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Oscilloscope Bandwidth!

Discussion in 'Electronic Design' started by Myauk, Jan 4, 2007.

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  1. Myauk

    Myauk Guest

    Can anybody tell me the highest frequency that can be measure with the
    oscilloscopes these days.
    As far as I have known, it is about 1GHz I think.
    How will they capture of the waveforms of the clock signals for
    How can we measure the characteristics of the waveforms in High Speed
    There are many application notes but still I need some initiatives.
    I think the highest clock speed is about 4GHz.
  2. You are a couple of years late...
    With sampling scopes (ie working in undersampling mode on repetitive
    signals) the best scope you can find are as far as I know the Lecroy
    Waveexpert series... with a bandwitdh of 100GHz ! For realtime sampling you
    can find products with bandwidths up to 15GHz/40Gsps (TDS6154C from Tek or
    similar from Agilent), or even 18GHz/60Gsps with more specialized serial
    data analyzers (Lecroy SDA18000). Of course this all depends on how deep
    your pockets are...

  3. Myauk

    Myauk Guest

  4. Nope, try 100GHz analog bandwidth for repetitive sampling scopes, like
    this one:
    Same way they always have! :->
    Repetitive or single shot? Do you know the difference?, it's
    In either case you do it with a very careful probing, and specially
    designed high bandwidth probes.
    You want to measure a 4GHz clock signal?
    If that is the case then you need a VERY serious oscilloscope, a VERY
    serious amount of money, and even more serious probing. If you have to
    ask this sort of question then I'd question whether or not you actually
    have the ability to build or measure this sort of stuff, even if you
    had the right gear.
    And no, a 4GHz bandwidth scope will not allow you to view the
    characteristics of a 4GHz clock signal.

    Dave :)
  5. Hi Myauk,
    You will never have success for probing a 4 GHz microprocessor clock,
    because this signal is not available on any pin outside the chip. Even if
    you find a clock signal > 500 MHz outside a processor be aware and don't
    touch this. You will destroy this clock with your probe. The useful
    frequencies for monitoring wit an osci end at about 20 to 100 MHz depending
    on your equipment and knowledge. All above is very special for very high
    sophisticated users solvinf´g very sophisticated problems with a huge

  6. Myauk

    Myauk Guest

    I am not working on it this time.
    I am just curious to know about it because the application note from
    Tektronix wrote something about high speed circuit designs.
    The signals I am measuring are some audio signals, video signals, and
    the clock signal not higher than 100MHz for the signal processing
    Any way, I am learning from your answers.
    Thank you.
  7. John  Larkin

    John Larkin Guest

    Fet probes now go into the low GHz with fractional pF capacitance.
    Right now I'm using a Tek SD-14 sampling probe, an ebay find, which
    has better than 3 GHz bandwidth at the probe tip and about 0.3 pF

  8. tlbs101

    tlbs101 Guest

    In the early 1990's, EG&G/Energy Measurments came up with an analog
    oscilloscope tube (not a sampling 'scope) and the accompanying
    amplifiers and interfaces that was good to 18 GHz, and would still
    function out to 54 GHz (the highest frequency the Naval test lab could
    produce). These oscilloscopes were to be used in nuclear weapon
    testing, but the US quit testing nuclear weapons in 1992. Five were
    built. I was privileged to see one of these units in operation in
    1993. To see a 55 pico-second one-shot (not sampled) rise time was
    pretty cool.

    In the 1980's and 1990's, some French company had also produced analog
    oscilloscopes with 10+ GHz bandwidths for use at CERN and other
    high-energy physics experiments.

    Bottom line: fast analog oscilloscopes exist, but at a high price.
  9. John  Larkin

    John Larkin Guest

    A 55 ps risetime computes to about a 6.5 GHz bandwidth.
    My friend Bernard still makes it:

    It uses a traveling-wave-deflection scan converter tube inside. It
    used to be relabeled and sold by Tektronix.
    Tek 7104's (1 GHz, microchannel plate CRT) are available on ebay. Nice

  10. Myauk

    Myauk Guest

    Massive Precious Knowledge for me.
    Thank you so much.
    I got initiative to own my first oscilloscope.
    I hope I need to buy one for my experiments!
  11. Myauk

    Myauk Guest

    Massive Amount of Precious Knowledge for me!
  12. redbelly

    redbelly Guest

    John, I'm getting a different answer. From what I can remember, 55 ps
    would give a 250 GHz bandwidth:

    55 ps risetime (10%-90%) computes to about 25 ps 1/e time (or "RC time
    25 ps time constant computes to a bandwidth of 1/25ps = 40 G-rad/s
    = 2*pi*40 GHz = 250 GHz

    18 GHz should correspond to a 770 ps risetime.

    Am I figuring this correctly?

  13. The rise time and bandwidth of a signal are approximately related by the
    following equation:

    Signal bandwidth = 0.35 / Signal rise time

    For a 55 ps signal we have:

    BW = 0.35 / 0.055 ns = 6.36 GHz

    Now, to *measure* this signal with some useful accuracy we need an
    oscilloscope with a much higher bandwidth than 6.36 MHz.

    Costas Vlachos Email:
    SPAM-TRAPPED: Please remove "-X-" before replying
  14. In my last sentence I meant 6.36 GHz of course!

    Costas Vlachos Email:
    SPAM-TRAPPED: Please remove "-X-" before replying

  15. = 40 G-rad/s = w = 2.pi.f

    so f = 40G/2.pi = ~6.5GHz.

    (You multiplied by 2 pi instead of dividing).

    No :)

    Don't worry, I did exactly the same thing a few months ago. For a
    while I was trying to design a photodiode amplifier that was 40 times
    as fast as it needed to be. Doh.
  16. tlbs101

    tlbs101 Guest

    That was the fastest rise-time pulse generator we had in the lab, at
    the time. I was told the 'scope could do much better (i.e. showing a
    real-time sine wave display at 54 GHz at some Naval test and
    measurement lab).
    Thanks for the link. I always wondered about who 'they' were.

    The EG&G 'scope, I am told, was a breakthrough for the guys in Woburn,
    Mass. because they changed their way of thinking about the electron-gun
    and deflection system: from fine tuning a TWT, to treating the system
    like an electron linear accelerator.
    Right! I forgot about the 7100 series systems.

  17. John  Larkin

    John Larkin Guest

    I've finally become a full convert to digital, color, LCD scopes. My
    personal scope (in my office) is a Tek TDS2012, which handles 90% of
    what I do. The digital storage, averaging, and FFT things are neat, as
    it the fact that you can hold it in one hand.

  18. redbelly

    redbelly Guest

    Frackin' A, you're right. Doh!


  19. redbelly

    redbelly Guest

    Thanks Costas, I've got it now. My 2*pi factor went the wrong way.

    0.35 = (ln(0.9)-ln(0.1)) / (2*pi)


  20. Most of the useful energy in an edge is contained within the bandwidth
    defined by (roughly) 0.5 / tr which in this case would be 9.1GHz, so a
    10GHz scope might suffice.

    Dave :)
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