gain of an amplifier.

Discussion in 'Homework Help' started by screen1988, Mar 9, 2013.

  1. screen1988

    Thread Starter Member

    Mar 7, 2013
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    The attachment is equivalent circuit of an amplifier.
    I know that the gain of the circuit is -g_{m}R_{L}. In next exercise require to compute gain if r_{\pi } (resistor in the input) approach to infinity. Then, I see no difference in gain of the circuit.
    It make me curious, if the gain isn't depend on r_{\pi } then I can choose any value?
     
    Last edited: Mar 10, 2013
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    You don't see any difference in voltage gain because you Vin is a ideal voltage source.
    Simply add a serial resistor with Vin that will be represent input signal internal resistance. And now check the gain for Rpi and when Rpi approach to infinity.
     
    screen1988 likes this.
  3. screen1988

    Thread Starter Member

    Mar 7, 2013
    310
    3
    Hello Jony:
    Thank for help.
    I see it now. I also see it is useful to have input resistance large.
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    screen1988 likes this.
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