Even though I do have some very old PP215 (which probably aren’t quite the same as the current ones), I don’t have access to them right at the moment, hence make do with the only slightly younger 100 MHz PP510, just to give you an idea.

First the frequency response up to 500 MHz:


SDS824X_HD_Probe_PP510_FR

It can be seen, that even Siglent’s cheapest 100 MHz probe extends the system bandwidth to ~274 MHz (244 MHz with direct coax connection). So much for the practical relevance of probe ratings and textbook formulas, which are way to simplistic as to actually model the real world.

Of course, the probe has been properly LF-compensated prior to the measurements:


SDS824X_HD_Probe_PP510_PR_1kHz

The transition times are about 2 ns, which is slightly slower than with the direct coax connection. This is another occasion, where we can see the (ir)relevance of textbook formulas when it comes to real-world performance. The bandwidth was wider, yet the rise time is slower – how can that be?

Of course it’s in the frequency response, which is a far cry from the first order low pass, that is assumed in a textbook. The sudden drop of ~1.5 dB at about 120 MHz is most likely responsible for the slower rise time.

The ultimate test for proper HF-compensation is done with a fast (1 ns) risetime 1 MHz square wave.


SDS824X_HD_Probe_PP510_PR_1MHz_Zoom

It can be seen, that the PP510 isn’t an ideal match for this scope because of an overdamped edge. In other words, the HF-compensation, which is not user adjustable, is not perfect for this probe-scope combination.

The screenshot above is also another demonstration how such details can be observed on a 12 bit DSO with proper zoom implementation, without the need to take a chance by overdriving the inputs.

« Last Edit: January 29, 2024, 08:58:18 am by Performa01 »
 
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Re: SDS800X HD Review & Demonstration Thread
« Reply #6 on: January 23, 2024, 08:38:00 am »
Poor Men’s Differential Probing

With analog scopes, we were able to combine two regular (single ended, ground referenced) channels into one differential channel. This was done by adding both channels with the 2nd channel inverted, whose gain had to be fine-tuned in order to get the maximum common mode rejection. Of course, this solution was far from ideal and sensitivity as well as common mode rejection were rather limited, especially at higher frequencies, which made it hard to get meaningful results when common mode voltages were high compared to the differential signal.

We can’t do the same on a modern DSO, for a number of reasons:

•   The fine adjust of the vertical gain has only ~2% resolution, so it is not suitable to balance the channels for a CMMR >34 dB.
•   The difference has to be computed by a math channel, which always takes the vertical gain setting into account and scales to the true value, thus ignoring any gain adjustments.
•   Finally, with only 8 bits the math result doesn’t have enough resolution to properly analyze the differential signal. It is the same problem as with having vertical zoom on an strict 8-bit DSO.

The screenshot below demonstrates the result of two identical 10 MHz signals fed into channels 3 and 4 at 100 mV/div and a difference math channel is set to a 100 times higher gain at 1 mV/div:


SDS824X_HD_PMDiff_10MHz

Common mode rejection can be estimated from the amplitude measurements and would be 606.7/2.44 = 248.6 ~ 47.9dB, which is not bad at all – but we can do even better...

Of course, the balance is not perfect out of the box. Input channels and probes will both have gain tolerances, which compromise the common mode rejection. With a fairly precise instrument like the SDS800X HD we can just measure that:


SDS824X_HD_PMDiff_10MHz_corr1

As expected, there are slight differences. In this particular case, we get 516.955 mVpp for Ch.3 and 519.555 mVpp for Ch.4, so we can calculate the correction factor as 516.955/519.555 = 0.995. Consequenty, we just replace C4 in the formula by the expression C4*0.995.

The common mode rejection can be estimated from the amplitude measurements and would be 519.555/1.613 = 322.1 ~ 50.16 dB, just 2.25 dB better than before. But the correction would certainly make a much more significant difference when the initial imbalance is more pronounced.

For best accuracy, (especially external) 50 ohms termination cannot be used at the scope input, as their tolerances could be up to 2%. Without termination, a direct coax connection of 1 meter length can work reasonably well up to a couple MHz, but at higher frequencies, amplitude accuracy and common mode rejection degrade considerably. Even at only 10 MHz, the 600 mVpp signal was measured ~14 % low. The next screenshot demonstrates the same test at 100 MHz:


SDS824X_HD_PMDiff_100MHz_corr1

Peak amplitude is totally off now and common mode rejection is degraded to 173.2/3.82 = 45.34 = 33.13dB, which could still be acceptable for some tasks, yet is clearly degraded compared with the 10 MHz test. Even more importantly, the amplitude ratio has significantly changed now. This means, that the correction factor is not valid over the entire DSO bandwidth.

Just for fun, we could try to alter the correction factor; now we get 173.236 mVpp for Ch.3 and 170.833 mVpp for Ch.4, so we can calculate the correction factor as 173.236/170.833 = 1.014.


SDS824X_HD_PMDiff_100MHz_corr2

Common mode rejection would now be respectable 173.25/1.288 =134.5 ~ 42.5 dB.

