Oscillo-confusion MHz GSa/s wfm/s Mpts - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: December 31, 2018, 02:14:55 pm
content: When trying to find the "best" scope for the money, I stumble over all sort of technical data as sample rade, memory depth, bandwidth and a lot more.350Mhz 14M wms/s or 200Mhz 140M wms/s and so on, what is important and why (MHz - GSa/s - wfm/s - Mpts or:-)

author: tggzzz
author_rank: Super Contributor
timestamp: December 31, 2018, 02:40:55 pm
content: Bandwidth and samples/second arecompletelyindependent. Bandwidth is all that matters in a scope, except to salesmen. I have an ~4GHz scope with ~40kS/s.Apart from that fundamental, there are many threads on "scopes for beginners" on this forum.The key points are to define what you will use the scope for, and whether you have other necessary equipment. Plus you shouldn't forget the cost of probes

author: mvs
author_rank: Frequent Contributor
timestamp: December 31, 2018, 03:46:31 pm
content: Quote from: tggzzz on December 31, 2018, 02:40:55 pmEquivalent time sampling scopes work with repetitive signals only.For general use one needs both ADC with fast sampling speed and analog frontend with high bandwidth.

author: tggzzz
author_rank: Super Contributor
timestamp: December 31, 2018, 04:54:43 pm
content: Quote from: mvs on December 31, 2018, 03:46:31 pmOf course.Your statements, while correct, neither conflict nor change my statements.

author: helius
author_rank: Super Contributor
timestamp: December 31, 2018, 05:10:43 pm
content: Those are only the headline specs! Depending on what you need to do, there are many more things that can matter, like sensitivity, ENOB, blind time, channel-to-channel matching, and more picayune stuff like measurements, math functions, fft, go/no-go, etc etc

author: tggzzz
author_rank: Super Contributor
timestamp: December 31, 2018, 05:21:45 pm
content: Quote from: helius on December 31, 2018, 05:10:43 pm... hence the third sentence in my original reply, viz "the key points are to define what you will use the scope for, and whether you have other necessary equipment"

author: rstofer
author_rank: Super Contributor
timestamp: December 31, 2018, 06:45:21 pm
content: Quote from: FriedMule on December 31, 2018, 02:14:55 pmDefine the money first! There is no way in the world that a $350 Rigol DS1054Z is on the same planet with a $200k Keysight. If you aren't in the market for the Keysight, what does it matter how good it specs out?Bandwidth is up to you. What do you want to see? If it is a sine wave at 100 MHz, then a 100 MHz scope will do. If it is a square wave at 20 MHz and you think seeing only up to the 5th harmonic is good enough, a 100 MHz scope will do. Remember, that square wave has harmonics from DC to daylight. How many need to be displayed? What happens is that the square wave looks more like a sine wave as the frequency is increased and the ability to display a lot of harmonics is decreased.Remember the number 2.5, there will be a test later. The industry standard seems to be to sample at 2.5 times the maximum signal frequency - minimum. Technically, 2 would get it done under ideal circumstances but the industry has chosen 2.5DS1054Z - 4 channels times 100 MHz times 2.5 => 1 GHz sample rate. It all lines up! If all of the channels aren't in use, the 2.5 number can be increased. 1 channel times 100 MHz times 10.0 => 1 GSps on just one channel. Sampling at 10x will produce a better display than sampling at 2.5x but what you see on the screen is really just a drug induced hallucination in any event. There's a lot of interpolation going on down inside that FPGA. On some scopes you can just display the samples as dots without a line and magic interpolation. I don't know what use that is.Page 10 here for record length and waveforms per second (neither of those specs are particularly important to me):http://ecee.colorado.edu/~mcclurel/txyzscopes.pdfClearly, more of anything is better than less. The real questions are "Does it matter?" and "Can I afford it?".There is no such thing as 'best for the money' if money is also a variable. It's better to drive a stake in the ground ("I won't spend more than $xxx, no matter what!") and work back from there. A more expensive scope will almost always be a better scope.For entry level scopes, the DS1054Z and the Siglent SDS1104X-E seem to be popular. The Siglent is newer and the user interface is said to be much faster than Rigol's. If I didn't already have the DS1054Z, I would be looking at the SDS1204X-E 200 MHz, 4 Channel. Or unlocking a SDS1104X-E to get the bandwidth. See the "Test Equipment" forum here on EEVblog.

author: FriedMule
author_rank: Frequent Contributor
timestamp: December 31, 2018, 07:29:01 pm
content: Your answers are all great! :-)Hmm what I will use it for... It shall be my main scope used for whatever I find interesting. Both digital, analog and whatever. I know that this not an answer but I do not know what I will play with in 5 years from now.I am now looking at theSiglent SDS1204X-E 200Mhz 1 GSa/sbut may be willing to buy theSiglent SDS2352X-E 2Ch 350MHz 2 GSa/sBut 800$ is my limit! :-)Why Siglent, no fantastic reason but I like the interface, functions and the price.

