Scope Wars

[2N3055]

Very nice post Jay.

[tomato]

Just in case there are people reading this who are actually interested in in my original project of comparing low end scopes, I created scope-wars@groups.io a while back when this thread got out of control.  If you are interested in scope evaluations I invite you to join.  It will be moderated to prevent the level of sheer idiocy that has dominated this thread.  Join the group, but don't post and if enough people join I'll repost stuff from this thread and we can continue discussing what is right, wrong and a "feature" of DSOs.

Suggestion: Since this isn't the first time you've gone this route, maybe it would be more efficient to launch your next thread on groups.io, so you can maintain control of the content from the beginning. 

[2N3055]

[...]

Sampling Rate and memory depth

In my mind there is no substitute for sampling speed and memory depth.

[...]

That reminds me of old school hot rodders saying "There's no substitute for cubic inches"...   until a smaller, lighter car with a four cylinder engine and a high pressure turbo blows them off the track! 

Basically you are right, of course, but making the best use of whatever sampling rate the hardware can provide is still going to make for a better scope.

For example, the dithering of samples that HP/Agilent introduced.  It seems to me that by dithering the samples slightly, you end up with more fine grained results that would otherwise have to come from using a much higher sample rate - but the "punishment" is probably a longer acquisition time, as the dithered samples slowly build up the complete picture?

Yeah, but increasing displacement is very simple and reliable and easy to manufacture. In real life it is cheaper to use bigger engine than high tech.

And easiest way to accomplish that scope newer aliases IS to have a scope that has massive oversampling and large memory. But that is expensive in BOM and processing power needed. So compromises must be made.

[2N3055]

Just in case there are people reading this who are actually interested in in my original project of comparing low end scopes, I created scope-wars@groups.io a while back when this thread got out of control.  If you are interested in scope evaluations I invite you to join.  It will be moderated to prevent the level of sheer idiocy that has dominated this thread.  Join the group, but don't post and if enough people join I'll repost stuff from this thread and we can continue discussing what is right, wrong and a "feature" of DSOs.

Suggestion: Since this isn't the first time you've gone this route, maybe it would be more efficient to launch your next thread on groups.io, so you can maintain control of the content from the beginning.

And if you are going to compare cheapest scopes available, it would help to compare them in terms that are going to useful to people in real life scenarios. I can tell you up front what you going to see if you shoot a 100 ps pulse into 100MHz cheap scope. Some useless squigle that will tell something about how scope handles signals it was never meant to see.....

On the other hand if this was meant to be a theoretical treatise on correlation of oscilloscope pulse response with scope design and filter performance, that would be very interesting to many people. But it wasn't  driven in that direction.

[SilverSolder]

[...]

Sampling Rate and memory depth

In my mind there is no substitute for sampling speed and memory depth.

[...]

That reminds me of old school hot rodders saying "There's no substitute for cubic inches"...   until a smaller, lighter car with a four cylinder engine and a high pressure turbo blows them off the track! 

Basically you are right, of course, but making the best use of whatever sampling rate the hardware can provide is still going to make for a better scope.

For example, the dithering of samples that HP/Agilent introduced.  It seems to me that by dithering the samples slightly, you end up with more fine grained results that would otherwise have to come from using a much higher sample rate - but the "punishment" is probably a longer acquisition time, as the dithered samples slowly build up the complete picture?

Yeah, but increasing displacement is very simple and reliable and easy to manufacture. In real life it is cheaper to use bigger engine than high tech.

And easiest way to accomplish that scope newer aliases IS to have a scope that has massive oversampling and large memory. But that is expensive in BOM and processing power needed. So compromises must be made.

The trend in the auto industry is towards smaller and more efficient engines.

E.g. the Ford Mustang 2020 Eco Boost four cylinder...   not your grandfather's four cylinder.  ( This is a 4-cylinder Mustang that hits 60 mph in 4.5 seconds, with a top speed of 155 mph, from its 332 horsepower, 350 lb-ft torque 2.3 liter four banger...  )  And this isn't somebody's hot rod, it is a stock production car that you can buy today.

