h parameter model of the given circuit?

Discussion in 'Homework Help' started by ladyeve, Jun 8, 2009.

  1. ladyeve

    Thread Starter New Member

    Jun 8, 2009
    I have a bit of a problem with drawing the h parameter model of a voltage amplifier circuit. Schematics are in the attachment.

    I've sketched h model, having in mind that hre~=0.
    I know that if amplifier works in medium frequency range, C can be changed with a conductor because it's impedance is small.

    But, where do I wire the Rb and Rl?
    On their upper side, they are on Vcc potential. For signals, Vcc is bypassed to ground potential, therefore, on one side, Rb and Rl are on ground potential.
    On their down side, Rb and Rl are on the same potential [or that is what I assume]. But, what potential?

    Oh yaeh, problem is to find amplification given as vo/vi :). I think I could do that by myself if only I could draw this h model.

    Thank you for your time :).
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    For me the small-signal schematics should look like this.
    And capacitor seems to be in a wrong place.
    Last edited: Jun 8, 2009
  3. ladyeve

    Thread Starter New Member

    Jun 8, 2009
    Thanks for answering :)!
    You're definitely right about the position of the resistors. Rb is on vbe potential and Rl is on vce potential. But, capacitor can be removed and replaced with a conductor which conects Rb and Rl, so it seems that vo/vi=1 [vi being vbe and vo being vce]. This was one of the solution I thought of, but it seemd... highly unlikely that professor would give such a problem on an exeam :). I mean, you can see that vo/vi is 1 when you draw h model, and that is just to easy, considering all the other other problem that were given [vo/vi are usauly some compicated expresion derived form Kirchoff's circuit laws]. I tried by all means to complicate it a bit more :).
    I've checked solution with the professor, and I've attached it.