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 31, 2018, 07:37:53 pm
content: In addition to the valuable information already provided:Please note that the quoted bandwidth is usually @ -3dB down.

author: rstofer
author_rank: Super Contributor
timestamp: December 31, 2018, 07:49:14 pm
content: Quote from: FriedMule on December 31, 2018, 07:29:01 pmThis is the latest "shiny thing". It is the scope I would buy had I not bought the DS1054Z a while back. In fact, I am thinking of dedicating the 1054 to my analog computers as an excuse to buy it anyway.QuoteI get my 350 MHz needs satisfied by an old Tektronix 485 I bought used 12+ years ago for about $200. The Rigol is more fully featured and I want 4 channels more than I want bandwidth so the 1054Z is a good fit. The most important spec for a scope is bandwidth - except channels.In the micro world, decoding SPI is easier with 4 channels. Yes, the logic analyzer might be better but it won't give any indication of signal integrity and things like setup and hold times may not be accurately displayed due to the relatively low sample rate.Since I already had bandwidth, I bought the Rigol for DSO features like channels, decoding, single shot (MOST important), measurements, etc. All the things that a DSO brings to the dance that an older analog scope simply doesn't have.QuoteNo reason why not! Check for particular models in the "Test Equipment" forum here on EEVblog.

author: FriedMule
author_rank: Frequent Contributor
timestamp: December 31, 2018, 09:50:42 pm
content: How important would you mean that 4CH is compared to 2CH for everyday use?I think that a later 4CH analog scope could be a good addition?

author: rstofer
author_rank: Super Contributor
timestamp: December 31, 2018, 11:02:57 pm
content: Quote from: FriedMule on December 31, 2018, 09:50:42 pmI bought the DS1054Z because a) it had 4 channels and b) I could afford it. I already had a 350 MHz Tek 485 but it was only 2 channels. The DSO measurements are handy but I could do without them. So, in the end, the decision was for 4 channels. SPI bus...There's at least one thing a DSO can do that an analog scope can't and that's single shot capture. If a signal comes along every day or two and I can figure a way to trigger on it, I can come back a week later and the image will still be on the screen. I realize the time scales are ridiculous but the idea is the same. An event happens, I trigger and capture it. It doesn't need to be a repetitive signal to accommodate an analog scope and I don't have to try to buy an analog storage scope.It is impossible to overstate the importance of single shot mode.There are just too many advantages to the DSO. Yes, the analog scope has a place (mine is under the bench) but most people will be well served by the features of a modern DSO. If they need an analog scope, they'll know why they need it!All that said, I got along with 2 channel scopes since I gave up on a 1 channel scope decades ago. Somehow I was able to troubleshoot SPI without 4 channels. And I could do it without single shot mode. And I got along without all the measurements. Everything worked out fine! But it's just so much easier with a 4 channel DSO.

author: rstofer
author_rank: Super Contributor
timestamp: December 31, 2018, 11:08:04 pm
content: There is certainly something to be said for the idea that 2 channels are sufficient. For just about everything, 2 channels is just fine. I hardly ever use all 4 channels simultaneously. But they're there when I want to work on something like SPI which just happens to be my favorite serial protocol.Yes, things get done with 2 channel scopes. But there are some things that really take advantage of 4 channels. The question is: "What are they worth to you?". To me, the 4 channels was the only reason to buy the DS1054Z. I could get along without single shot mode. But I don't have to!

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 01, 2019, 01:31:23 am
content: So would you buy a 4ch 200MHz 1GSa/s or a 2ch 350MHz 2GSa/s for "whatever use"?

author: tggzzz
author_rank: Super Contributor
timestamp: January 01, 2019, 01:44:30 am
content: Quote from: FriedMule on January 01, 2019, 01:31:23 amFor "whatever" == "signal integrity", go for 350MHz since it is higher than 200MHz. Add cost of probes of course, foreverychannelFor "whatever" == "protocol decode", go for a logic analyser, since it is much cheaper, is faster, and is more flexible and powerful in the digital domain.

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: January 01, 2019, 01:46:02 am
content: Quote from: FriedMule on January 01, 2019, 01:31:23 amI've seen this question before and my answer is still the same. Given a choice between one scope with an extra two channels for extra $200 and a scope with extra 100 MHz bandwidth for only $100 more I would take the extra two channels in a heartbeat. There are fairly few situations where an extra 100 MHZ would make much difference but many times an extra two channels can make a testing situation MUCH easier. The extra channels will give you MUCH more information on a situation than being able to see a pulse or an edge with a bit more precision.

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 01, 2019, 02:06:59 am
content: So it is not so easy after all:-)I am in no way doubting any of your answers, just trying to understand.basinstreetdesign the difference is 150MHz and 1GSa/s more and about twice the money.tggzzz how often and to what would you say that faster is better then twice the channels and where not?

author: james_s
author_rank: Super Contributor
timestamp: January 01, 2019, 07:22:09 am
content: It's easy to get paralyzed with indecision, but you can think of it another way. These are relatively low cost instruments being discussed here, it's not exactly impulse buy territory for most people but it isn't a major life decision either. Some day down the road you can upgrade to a fancier scope if you end up needing it. Take good care of whichever one you buy and it will likely hold a good portion of its value, if you decide you don't like it, you can sell it to someone else.

author: tautech
author_rank: Super Contributor
timestamp: January 01, 2019, 08:01:24 am
content: Quote from: FriedMule on January 01, 2019, 02:06:59 amIt’s not hard either.For hobbyist use a SDS1204X-E is an excellent choice, sufficient memory depth, sampling, WF/s, all the I/O’s you might need and priced well enough to allow change left to get things like a dedicated AWG.You might even get the cheaper 1104X-E and if needing additional BW apply one of the cracks to it to soup it up to the the 200MHz model.The SDS2352X-E will be a better GP scope but primarily for the higher BW it offers......it’s not so much the scope but knowing how to drive it.My 2c, get the SDS1104X-E.