Is there any doubt that improvements in silicon will eventually make your $20 scope on a chip possible? -  except I don't think the A brand manufacturers will end up shrinking today's tech onto such as chip (the B brands probably will).  The A brands will be building new and improved stuff that pushes the new chip to its limits, instead!

[bdunham7]

Basically you are right, of course, but making the best use of whatever sampling rate the hardware can provide is still going to make for a better scope.

"making the best use of" samples also costs money.  The point I've been trying to make regarding wanting fs/10, that Jay Diddy makes very well here, is that fs/10 works even if the implementation lacks sophistication is crude.  A system with fs/5 and a 4-pole Bessel input filter or fs/2.5 with even more sophisticated systems may work acceptably, but if, for a given bandwidth, fs/10 with a lame input filter and some simple DSP you can accomplish the same thing for less money, that's the ticket, IMO.

For example, the dithering of samples that HP/Agilent introduced.  It seems to me that by dithering the samples slightly, you end up with more fine grained results that would otherwise have to come from using a much higher sample rate - but the "punishment" is probably a longer acquisition time, as the dithered samples slowly build up the complete picture?

ETS (Equivalent Time Sampling) resolution is only limited by the ability to time the samples, given a repetitive signal.  I think earlier Rigols even had it, but they've dropped it as a feature, which I'm guessing is because of how the trigger is implemented now.  You still get a sort of random dot-walk effect that will give you a picture similar to an old ETS scope but this is not controlled and is due to the varied relationship between the trigger point and the sampling points. 

[tv84]

A few more points:

The purpose of the thread is to document what is wrong with DSOs on the market.

I am not interested in teaching DSP 101.

I am not willing to spend the time to address every misunderstanding of DSP someone has.

I appreciate having someone point out an error I make.

If you are not willing to take the time to demonstrate an alleged error on my part, I shall ignore you unless it is stated such that it is immediately obvious.

Please do not raise issues which are amply addressed by references I provide.  If you are not willing to read the references, I'm not willing to explain it to you.

I'm sorry, but I'm not a "nice" guy.  I am not willing to indulge adults who still behave like children.

Have Fun!
Reg

Reg, I'm sorry to say this but it was you who wrote these conditions... And it was you that throwed in the towel. 

I sincerely hope all the "sheer idiots" that have been around continue to post here because I liked to read most of the discussions. I only regret that my level of real "idiocy" doesn't allow me to understand many of the concepts right away but I surely apprecciate most of the comments and been learning some things.

OTH, I can easily recognize that doing a 1 or 2 chips scope is a massive endeavour. My deep respect for those guys (US, chinese, germans, etc). And, some times, we take these equipments to debug our own 1-processor circuit!! And we like to expect/demand the equipment to be flawless and be as cheap as possible!

[SilverSolder]

And easiest way to accomplish that scope newer aliases IS to have a scope that has massive oversampling and large memory. But that is expensive in BOM and processing power needed. So compromises must be made.

Understood - and this is presumably the birth place of sample dithering and other creative methods of making the best of the hardware we can realistically budget for?

After all, the marketing department would massacre the competition if "our" scope e.g. had higher bandwidth or some other improved spec using the same level of hardware?

[David Hess]

ETS (Equivalent Time Sampling) resolution is only limited by the ability to time the samples, given a repetitive signal.  I think earlier Rigols even had it, but they've dropped it as a feature, which I'm guessing is because of how the trigger is implemented now.

Low end DSO manufacturers dropped ETS when digital triggering became less expensive than analog triggering.  Digital triggering is less expensive now because increases in integration made digital logic less expensive.  Analog triggering does not benefit from increases in integration.

What does analog triggering require than digital triggering does not?

1. Trigger pickoffs for each channel.
2. Analog multiplexing to select the trigger channel.
3. Analog multiplexing to select the trigger coupling.
4. A fast analog comparator.
5. An optional time delay counter to measure the difference between the sampling clock and trigger.