In most practical scenarios, we’ll use probes; this is problematic because of their complex impedance and transmission characteristics, so that the tolerances cannot be eliminated by applying a simple correction factor. I’ll demonstrate the use of probes for a low frequency like 1 MHz. I only have a set of SP5050A probes here, yet I’m pretty confident my test results are still representative for any suitable 10x probe:


SDS824X_HD_PMDiff_SP5050A_1MHz_corr

We get 3.0097 Vpp for Ch.3 and 3.0633 Vpp for Ch.4, so we can calculate the correction factor as 3.0097/3.0633 = 0.9825.

With this, common mode rejection is 3.0633/0.02541 = 120.55 ~ 41.6 dB. This degrades quickly at higher frequencies.


As a conclusion, thanks to 12 bit resolution, 16 bit data processing and high accuracy of 0.5%, poor men’s differential probing can be an option at low frequencies with this scope, whereas it didn’t work at all with the older 8-bit SDS1000X-E series.


Distortion measurements

General purpose oscilloscopes cannot have ultra low distortion frontends, especially nowadays, where even entry level instruments start at 70 or 100 MHz bandwidth. And even a low end device like the SDS800 goes up to 200 MHz for the top model within the line, and I’d bet the integrated PGA (Programmable Gain Amplifier) in these devices has more than 0.5 GHz bandwidth.

To cut a long story short: the usual techniques to keep distortions down in audio devices, particularly global feedback, cannot be applied to wideband amplifiers. Taking this into account, it’s still amazing what can be achieved with modern integrated circuits, yet it’s the main reason why 12-bit DSOs fail to come even close to 12 bit ENOB.

Let’s start with the harmonic spectrum of a low distortion 10 MHz sine wave:


SDS824X_HD_FFT_THD_10MHz

Strongest harmonic is the 2nd at -66 dBc. Since all other harmonics have considerably lower amplitude, we can safely state that THD is about 0.05%, which isn’t bad at all.

Yet such results cannot be guaranteed; the individual gain stages within the PGA can have differences in linearity, so we need to know our instrument and take note of the weak as well as sweet spots within the vertical gain range. My particular sample of the SDS824X HD has a weak spot at exactly 100 mV/div, whereas all the settings >100 mV/div up to (at least) 110 mV/div yield results like the one shown above.

Whenever we do distortion measurements of the DSO frontend, we need to be confident that the distortion products actually come from the DSO and not the signal source. It can be tricky to verify this, hence a different approach might be more precise: the dual tone intermodulation test.


SDS824X_HD_FFT_IMD_10MHz_95FS

Two independent +6 dBm signals at 9.5 and 10.5 MHz are fed into a resistive wideband power combiner. To ensure proper isolation between the two signal sources and avoid intermodulation distortion at their output stages, a 10 dB inline attenuator has been added to each generator output. Together with the 6 dB attenuation of the splitter, we’d expect two -10 dBm input signals.

Quite obviously, the external termination of the DSO input, which cannot compensate for the ~17 pF input capacitance, is responsible for the higher-than-expected losses, hence inaccurate input level. Since we use relative measurements anyway (delta amplitude in the markers list), this doesn’t matter though.

A vertical gain of 50 mV/div doesn’t appear to be a weak spot in this instrument, so we get respectable -69 dBc for the third order intermodulation products.


SDS824X_HD_FFT_IMD_140MHz_95FS

Two independent signals at 140 and 141 MHz are fed into the power splitter. At these higher frequencies, the problems with the external termination get even more obvious and instead of the nominal level of -10 dBm we get up to 2.2 dB less. Once again we don’t care because we’re only interested in relative levels.

The vertical gain of 50 mV/div from the last test is used again and we get respectable -67 dBc for the third order intermodulation products. Other than an OpAmp with global feedback, distortion performance does not necessarily get much worse at higher frequencies.

« Last Edit: February 01, 2024, 03:29:05 pm by Performa01 »
 
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Re: SDS800X HD Review & Demonstration Thread
« Reply #7 on: January 23, 2024, 08:38:36 am »
Digital Channels

All contemporary Siglent DSOs can be upgraded to MSOs. The cheaper low end devices like the SDS800/1000X HD don’t have the required hardware built in, but communicate with a completely autonomous subsystem: it’s the SLA1016, which has already been introduced back in early 2018 to add MSO capabilities to the SDS1004X-E and later 2000X-E series.

Reply #64 in my review from that time shows the hardware, which is nowhere near as sexy as the fully integrated SPL2016 solution:

https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/msg1449168/#msg1449168

In order to work with the SDS800/1000X HD, the firmware in the SLA1016 needs to be upgraded. Unfortunately, the current beta version 8.2.3 provides no backward compatibility; once upgraded, the SLA1016 no longer works with SDS1004/2000X-E. If a single SLA1016 shall be shared between older SDS1004/2000X-E and new SDS800/1000X HD, the FW would have to be up- and downgraded accordingly.

The external subsystem approach has a few disadvantages:

•   Since it incorporates a complete SOC and local memory, it cannot be cheap even though the probe head and the grabbers leave a cheap impression.
•   Mixed analog / digital pattern trigger is not possible.
•   Zoom mode cannot be used as soon as digital channels are enabled.
•   History doesn’t work either when digital channels are activated.