author: tggzzz
author_rank: Super Contributor
timestamp: January 01, 2019, 09:56:13 am
content: Quote from: FriedMule on January 01, 2019, 02:06:59 amTo simplify, either 0% or 100%, depending on what you are trying to achieve. There's a hint thereOnce you have defined what you are trying to achieve, you can match different tool's characteristics to the job at hand.I designed and built my first computer in the mid 70s (6800 + 128bytesRAM + TTL) mostly using switches, LEDs, and a multimeter. One one occasion I used a scope for 10 minutes, to check the critical clock waveform. In that 10 minutes I learned that probing technique is critical and that 6" ground leads are a problemMore recently for digital circuits I use a logic analyser, printf() statements and the debugger with an IDE. But only after I have checked that all the analogue signals will be interpreted correctly as digital signal (i.e. setup/hold, clean transition, voltages). The key is to plan implementation so that each stage is known to be correct before the next stage is implemented.Look at my .sig, and replace "gliding" and "span" with "electronics" and "scopes"

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 01, 2019, 02:58:28 pm
content: So the smartest would be to find out if Siglent or other makes 4ch version of the 350MHz?

author: tggzzz
author_rank: Super Contributor
timestamp: January 01, 2019, 04:54:10 pm
content: Quote from: FriedMule on January 01, 2019, 02:58:28 pmYou can always throw money at a "problem"i suspect the smartest thing is to (1) define a project (2) define what needs to be tested and theclassesof tools that can do that (3) buy a cheap example of each class.You will make mistakes, learn a lot, and then be in a position to know whatyoureallyneed.

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 01, 2019, 07:33:47 pm
content: Great advice, I know that SMPS, linier supplies, amplifier, d/a convertere, bluetooth and that kind is what I am interested in rght now.My thought by buying a good scope now, was that I then only have to buy a scope once in the next many years instead of a cheep now that I need to change in 2 years.I was thinking of buying a great beginner scope now and if I ever need to, then buy a 500MHz-1GHz 4 channel analog scope later on to use when the normal scope is not enough.

author: james_s
author_rank: Super Contributor
timestamp: January 01, 2019, 07:39:13 pm
content: I think that's a reasonable approach. The thing is, there are lots of great beginner scopes now, it's really hard to go wrong as long as you avoid the very low cost toy scopes like those pocket models you can get for <$100. Any one of the popular entry level DSOs mentioned here will likely do what you need so just pick one and then focus on learning to make the most of it, remembering that for decades engineers designed incredibly sophisticated machines using scopes less capable than the $350 DSOs you can get now.

author: rstofer
author_rank: Super Contributor
timestamp: January 01, 2019, 08:40:11 pm
content: There is still the possibility that for high bandwidth you don't need the features of a DSO. They're handy but not really necessary.For things related to microcontrollers and FPGAs (and certainly audio and SMPSs), the external speeds are usually 50 MHz or less. SPI, which I might want to decode, is probably running at 20 MHz or less. The DS1054Z (unlocked to 100 MHz) handles that well. I get all the bells and whistles for lower frequencies for a really low price.Then for the faster stuff, I still have the analog scope. I could also buy a used 500 MHz scope for something on the order of $800. But only when I need it. Of course, I already have a 350 MHz scope but if I didn't, that's an approach I would take.Buy the lower bandwidth DSO for the bells and whistles and buy a high bandwidth analog scope later, if ever.It seems like the extra cost of a higher performing scope in early times would take away money from everything else. Bench meters, handheld meters, function generator, lab power supply, etc. There's only so much money to go around and each of those tools needs to be represented on the bench.Or maybe money isn't the issue. That's not my situation!

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 01, 2019, 08:52:54 pm
content: Maybe I have read wrong but for me it sounds as some of you writes:Buy high bandwidth, you will rarely use 4 channelsand other saysBuy 4 channels, you will properly not use high bandwidth anyway?

author: tautech
author_rank: Super Contributor
timestamp: January 01, 2019, 11:09:23 pm
content: In the some years I had a 4ch 300MHz DSO there were very few times I needed the BW and when I did a scope wasn’t really the right tool for the job and when Siglent SSA’s and SVA’s became available I grabbed one of each.I won’t be selling my beta tester SDS1104X-E SN#0012 anytime soon.

