Author Topic: Rigol DS1054Z bandwidth  (Read 6774 times)

0 Members and 1 Guest are viewing this topic.

Offline TheoB

  • Regular Contributor
  • *
  • Posts: 56
  • Country: nl
Rigol DS1054Z bandwidth
« on: December 19, 2016, 05:17:25 AM »
To measure the bandwidth I've put a 20MHz square wave signal terminated in 50Ohm to my DS1054Z and measured the rise and falltime. I did this before and after adding the 100MHz bandwidth option.
I determined the bandwidth from the measured 20%/80% rise and falltime as BW=1.39/(6.28*Trf)=0.22/Trf. Trf is the average between rise and fall time.
For completeness I also measured the probe in X1 and X10.
Vert settingNo option100MHz option20MHz BW limitX1 probe (with 100MHz option)X10 probe (with 100MHz option)
200mv113MHz147MHz24.6MHz22.9MHz142MHz
500mv170MHz184MHz25.7MHz22.7MHz*
*) Could not measure as I would need 10x bigger signal

I don't know the input rise fall time as I have no other means to measure it. The instrument I use is a pulse generator with max output frequency of 200MHz. What I do find peculiar is that the measured bandwidth is a lot higher than the 50MHz specified (up to three times). And there is quite some difference in bandwidth between the lower gain settings (<=200mV/div) and the higher ones (>=500mV/div). I can hear a relay click when changing from 200mV/div to 500mV so I guess an amplifier is switched. Anyone else noticed this difference in bandwidth as a function of vertical gain?
 
The following users thanked this post: Fungus, daybyter

Offline saturation

  • Super Contributor
  • ***
  • Posts: 4750
  • Country: us
  • Doveryai, no proveryai
    • NIST
Re: Rigol DS1054Z bandwidth
« Reply #1 on: December 20, 2016, 05:57:18 AM »
You only need the rise time.  The standard measurements use 10-90.

The standard way is:
http://literature.cdn.keysight.com/litweb/pdf/5988-8008EN.pdf

For Gaussian roll off its ~0.35/Rise time; for brick wall roll off its ~0.45/Rise time.

You need only the fastest edge, because the basis of the bandwidth calculation is that of a unit impulse or Dirac delta function.

I rarely see anyone use the unit impulse alonse to measure BW because its calculation intensive.  You would differentiate the impulse then apply an FFT to it, which new fast DSO can do easily:

https://community.keysight.com/community/keysight-blogs/oscilloscopes/blog/2016/09/01/how-to-measure-your-oscilloscope-and-probe-s-bandwidth-yourself

In pure math:

http://lpsa.swarthmore.edu/BackGround/ImpulseFunc/ImpFunc.html

To measure Tr accurately you need to spread it out on the screen to confirm the automated readings match the graticule readings.

Hope this helps.  Eyeballing you graphs your data gives the DSO bandwidth as 233-300 MHz, if your measurements are true.
Best Wishes,

 Saturation
 
The following users thanked this post: MarkL, MrWolf

Offline MrWolf

  • Regular Contributor
  • *
  • Posts: 209
  • Country: ee
Re: Rigol DS1054Z bandwidth
« Reply #2 on: December 20, 2016, 06:48:29 AM »
Since this test may be vaguely related to my doings... Actually been telling from day 1 that this box is good for speed freaks sitting at lowest timebase pedal to the metal - no surprises here  :-DD Go down to 20ns timebase at most to not stall it.
 

Offline TheoB

  • Regular Contributor
  • *
  • Posts: 56
  • Country: nl
Re: Rigol DS1054Z bandwidth
« Reply #3 on: December 21, 2016, 01:00:25 AM »
Quote
You only need the rise time.  The standard measurements use 10-90.
I used 20%/80% as the step response is not OK of the rigol below 500mV/div. This means it does not have a Gaussian or flat frequency response in the 200mV range and below. To show I captured the exact same signal in both 200mV and 500mV range. The saved waveform in 500mV range I amplified to match the display in 200mV range so to make comparison easier (now you see the finite resolution also clearly).

You can also see that with 10%/90% the measured rise time starts to become affected by the "knee". 2.4ns  gives a 350/2.4=146MHz.
Quote
The standard way is:
http://literature.cdn.keysight.com/litweb/pdf/5988-8008EN.pdf
Thanks I've read it. In the 500mV/div range the rise time is 1.62ns. Because of the ringing it's probably a flat response. So bandwidth would even be 450/1.62=278MHz (instead of 350/1.62=216MHz). Both really impressive for a 50MHz scope  :-+
Quote
For Gaussian roll off its ~0.35/Rise time; for brick wall roll off its ~0.45/Rise time.

