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Why do oscilloscopes have bandwidth limits?

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Black Phoenix:

--- Quote from: Fungus on November 04, 2022, 06:43:36 am ---
--- Quote from: james_s on November 04, 2022, 06:24:04 am ---One of the issues you run into is making wheels that can spin as fast as they need to without the tires and even the rims themselves breaking up from the centrifugal force.

--- End quote ---

That's the reason CD drives (remember those?) stopped getting faster at 56x.

--- End quote ---

And even some of the 52x would start to create cracks in the centre of the disc after some time. I have some Microsoft Windows CDs with airline cracks in the centre and fixed (at least one that I remember) drive who a CD just disintegrated inside.

TimFox:

--- Quote from: ejeffrey on November 04, 2022, 04:49:11 am ---
--- Quote from: glarsson on November 03, 2022, 08:51:51 am ---
--- Quote from: TimFox on November 02, 2022, 03:55:37 pm ---If you had an infinite (or much too high for the application) analog bandwidth, the amplified thermal noise added to your MHz-bandwidth signal would be huge.

--- End quote ---
I don't have anything infinite at hand to test with, but wouldn't infinite bandwidth result in infinite thermal noise?

--- End quote ---

No the plank law cuts in above a few THz and the thermal noise drops off exponentially and has a finite integral out to infinite frequency.

--- End quote ---

Yes, that was Planck's solution to the "ultraviolet catastrophe", keeping the total radiated power output from a black body finite.  The rest is history.

james_s:

--- Quote from: Fungus on November 04, 2022, 06:43:36 am ---
--- Quote from: james_s on November 04, 2022, 06:24:04 am ---One of the issues you run into is making wheels that can spin as fast as they need to without the tires and even the rims themselves breaking up from the centrifugal force.

--- End quote ---

That's the reason CD drives (remember those?) stopped getting faster at 56x.

--- End quote ---

Of course I remember those, I still use them often.

Anding:

--- Quote from: Anding on November 02, 2022, 06:36:08 am ---From experience how far can you use an oscilloscope beyond it's bandwidth limit?   Specifically, I'd like to compare the phase difference between in and out DDR2 data busses between an FPGA and a DRAM chip.  This is important because the input signals will need to be captured inside the FPGA using a clock with a phase delay to the output clock.  The slowest speed of the DRAM is 125MHz, which is starting to imply a 1GHz 'scope for many thousands of dollars.  Just for one measurement!  Will a 350MHz (soft upgraded) scope be any help to me at all?

--- End quote ---

Not perfect but the MSO5000 with 100MHz bandwidth limit can help me measure the phase difference of 100MHz clock signals.  The generated duty cycle is 50% and the phase difference is 90 degrees whereas the reading is 64% and 100 degrees - but this is close enough to be helpful to problem solving with entry-level equipment





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