author: tggzzz
author_rank: Super Contributor
timestamp: January 01, 2019, 11:18:48 pm
content: The OP must ensure they use the correct type of probe for the job. In particular, for some jobs such as SMPSs connected directly to the mains it is necessary to have an isolating differential probe; these cost as much as a cheap scopehttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: rstofer
author_rank: Super Contributor
timestamp: January 02, 2019, 12:37:05 am
content: Quote from: FriedMule on January 01, 2019, 08:52:54 pmIt goes either way!Using 4 channels may never happen for some users or it may happen all the time. It was my most important purchase criteria. I already had 2 channels (analog scope). Since I had never used a DSO, I had no idea how important Single Shot would be. It solves so many problems.In the old days of the analog scope, I would have to butch up my logic or code in order to have a pulse train repeat often enough to stay on the screen. With single shot I don't need to modify anything. I just select single shot and one pass is all it takes. This is a HUGE deal and one of the great benefits of the DSO.High bandwidth will never be an issue for those interested in audio. My interests are up to around 50 MHz on uC pins and usually not that high. Maybe something in the 2-5 MHz range.You never said exactly what you want to do with a scope and that's good because you aren't locking yourself into one mindset and overlooking others. Sure, in a perfect world, you would have both channels and bandwidth. Few of us live in that world!As also mentioned above, this is just a scope. Better than some, not as good as others. When you need something better, you will sell this scope for nearly as much as you paid for it and use the money toward something better. Or you will just consider it a sunk cost and keep it.I have mentioned that I want the Siglent SDS1204X-E. What to do with my DS1054Z? Well, it sits on top of one of my Comdyna analog computers, it works perfect in that application, maybe I'll just leave it there and fill the hole on my bench with the Siglent. See? It all works out!

author: vk6zgo
author_rank: Super Contributor
timestamp: January 02, 2019, 01:04:03 am
content: Quote from: tggzzz on December 31, 2018, 02:40:55 pmThere are times when you want to look at signals with quite high frequency components, whilst using a very long time/cm setting.The classic case is looking at analog video at field rate.DSOs with very small memories commonly reduce the sampling rate savagely at such settings, to the point where the required display is lost in a forest of aliasing.The early DSOs ( & some currently available really cheap ones) cannot even display analog video accurately at line rate.OK, analog video is no more, but try looking for 50/60Hz "hum" on any pulse train with HF components!

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 02, 2019, 02:29:33 am
content: That helped me a lot and maybe I should define the data before the model?Am I understanding correct in these data titles?All with the thought on selecting a "do whatever beginner scope that I can use to most run of the mill electronic)bandwidth (Maybe not so extremely important but 100MHz+)sample rate (1GSa/s+)memory depth (As large as possible)resolution (as many bit as possible "16bit best)update rate (faster is better)Capture rate (higher is better)What would you put in as value for getting a cheap, max 1.000$ but "best" scope?

author: james_s
author_rank: Super Contributor
timestamp: January 02, 2019, 05:46:52 am
content: Quote from: vk6zgo on January 02, 2019, 01:04:03 amAnalog broadcast TV is gone but analog video is alive and well. I use it for the FPV video link on a couple of my RC airplanes and multirotors, it's widely used in retro computers and video games, amateur broadcast, many security cameras are still analog, it's not uncommon that I find myself looking at a video waveform.

author: tggzzz
author_rank: Super Contributor
timestamp: January 02, 2019, 01:42:32 pm
content: Quote from: vk6zgo on January 02, 2019, 01:04:03 amThe early digitising scopes were awful to use, except in some circumstances. Hence the correct statement that analogue scopes were usually better.It is only relatively recently (by my standards!) that digitising scopes have been equally usable.

author: tggzzz
author_rank: Super Contributor
timestamp: January 02, 2019, 01:52:31 pm
content: Quote from: rstofer on January 02, 2019, 12:37:05 amAs you note, it is usually possible to design and implement a circuit in such a way that the waveforms are repetitive - in which case single-shot is not necessary.However, there are a few events that are one-offs (e.g. monitoring bomb explosions, PSU startups), and for these a storage scope is necessary. Before digitising scopes, we had analogue storage scopes - and they were as horrible to use as the early digitising scopes were for repetitive waveforms.QuoteThere bits/resolution and linearity are probably more important. The Analog Discovery is pretty good in that respect.QuoteAhem. That 2Mb/s signal could have components above 1GHz, depending on logic family. Butyouknow that!Personally I'd use a cheap and nasty LA to capture/decode such signals.

author: rstofer
author_rank: Super Contributor
timestamp: January 02, 2019, 03:15:46 pm
content: Quote from: tggzzz on January 02, 2019, 01:52:31 pmIn my view, the Analog Discovery is unappreciated. The lab courses associated with Digilent's Real Analog course demonstrate many of the features. It truly is an electronics lab in a small box.QuoteWhether the LA can display setup and hold times will be a function of its sample rate. I have a LA that will sample at 200 MSa/s which is pretty good but before I went for one of the $8 units, I would want to look carefully at sample rate. My scope will sample at 1 GSa/s which will more accurately display the time difference between events.ETA: True, the DS1054Z will only sample 4 channels at 250 MSa/s but I could momentarily be more selective and display just 2 channels with a sample rate of 500 MSa/s.At high SPI rates, a LA sampling at 100 MSa/s might be just fine.ETA: Logic Analyzers will have much better triggering options. I sometimes have to add logic just to create a trigger when using a scope. There are a number of reasons that LAs are popular.https://sump.org/projects/analyzer/Note how the sample rate drops when the device is used for state analysis and the device under test provides the sample clock. State analysis is my primary use of a LA. I don't care what the state of logic signals is relative to some arbitrary internal LA clock, I want to know what their state is relative to the internal logic clock.