You need only the fastest edge, because the basis of the bandwidth calculation is that of a unit impulse or Dirac delta function.

I rarely see anyone use the unit impulse alonse to measure BW because its calculation intensive.  You would differentiate the impulse then apply an FFT to it, which new fast DSO can do easily:

https://community.keysight.com/community/keysight-blogs/oscilloscopes/blog/2016/09/01/how-to-measure-your-oscilloscope-and-probe-s-bandwidth-yourself

In pure math:

http://lpsa.swarthmore.edu/BackGround/ImpulseFunc/ImpFunc.html
I tried but that's too much for the little rigol. It cannot do math over math.
Quote
To measure Tr accurately you need to spread it out on the screen to confirm the automated readings match the graticule readings.

Hope this helps.  Eyeballing you graphs your data gives the DSO bandwidth as 233-300 MHz, if your measurements are true.
What is truth. Any of these measurements must be compensated for the rise time of my E-H research Model-122 pulse generator. So bandwidth of scope must even be higher.
« Last Edit: December 21, 2016, 01:16:27 AM by TheoB »
 

Offline MrWolf

  • Regular Contributor
  • *
  • Posts: 209
  • Country: ee
Re: Rigol DS1054Z bandwidth
« Reply #4 on: December 21, 2016, 01:39:45 AM »
Good to see some practical stuff for once. Care to sample same wfm on same timebase, but with more channels enabled to drop sampling rate to 500 and 250 MSa/s? Lots of pages have written if this is a problem or not... Experiment could decide.
 

Offline saturation

  • Super Contributor
  • ***
  • Posts: 4750
  • Country: us
  • Doveryai, no proveryai
    • NIST
Re: Rigol DS1054Z bandwidth
« Reply #5 on: December 21, 2016, 03:46:30 AM »
That is improved but its still suboptimal.

You simply need to measure the rise time, not the whole pulse to insure most accurate placement of the cursors and insure most accurate horizontal resolution.



You can confirm the auto measurement thus more easily with manual cursors as well the visual graticule readings as you choose. 

Enjoy.

Also be aware of problems Mr Wolf's thread has shown were the timebase affects the automated measurements.

http://www.eevblog.com/forum/testgear/testing-dso-auto-measurements-accuracy-across-timebases/msg1093842/#msg1093842

What is truth. Any of these measurements must be compensated for the rise time of my E-H research Model-122 pulse generator. So bandwidth of scope must even be higher.

Yes, but you must eliminate sources of removable error before accepting the limits of real world equipment.   FWIW what the Instek shows is a Heaviside step function, but limited by real world equipment, and its derivative is the Dirac delta as discussed earlier.  They are all 'related' and thus the step alone is valid to calculate the frequency response.

https://en.wikipedia.org/wiki/Heaviside_step_function
« Last Edit: December 21, 2016, 04:10:04 AM by saturation »
Best Wishes,

 Saturation
 

Offline TheoB

  • Regular Contributor
  • *
  • Posts: 56
  • Country: nl
Re: Rigol DS1054Z bandwidth
« Reply #6 on: December 21, 2016, 06:01:28 AM »
I was not doubting the auto measurement of the scope. I can already see myself that the measured value is about what is shown on the screen. Timebase cannot be further zoomed in (5ns is the fastest) so the measurement resolution is not that great. I did notice that the timebase itself affects the measurements. All measurements are done from the screen buffer not from the bigger capture memory. I've seen that with time and voltage measurements (up to FFT). The FTT they improved a bit by using 2400 samples from the internal buffer. Vertical resolution could be improved by averaging. That not done. Instead you get truncated vertical values, not higher resolution.

Just to make you happy, I manually placed the cursors at the 10%/90% points and removed the falling edge. I then measure 1.5ns, but it could also be 1.6ns as that's the resolution you get. The raw data shows points every ns (of course). My message is only that the bandwidth depends (a lot) on the vertical settings that is chosen. And it should not matter if you measure rise or fall time and if you show one or both (I checked and it did not affect the measurement having both on the screen). I showed both as my risetime is not the same as the falltime. Could be my generator, could be the scope. I have no means to tell.
 
The following users thanked this post: saturation

Online Fungus

  • Super Contributor
  • ***
  • Posts: 6330
Re: Rigol DS1054Z bandwidth
« Reply #7 on: December 21, 2016, 06:26:01 AM »
Just to make you happy, I manually placed the cursors at the 10%/90% points and removed the falling edge. I then measure 1.5ns, but it could also be 1.6ns as that's the resolution you get.