If you wonder where these limitations come from, it’s simply because this is a separate subsystem connected via a (probably only moderately fast) serial interface. Because of the long memory, the DSO cannot have instant access to the full sample data through the SBUS interface (about 200 Mbit/s transfer speed needed for even only a single frame per second). Consequently, the SLA1016 only transfers the decimated screen data during normal operation.

I’ve already demonstrated its performance here in Reply #1068:

https://www.eevblog.com/forum/testgear/siglent-sds1204x-e-released-for-domestic-markets-in-china/msg2007983/#msg2007983

Now let’s add some more content. First, it might be important to know that the SDS800X HD doesn’t collapse when its advertised capabilities are actually called up.


SDS824X_HD_Digital_4Ch_P16_Deskew

In the above screenshot we can see 16 digital channels at 1 GSa/s sample rate together with 4 active analog channels at 500 MSa/s each.

We can further see one digital parallel bus decoder placed right under the digital traces, showing hexadecimal values.

The Deskew parameter is there to compensate for runtime differences between analog and digital probes; it can be adjusted in 10 ps steps.

There is a digital Edge trigger set on channel D0.

We can enable just 8 bits if we want to show e.g. the activity of a 7-bit counter:


SDS824X_HD_Digital_4Ch_P8_Counter


Now let’s check a fast clock signal (on 7 channels):


SDS824X_HD_Digital_4Ch_P8_200MHz_1ms

In order to see the details. We need to stop the acquisition and then zoom in using a faster time base:


SDS824X_HD_Digital_4Ch_P8_200MHz_Stop_Zoom_5ns

Who said we cannot have a perfect 200 MHz square wave on a 200 MHz bandwidth oscilloscope 😉

Here’s another challenge: a 2 ns wide pulse with 500 ps rise time, captured analog and digital at the same time:


SDS824X_HD_Digital_1Ch_p4_Pulse_2ns

A digital Deskew value of 6.52 ns was required to get both domains reasonably aligned; as expected, the digital channel shows a simplified representation of the pulse, which can be characterized by the measurements of the analog channel. Of course, 200 (or even 245) MHz bandwidth is not nearly enough to even remotely reproduce such a pulse; for this, at least 1 GHz bandwidth would be required. Yet it looks clean and good within the capabilities of a low bandwidth DSO and the transition time measurement results of 1.4 and 1.25 ns suggest an unexpected good oscilloscope risetime.


Probably the most popular use case nowadays would be serial decoding. I’ll just demonstrate I2C, even though this protocol only requires two channels.


SDS824X_HD_Digital_1Ch_I2C_Run

We can see some I2C messages in the decoder table at the bottom and two digital channels together with an analog trace in the upper half of the screen. Right in the middle, there is still the parallel bus decoder line, which is of course unreadable at this time base. The I2C decoder line right under the digital channels is readable, yet messages are truncated, as indicated by the red dots.

In stop mode, we can choose a faster time base and show the complete I2C messages in the decoder line.


SDS824X_HD_Digital_1Ch_I2C_Stop_Zoom_200us

There’s finally the question: what if we want some advanced measurements (with statistics and Histicons) on top of that all?


SDS824X_HD_Digital_1Ch_FullHouse

Well, this looks a bit cramped, yet still not so bad if only we’d disable that useless parallel bus decoder line. Maybe we could make do with simple measurements, then we’d get a bigger signal display again.

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Re: SDS800X HD Review & Demonstration Thread
« Reply #8 on: January 23, 2024, 08:39:11 am »
Measurements 2 (Trend/Track)

Even the entry level DSOs like the SDS800X HD provide advanced features like Trend and Track Plots for measurements. They can be a bit fiddly at times, but the results are definitely worth it.


Trend Plots

Let’s start with the more familiar (to most) Trend charts. As the name suggests, they plot a measurement value over time. For this, the record length of the raw acquisition can be short – a single full signal period would already be enough. Shorter records have the advantage of faster processing and less memory consumption.


SDS824X_HD_Measure_Trend_AM_Interval

Of course, even a 12-bit DSO is not a metrology-grade instrument, hence we cannot use Trend Plot to observe the stability of a voltage standard; yet there are still plenty of applications where 0.5% accuracy is sufficient.

For the example above, we have used a 1 s time interval Trend Plot, measuring the peak to peak amplitude of a 10 MHz sine wave, 100% amplitude modulated by a 10 mHz ramp signal. The minimum time interval for Trend Plot would be 0.5 s.


SDS824X_HD_Measure_Trend_AM_enlarged

It can be seen that the Trend Plot has a separate statistic, as it is significantly slower than the regular measurements, hence works on a decimated subset of the original measurement data. Consequentially, since the time interval of the Trend Plot is one second, the measurement rate of the PK-Pk measurement can be calculated as ~19.4 per second, while at the same time we get 174 frequency measurements per second.

Instead of a fixed time interval, we can alternatively use sequence record mode. Now the trend plot window behaves like a scope in roll mode, i.e. the update rate is faster, but the time axis shows measurement samples instead of time units now.


SDS824X_HD_Measure_Trend_AM_Sequence


Track Plots

Track plots also show the developing of a measurement value, but not over time but within a single record. As opposed to trend plots, this works best with long record lengths and only with certain measurements – the ones that are computed for the entire record, i.e. all the time related measurements.

