Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant? - Page 1
Forum section: electronics / beginners

author: bmdaly
author_rank: Contributor
timestamp: March 02, 2018, 11:28:22 am
content: Hi,I'm a hobbyist proposing to upgrade from my 10MHz Picoscope 2204 to a Siglent SDS1104X-E, primarily for the 4 channels.My main area of interest at the moment is analogue electronics, and I'm working my way through a series of lab tutorials in "Learning the Art of Electronics". I expect that being able to monitor multiple points on the circuits I'm building and view the signals' relative phases and amplitudes on a single screen will be a big help to learning.I've also done a couple of microcontroller courses in the past (using TI MSP432 and TM4C123 boards), and also use Arduino boards.I've read Performa01's in-depth reviewhttps://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/of the SDS1104X-E and the SDS1202X-E, including his chapter comparing the bandwidth of these devices, and have decided that the 100MHz model is sufficient for what I need - particularly given the 50% cost premium for double the bandwidth (but no corresponding increase in sampling rate), and limited (lack of???) anti-aliasing on the 200MHz model.Before finalizing the decision, I wonder if there are any use cases where the extra bandwidth would really make asignificantdifference to understanding what's going on in a circuit?I don't want to be in a position a few months down the road thinking "if only I had a little extra bandwidth...", but equally, I need to be pragmatic and draw the line somewhere.Any comments from people who have been down this road would be appreciated.Thanks in advance,Brian

author: capt bullshot
author_rank: Super Contributor
timestamp: March 02, 2018, 12:03:17 pm
content: For your applications, you'll be fine with a 100MHz scope. My most used scope is an old and crusty 100MHz TDS220, next stop is the good old analog 7603.4 channels is pretty useful, most of the time you'll find yourself using one or two channels.Having more than 100MHz BW also requires more advanced probing techniques, and often 50 Ohm terminated inputs. Your vanilla 10x scope probe won't make any use of more than 100MHz BW - you'll just see more ringing. So 100MHz, or even as low as 50MHz is enough for the most tasks in debugging analog and uC circuitry.

author: danadak
author_rank: Super Contributor
timestamp: March 02, 2018, 01:25:14 pm
content: More important for analog work are things like high G differential preamp withhigh CM rejection.Or spectrum analyzer.You can look at older Tek series 7000, its a mainframe that takes many different plugings.Still very useful in today's work. Plugins like DMM, High G diff preamp, spectrum analyzers(several), FET input plugin, curve tracer.........http://w140.com/tekwiki/wiki/7000-series_plug-insRegards, Dana.

author: tggzzz
author_rank: Super Contributor
timestamp: March 02, 2018, 01:48:27 pm
content: It depends on what frequency analogue signals you will be using, what you will be looking for, and what logic family you will be using.Sometimes analogue circuits can oscillate at a much higher frequency than you are expecting ("amplifiers oscillate, oscillators won't").In some analogue applications, harmonics of the fundamental frequencies are important; factor that into your assessment.A 100MHz scope will (just about) allow you to see a 3.5ns risetime; a 200MHz scope 1.8ns. Logic families from the early 80s (LSTTL, STTL) have that kind of risetime. Some modern jellybean logic families have sub-nanosecond risetimes (e.g. 74lvc). If using similar families, a principal use of a scope is to check "signal integrity", which needs all the bandwidth you can get.Most "high" impedance *10 scope probes with a 6"/15cm ground lead self-oscillate at ~100MHz. A 200MHz scope will show you that, but a 100MHz scope will disguise itAt such frequencies construction techniques and probing techniques become important.

author: rstofer
author_rank: Super Contributor
timestamp: March 02, 2018, 04:15:01 pm
content: The question "How much bandwidth do I need?" comes up about once a week or so. There will be threads here in the Beginners forum as well as over in the Test Equipment forum. But mostly here...For most projects using sine waves (audio) a 100 MHz scope is probably overkill. Where 100 MHz tends to come up short is looking at square waves. A 100 MHz scope can do a decent (but far from perfect) representation of a 20 MHz square wave and that is because it can only faithfully display the 5th harmonic (and even that will be attenuated). A 200 MHz scope can similarly display a 40 MHz square wave. For Arduino projects, the clock is just 16 MHz so pin signals won't be running anywhere near that fast. Serial decoding (all 4 channels of SPI) will be quite helpful.Move up to FPGAs and the bandwidth requirement goes way up. Probably much farther than 200 MHz.