And that's not bad for a "100MHz" oscilloscope.  :popcorn:
 

Offline saturation

  • Super Contributor
  • ***
  • Posts: 4750
  • Country: us
  • Doveryai, no proveryai
    • NIST
Re: Rigol DS1054Z bandwidth
« Reply #8 on: December 21, 2016, 06:38:54 AM »
Theo, that is a good clean result.  I can reference the graticule against your measurements and the slope remains quite sharp.  That would mean fairly certain that your bandwidth is ~> 200 MHz - 280 MHz depending on the type of filter it has on input amps.   Congratulations!
Best Wishes,

 Saturation
 

Offline janoc

  • Super Contributor
  • ***
  • Posts: 1703
  • Country: fr
Re: Rigol DS1054Z bandwidth
« Reply #9 on: December 21, 2016, 06:45:39 AM »
AFAIK, the ~200MHz bandwidth on an unlocked DS1054 seems to match the measurements done previously of this scope, if I recall right. If you search the forum you will find the thread. So your values are likely correct. This scope is quite a value for the money.
 

Online Fungus

  • Super Contributor
  • ***
  • Posts: 6330
Re: Rigol DS1054Z bandwidth
« Reply #10 on: December 21, 2016, 06:56:34 AM »
AFAIK, the ~200MHz bandwidth on an unlocked DS1054 seems to match the measurements done previously of this scope. This scope is quite a value for the money.

Yep. That's why I put the "100MHz" in quotes. Most people get over 150MHz after unlocking it.


 

Offline guenthert

  • Regular Contributor
  • *
  • Posts: 145
  • Country: us
Re: Rigol DS1054Z bandwidth
« Reply #11 on: December 21, 2016, 07:00:19 AM »
[..]
All measurements are done from the screen buffer not from the bigger capture memory. I've seen that with time and voltage measurements (up to FFT). The FTT they improved a bit by using 2400 samples from the internal buffer. Vertical resolution could be improved by averaging. That not done. Instead you get truncated vertical values, not higher resolution.
[..]
Do you happen to have means (and inclination  ;D ) to download the measurements and perform the calculations on a PC?  I'd wished I had a well-defined fast enough signal source, then I'd do it myself.
 

Offline ebastler

  • Super Contributor
  • ***
  • Posts: 1111
  • Country: de
Re: Rigol DS1054Z bandwidth
« Reply #12 on: December 21, 2016, 07:02:37 AM »
Many thanks, TheoB! Good to see posts from someone who (a) knows what he is doing, and (b) gives a balanced view of the DS1054Z, putting things in perspective, mentioning strengths and limitations without much fanfare.
 

Online Fungus

  • Super Contributor
  • ***
  • Posts: 6330
Re: Rigol DS1054Z bandwidth
« Reply #13 on: December 21, 2016, 07:19:47 AM »
Do you happen to have means (and inclination  ;D ) to download the measurements and perform the calculations on a PC?  I'd wished I had a well-defined fast enough signal source, then I'd do it myself.

All you need to measure rise times is a mechanical switch.

(...in the 100-200Mhz range)
 

Offline guenthert

  • Regular Contributor
  • *
  • Posts: 145
  • Country: us
Re: Rigol DS1054Z bandwidth
« Reply #14 on: December 21, 2016, 07:21:25 AM »
Do you happen to have means (and inclination  ;D ) to download the measurements and perform the calculations on a PC?  I'd wished I had a well-defined fast enough signal source, then I'd do it myself.

All you need to measure rise times is a mechanical switch.

(...in the 100-200Mhz range)
Do you happen to have some mercury-wetted relays for me to borrow?
 

Online tggzzz

  • Super Contributor
  • ***
  • Posts: 5254
  • Country: gb
    • Having fun doing more, with less
Re: Rigol DS1054Z bandwidth
« Reply #15 on: December 21, 2016, 07:21:56 AM »
My message is only that the bandwidth depends (a lot) on the vertical settings that is chosen.

Do you have a rough indication of how it varies and by how much?