author: hamiltont
author_rank: Contributor
timestamp: January 02, 2019, 06:01:31 pm
content: The problem I had in your situation was I had no idea what my base MHz requirements were. I understood that bandwidth was a core consideration, and more bandwidth lets me scope faster signals, but....how fast are the signals I am interested in?!?!?!To solve this I looked into common bit rates for digital protocols (my main interest area) and used a trick from stackexchange to turn them into megahertz. Here is a good table -https://en.wikipedia.org/wiki/List_of_interface_bit_ratesFor example, USB 1.0 in full speed mode runs at 12Mbit/s. It's digital, so a 1 followed by a 0 would look like a square wave e.g |▔▔|___| so 12/2 (two bits per entire "wave") means it runs at about 6MHz. So if you want to play with USB 1.0, you need a scope that can reliably handle a wave of 6MHz - typical advice is to get a scope with more bandwidth than you need due to attenuation(see image belwo). Once you know what MHz your signal of interest will require, other posters can give you lots of guidance on how to choose the best scope.Some other examples:USB 2.0 High speed - 480Mbit/s e.g. 240MHzUSB 3.0 Superspeed - 5Gbit/s e.g. 2.5GHzEthernet 10-Bx - 10Mbit/s e.g. 5MhzEthernet 100-Bx - 100Mbit/s e.g. 50MHzI2C - 3.4Mbit/s e.g. 1.7MHzHDMI 1.0 video - ~5Gbit/s e.g. 2.5GHz

author: tggzzz
author_rank: Super Contributor
timestamp: January 02, 2019, 06:23:32 pm
content: Quote from: rstofer on January 02, 2019, 03:15:46 pmAtwochannel scope is better for measuring setup and hold times than an LA, and will also do the other necessary signal integrity measurements.Only after that is it worth flipping to the digital domain with an LA.QuoteExactly. LAs are better at allowing you to ignore irrelevant stuff, and concentrate on the rarer important information.QuoteAgreed on all counts (pun intended).At high data rates in general purpose LAs, usually the synchronous state capture rate is only 25% of the asynchronous capture rate, since 4 samples are used to detect two edges. The memory length may or may not be reduced.Some LAs, especially those operating at low speed or special purpose LAs, have separate clock inputs which clock the LAs logic directly. They can operate at full speed.Often a high speed LA has "strange" speed/size limitations. These can often be understood if you know the input structures in modern FPGAs, especially the SERDES blocks.

author: tggzzz
author_rank: Super Contributor
timestamp: January 02, 2019, 06:45:20 pm
content: Quote from: hamiltont on January 02, 2019, 06:01:31 pmStackexchange is worth what you pay for it. I'm afraid your understanding is simply and completely wrong.For digital signals, theonlything that matters is the transition speed, tr; the period is completely and utterly irrelevant. The usual rule-of-thumb is that the signal bandwidth is0.35/tr. There are a few nuances, but at this level they can be ignored.If you don't believe standard theory and practice and my statement, perhaps the measurements shown athttps://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/will convince you. It shows thevery differentfrequency content of three different 1kHz signals:a 1kHz square wave with 120μs rise and fall times – the baseline for comparisona 1kHz square wave with 120ns rise and fall times – representative of a 1kHz digital clock signala 1kHz signal with a width of 10μs (1% duty cycle), 120ns rise and fall times – representative of a general digital signalIn reality the digital signals won't have tr=120ns. Instead 12ns, 1.2ns and 0.12ns can all be found in modern jellybean logic. Even a 74LVC1G04 gate is 250ps with frequency content above 1GHz: seehttps://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg1902941/#msg1902941Hence if you have, say, an Arduino which changes the output once perhour, and it takes 5ns to go from high to low, then the maximum bandwith in the signal is 70MHz (i.e. 0.35/5e-9) - and you scope needs to be faster than that.

author: james_s
author_rank: Super Contributor
timestamp: January 02, 2019, 07:08:32 pm
content: I don't think that's necessarily true. Yes you need a lot of bandwidth to display a really square looking square wave accurately, but the thing is most of the time you don't really need to display it accurately, you just need to understand the limitations of your test gear. Thousands of hobbyists have gotten by with scopes of 20MHz or less debugging digital circuitry. Occasionally seeing the rise time of a signal matters but most of the time you just need to see the pattern of 1s and 0s or see when a signal is changing states relative to another signal. To say someone *needs* x amount of bandwidth is somewhat subjective, more bandwidth is always nice, but you don't need a 400MHz scope to debug an Arduino, a much less exotic instrument will do the job, even if it rounds off the edges of your square waves. Even by the time you get to a 100MHz scope probes and probing technique starts to become an art and IMO it's simply not something a beginner needs to worry too much about.

author: mvs
author_rank: Frequent Contributor
timestamp: January 02, 2019, 07:41:10 pm
content: Quote from: FriedMule on December 31, 2018, 07:29:01 pmThis specs are not quite correct.SDS1204X-E has actually two 1GSa/s ADCs, each serving a pair of inputs (1+2, 3+4). It can sample at 1GSa/s in dual channel mode, if inputs are chosen from different ADCs.SDS2352X-E has only one 2GSa/s ADC and it will reduce sampling speed to 1GSa/s in dual channel mode.

