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200mhz oscillorscope probe question

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Gazmon:
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 circuit

will i see a difference in readings using the higher rated scope probe.

basice question but still learning

thansk

Gazmon

tggzzz:

--- Quote from: Gazmon on March 29, 2019, 12:29:14 pm ---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 circuit

will i see a difference in readings using the higher rated scope probe.

basice question but still learning

thansk

Gazmon

--- End quote ---

Good to see someone thinking before doing. 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 at https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

TK:
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).

ebastler:
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.

Gazmon:
Thanks for the reply’s


Ok so how can I check my 200mhz oscilloscope and 200mhz probe are what they say , with limited kit

I have a 24 MHz sigen, I’m into op amps etc

I’m guessing I can’t set up an experiment very easily without a better kit yes?

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