author: rhb
author_rank: Super Contributor
timestamp: March 02, 2018, 05:35:16 pm
content: I agree with pretty much everything said. My minor quibble is with Dana. He's correct, but he's quite a bit ahead of where you are. And keeping a Tek 7000 series going is not for a novice. You'll also need test gear to do it.I bought a used dual trace 60 MHz Dumont 1060 in 1990 for over $300 with a 30 day warranty. About day 35 the horizontal section failed. The only instrument I had was a 5 MHz recurrent sweep Heathkit scope, In retrospect it should have been "good enough", but I was too intimidated to try. A few years later I picked up a Tek 465 which sort of worked. It had lots of issues so I got it in trade for a couple of ESDI disk drives. It was enough to let me trace my way through the horizontal section until I found the bad solder joints. Once I had the Dumont working I went though and fixed the bad solder joints in the 465.There was a long hiatus in my electronics tinkering. When I started back up I bought a Rigol DS1102E because I did not want to face fixing the Tek and the Dumont so I could do something else. I wanted something I knew would work when I turned it on.As noted, the Rigol has a crap FFT. But my Instek MSO-2204EA doesn't have vernier adjustment on the vertical channels which is a huge nuisance.FFT length can be important. The big failing in the Rigol scopes is short FFT windows make the FFT function pretty useless. The Instek scopes will do a 10 million point FFT and sampling at 1 GS/S gives you some spectrum analysis capability to 500 MHz. It's not great, but better than nothing. If you're playing around at HF you can look at the 3rd harmonic.I think that if you *need* 200 MHz, you'll know it and why.

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: March 02, 2018, 05:49:33 pm
content: I too would recommend you take the 100MHz option unless you have a specific need for more. I hacked my Rigol 2072A to the full 200MHz bandwidth but I usually leave the bandwidth limitation at 100MHz or even 20MHz for most stuff.Save that money until you have a specific need and than buy what you need. Or get into a local makerspace which has equipment with higher bandwidth / specs than you might ever want to buy on your own. Might be a lot cheaper. You also get to know people which can give you inputs.

author: tautech
author_rank: Super Contributor
timestamp: March 02, 2018, 08:04:29 pm
content: The OP will notice differences in signal fidelity using both scopes for the same measurement BUT with the level of experience already gained from owning a scope he will understand the limitations of having less BW.The complete scope novice.....not so much.Absolutetrace fidelity is beyond the realm of 200 MHz scopes.

author: Zero999
author_rank: Super Contributor
timestamp: March 04, 2018, 10:47:41 am
content: Quote from: capt bullshot on March 02, 2018, 12:03:17 pmYes, the ordinary x10 probe won't work well at those frequencies. Fortunately it's easy to make your own low-Z probe. I made mine from 75R co-axial cable and some resistors, giving a total input impedance of 750R. 50R cable will work too, but the total impedance will be 500R.

author: tggzzz
author_rank: Super Contributor
timestamp: March 04, 2018, 10:51:56 am
content: Quote from: tautech on March 02, 2018, 08:04:29 pmThat is beyond the realm ofanyscope!There's no substitute for understanding your tool's limitations and how to live with them.

author: bmdaly
author_rank: Contributor
timestamp: March 04, 2018, 05:45:34 pm
content: Quote from: Hero999 on March 04, 2018, 10:47:41 amMay I ask, why did you choose 75Ohm over 50Ohm? Do you have a 75Ohm input impedance on your scope?

author: bmdaly
author_rank: Contributor
timestamp: March 04, 2018, 11:18:41 pm
content: Thanks everyone for your comments.Quote from: tggzzz on March 02, 2018, 01:48:27 pmThanks for raising these limitations/pitfalls - some links that address some of them, that might be of interest to others:some interesting info on probing here -https://youtu.be/zodpCuxwn_o- from You Tuber Alan Wolke (w2aew)... and here, tggzzz's own blog -https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/(Surprisingly, Tektronix'shttp://w140.com/tek_ABCs_of_Probes_1990.pdfincorrectly uses S (Siemens) instead of s (seconds) at various points throughout the article!)some useful articles on unexpected/unwanted oscillations and how to deal with them in this series of articles -https://e2e.ti.com/blogs_/archives/b/thesignal/archive/2012/05/23/why-op-amps-oscillate-an-intuitive-look-at-two-frequent-causesIn the absence of any way of seeing high frequency oscillations (frequency beyond limits of scope/probes), are there any standard tell tale signs to look out for? Is it possible the circuit would still function, but waste power at unobserved high frequencies, or are the signs more obvious?