In comparison, digital triggering might as well be free with increases integration.

[2N3055]

OTH, I can easily recognize that doing a 1 or 2 chips scope is a massive endeavour. My deep respect for those guys (US, chinese, germans, etc). And, some times, we take these equipments to debug our own 1-processor circuit!! And we like to expect/demand the equipment to be flawless and be as cheap as possible!

Agree!!

To be honest, I would like to apologize everybody for being persistent. I was really ticked off by " My goal in this is to embarrass the OEMs into improving their products.".
It just bothers me. The older I am, I seem to have harder time letting go..  I will be one grumpy old man one day...

[nctnico]

To be honest, I would like to apologize everybody for being persistent. I was really ticked off by " My goal in this is to embarrass the OEMs into improving their products.".

Nahh. In the end it was 'much ado about nothing'. There ain't no such thing as a free lunch. Or better put: 'you can not break the rules of physics'. If you want to get maximum bandwidth from a given samplerate you'll need a steep anti-aliasing filter. Steep filters come with lot's of phase shift. However, if you set a bandwidth limit (higher frequency oscilloscopes usually have several settings) you can get a more gradual roll-off which also has a better phase performance. But in the latter case you'll need a higher samplerate (and likely spend more money) to achieve a higher bandwidth compared to steep filtering. Pick your poison...

edit: typo

[Sighound36]

As has been pointed out the discussion already has some really interesting technical discussions revolving around whether scope FFT's can actually be useful enough to make a meaningful contribution to your working environment.

My answer is yes, are they the best way of viewing frequency domains? to a degree yes for a good look at what's going inside a signal and its artifacts whilst looking at the voltage simultaneously then it gives you another aspect of investigation which is great. For a more in-depth analysis then a SA or if you can a RTSA will allow a more useful look at the signal, these are though at a cost.

These days I perform more multi domain analysis far more, by tying in the RTSA and 2Ghz scope via IF output on the RSA5000.

By enabling both time and frequency analysis together your ability to really look deep into stubborn problem is greatly eased.

The new Keysight MXR with its massive hardware horsepower and DDC 320Mhz RTA then maybe the tide is turning now.

However I am firm believe of raw horsepower (well torque actually!) yes the new cars have more horse per CC however they are incredibly  complex and use many tricks and DSP side routes to achieving their desired results.

Decent sample rates and long memory and ideally with a 12 bit ADC and low noise front end will make a very positive difference.

Thanks to all of the contributors on this thread, though Reg may wish to take a short break and contemplate life and treating people like little semi trained minions does you no favours when making friends and asking for help. From time to time we all need a little assistance and EEV blog is great community for sharing

Considering the amount of experience on this subject shown here its been great thank you all

[nctnico]

As has been pointed out the discuss has some really interesting technical discussions revolving around whether  scope FFT's can actually be useful enough to make a meaningful contribution to your working environment.

My answer is yes, are the the best way of viewing frequency domains to a degree yes for a good look at what's going inside a signal and its artefacts whilst looking at the voltage simultaneously then it gives you another aspect of investigation great,

That is absolutely true as well. Every now and then I implement signal processing algorithms and looking at the frequency and time domain of a signal is very helpful so optimise the algorithm / see where the algorithm goes wrong.

[Fungus]

That reminds me of old school hot rodders saying "There's no substitute for cubic inches"...   until a smaller, lighter car with a four cylinder engine and a high pressure turbo blows them off the track! 

Yeah, but increasing displacement is very simple and reliable and easy to manufacture. In real life it is cheaper to use bigger engine than high tech.

A lot of those hot rodders have high pressure turbos too. And nitrous.

In a straight line they'll have 1000ft/lb of torque to destroy you with.

[2N3055]

As has been pointed out the discuss has some really interesting technical discussions revolving around whether  scope FFT's can actually be useful enough to make a meaningful contribution to your working environment.

My answer is yes, are the the best way of viewing frequency domains to a degree yes for a good look at what's going inside a signal and its artefacts whilst looking at the voltage simultaneously then it gives you another aspect of investigation great, for a more in-depth analysis then a SA or if you can a RTSA will allow a more useful look at the signal, these are though at a cost.

