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How to find (mos)fet transistors maximum operating frequency?

Discussion in 'Electronic Components' started by asdf, Oct 30, 2009.

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  1. asdf

    asdf Guest

    Data sheets for BJTs usually report the maximum frequency they can be
    used to amplify a signal, while this data is omitted in (MOS)FET data
    sheets. How do I determine if a field effect transistor is suitable to
    work in, say, an UHF preamplifier?

    Thanks!
     
  2. legg

    legg Guest

    The transition frequency Ft of a bjt is not the 'maximum frequency'of
    use, it is the frequency where the current transfer ratio beta can be
    expected to drop to 1.4 (3dB). As the voltage or power gain of a
    circuit is only partially dependant on beta, useful frequency ranges
    are application dependant - the requirements to produce an input
    current and the effect of the resulting output current are
    device(parasitic or stray) and circuit (source and load) dependant.
    High frequency characteristics are better illustrated by measured
    typical spot frequency parameters.

    Fets, in general, are specified for tranconductance gm or forward
    transfer admittance yfs. As with bipolars, the requirements to produce
    an input voltage and the effect of the resulting output current are
    both device(parasitic Ciss Crss Coss or stray) and application
    dependent, over frequency. If the parts aren't characterized for the
    frequency range of interest (a value-added design feature), the work
    of doing so is left to the end-user without any assurance of
    consistency between fabs.

    RL
     
  3. legg

    legg Guest

    Try reading Motorola AN211

    http://www.datasheetarchive.com/pdf-datasheets/Datasheets-12/DSA-221673.pdf

    RL
     
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