author: tggzzz
author_rank: Super Contributor
timestamp: March 05, 2018, 12:26:58 am
content: Quote from: bmdaly on March 04, 2018, 11:18:41 pmThanks for the video URL; it is a useful practical demo of the effect of the ground connections. (I also like his taste in using a Tek 485 as the demo vehicle) If you are interested in the theory behind that, plus practical examples, have a look at:https://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/and the later higher bandwidth variant:https://entertaininghacks.wordpress.com/2016/09/17/scope-probe-accessory-higher-frequency-results/I'm no longersurprisedat Tek's historic misuse of SI units; I wasappalledabout them 40 years agoIn extreme cases even a probe's tip capacitance can cause an amplifier to oscillate, but in such cases that is probably a benefit since it highlights something that is too close to the edge of the envelope.Don't forget that a 15pF capacitor (think probe tip) has an impedance of ~100at 100MHz (50at 200MHz). The 0.7pF "low" impedance Z0 resistive divider probe is still ~450at500MHz)

author: rhb
author_rank: Super Contributor
timestamp: March 05, 2018, 12:44:34 am
content: The "digital black magic" books by Graham and Johnson go into considerable detail about the probing problem. Their recommendation is to design in test points that can be enabled with 0 ohm resistors. They discuss using pins, but U.FLs seem a better choice to me. With an ARM clocked at 200 MHz, the harmonics extend to well over 1 GHz.

author: tggzzz
author_rank: Super Contributor
timestamp: March 05, 2018, 12:51:05 am
content: Ignore the frequency since it is only indirectly relevant. Concentrate on the rise/fall time since that is directly relevant.Why? Because if you have an Xns risetime, the bad effects are the same with a 1Hz or 100MHz frequency.

author: EEVblog
author_rank: Unknown
timestamp: March 05, 2018, 12:56:18 am
content: Quote from: bmdaly on March 02, 2018, 11:28:22 amNot hugely, no.Signal integrity on a 10MHz square wave for example you get some more harmonics adding to the detail, but nothing to write home about. Probing is vastly more important at this point.Maybe if you were actually measuring amplitudes of >100MHz signals it helps a lot of course, but few people actually have that requirement.Most people simply won't notice any real usable difference between between 100MHz and 200MHz bandwidth.

author: rhb
author_rank: Super Contributor
timestamp: March 05, 2018, 01:06:44 am
content: It might be worth pointing out that in the 60's the 50 MHz Tek 547 was the main work horse for the Apollo program. So you can do a lot with a 50 MHz scope. And the 100 MHz Tek 465 was the standard for a long time after that. When I worked for Amoco in the early 80's there was typically a row of 2-3 465s by the window where I took my punch card decks.

author: tggzzz
author_rank: Super Contributor
timestamp: March 05, 2018, 08:55:18 am
content: Quote from: EEVblog on March 05, 2018, 12:56:18 amThefrequency(or more accurately baud rate) of digital signals iscompletely unimportantw.r.t. signal integrity. I've even seen a problem on line with<<1Hz"frequency".How so? The line signalled an infrequent error condition. When an error was signalled therisetimewas sufficiently fast to cause overshoot which caused internal diodes to conduct - and circuit malfunction.If an anthropomorphic explanation helps... When a circuit "receives" a transition it responds to that transition. Since it doesn't "know" when the next transition might be arriving, it doesn't "know" the frequency and hence doesn't "care" about frequency.Here's a quick, dirty and somewhat unrealistic example designed to emphasise the problem. It is modern jellybean logic (3* 74lvc1g gates in parallel) closely decoupled, 5V supply, driving a <1inch unterminated line. The probe is a 1.5GHz low impedance Z0 probe (0.7pF) and a 350MHz scope. The scope is set to 10ns/div and 1V/div.You can see that there is a 1.6V overshoot, which is more than enough to turn on diodes in a receiver (causing malfunction and/or long-term overstress) The overshoot occurs on a transition, and the frequency is so low that it is not visible in that trace; in fact it ~100kHz.