Consider a 10 MHz carrier frequency modulated with a 20 kHz sine wave and a frequency deviation of +/-1 MHz. Other than e.g. AM, we cannot really see this in the regular y-t display. This is where the Track Plots come in handy; they let us “demodulate” frequency and phase modulated signals – and such modulations could also come from noise, drift and jitter.


SDS824X_HD_Measure_Track_FM

Take a closer look at the above screenshot: the record length is 5 Mpts and there are 1000 times more frequency measurement samples than Pk-Pk amplitude measurement samples. Experienced people could tell from the histogram that the modulation signal would very likely be a sine wave, but they would not be able to determine the deviation and modulation frequency.

From the Track Plot we can see that the modulation signal is a sine wave with exactly 50 µs period (=20 kHz) and it alters the carrier frequency between 9 and 11 MHz.


FFT Dynamic range

Since the introduction of the SDS1004X-E in early 2018, FFT has always been a strong point of Siglent DSOs. The SDS800X HD is no exception and numerous examples have been published already in this review, as the FFT is an incredibly universal tool to demonstrate fundamental features like frequency response, noise distribution and signal spectra in general, as well as measure distortion products, spurious signals and weak signals, deeply buried under the noise floor.

One of the concerns with the FFT in DSOs is the dynamic range. For 8-bit acquisition systems, this is only about 49 dB according to the textbook, as it is some 73 dB for 12 bits. And indeed we need to be careful when acting outside these “guaranteed” dynamic ranges. Yet the wonders of process gain in an FFT and other resolution enhancement techniques can extend the usable dynamic range quite a bit, and this shall be demonstrated for the SDS800X HD in some best case scenario.

What is the “best case” scenario? It is a frequency at or above 1 MHz in order to escape the 1/f noise, but at the same time the frequency should be low enough so we can get rid of all the high frequency noise by using the 20 MHz bandwidth limiter plus an additional steep 20 MHz lowpass filter. Consequently, we practice math on math (the SDS800X HD could also have combined it in one formula instead) and calculate the FFT on the filter output instead directly on the Ch.4 data.

Two signals from an AWG at 9.9 and 10.1 MHz are fed into a wideband signal combiner, where the second signal goes through a fixed 20 dB attenuator together with a 1 GHz step attenuator before it hits the combiner, whose output is connected to the SDS824X HD Channel 4 input via another 10 dB inline attenuator and a 50 ohm through terminator. Of course, the tolerances of these various components sum up, so I have calibrated the whole setup for a 0 dB setting of the step attenuator first by means of the AWG output levels, but left them untouched for all subsequent measurements. As a consequence, any tolerances of the step attenuator settings will affect the results. The step attenuator is a Wavetek 5080.1 with a specified tolerance of +/-1 dB up to 400 MHz. After using it many decades, I can tell from experience that it thankfully is clearly more accurate than that.

In order to get a low RBW (Resolution Bandwidth), hence also a low noise floor, we don’t want an excessively high sample rate; 100 MSa/s and a Nyquist frequency of 50 MHz is plenty to deal with a 10 MHz signal and also a 20 MHz FIR filter.

Here's the calibration result:


SDS824X_HD_FFT_DR_500kpts_10MHz_40dB

The error is <0.05 dB. Going from there, here’s the measurement for 80 dB level difference:


SDS824X_HD_FFT_DR_500kpts_10MHz_80dB

The error is < 0.25 dB, which could well be attributed to the step attenuator.

Now let’s try 100 dB with the same setting:


SDS824X_HD_FFT_DR_500kpts_10MHz_100dB

The measurement error is still <0.7 dB, yet the 2nd signal is almost down in the noise.

Up to now, we’ve only computed a 512 kpts FFT, so let’s try 1 Mpts now, thus cutting the RBW in half.


SDS824X_HD_FFT_DR_1Mpts_10MHz_100dB

Now the 2nd signal is clearly above the noise floor and the total error is less than 0.15 dB!

Even if we assume the step attenuator would have no tolerances at all, this still is a remarkable result.

« Last Edit: February 17, 2024, 01:14:17 pm by Performa01 »
 
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Re: SDS800X HD Review & Demonstration Thread
« Reply #9 on: January 23, 2024, 08:39:43 am »
True Vertical Sensitivity

The SDS800X HD has a specified vertical gain range from 500 µs/div up to 10 V/div. Many contemporary DSOs have similar specs, yet only a small minority of them can provide true 500 µV/div as the real highest sensitivity at full resolution. The real sensitivity of many instruments is lower, sometimes significantly so (up to 5 mV/div). As a consequence, anything above the true highest sensitivity is just software zoom and won’t provide full resolution anymore. This might be not that much of a problem for a 12 bit DSO, but 8 bit instruments degraded to 6 bits at 1 mV/div could get problematic. On the other hand, most of those instruments also exhibit high noise levels, so the ENOB (Effective Number of Bits) drops below 6 bits at these higher sensitivities anyway.

