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Transimpedance op amps?

Discussion in 'Electronic Design' started by jack, Sep 1, 2003.

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  1. jack

    jack Guest

    As part of an ongoing learning project I've come up on a bit of
    confusion I hope someone can help me with. I will just list the
    issues...
    1. Is a voltage feed back op amp wired to be a transimpedance
    op amp the same as a "charge sensitive" op amp?
    2. Can a current feed back op amp be wired to be a transimpedance
    device in the same way one would do it with a voltage feedback op
    amp,
    in order to take advantage of its high slew rates and thus be a easy
    way to make a short current pulse amplifier?
    AofE ( thanks to Winfred Hill's suggestion) has a nice high speed
    pulse amp but I am still looking for a easier way to implement it with
    op amps, hopefully with current feedback , is it possible? thanks
    again for any help with this. jack
     
  2. John Larkin

    John Larkin Guest

    A charge amp has a capacitor as the feedback impedance, whereas a
    transimpedance amp uses a resistor.
    Yup; but eyeball the current noise specs first. There are also some
    specific transimpedance amps, designed for amplifying the output of
    PIN diodes in fiberoptic systems; they're very good at this, but are
    generally intended to be used in AC-coupled systems. Maxim has a few
    nice ones.

    John
     
  3. Could you specify the pulses you're intending to measure ?
    Length, current and from what source ?

    Rene
     
  4. jack

    jack Guest

    Yes,thankyou. I posted alot of the parameters above in a thread called
    "advice needed...PMT" . Also apologies to winfield hill for the
    misspelling of his name.
     
  5. John Larkin

    John Larkin Guest


    Why use a TIA? Just run a coax from the PMT, terminate in 50 ohms
    (plus some overload clamps!) and use a voltage amp. PMTs generally
    deliver lots of signal. If s/n is critical, run the coax into a 50-ohm
    input SiGe MMIC.

    Oh, yeah, I think he spells his name Winfield Hill.

    John
     
  6. Bill Sloman

    Bill Sloman Guest

    Over on his PMT thread, we can see that he is looking at 0.8mV pulses,
    with a FWHM of 6.5nsec, so he doesn't more than about 100MHz of
    bandwidth. SiGe would be something of an overkill - most of the
    silicon-based op amps that would give him enough gain-bandwidth have
    got about the same sort of voltage noise as the 50R resistor, so a
    quieter amplifier would be similarly pointless.
     
  7. jack

    jack Guest

    Yep,I'm gona start there. The Hamamatsu Handbook throws a lot of
    issues at you (noise,linearity ect) so I'll try all three approaches
    just for learning,i.e. resistor terminated,TIA,and charge sensitve op
    amp. Thanks all for the contributions......jack
     
  8. Ian Buckner

    Ian Buckner Guest

     
  9. Ian Buckner wrote...
    Don't forget the OPA687 has a 20uA or more input bias current.

    Thanks,
    - Win
     
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