These days I perform more multi domain analysis far more, by tying in the RTSA and 2Ghz scope via IF output on the RSA5000.

By enabling both time and frequncy analysis together your ability to really look deep into stubborn problem is greatly eased.

The new Keysight MXR with its massive hardware horsepower and DDC 320Mhz RTA then maybe the tide is turning now.

However I am firm believe of raw horsepower (well torque actually!) yes the new cars have more horse per CC however they are incredibly  complex and use many tricks and DSP side routes to achieving their desired results.

Decent sample rates and long memory and ideally with a 12 bit ADC and low noise front end will make a very positive difference.

Thanks to all of the contributors on this thread, though Reg may wish to take a short break and contemplate life and treating people like little semi trained minions does you no favours when making friends and asking for help. From time to time we all need a little assistance and EEV blog is great community for sharing

Considering the amount of experience on this subject shown here its been great thank you all

I would also like to thank you for your very valuable insight and for sharing real life experience with equipment you use.

[tomato]

To be honest, I would like to apologize everybody for being persistent. I was really ticked off by " My goal in this is to embarrass the OEMs into improving their products.".
It just bothers me. The older I am, I seem to have harder time letting go..  I will be one grumpy old man one day...

Your reaction is understandable.  There's nothing more insufferable than someone -- whose experience is in another field -- who thinks they know more than everyone else.

[Sighound36]

Fungus

A previous life used to run a race team

You may laugh my personal occasional  ride has 1400lbs torque with two turbos and nitrous but propane to go with the gas it weighs 1300kg, here's the rub it's a diesel. The last set of rollers we tested it it broke the retardation device

Always exceptions to rule i would  agree

Lots of ways of skinning  a cat

Sorry back on topic

[tautech]

OTH, I can easily recognize that doing a 1 or 2 chips scope is a massive endeavour. My deep respect for those guys (US, chinese, germans, etc). And, some times, we take these equipments to debug our own 1-processor circuit!! And we like to expect/demand the equipment to be flawless and be as cheap as possible!

Agree!!

To be honest, I would like to apologize everybody for being persistent. I was really ticked off by " My goal in this is to embarrass the OEMs into improving their products.".
It just bothers me. The older I am, I seem to have harder time letting go..  I will be one grumpy old man one day...

Yes Reg certainly went out on a limb stating that.
Here's another thread investigating similar scope response characteristics:
https://www.eevblog.com/forum/testgear/oscilloscope-frequency-response-correction-program/

Fungus

A previous life used to run a race team

You may laugh my personal occasional  ride has 1400lbs torque with two turbos and nitrous but propane to go with the gas it weighs 1300kg, here's the rub it's a diesel. The last set of rollers we tested it it broke the retardation device

Always exceptions to rule i would  agree

Lots of ways of skinning  a cat

Sorry back on topic

Topic ! 
Reg has left the nest in disgust of all of us.

Been involved with a tiny bit of drag racing too helping the neighbor reach deadlines for meets.
All rotary powered, some 2r, some 3r, NA and turbed.

20B on meth and 40lb boost. First runs on hub dyno getting a basic tune. At a later date pushed to 1400 HP. 

[egonotto]

The discrete Fourier transform of a band limited impulse is a constant value.   

No. If a impulse is band limited than the spectrum is confined to a finite frequency interval.

Best regards
egonotto

[SilverSolder]

That reminds me of old school hot rodders saying "There's no substitute for cubic inches"...   until a smaller, lighter car with a four cylinder engine and a high pressure turbo blows them off the track! 

Yeah, but increasing displacement is very simple and reliable and easy to manufacture. In real life it is cheaper to use bigger engine than high tech.

A lot of those hot rodders have high pressure turbos too. And nitrous.

In a straight line they'll have 1000ft/lb of torque to destroy you with.

No question - big displacement AND all the tricks, is really at the edge of what is possible!