Such gain variations aren't uncommon. Sometimes it is due to a differing number series amplifiers being switched in/out, or because an analogue multipliers bandwidth is level dependent.
There are lies, damned lies, statistics - and ADC/DAC specs.
Gliding aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline TheoB

  • Regular Contributor
  • *
  • Posts: 56
  • Country: nl
Re: Rigol DS1054Z bandwidth
« Reply #16 on: December 21, 2016, 07:34:08 AM »
With two channels selected, the sample rate drops to 500Msa/s and the 10%/90% rise fall time becomes 2.095ns. With four channels on (250Msa/s) bandwidth cannot be higher than 125MHz. Now it becomes interesting as I have some options. In normal display the edge becomes very wobbly (as there are not many points remaining for the 1.5ns edge). So I can average. But the risetime also depends on the sin(x)/x option being on or off. Only with four channels enabled the sin(x)/x option can be disabled. With one or two channels it's always enabled. The sin)x)/x option seems to change the filtering from flat to Gaussian. So less ringing but also less bandwidth if you disable the option.
CH #SincAverageRisetime
1OnNormal1.5ns
2OnNormal2.11ns
2OnAveraged2.09ns
4OffNormal4.61ns
4OnNormal2.83ns
4OffAveraged4.53ns
4OnAveraged3.34ns

I also captured the single channel data and plotted it with octave. That gives a feeling of the raw data the scope captures. You can image what happens for lower sample rate:

 
The following users thanked this post: saturation, guenthert, MrWolf

Offline nctnico

  • Super Contributor
  • ***
  • Posts: 12197
  • Country: nl
    • NCT Developments
Re: Rigol DS1054Z bandwidth
« Reply #17 on: December 21, 2016, 07:40:26 AM »
I'd use an (RF) generator and use that to determine the -3dB point. No need to derive anything from the risetime which may not be measured accurate enough.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline TheSteve

  • Supporter
  • ****
  • Posts: 1996
  • Country: ca
  • GHz or bust
Re: Rigol DS1054Z bandwidth
« Reply #18 on: December 21, 2016, 07:52:38 AM »
I'd use an (RF) generator and use that to determine the -3dB point. No need to derive anything from the risetime which may not be measured accurate enough.

Agreed - and people will find the 3dB point is not 150 MHz(or 200 lol), it is generally between 115 and 135 MHz.
VE7FM
 

Offline TheoB

  • Regular Contributor
  • *
  • Posts: 56
  • Country: nl
Re: Rigol DS1054Z bandwidth
« Reply #19 on: December 21, 2016, 08:00:22 AM »
Quote
Do you have a rough indication of how it varies and by how much?

Such gain variations aren't uncommon. Sometimes it is due to a differing number series amplifiers being switched in/out, or because an analogue multipliers bandwidth is level dependent.
That's the information I posted when I started the thread. For a not upgraded scope the difference I find huge (+50% more bandwidth at 500mV and higher). I think indeed it has to do with amplifiers being switched in. Since they try to limit a faster intrinsic scope I would have expected a much more accurate bandwidth.
And the scope only need to do 50MHz, so there is no issue at all. It's just something to mention if you are considered about the bandwidth. I use my scope as spectrum analyzer. It has a dynamic range of 100dB (yes, that's not what you get on your screen, that's with postprocessing in Matlab/octave). From my experiments I can use this scope up to about 150MHz as an SA. It has some shortcomings, but I don't want to spend a lot of money on the real thing  :popcorn:
 

Offline TheoB

  • Regular Contributor
  • *
  • Posts: 56
  • Country: nl
Re: Rigol DS1054Z bandwidth
« Reply #20 on: December 21, 2016, 08:06:58 AM »
Quote
I'd use an (RF) generator and use that to determine the -3dB point. No need to derive anything from the risetime which may not be measured accurate enough.
I don't have one  at home :=\
A step response says more about the quality of the scope frontend than a single figure of merit like bandwidth or risetime. At the end you might be using the scope to measure a fast changing signal and wonder if the signal is not properly terminated. It is, it's your scope not performing so great. I traded my 30kg Philips 200MHz sampling scope for this little baby. And I'm very happy about it, but there are things that are just not as good anymore. You know what I also missed today? The scope has no variable horizontally  timebase (vernier)  |O.
After I discovered I saw others had already reported it before. That's a much bigger problem of this scope for me than any bandwidth above 100MHz.....
« Last Edit: December 21, 2016, 08:09:21 AM by TheoB »
 

Offline nctnico

  • Super Contributor
  • ***
  • Posts: 12197
  • Country: nl
    • NCT Developments
Re: Rigol DS1054Z bandwidth
« Reply #21 on: December 21, 2016, 08:23:10 AM »
A step response says more about the quality of the scope frontend than a single figure of merit like bandwidth or risetime.
That is a different discussion. You can also choose to make a graph of the amplitude versus frequency using a levelled (or somewhat accurate) generator. Still you have to take into account that getting a signal into a 1M Ohm with (ball park) 15pf paralllel typical oscilloscope input is somewhat challenging if you want to get it absolutely right. A 50 Ohm terminator doesn't really do the trick here because the 15pf capacitor has an impedance around 100 Ohms at 100MHz.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online TurboTom

