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How fast do modern op-amps go?

Discussion in 'Electronic Design' started by renan, May 29, 2004.

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  1. renan

    renan Guest

    Hello people!

    What is the maximum bandwidth that can be achieved
    with modern op-amps? Are op-amps of, let's say 500MHz,
    already available?

    Thanks!
     
  2. Not traditional op-amps because the feedback loop is too slow. There
    are fast differential amps on a chip with abilities into the GHz range.
    They're what's in all the tiny GHz gadgets these days (WiFi, phones,
    etc.).
     
  3. Leon Heller

    Leon Heller Guest

    Elantec has just announced the EL51671C with a fixed 2X gain bandwidth of
    800 MHz. It's actually good for 1.4 GHz.

    Leon
     
  4. Max Hauser

    Max Hauser Guest

    "Kevin McMurtrie" in
    Come ON Kevin McMurtrie, Optical Electronics Inc. (OEI) in Arizona was
    selling 1000 MHz traditional op amps in the 1970s. (Developed for a
    specific market but sold to the public.) I have their literature and so do
    many other people. Modern monolithic traditional op amps have GBWs into the
    100s or low 1000s of MHz as necessary. Applying such products is not for
    beginners -- one picofarad at 1000 MHz is only 160 ohms of course, for
    example. (Op amps at extremes of performance are generally specialized
    devices optimized for the extreme of interest.)

    On the other hand, I agree completely with the later sentences. GHz
    specialized differential amps have been around for decades but recently
    important and refined in portable wireless products. Customized amplifiers
    are often optimal solutions in demanding applications even at low
    frequencies. George A. Philbrick himself reportedly regretted overselling
    the op-amp concept to the extent that it became the knee-jerk approach to
    amplification tasks, including those where a custom design would be better
    or cheaper -- to some extent it displaced the skill of amplifier design.
    (Though supporting employment for op-amp designers -- eh, Jim? ;-)
     
  5. If you include current feedback amplifiers it extends into the GHZ
    range. See for example the THS3202.
     
  6. John Larkin

    John Larkin Guest


    THS4303 is a current-feedback amp with internal feedback resistors set
    for a gain of 10. Its closed-loop bw is 1.8 GHz, for a net gbw of 18
    GHz. I think that's the current record for a real opamp.

    Too bad Vcc max is so wimpy.

    John
     
  7. Strange enough they (usually CFAs) are called 'Low noise' or
    'Ultra low noise' for their low noise density. However
    the root-bandwidth adds up to a significant factor.

    Examples : THS3201 with 1.8GHz GBW, THS 4275 with 1.4GHz GBW,
    They also feature impressive slew rates, such as 10V/ns for the first.
    And they drive 50 Ohms. Only 5V though.

    Rene
     
  8. Joerg

    Joerg Guest

    Hi Renan,

    Even back in the late 70's early 80's you had those:

    uA733 was a not so well know but cheap video amp that could do more than
    100MHz no sweat. Used these a lot.

    This may have been the hot rod of amps back then: Philips NE5539,
    1.2GHz, October 1986.

    Regards, Joerg
     
  9. Ian Buckner

    Ian Buckner Guest

    Many CFA designs have one input with pretty low En, but
    invariably the current noise density is very poor on the negative
    input.

    There are a few voltage feedback op amps out there with GBW
    approaching 4GHz, decent En (<1nV/rtHz) and In (<3pA/rtHz).
    AD8099, OPA847 for example. These don't have the slew rate
    of the CFA's, coming in at 950-1450 V/usec.

    As Rene mentioned, the really fast parts have decent drive
    capability, but only run off +/-5V rails.

    The AD8351 is a differential amp rather than an op amp, but
    does do 2.2GHz at 12dB gain, with 13kV/usec slew rate. DC
    operation can be tricky. That one uses a +5V rail.

    Regards
    Ian
     
  10. WDino

    WDino Guest

    It really depends on what you want to do with an op-amp.
    True op-amps, ie amplifiers that have their operation controlled by the
    external feedback components, are limited by the environment in which
    they are used. External capacitance and conductance usually limit
    performance to the mid hundreds of MHz.
    Price is also an issue at the high end of the performance scale.

    Low cost ones like the Max4451 have a small signal -3dB bandwidth of 210MHz.

    William
     
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