[SilverSolder]

[...]
For example, the dithering of samples that HP/Agilent introduced.  It seems to me that by dithering the samples slightly, you end up with more fine grained results that would otherwise have to come from using a much higher sample rate - but the "punishment" is probably a longer acquisition time, as the dithered samples slowly build up the complete picture?

ETS (Equivalent Time Sampling) resolution is only limited by the ability to time the samples, given a repetitive signal.  I think earlier Rigols even had it, but they've dropped it as a feature, which I'm guessing is because of how the trigger is implemented now.  You still get a sort of random dot-walk effect that will give you a picture similar to an old ETS scope but this is not controlled and is due to the varied relationship between the trigger point and the sampling points.

I don't think the dithering that HP did (still does?) is the same at ETS?   

If you have a constant e.g. 200MSa/s,  and you can dither the samples e.g. by 5 discrete steps, you end up with a "slow" 1GSa/s.

Maybe that effectively is actually the same as equivalent time sampling, just done by random steps instead of one long linear sequence?

[SilverSolder]

Fungus

A previous life used to run a race team

You may laugh my personal occasional  ride has 1400lbs torque with two turbos and nitrous but propane to go with the gas it weighs 1300kg, here's the rub it's a diesel. The last set of rollers we tested it it broke the retardation device

Always exceptions to rule i would  agree

Lots of ways of skinning  a cat

Sorry back on topic

Sounds like adequate performance for the morning commute! 

[bdunham7]

I don't think the dithering that HP did (still does?) is the same at ETS?   

If you have a constant e.g. 200MSa/s,  and you can dither the samples e.g. by 5 discrete steps, you end up with a "slow" 1GSa/s.

Maybe that effectively is actually the same as equivalent time sampling, just done by random steps instead of one long linear sequence?

AFAIK it is the same, although there might be different ways of implementing it.  If you use a uniform ramp of time displacement, you can create artifacts--the details of that I can't explain very well.  However, if you vary the sample timing randomly or at least pseudo-randomly, as long as you can accurately measure the time that it was captured, you can put it in it's place and slowly build a record.  Or something like that.

[bdunham7]

That reminds me of old school hot rodders saying "There's no substitute for cubic inches"...   until a smaller, lighter car with a four cylinder engine and a high pressure turbo blows them off the track! 

The saying is "there is no replacement for displacement".  When your turbo car can win against a Pro Stock team (6.5 seconds) you can claim turbo-victory. Then you have to race against mountain motor wildcats.

Basically you are right, of course, but making the best use of whatever sampling rate the hardware can provide is still going to make for a better scope.

Not if 'making best use of' costs more than greater sampling rate.

[nctnico]

[...]
For example, the dithering of samples that HP/Agilent introduced.  It seems to me that by dithering the samples slightly, you end up with more fine grained results that would otherwise have to come from using a much higher sample rate - but the "punishment" is probably a longer acquisition time, as the dithered samples slowly build up the complete picture?

ETS (Equivalent Time Sampling) resolution is only limited by the ability to time the samples, given a repetitive signal.  I think earlier Rigols even had it, but they've dropped it as a feature, which I'm guessing is because of how the trigger is implemented now.  You still get a sort of random dot-walk effect that will give you a picture similar to an old ETS scope but this is not controlled and is due to the varied relationship between the trigger point and the sampling points.

I don't think the dithering that HP did (still does?) is the same at ETS?   

If you have a constant e.g. 200MSa/s,  and you can dither the samples e.g. by 5 discrete steps, you end up with a "slow" 1GSa/s.

Maybe that effectively is actually the same as equivalent time sampling, just done by random steps instead of one long linear sequence?

In the end it all comes down to aliasing. If your sample points are random then aliasing is less of a problem. But in the end the random samples will have a finite interval and that becomes your sampling interval (and thus sets the effective sampling frequency). The Tektronix DSOs I have owned didn't use random intervals for ETS; they just shifted the sample clock a little bit for each 'sweep'. As long as the anti-aliasing filter does its job it will work just find.