-3dB frequency

Discussion in 'Homework Help' started by bug13, Aug 21, 2013.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    [​IMG]

    My question is, does C(E) and r(E)(not showed) at Q1 have effect on the lower or upper -3dB frequency? I think there is, depending on the value of the C(E). Am I correct?

    But the solution give for this question is:

    Lower -3dB:
    decide by : R(L1)//H(oe)+R3//R4 and C(c)

    Upper -3dB:
    decide by: R(L1)//H(oe)//R3//R4 and C(s)
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Perhaps you are meant to assume CE is sufficiently large that it doesn't impact the -3dB cut-off point and plays a role well below the initial -3dB frequency transition.
     
  3. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
    1,208
    38
    So do you mean I am correct in theory, but the question here want me to assume C(E) is large enough.

    Practically, in most situations, would C(E) play a role in the -3dB cut-off point, or usually not the case. Or it really depends on the specify circuit?
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    782
    Yes that's what I mean.

    It depends on the relative time constants for the emitter and collector topologies. If one sees [say] 50Ω looking back into Q1 emitter terminal then what value of CE would ensure the emitter time constant is an order of magnitude greater that the derived collector time constant?
     
    bug13 likes this.
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