Calculating 3db freq. using open-circuit time constant method

Discussion in 'Homework Help' started by Steve|, Nov 10, 2008.

  1. Steve|

    Thread Starter Member

    Nov 4, 2008
    17
    0
    Hi, this is the original circuit:

    [​IMG]

    They ask me to calculate the corner frequency using the open-circuit time-constant method assuming ro->infinity and rb =0. The previous question asked to draw the small signal equivalent circuit for high frequency AC analysis. So I assumed from this circuit, I could reduce it into a simpler form:

    [​IMG]
    I don't understand why R1 has disappeared...

    Thanks.
     
  2. Steve|

    Thread Starter Member

    Nov 4, 2008
    17
    0
    Ah nm I think i figured it out, since R1 is parallel to Rb and they're both grounded, with rb=0, you can ignore r1. That's just my guess.. =\
     
  3. bhavesh96el

    Member

    Apr 24, 2006
    11
    0
    Yup you are right!
     
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