author: tggzzz
author_rank: Super Contributor
timestamp: January 02, 2019, 07:45:37 pm
content: Quote from: james_s on January 02, 2019, 07:08:32 pmI first learned the strengthsand weaknessesof that approach in 1976, as I noted above inhttps://www.eevblog.com/forum/beginners/oscillo-confusion-mhz-gsas-wfms-mpts/msg2082310/#msg2082310In that you will note I designed, built and debugged a computer using test equipment with a bandwidth<1Hz(let alone MHz or kHz!).Hobbyistsfrequentlyunwittingly create the conditions in which there are infrequent random failures or failures that take a long time to become apparent. Classic examples: failing to observe data hold times (setup times are comparatively easy), incorrect termination leading to voltage spikes which slowly damage receiver inputs, non-monotonic transitions on clock lines, ground bounce, and several others.If present, those signal integrity problems probably won't be seen on a 20MHz scope. So when their design doesn't work as expected, people will start looking in the wrong place. Seen that far too many times!Onceyou can be sure signal integrity problems do not exist,thenyou can concentrate on the "higher level" debugging - and low bandwidth equipment is often completely sufficient.BTW all probing is an art! Even at 50Hz you need to use the right probes for the job, lest you kill your equipment or yourself or someone else.

author: hamiltont
author_rank: Contributor
timestamp: January 02, 2019, 07:51:19 pm
content: Quote from: tggzzz on January 02, 2019, 06:45:20 pmThanks for clarifying! It'll take me some time to grok the replies completely, but I appreciate the help - even though I didn't pay for it

author: ebastler
author_rank: Super Contributor
timestamp: January 02, 2019, 08:00:41 pm
content: Quote from: FriedMule on December 31, 2018, 09:50:42 pmA lot of good info in the above posts. But I don't think the following point has been made:For me, 4 channels are much more helpful in a digital scope than in an analog one.If you have repetitive signals (for which an analog scope works well), you can always work around the 2-channel limitation by using one channel as the "reference", then looking at various other signals in the second channel, one after the other. In contrast, for on-repeating signals or rare events involving more than two signals, you do not have the opportunity to look at the signals successively. That's where a digital scope shines, and that's where only a 4-channel digital scope will help if you need to look at more than two signals.

author: james_s
author_rank: Super Contributor
timestamp: January 02, 2019, 08:03:59 pm
content: Yes but on the same note even a state of the art scope is not a silver bullet. You could have a 10 GHz scope and still if you are not using it properly it will not tell you what you need to know. Throwing money at the problem beyond a point is usually not the best solution, there is no substitute for understanding what you are trying to do, the limitations of your test gear and how to use it properly. This is where most hobbyists fall short anyway, and why I say that learning to properly use whatever test gear you have, and understanding its limitations is far more beneficial than obsessing over the specs.Until very recently, a scope with more than 100MHz bandwidth was an exotic and very expensive instrument. In most cases there is simply no need for more bandwidth, and other details will be the limiting factor.

author: tggzzz
author_rank: Super Contributor
timestamp: January 02, 2019, 08:05:07 pm
content: Quote from: hamiltont on January 02, 2019, 07:51:19 pmI'm trying to reduce the cost (of your time and enthusiasm) due to misunderstandingsYou have the right attitude, so you will need less good luck.

author: tggzzz
author_rank: Super Contributor
timestamp: January 02, 2019, 08:06:42 pm
content: Quote from: james_s on January 02, 2019, 08:03:59 pmThose are strawman arguments in this context. I frequently explicitly make the same points, and implicity in my .sig.

author: james_s
author_rank: Super Contributor
timestamp: January 02, 2019, 08:07:10 pm
content: Quote from: ebastler on January 02, 2019, 08:00:41 pmAgreed, I never felt any need for 4 channels on an analog scope. I have a 4 channel DSO and once in a while the extra channels are handy but 99% of the time I use only one or two.

author: rstofer
author_rank: Super Contributor
timestamp: January 02, 2019, 08:07:54 pm
content: Back when we were using 20 MHz scopes, it was rare to have anything running over a couple of MHz and the external bus signals would be some fraction of that. I agree, that 10 MHz Heathkit I had helped me build an 8" floppy controller (based on WD1771) back in '77. It was awkward, it was ugly, but it got the job done. Scoping the PLL was a challenge.Today those data rates are laughable. We could probably carry them on calibrated tin cans with impedance matched strings. We get into things like SPI running at 12.5 MHz and I have no idea what the rise time is. I know that I want to see at least the 7th harmonic so somewhere around 100 MHz is good. It turns out that the DS1054Z far exceeds its specs (measured 3 dB point is around 130 MHz) so I can even see the 9th harmonic. That's a pretty good square wave.But if I want to see the DDR buses, I'm probably out of luck other than to see if they wiggle around. But I don't use DDR (at the moment) so it's not very important.Internally, my FPGA projects run at 100 MHz (I could push most of them to 200 MHz). Signals I can scope external to the FPGA are seldom running this fast. On my projects...It really gets back to my stake in the ground in terms of money. How much can you afford to spend and what can you get for the money?Unlocking the DS1054Z to get 100 MHz is done all the time. There is a process to unlock the Siglent SDS1104X-E to get 200 MHz (identical to the more expensive SDS1204X-E) and this is probably the new sweet spot in the market. 4 Channels, 200 MHz, upgrade a $500 scope to an $800 scope, what's not to like? Caveat: I don't know anything about the Siglent unlocking. Check the Test Equipment forum. Even buying the SDS1204X-E outright is still a bargain!