author: Zero999
author_rank: Super Contributor
timestamp: March 05, 2018, 09:57:40 am
content: Quote from: bmdaly on March 04, 2018, 05:45:34 pmMy oscilloscope has an input impedance of 1M, in parallel with 13pF.I chose 75Ohm, because it would result in less loading, on the device under test, than 50R. If your 'scope has a 50R input, then use the built-in resistor and 450R on the end of the cable.One thing to note is that the input impedance of the 'scope becomes a factor, at high frequencies. In my case 675R in parallel with 75R is 67.5R, forms a low pass filter with the 13pF capacitance on my oscilloscope's input FC= 1/(2pi*13*10-12*67.5) = 181*106= 181MHz, which is a non-issue for a 100MHz 'scope.

author: Harb
author_rank: Regular Contributor
timestamp: March 05, 2018, 10:22:43 am
content: From my experience, few people need more than 100Mhz.........Usually the extra money is forked out because the bigger the bandwidth number the "Cooler" it looks to have one.......same goes with most test equipment actually......

author: tggzzz
author_rank: Super Contributor
timestamp: March 05, 2018, 11:01:22 am
content: Quote from: Harb on March 05, 2018, 10:22:43 amJust so, but it is worth knowing the conditions under which you do need more bandwidth, and the consequences of having less bandwidth. There is no substitute for bandwidth.(Actually, insomecircumstances there is, but it requires skill imagination and knowledge. But you can buy bandwidth)

author: daybyter
author_rank: Frequent Contributor
timestamp: March 05, 2018, 10:58:28 pm
content: Found this page recently, and was surprised how good a 500 MHz signal looks on a 100 MHz scope...https://hackaday.io/project/4327-stretching-the-limits-of-a-rigol-ds-1102e-scope

author: tggzzz
author_rank: Super Contributor
timestamp: March 05, 2018, 11:34:56 pm
content: Quote from: daybyter on March 05, 2018, 10:58:28 pmI wonder what the phase response is; I would have preferred he did the experiment with a square wave.My Tek 485 (350MHz) will happily display and trigger on a signal that is >1GHz. The amplitude is somewhat reduced, of course

author: rhb
author_rank: Super Contributor
timestamp: March 05, 2018, 11:45:07 pm
content: To avoid aliasing, an 8 bit, 1 GS/S DSO needs to be 48 dB down at 500 MHz. So a 1 Vpp sine wave input displayed on the 100 mV/div scale needs to be reduced to 4 mV or less at 500 MHz. But you'll be able to view it if you switch to a lower input range.I would not describe those traces as very good as there is a lot of obvious distortion.

author: Claudius2k
author_rank: Newbie
timestamp: February 12, 2020, 03:58:30 pm
content: Wow. Not the answer I was expecting. I thought people would say if you can afford it go for it. But their rationale was very logical. I just purchased a 100Mhz 1104 and was considering returning it for the 1204. No I think you have me convinced 100 Mhz is adequate for me the hobbyist. Of course this is an old post. porches are now $499 vs $759

author: IDEngineer
author_rank: Super Contributor
timestamp: February 12, 2020, 04:29:35 pm
content: Quote from: tggzzz on March 05, 2018, 11:01:22 amI'd argue the other way. In many circumstances you can mentally compensate for insufficient bandwidth. But you cannot "fake" your way to a missing third/fourth channel - they're either present or not. Sure, theoretically you can use two scopes with a shared external trigger... but then you still can't compare phase on a single screen across all four signals.Bandwidth rolls off gracefully. A lack of channels is a brick wall. IMHO always buy four channels, and then get as much bandwidth as you can afford. (Of course there will always be edge cases where this rule doesn't apply, I'm talking about the generic "I need a single scope for all around use" situation.)

author: tggzzz
author_rank: Super Contributor
timestamp: February 12, 2020, 05:07:48 pm
content: Quote from: IDEngineer on February 12, 2020, 04:29:35 pmWell, that's a necropost!The answer is "it depends on what you are doing", and what other equipment you have. You aren't limited to a single tool.Basically I've found that in the analogue domain 2 channels plus a trigger are neccesary and sufficient. But in the digital domain 4 channels are woefully inadequate; you often need ~16 channels.So, use the right tool for the job:use an (expensive) scope to do measurements in the analogue domain. Only a scope can assess logic signal's integrity and you simplycannotmentally fill in the "missing" bandwidththereafter flip to using a (cheap) logic analyser in the digital domain. You will have far more than 4 channels, and triggering/clocking/filtering are a far better way of ignoring irrelevant signals

author: IDEngineer
author_rank: Super Contributor
timestamp: February 12, 2020, 05:19:58 pm
content: Quote from: tggzzz on February 12, 2020, 05:07:48 pmThat's just the point: Beginners (who are often the ones asking questions like "What scope features should I buy?") don't always have a lab full of equipment. For you and me, sure. But I remember when I was a teenager just starting out... my "bench" consisted of a scope and a multimeter. Period. No 16+ channel logic analyzers, no multiple scopes at the ready. For folks like that, buying their first and (for a while) only scope, I think more channels is more important than a little more bandwidth.Just my $0.02. YMMV. Standard disclaimers. Etc. There's no obvious correct answer to questions like this, I was trying to genericize the best possible.