For the SDS800X HD, I stumbled across the unexpected property of nearly equal noise levels for all vertical sensitivities from 500 µV/div to 5 mV/div:


SDS824X HD_ND

These numbers are not totally accurate because it proves very difficult to place the markers close to the intended frequency without hitting a minor spur. Consequently, I would think that the noise level is fairly uniform across all the higher sensitivities from 500 µV/div to 5 mV/div and the minima across all measurements would be the best representation of the truth:

Noise 500 µV/div – 5 mV/div :
  1 kHz : 232.9 nV/√Hz
  3 kHz : 174.2 nV/√Hz
 10 kHz :  62.5 nV/√Hz
 30 kHz :  16.0 nV/√Hz
100 kHz :   5.7 nV/√Hz
300 kHz :   2.7 nV/√Hz
  1 MHz :   2.4 nV/√Hz
 10 MHz :   2.5 nV/√Hz

This made me suspicious: does Siglent cheat after all? Are all vertical gain settings below 5 mV/div just fake? First, I’ve checked the raw acquisition data for 500 µV/div vertical gain and found the lowest voltage step to be 1.042 µV.

Time [sec]                Value [V]              Delta [V]
-4.0000000000E-08   -4,166667E-05   5,208E-6
-3.9500000000E-08   -4,166667E-05   000,000E+0
-3.9000000000E-08   -4,270833E-05   1,042E-6

The SDS800X HD has 480 LSB per vertical division (just like the SDS2000X HD), thus 3840 LSB on the visible part of the screen. Since a 12 bit acquisition system provides a total 0f 4096 LSB, there is very little headroom outside the visible screen area.

The interesting part is when we multiply the 1.042 µV resolution with the 480 LSB of one division: 1.042 * 480 ~ 500 µV/div; -> Bingo!

A less accurate, but quicker and simpler method to verify the resolution of the SDS800X HD is using vertical zoom; we can zoom into the noise in dots display mode, thus getting horizontal lines vertically spaced according to the true resolution of the instrument.

At a vertical gain of 500 µV/div and a vertical zoom window at 2 µV/div, we get the following picture:


SDS824X_HD_Resolution_Demo

Since we still have 8 vertical divisions also in the zoom window, the total visible screen height covers 16 µV at 2 µV/div. We can count 15 horizontal lines, hence 16 steps and can conclude that each step has to be close to one microvolt.

Verdict: Siglent don’t cheat. The uniform noise level at and below 5 mV/div is just a property of the integrated PGA (Programmable Gain Amplifier) used in this instrument.


Peak Detect

The peak detection capability of the SDS800X HD is specified as 2 ns. Let’s have a closer look at that.

First a 2 ns wide pulse with 300 mV amplitude and 500 ps rise time in normal acquisition mode at sufficient sample rate (2 GSa/s):


SDS824X_HD_Pulse_W2ns_RT500ps_2GSa_Norm_Zoom

It can be seen that such a narrow pulse is already a bit too much for a 200 (244) MHz oscilloscope; the amplitude has already dropped a bit and pulse width measurement isn’t quite accurate either. As expected, the rise time measurement approaches the scope’s own rise time.

With all these shortcomings, we still get a fairly stable picture – look at the main window and the peak and standard deviations in the measurements statistics.

In the screenshot above, the time base was at 5 ms/div and the sample memory was already at its maximum of 100 Mpts; slowing down the time base any further will inevitably lower the sample rate:


SDS824X_HD_Pulse_W2ns_RT500ps_100MSa_Norm_Zoom

At 100 ms/div and 100 Mpts record length the sample rate has to be decimated to just 100 MSa/s – far too slow for capturing a 2 ns wide pulse. As a consequence, many pulses get lost. In the main window we would expect to see about 1000 pulses at a pulse repetition rate of 1 kHz, but there are actually much less and the amplitudes vary wildly.

This isn’t a very realistic scenario; not many engineers would try to watch 2 ns wide pulses at a time base of 100 ms/div and have to use 2 million times zoom to watch the pulse details. Yet this is where Peak Detect acquisition mode comes into play:


SDS824X_HD_Pulse_W2ns_RT500ps_100MSa_Peak_Zoom

The main window now shows all the pulses; the amplitudes still vary a bit, but at least we don’t miss any pulses anymore. Pulse shape has nothing to do with reality anymore and measurements yield just house numbers. This should be a clear warning to not use Peak Detect for anything serious, as any math and measurements on such waveforms are of artistical value at best.

All that Peak Detect really can do is to hint on any pulses within the record.

Of course peak detection works for even narrower pulses just as well. This is not because the specification is not correct, but the simple fact that a 244 MHz DSO like the SDS824X HD simply cannot process even faster pulses:


SDS824X_HD_Pulse_W1ns_RT500ps_2GSa_Norm_Zoom

This is now a 1 ns wide pulse at maximum sample rate of 2 GSa/s. The amplitude is still 300 mV, yet the SDS824X HD cannot cope with it anymore and the amplitude measurement result has dropped to just 173 mV. The pulse width is still measured as 1.8 ns, so the relative slowness of the frontend widens shorter pulses at the expense of amplitude, hence makes an even faster peak detection unnecessary.


Bode Plot at a glance

Instead of showing an inexpressive first order RC-lowpass filter demonstrating less than 40 dB dynamic in the audio range, I’d rather check the most important characteristics of a Bode Plot: frequency- & dynamic range and accuracy.

For this, I’ve refrained from using inline terminators at the scope inputs but fed them from 50 ohms sources directly via ~25 cm long coaxial cables. The source resistance of 50 ohms, together with the cable and scope input capacitances, forms a first order lowpass filter at ~10 MHz. This can also serve as a warning how even very short cables can introduce significant amplitude errors at relatively low frequencies, as long as a transmission line is not properly terminated.

