200mhz oscillorscope probe question - Page 1
Forum section: electronics / beginners

author: Gazmon
author_rank: Regular Contributor
timestamp: March 29, 2019, 12:29:14 pm
content: Hi,If i have a 200mhz scope with a 100mhz probe attached and measure a 555 timer circuit connected to an flashing LED for example, then i attach a 200mhz probe to measure the same circuitwill i see a difference in readings using the higher rated scope probe.basice question but still learningthanskGazmon

author: tggzzz
author_rank: Super Contributor
timestamp: March 29, 2019, 02:32:19 pm
content: Quote from: Gazmon on March 29, 2019, 12:29:14 pmGood to see someonethinkingbeforedoing. The former gives you a better chance of doing the latter correctly. The latter confirms/denies your understanding of the former. Both are necessary.First rule of thumb: risetime = 0.35/bandwidth.Second rule of thumb: risetimes add as sqrt(t1*t1+t2*t2).Different scope probes and scopes use slightly different definitions of bandwidth, but in your case the differences will be moot. Just plug in the 100MHz and 200MHz, and compare to the 555's waveforms.For more information about probe types, measurements, and safety, have a look at the references athttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: TK
author_rank: Super Contributor
timestamp: March 29, 2019, 02:45:53 pm
content: I don't think you will see any difference with a standard 555 (LM555, NE555) as rise time is 100ns. It can make a difference when using LMC555 (rise time of 15ns).

author: ebastler
author_rank: Super Contributor
timestamp: March 29, 2019, 02:53:40 pm
content: As TK and tggzz have said -- a regular 555 is far slower than 100 MHz, hence you will not observe any difference. But for signals which are approaching the bandwidth limit fo your scope and probes, the amplitude drops caused by the scope and the probes, respectively, will add up.While you are learning, keep an eye on the unit designations and make it a habit to capitalize them correctly. The "m" prefix stands for milli = 1/1000. The "M" prefix stands for Mega = 1 000 000. And the unit for frequency, Hertz = 1/s, is abbreviated as "Hz" with a capital H. While spelling Hz as "hz" is merely irritating, mixing up "m" and "M" is really messing up your numbers.

author: Gazmon
author_rank: Regular Contributor
timestamp: March 29, 2019, 04:13:02 pm
content: Thanks for the reply’sOk so how can I check my 200mhz oscilloscope and 200mhz probe are what they say , with limited kitI have a 24 MHz sigen, I’m into op amps etcI’m guessing I can’t set up an experiment very easily without a better kit yes?

author: TK
author_rank: Super Contributor
timestamp: March 29, 2019, 04:23:16 pm
content: What brand and model is your oscilloscope?

author: TK
author_rank: Super Contributor
timestamp: March 29, 2019, 04:24:29 pm
content: You need to get a fast edge pulse generator

author: tggzzz
author_rank: Super Contributor
timestamp: March 29, 2019, 04:47:44 pm
content: Quote from: Gazmon on March 29, 2019, 04:13:02 pmObvious question: if the equipment is usefully faster than your circuit, why do youneedto verify the equipment's performance. (Don't look at the TEA thread.Opamps won't help, and a 24MHz siggen is likely to have well controlled edges that will be too slow to be useful.For digital signals, remember to concentrate on therisetime- the fundamental frequency (e.g. 24MHz) is completely irrelevant, e.g. seehttps://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/

author: Gazmon
author_rank: Regular Contributor
timestamp: March 29, 2019, 05:07:29 pm
content: I have a GW Instek 1000b 2 channel, i upgraded it to the 200mhz via the softwareThe scope says it’s 200 MHz , I just want to try and confirm it’s is

author: ebastler
author_rank: Super Contributor
timestamp: March 29, 2019, 05:14:47 pm
content: Quote from: tggzzz on March 29, 2019, 04:47:44 pmOff-topic, but I have meant to ask a few times when I came across your signature:What do you mean by "span" here, and how can it be bought?(Honest question from a non-native speaker. Thanks!)

author: TK
author_rank: Super Contributor
timestamp: March 29, 2019, 05:16:13 pm
content: You have 2 options:1) Get a fast edge pulse generator and it will push the scope input to the limits and measure the min rise time it is capable of2) Input a 1Vpp sinewave and measure the attenuation. It should be 3dB attenuation at 200MHz and increase the attenuation as you increase the frequency. You need a signal generator that can generate higher than 200MHz sinewave.

author: james_s
author_rank: Super Contributor
timestamp: March 29, 2019, 06:24:08 pm
content: Build an avalanche pulse generator, the classic design by Jim Williams can be built using many common inexpensive transistors, to get rise times well beyond the capabilities of a 200MHz scope you don't need anything exotic.

author: tggzzz
author_rank: Super Contributor
timestamp: March 29, 2019, 07:29:53 pm
content: Quote from: ebastler on March 29, 2019, 05:14:47 pmI doubt many native speakers would understand it, at least not without thought!Span as in wingspan. Basically longer thinner wings are better at gliding speeds - you can go further and/or faster between thermals. As you can imagine, longer and thinner tends to be more expensive.

author: tggzzz
author_rank: Super Contributor
timestamp: March 29, 2019, 07:35:40 pm
content: Quote from: james_s on March 29, 2019, 06:24:08 pmPulses don't tell you much,unlessyou know the shape and size of the pulse, and do the deconvolution to find out the UUT's response.The latter is tedious, especially with non-digitising scopes.

author: ebastler
author_rank: Super Contributor
timestamp: March 29, 2019, 07:59:03 pm
content: Quote from: tggzzz on March 29, 2019, 07:29:53 pmAhaa! Thank you!I had totally misconstrued the "gliding" bit, although it's obvious in hindsight. Had been wondering how an aphorism can glide...

author: joeqsmith
author_rank: Super Contributor
timestamp: March 29, 2019, 08:05:55 pm
content: Quote from: Gazmon on March 29, 2019, 12:29:14 pmAssuming they are both 10X, you compensate them, you don't use that 6" groundish lead that comes with probes and you attach them the same way, then I doubt you would see much if any difference.

author: tggzzz
author_rank: Super Contributor
timestamp: March 29, 2019, 08:32:27 pm
content: Quote from: ebastler on March 29, 2019, 07:59:03 pmCoffee meets keyboard!I ran into character limits in the .sig, and had to be too brief.sig changed: s/Gliding/Glider pilot's/

author: David Hess
author_rank: Super Contributor
timestamp: March 29, 2019, 10:51:14 pm
content: The edge from AC or LVC logic is fast enough to reveal the difference between 100 and 200 MHz operation. The circuit will need to be directly connected to the probe tip without using the probe's standard ground lead which is too long for accurate results even at 100 MHz.The bandwidth rating of an oscilloscope probe is better understood as the bandwidth within which the probe will faithfully reproduce the input.