author: rstofer
author_rank: Super Contributor
timestamp: January 02, 2019, 08:19:44 pm
content: Quote from: hamiltont on January 02, 2019, 06:01:31 pmIt would seem to me that you need a lot more than 6 MHz of bandwidth to display a 6 MHz signal. At a minimum I would want to see the 5th harmonic (30 MHz) and preferably more (like 7th, 9th, 11th, 13th and 15th) with a 100 MHz scope. If you were to view a 6 MHz square wave on a 6 MHz scope (or 10 MHz scope) all you would see is a sine wave at the fundamental frequency.

author: james_s
author_rank: Super Contributor
timestamp: January 02, 2019, 08:22:30 pm
content: Quote from: rstofer on January 02, 2019, 08:19:44 pmBut does that really matter? It depends on what you're trying to see here, whether it is the data/timing or signal integrity which is going to need more bandwidth.I actually do not recall ever using a scope to look at USB, signal integrity is rarely the issue there, normally USB problems are down to drivers and software issues.

author: tggzzz
author_rank: Super Contributor
timestamp: January 02, 2019, 09:03:07 pm
content: Quote from: james_s on January 02, 2019, 08:22:30 pmYes, it does matter, all too often.What you are trying to see is of key importance withanytool. Often it indicates that a different type of tool is possible or preferable.Of course you don't look at a USB line with a scope to verify signal integrity. If you haven't designed the hardware, if there are problems then it shouldn't have escaped the factory. Alternatively if you are the hardware designer, then you ought to know what the data sheets and app notes indicate. If you don't then signal integrity is the least of your problems!

author: james_s
author_rank: Super Contributor
timestamp: January 02, 2019, 10:03:36 pm
content: I just don't fully agree. I got by for many years with a 100MHz scope, before that I was using a 20MHz scope. It worked just fine for the stuff I was doing, microcontrollers and analog circuits. It simply did not matter that higher frequency square waves had the corners rounded off, I knew that was a limitation of the scope and it didn't matter, it was an irrelevant detail. I needed to see the data, and I could read rounded square waves just as easily as I could read nice square ones. It's just funny to see people going on like a hobbyist absolutely NEEDS things that no hobbyist could ever hope to afford until very recently. High bandwidth is a nice luxury, but outside of certain specialized use cases you don't NEED high bandwidth unless it's just to satisfy some kind of OCD. You bring up edge cases like looking at USB, why would someone even be looking at USB with a scope? That's using a hammer to drive a screw, it may work, sort of, but it's not the right tool for the job.When it comes to digital circuits, signal integrity is exactly what a scope is ideal for, otherwise a logic analyzer is often a more appropriate tool. The logic analyzer doesn't show you the true shape of the waveform either but that doesn't matter because unless you're looking at signal integrity the precise shape of the digital waveform is irrelevant so long as it is read as 1s and 0s and there is not something waaaaaaaaaaay out of whack.

author: tggzzz
author_rank: Super Contributor
timestamp: January 02, 2019, 10:14:44 pm
content: Quote from: james_s on January 02, 2019, 10:03:36 pmI didn't bring up USB; I was responding to it inyourpost - which you have conveniently snipped.Your contentions are mutually contradictory and/or claiming the same points I haverepeatedlyadvocated - without acknowledging that.For example, you claim a scope is ideal for signal integrity, but then claim that 20MHz scopes are adequate - which they demonstrably are not.

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 03, 2019, 07:59:03 pm
content: Right now I am thinking that better data always give higher resolution and accuracy while more channels only are useful the times I do need to measure 3+ places, is that stupid thinking or good thinking?

author: ebastler
author_rank: Super Contributor
timestamp: January 03, 2019, 08:48:28 pm
content: Quote from: FriedMule on January 03, 2019, 07:59:03 pmYes, that's right. Requiring more than two channels is relatively rare.But on the other hand: In most cases, having a lower bandwidth will only give you gradually reduced information. (The bandwidth rolls off at 3dB/octave or such, so you can still see signal above, although at limited resolution and maybe noticeably distorted.) In contrast, not having the two extra channels when you need them will often mean a "hard stop"; you just can't observe the required connection between the signals.Sorry, that argument doesn't make your decision any easier... I had it easier when the DS1054Z was a breakthrough in bandwidthandnumber of channels a few years ago.

author: rstofer
author_rank: Super Contributor
timestamp: January 03, 2019, 09:31:16 pm
content: Quote from: FriedMule on January 03, 2019, 07:59:03 pmIf the ADC had many more bits than log base 2 of vertical pixels on the screen, what would be the purpose? Many very high dollar scopes are still using 8 bit ADCs. Oh, I guess you could download the conversion data to a PC and produce a much higher resolution display but before going to all that work, check the specified accuracy for the scope itself. It's not going to be a 0.001% device.Scopes are 'about' kinds of measuring tools, you don't get many digits of precision eyeballing the trace. What you're looking for is "does it look 'about' right?". The measurement tools can bring along more precision than you get from the display but I wouldn't substitute a voltage reading on a scope for a reading on a DMM. At best, the DS1054Z is a 3% kind of tool.Watch the transistor video linked below. Notice how the author doesn't even pretend to try for a high degree of accuracy in his measurements. He just picks out the 'about' value and moves on. More often than not, this is exactly how a scope is used.The problem with the 4 vs 2 channel debate is that it is binary. If you need 4 channels and don't have them, you have to come up with some other solution. If you need 2 channels and have 4 channels, everything is great.Bandwidth is the same argument on a sliding scale. Yes, if you need 500 MHz and you only have 100 MHz, you're stuck. But if you need 110 MHz and you have 100 MHz, you're probably still in the game.It's like cars: You never have too much horsepower. OTOH, speed costs money, how fast can you afford to go?