We can see this characteristic when using the “Vout” mode of the Bode Plot, where we get the absolute amplitude of the DUT output (where the DSO itself represents the DUT).


SDS824X HD_Bode_1M_Vout

The amplitude drops quite significantly above 10 MHz. It is not the 20 dB/decade like a classic first order lowpass – and this is for a number of reasons that I won’t discuss in this article. Bottom line is, that even with very short cables, accuracy of the absolute signal level is gone already at moderate frequencies of a couple MHz.

The phase plot does not resemble this, as it stays within +/-1° up to 120 MHz quite easily. It almost looks like this would not be a minimal phase system, yet it’s just the nature of a multi-channel oscilloscope, where the input signals are always phase aligned.

When using the relative (Vout/Vin) mode (as we usually do), things look completely different:


SDS824X HD_Bode_1M_S21

Bode Plot now shows the difference between reference channel 1 and the other channels. It is indicative of the quality of the SDS800X HD that the differences between channels are really negligible: less than 0.3 dB amplitude error as well as less than 1° phase error up to 120 MHz, and almost no differences between channels 2-4, speaks for itself.

Let’s check the accuracy and dynamic range now. Two signals are used to visualize a 60 dB amplitude difference. This time, 50 ohm inline termination has been used.


SDS824X HD_Bode_50_S21_60dB

There is a significant phase difference, and this comes from the additional 3-stage step attenuator + Inline attenuator + some 50 cm additional coaxial cable for channel 4.

As a final experiment, here is a 100 dB amplitude difference (phase has been adjusted by means of the channel skew parameter):


SDS824X HD_Bode_50_S21_100dB

Noise is getting a major problem, yet amplitude measurements can still yield useable results in the range 100 kHz to ~20 MHz.

The reference level is low (~570 mVrms), hence channel 4 input sees only 5.7 µVrms!

I’ve not nearly exploited the dynamic range of the SDS800X HD, which could handle up to 28 Vrms (but then with beefy external >16 W terminators) if the need should be.

« Last Edit: February 13, 2024, 10:09:45 am by Performa01 »
 
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Online Martin72

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Re: SDS800X HD Review & Demonstration Thread
« Reply #10 on: January 23, 2024, 09:23:12 am »
Quote
it’s almost a completely different world.

Absolutely, no contest.

Offline Wintel

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Re: SDS800X HD Review & Demonstration Thread
« Reply #11 on: January 23, 2024, 02:32:02 pm »
Is this a real or a "hack" SDS824X HD?

 

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Re: SDS800X HD Review & Demonstration Thread
« Reply #12 on: January 23, 2024, 02:35:17 pm »
Is this a real or a "hack" SDS824X HD?
I presume real one...
What would be the difference anyways?
 
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Offline chillidog

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Re: SDS800X HD Review & Demonstration Thread
« Reply #13 on: January 23, 2024, 02:36:08 pm »
Thanks for the elaborate testing! Looks like a very capable scope indeed. Is this still a pre-release/China version or the real deal?
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Re: SDS800X HD Review & Demonstration Thread
« Reply #14 on: January 23, 2024, 03:14:11 pm »
This is a genuine SDS824X HD, an early production unit ment for the international market. I've got this unit for beta tests and now that the official introduction comes nearer, I had asked Siglent product management for permission to publish the most relevant details, so you can know what you might be waiting for ;)

I most definitely don't know it, but from the datasheet I would not rule out that the SDS822/4X HD might have slightly different hardware compared to the SDS802/4 and 812/4X HD, because SDS822/4X HD provide slightly higher waveform update rates.

 
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Offline Wintel

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Re: SDS800X HD Review & Demonstration Thread
« Reply #15 on: January 23, 2024, 06:44:54 pm »
This is a genuine SDS824X HD, an early production unit ment for the international market. I've got this unit for beta tests and now that the official introduction comes nearer, I had asked Siglent product management for permission to publish the most relevant details, so you can know what you might be waiting for ;)

I most definitely don't know it, but from the datasheet I would not rule out that the SDS822/4X HD might have slightly different hardware compared to the SDS802/4 and 812/4X HD, because SDS822/4X HD provide slightly higher waveform update rates.
Hi,

Could you please do 2 tests?

1. Set the coupling of channel 1 to GND, Timebase to 1ms and 500uV/div to test the noise floor.

2. Set the coupling of channel 1 to GND, Timebase to 20ms and 1mV/div to test the noise floor.

 

Offline rf-loop

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Re: SDS800X HD Review & Demonstration Thread
« Reply #16 on: January 24, 2024, 05:10:57 am »
This is a genuine SDS824X HD, an early production unit ment for the international market. I've got this unit for beta tests and now that the official introduction comes nearer, I had asked Siglent product management for permission to publish the most relevant details, so you can know what you might be waiting for ;)

I most definitely don't know it, but from the datasheet I would not rule out that the SDS822/4X HD might have slightly different hardware compared to the SDS802/4 and 812/4X HD, because SDS822/4X HD provide slightly higher waveform update rates.
Hi,

Could you please do 2 tests?

