Simplify AC analysis of bjt amplifier circuit with two-ports

Discussion in 'Analog & Mixed-Signal Design' started by Hangster, Sep 23, 2016.

  1. Hangster

    Thread Starter New Member

    Sep 23, 2016
    I recently got interested in signal processing and amplifiers. In the following file "Two_port_network_bjt" on the first page i could simplify a simple common emitter amplifier with two ports. Afterwards i think its easier to tell the input impedance Zi, ouput impedance Zo and the voltage gain Vu...

    Am i right if:
    (without R load and R collector)

    Zi = (B+1)*RE+rBE
    Zo = RE+rCE

    Vu = VCE/VBE = (RE-BrCE) / ((RE+rCE) * ((B+1)*RE+rBE))

    On the second page i am stuck at this collector feedback circuit with emitter resistor RE and feedback resistor RF. Could please anybody help me out or give an advice and correct me if i made a mistake? Its not clear how the two port would look like if there is this RF resistor.
  2. debdut123

    New Member

    Aug 30, 2016
    Hello Hangster, the circuit at page 2 is correct.
    I think you need to name the voltage at positive terminal of Re as, say, Vx, and solve it in terms of Vin, using KCL and KVL.
  3. Hangster

    Thread Starter New Member

    Sep 23, 2016
    Hello debut123, firstly thank you for your response.

    I am quite sure what you mean, but if i get this equations with KCL and KVL and after merging them, there is one equation left with Ic or B*IB, which i can't get rid of by using two port rules...

    Maybe i do not see the trick hiding behind this circuit, nethertheless i have already contacted a teacher on my university and hopefully i will get an answer :)