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 03, 2019, 10:09:08 pm
content: Maybe a new question can make my choice easier to make:-)If you forget about RF and high speed digital logic. What scope would you choose for less then 1,000$

author: maginnovision
author_rank: Super Contributor
timestamp: January 03, 2019, 10:12:29 pm
content: Quote from: FriedMule on January 03, 2019, 10:09:08 pmmicsig to1104 since you have no clue what you really want. Neither of my digital scopes was under 1k, and my analog isn't something I'd recommend to you(tektronix 475A)

author: David Hess
author_rank: Super Contributor
timestamp: January 04, 2019, 12:04:46 am
content: Quote from: vk6zgo on January 02, 2019, 01:04:03 amIt took a while for hardware integration and performance to reach the point where real time histograms as in DPOs (Digital Phosphor Oscilloscopes) or large sample memories were feasible. Even today the display quality of a DSO capable of displaying an analog video signal is poor.Personally I prefer the short record length and high acquisition rate of a DPO. See below about waveform acquisition rate.Quote from: tggzzz on January 02, 2019, 01:42:32 pmI would say the boundary between good and useless shifted with the Tektronix 2230/2232 which were the first DSOs to support peak detection. They lacked index graded displays but at least they could capture the envelope of a single on every acquisition.Quote from: tggzzz on January 02, 2019, 06:45:20 pmThis cannot be stressed enough; instead of thinking in terms of bandwidth, think in terms of transition time and the 0.35 rule:20MHz 17.5 High Voltage CMOS50MHz 7.0ns Standard and LS TTL and HCMOS100MHz 3.5ns Fast TTL200MHz 1.75ns ECLProbing above 100MHz becomes increasingly difficult. 200MHz is feasible for general troubleshooting with the shortest ground lead but higher will require a expensive active probes, low-z probes, or probe tip adapters. If you are not prepared to deal with these, then avoid instruments above 200MHz unless you plan on only using coaxial cables.Quote from: tggzzz on January 02, 2019, 07:45:37 pmThis is the place where waveform acquisition rate matters. A real time DSO display only requires 30fps but might take days to catch an elusive metastable event. In practice hobbyists will have to live with whatever they can find which is pretty good today compared to just a couple decades ago even on basic instruments.As far as the number of channels, almost all two channel instruments include a trigger input somewhat relaxing the requirement for a 4 channel oscilloscope. But if you want to decode 3 and 4 wire serial buses like SPI, 4 channels is a great improvement. Some low cost two channel instruments (HP? R&S?) can now use their trigger input as a third channel for SPI decoding.

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2019, 12:12:46 am
content: Quote from: FriedMule on January 03, 2019, 10:09:08 pmFor $1k you’re not gunna cover all bases and while your budget is more than double what the average novice is prepared invest in a new scope IMO getting a 2 GSa/s DSO is superfluous to the bulk of requirements.rstofer and ebastler have given sound advice and I’ll add the cheaper of you two initial choices is a lot of scope for the money and I confidently state you won’t have buyers remorse.Is something better just around the corner.....well probably but we don’t know exactly what is is just yet.Im suspecting SDS2004X-E models but way 2ch models are priced they could be $1k+.

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 04, 2019, 01:03:54 am
content: I have asked Siglent about a 4ch version of the 2000X-E but no, they don't expect to make one.I think that all have been here where I am now, I just have a lot more scope then most could afford then.I "just" want a scope that I do not regret as you all know and for me the Siglent looks as most smack for the diam, but there is also no reason for buying a 2MHz 20GS.I'll try to read all your comment again for maybe the 6th time to absorb your great advices better. :-)

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2019, 01:22:10 am
content: Quote from: FriedMule on January 04, 2019, 01:03:54 amSo have I and got the same reply but if you take a step back and look at their offerings knowing what they do have coming there is a gap in their lineup.The SDS2kX (not X-E) range has been out for a while and needs freshening up with a faster processor and while the new SDS5kX series will offer this and higher BW’s they will come at a much higher price so a mid range 2 GSa/s 4ch DSO like a SDS2354X-E will fill the gap in the lower price range of their lineup.....yet Siglent at this time maintains they’re not building one.....at least their sales dept says so.

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 04, 2019, 01:53:50 am
content: Yes you are right! :-) And they have a DSDXXX4 in every one of there scopes, so there are something missing here. Maybe wait some time while investing in other bench gear I also need? :-)

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2019, 02:09:57 am
content: Quote from: FriedMule on January 04, 2019, 01:53:50 amThe real question will be how quickly Siglent feel they need to address having to add SDS2004X-E models to their lineup while SDS2004X models are available and any possible impact 4ch X-E models will have on X model sales.Time will tell.

author: rstofer
author_rank: Super Contributor
timestamp: January 04, 2019, 04:25:15 am
content: Quote from: FriedMule on January 03, 2019, 10:09:08 pmI'm seriously thinking about the Siglent 1204X-E 200 MHz, 4 Channels for around $800.