author: tggzzz
author_rank: Super Contributor
timestamp: February 12, 2020, 05:55:13 pm
content: Quote from: IDEngineer on February 12, 2020, 05:19:58 pmHint: look at my .sig!Anyway, lucky you. I started out with a multimeter, some switches, some LEDs, some potentiometers, and components de-soldered from surplus equipment.That was sufficient tocreate this, and later a 6800-based computer with 128 bytes of RAM and a 16-byte ROM made from 16-to-1 multiplexers. I debugged that with a logic analyser made from LEDs and resistors, and used a scope once to check the signal fidelity of the 6800's clock input.So spare me the lectures about not having much.Doubly so since a cheap but useful LA can be bought for a few pounds.

author: IDEngineer
author_rank: Super Contributor
timestamp: February 12, 2020, 06:10:01 pm
content: Hey, this isn't a pissing match. Obviously I wasn't born with a scope in my bassinette. {grin} I was simply pointing out that not everyone has a bench full of gear. True for you at one time, true for me as well, true for everyone. We all start somewhere.We each have our opinions. We're sharing them here. That's the benefit of a forum like this. Hopefully the OP reads everything, considers his own situation, and makes a (more) informed choice for himself.

author: tggzzz
author_rank: Super Contributor
timestamp: February 12, 2020, 06:59:52 pm
content: Quote from: IDEngineer on February 12, 2020, 06:10:01 pmGood.QuoteAfter 1 year and 11 months, he has probably saved up enough money to buy a cheap LA.

author: IDEngineer
author_rank: Super Contributor
timestamp: February 12, 2020, 07:27:33 pm
content: Quote from: tggzzz on February 12, 2020, 06:59:52 pmGood point. But such things at such prices were not available when I started out, and depending upon your age perhaps not for you either. {grin}BTW, I wasn't thinking of a four channel scope as a logic analyzer. I was simply thinking of "signals" in the generic sense, whether analog or digital. A scope can certainly display four digital signals, but a LA cannot display analog signals. So in this sense more channels on a scope are more flexible. If you KNOW you're focusing on digital, maybe you don't need a true scope at all and can save a bunch of money.

author: tggzzz
author_rank: Super Contributor
timestamp: February 12, 2020, 08:25:00 pm
content: Quote from: IDEngineer on February 12, 2020, 07:27:33 pmWith the exception of photon counting and femtoamp circuits, everything is analogue.However, those values can be interpreted as digital signals. That's what LAs and logic inputs do; scopes show you how close the interpretations are to being incorrect. Once you can be sure the interpretation is correct, much simpler and cheaper circuits can process the digital signals.

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: February 12, 2020, 09:44:20 pm
content: I would not break the bank to go from 100-200MHz.Most experiments and insights for an beginner into analog could be gained with a 1MHz scope... Just pick your values and frequencies accordingly. E.g. doing the AoE coursebook, did you find something for which you actually need a digital 100MHz scope?I started with a 30MHz analog Hameg scope which I got for 20 bucks, lasted me 2 years. After that I knew what I would need and bought me a digital scope... That was about seven years ago.... Now I have a 2GHz and a 5GHz scope on my bench, but thats more of a TEA issueAnyway, you seem to be kind of in between. You did some stuff with simple entry level solution but you did not yet figure out whats really important to you. Otherwise you would not ask. So if I were you I would wait or buy something used which you can sell again. Those chinese scopes are great bang for the buck but their resale value is terrible...For digital stuff on the other hand I would recommend a decent USB logic analyzer. I never used digital channels on my scope even when I did have them. If you do Arduino stuff and you do not yet have one, invest here first.

author: IDEngineer
author_rank: Super Contributor
timestamp: February 12, 2020, 10:00:02 pm
content: Quote from: tggzzz on February 12, 2020, 08:25:00 pmI thought about mentioning that earlier, but decided to not be pedantic. My OCD thanks you for the friendly scratch between the ears!