1. Set the coupling of channel 1 to GND, Timebase to 1ms and 500uV/div to test the noise floor.

2. Set the coupling of channel 1 to GND, Timebase to 20ms and 1mV/div to test the noise floor.

Here with input coupling GND as you ask

Zoom window: Zoomed in vertically to max and horizontally so that every single real ADC sample dots are visible. Without interpolations.
In this oscilloscope, GND coupling is not done in start of analog input pathway. But it is also not after ADC zero binary data.
But it nicely tell what are ADC real steps...




coupling of channel 1 to GND, Timebase to 1ms and 500uV/div (and Zoom window (Z1) 10ns/div and 2uV/div)



coupling of channel 1 to GND, Timebase to 20ms and 1mV/div (and  Zoom window (Z1) 50ns/div and 2uV/div)

With 1mV/div ADC F.S. is ~8.5mV  and display full scale is 8mV
« Last Edit: January 24, 2024, 07:31:12 am by rf-loop »
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Re: SDS800X HD Review & Demonstration Thread
« Reply #17 on: January 25, 2024, 01:08:12 pm »
Subscribing, and giving this thread a little bump -- updates to the reserved posts don't move it up the "recent posts" list, I think. Many thanks for the in-depth review, Performa01, I am looking forward to the sequel!
 
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Offline Veteran68

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Re: SDS800X HD Review & Demonstration Thread
« Reply #18 on: January 25, 2024, 01:50:44 pm »
I'd love to see someone do a side-by-side with the Rigol DHO1000 line (not the DHO800 line). I know I could do a datasheet comparison but that doesn't tell the whole UX and real-world performance story.

I have the DHO1074 (upgraded to 200Mhz + 50Mpts memory) since the BF deal was too good to pass up, but I'd been holding out for Siglent's new HD scopes to arrive. I have a suspicion that the SDS1000 isn't going to be nearly as affordable as the DHO1000 series -- especially considering the BF discount -- but I'm wondering if the SDS800 series might be close enough and have some compelling improvements over even the "next-tier" DHO1000.

I realize it's not really fair to try and compare scopes from different tiers, but I wouldn't be surprised if Siglent's bottom-tier 800HD offering was as good or better in some ways than Rigol's next-tier 1000HD line.

Obviously the screen will be the major downgrade going from the DHO1000, and I do love the big, sharp Rigol screen. To give that up for the smaller Siglent would require some substantial improvements in other features.

Now if the SDS1000 comes to NA within the ballpark of Rigol's DHO1000 pricing, that's where I'll be looking, but I'm still curious where this 800 series fits in the comparison.
 

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Re: SDS800X HD Review & Demonstration Thread
« Reply #19 on: January 25, 2024, 02:19:39 pm »
I'd love to see someone do a side-by-side with the Rigol DHO1000 line (not the DHO800 line). I know I could do a datasheet comparison but that doesn't tell the whole UX and real-world performance story.

I have the DHO1074 (upgraded to 200Mhz + 50Mpts memory) since the BF deal was too good to pass up, but I'd been holding out for Siglent's new HD scopes to arrive. I have a suspicion that the SDS1000 isn't going to be nearly as affordable as the DHO1000 series -- especially considering the BF discount -- but I'm wondering if the SDS800 series might be close enough and have some compelling improvements over even the "next-tier" DHO1000.

I realize it's not really fair to try and compare scopes from different tiers, but I wouldn't be surprised if Siglent's bottom-tier 800HD offering was as good or better in some ways than Rigol's next-tier 1000HD line.

Obviously the screen will be the major downgrade going from the DHO1000, and I do love the big, sharp Rigol screen. To give that up for the smaller Siglent would require some substantial improvements in other features.

Now if the SDS1000 comes to NA within the ballpark of Rigol's DHO1000 pricing, that's where I'll be looking, but I'm still curious where this 800 series fits in the comparison.

Maybe SDS1000 will have better pricing ?  ^-^
I guess we will see soon...

Biggest differences  between 1000XHD and 800XHD are:
 
Screen size (same resolution though, so same screen content)
No 50Ω inputs. Only 1MΩ
Decodes: 1000XHD (I2C, SPI, UART, CAN, LIN, CAN FD, FlexRay) vs 800XHD(2C, SPI, UART, CAN, LIN)
Simpler I/O: one less USB port and no External Trigger IN
Some differences in measurement display options.

As for comparisons, truth is, SDS800XHD as a scope compares very favourably to DHO1000. I do understand the screen size is important (I'm nearsighted) though.

But, mind you, class numbers are not arbitrary. I expect for Siglent 1000XHD to be in a ballpark price wise compared to Rigol DHO1000 (list prices, not fire sale prices) and more capable. And 800XHD should be less than that, in it's class.. They might not try to undercut Rigol in prices, but should be in the same class, maybe bit more.
 

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Re: SDS800X HD Review & Demonstration Thread
« Reply #20 on: January 25, 2024, 05:02:43 pm »
I have updated the opening posting with a confirmed list of differences between SDS800X HD and SDS1000X HD and have added a contents overview.