  • Frequent Contributor
  • **
  • Posts: 255
  • Country: de
Re: Rigol DS1054Z bandwidth
« Reply #22 on: December 21, 2016, 08:39:34 AM »
Coudn't resist to test the DS1054Z (liberated) bandwidth the "classic" way. I'm not too sure how accurate my measurement is but the ballpark should be correct. I used the following setup: Signal source is an SSA3021X TG in zero span mode. The TG output is routed to the DS1054Z CH1 input where it is connected via a BNC T. The other side of the BNC T is routed back to the SA input by an identical BNC cable (so everything should be well terminated). I manually selected several individual frequencies and adjusted the TG output level to provide a constant reading on the SA input (within a range of +- 0.5dB). The input sensitivity on the o'scope was selected at 100mV/div. With this configuration, I found the measured Vpp to drop to 0.707 of the value at 50MHz not before I reached 299MHz!

Can someone try to confirm this -- possibly cable reflections might have affected my measurements?? A similar test without TG level compensation and a 50 Ohm terminator at the "free end" of the BNC T already showed soemthing like 263MHz 3dB single channel bandwidth on my DS1054Z, so the result may also well be accurate.

Cheers,
Thomas
 

Offline TheoB

  • Regular Contributor
  • *
  • Posts: 56
  • Country: nl
Re: Rigol DS1054Z bandwidth
« Reply #23 on: December 21, 2016, 08:49:50 AM »
Quote
Coudn't resist to test the DS1054Z (liberated) bandwidth the "classic" way. I'm not too sure how accurate my measurement is but the ballpark should be correct. I used the following setup: Signal source is an SSA3021X TG in zero span mode. The TG output is routed to the DS1054Z CH1 input where it is connected via a BNC T. The other side of the BNC T is routed back to the SA input by an identical BNC cable (so everything should be well terminated). I manually selected several individual frequencies and adjusted the TG output level to provide a constant reading on the SA input (within a range of +- 0.5dB). The input sensitivity on the o'scope was selected at 100mV/div. With this configuration, I found the measured Vpp to drop to 0.707 of the value at 50MHz not before I reached 299MHz!

Can someone try to confirm this -- possibly cable reflections might have affected my measurements?? A similar test without TG level compensation and a 50 Ohm terminator at the "free end" of the BNC T already showed soemthing like 263MHz 3dB single channel bandwidth on my DS1054Z, so the result may also well be accurate.
You still have a discontinuity at the scope. It's 20pF or so. So the signal from the TG reaches the scope input and sees 20pF in parallel with 50Ohm going to your SA input. That might give reflections that are frequency dependent. It will then depend on the length of your cables and the Instruments termination accuracy.
Note that I terminated the input at 50Ohm andere have the same issue. Any reflections should be covered by my 50Ohm generator (so not be reflected again). It would have been better to add an attenuator I guess. You better use a power splitter/isolater if you have those.
« Last Edit: December 21, 2016, 09:29:39 AM by TheoB »
 

Online TurboTom

  • Frequent Contributor
  • **
  • Posts: 255
  • Country: de
Re: Rigol DS1054Z bandwidth
« Reply #24 on: December 21, 2016, 09:32:19 AM »
Thanks TheoB -- Good idea! I'm a litttle bit short on SMA / BNC adapters but I managed to route a MiniCircuits 15dB directional coupler into the RF path which now looks like this:

SSA3021X TG -> Coupler IN
Coupler Coupled OUT -> SSA3021X SA IN
Coupler OUT -> BNC T on DS1054Z CH1 with 50 Ohm terminator on the free BNC T port

With this setup, the results look much more reasonable but still impressive: I find the 3dB point of the DS1054Z to be at 195MHz. By swapping the BNC end of my SMA -> BNC adapter cable between the BNC T at the o'scope input and the input of a second SA (Rigol DSA815TG), I verified the level was stable within +- 0.2dB. So this should actually be a pretty reliable test I guess. The only factor that could still lead to too high figures is the ancient BNC 50 Ohms terminator that I used on the BNC T (haven't got a BNC feed-through terminator, should put it on my shopping list...).

Okay, just checked the BNC terminator (with cable but less the scope input) with a return loss bridge to provide at least 25dB of reflection damping at 200MHz, so this should be good enough for this test.

Cheers,
Thomas
« Last Edit: December 22, 2016, 10:22:06 AM by TurboTom »
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf

 

http://opalkelly.com/