BJT model and fT simulation with PSpice

Discussion in 'General Electronics Chat' started by sudip, Feb 22, 2011.

  1. sudip

    Thread Starter New Member

    Mar 15, 2010

    I am trying to verify fT of 2N3904 (Fairchild Semi) using PSpice, [1] testbench.jpg shows my testbench ckt (analysis directives: .AC LIN 1000 1 500Meg), [2] result.jpg shows my simulation result and [3] datasheet.pdf

    Datasheet says fT=300MHz but my simulation result says fT=83.333MHz:eek:

    As I know fT is a frequency at which small-signal currect gain, |ic/ib|=1

    My questions are:

    [1] do you see any problem with my testbench?

    [2] what does f (=100MHz, 1.0MHz, 10Hz to 15.7KHz) mean in the datasheet's page #2 under small signal characteristics?:confused:

    your response would be highly appreciated,
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Try this method. fT for 2n3904 is specified at Ic=10mA, Vce=20V, but you can change Ie (≈Ic) to see Ft change as Ie changes. The current scale is basically irrelevant. You can change it to Amps (linear scale), but Ic and Ib will still be equal at the same frequency.
    I think the only problem with your test bench is the fact that Ic is only a few hundred microamps. Ft is lower at low currents.
    Last edited: Feb 22, 2011