The following content has been added:

Reply #3: Measurements, Vertical Axis Labels, DC Check, Counter

Reply #4: AC Trigger Coupling, Triggering noisy signals
 
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Re: SDS800X HD Review & Demonstration Thread
« Reply #21 on: January 25, 2024, 05:09:38 pm »
In the meantime I have a confirmed list of differences:

-SDS800X HD has no external trigger input.
-Only the 200 MHz SDS800X HD have 100 Mpts memory, the lower models have only 50 Mpts.
-SDS800X HD has no 50 ohm inputs.
-SDS800X HD has less serial protocols: CAN-FD and FlexRay are missing.
-SDS800X HD has only 2 USB host ports.
-SDS800X HD has only 7” capacitive touch screen, but at the same resolution 1024 x 600.
-SDS800X HD doesn’t support probe factor detection.
-SDS800X HD doesn’t support Tektronix Mode.
-SDS800X HD doesn’t support Advanced Measurements Display Mode M2.
-SDS800X HD doesn’t support Measurement Histograms Secondary Zoom.

+SDS800X HD supports NTP.

Thank you, that's a helpful summary.

Regarding bandwidth and memory depth, is it fair to assume that the basic model will be upgradable? Also, as the SDS1000X HD does not support NTP, I assume it has an on-board real-time clock with battery backup (while the 800X HD does not)?
 

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Re: SDS800X HD Review & Demonstration Thread
« Reply #22 on: January 25, 2024, 05:27:46 pm »
Regarding bandwidth and memory depth, is it fair to assume that the basic model will be upgradable? Also, as the SDS1000X HD does not support NTP, I assume it has an on-board real-time clock with battery backup (while the 800X HD does not)?
I honestly don't know, but the ugrade from 70 to 100 MHz goes without saying. Hackers will also find a way to upgrade to 200 MHz, even though there is a small chance that the memory depth and waveform update rate might not be upgradable. Who knows, maybe Siglent management holds the view that this product is such a great price/performance ratio that they actually want to optimize the BOM for the lower bandwidth models. Time (and the Hackers) will tell.

I think that this scope will become popular among amateurs on a budget, even if the memory depth would stay at 50 Mpts and the max. waveform update rate is 20% slower.

I don't have an SDS1000X HD, but rf-loop owns the previous version of it, so he should be able to answer that question. Yet it's a safe bet that it has a RTC - the missing NTP support is a dead giveaway.
 
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Re: SDS800X HD Review & Demonstration Thread
« Reply #23 on: January 25, 2024, 06:35:04 pm »
Regarding bandwidth and memory depth, is it fair to assume that the basic model will be upgradable? Also, as the SDS1000X HD does not support NTP, I assume it has an on-board real-time clock with battery backup (while the 800X HD does not)?
I honestly don't know, but the ugrade from 70 to 100 MHz goes without saying. Hackers will also find a way to upgrade to 200 MHz, even though there is a small chance that the memory depth and waveform update rate might not be upgradable. Who knows, maybe Siglent management holds the view that this product is such a great price/performance ratio that they actually want to optimize the BOM for the lower bandwidth models. Time (and the Hackers) will tell.

I think that this scope will become popular among amateurs on a budget, even if the memory depth would stay at 50 Mpts and the max. waveform update rate is 20% slower.

I don't have an SDS1000X HD, but rf-loop owns the previous version of it, so he should be able to answer that question. Yet it's a safe bet that it has a RTC - the missing NTP support is a dead giveaway.
I do, the early white version and indeed it has a RTC.
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Offline rf-loop

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Re: SDS800X HD Review & Demonstration Thread
« Reply #24 on: January 25, 2024, 09:25:59 pm »
Regarding bandwidth and memory depth, is it fair to assume that the basic model will be upgradable? Also, as the SDS1000X HD does not support NTP, I assume it has an on-board real-time clock with battery backup (while the 800X HD does not)?
I honestly don't know, but the ugrade from 70 to 100 MHz goes without saying. Hackers will also find a way to upgrade to 200 MHz, even though there is a small chance that the memory depth and waveform update rate might not be upgradable. Who knows, maybe Siglent management holds the view that this product is such a great price/performance ratio that they actually want to optimize the BOM for the lower bandwidth models. Time (and the Hackers) will tell.

I think that this scope will become popular among amateurs on a budget, even if the memory depth would stay at 50 Mpts and the max. waveform update rate is 20% slower.

I don't have an SDS1000X HD, but rf-loop owns the previous version of it, so he should be able to answer that question. Yet it's a safe bet that it has a RTC - the missing NTP support is a dead giveaway.
I do, the early white version and indeed it has a RTC.

Yes I can also confirm, SDS1000X HD (1G version) sure have internal HW RTC with battery backup (and I "believe" that 2G version also have hardware RTC). 

SDS800X HD do not have.
Of course it have date/time of day clock function where user can set date and time manually or configure it for get real time from NTP when it is connectd to network where NTP is available. Naturally if one have own NTP server it do not need connect to internet.
It keep time as long as it is ON. After shut down it loose time and it need get time manually or from NTP again after booted up. If user do not need real time at all. Time display can also shut off so that it do not start display date and time from year 1970

Also in my previous image can see there is clock displayed and all times when I turn it on (if cable is connected), it get right time from network NTP server (when configure it, user need know suitable NTP server IP, instead of name)
« Last Edit: January 25, 2024, 09:29:22 pm by rf-loop »
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