Impedance and Gain Problem

Discussion in 'Homework Help' started by moliver777, Aug 13, 2007.

  1. moliver777

    Thread Starter New Member

    Aug 13, 2007
    2
    0
    Hi people. I'm having difficulty finding the forumulae to work out this problem which is part of a large c programming project due next week. Not knowing how this problem works is hindering my progress a lot... Any solutions/insight would be a MASSIVE help. Thanks.

    Here's the problem:
    A system is made up of a number of Elements (picture below represents a single element) that are modelled as 2-port networks. They are connected in series. Each element is characterised by three values; input impedance (Zi), output impedance (Zo) and gain in dB (GVi).
    [​IMG]

    I need to know the formula or theory behind calculating the overall system's input impedance, output impedance, and end-to-end gain taking into account all gains and coupling losses. (What the hell are coupling losses!?)

    Please help!!!???
     
  2. spar59

    Active Member

    Aug 4, 2007
    51
    0
    If the systems are represented as shown i.e. simply input impedance, output impedance and an ideal amplifier of gain G then the only coupling losses are the power losses within the input and output impedances.

    If the ideal amplifier outputs a certain voltage not all that voltage will appear at the input to the next stage due to the voltage drop in the output impedance.

    From ohms law:-
    It will in fact be (V * Input impedance of next stage) / (Input impedance of next stage + Output impedance of this stage).

    i.e.
    Output current of stage 1 = Output V of stage 1 / (Input impedance of stage 2 + Output impedance of stage 1).

    Due to series circuit Input current of stage 2 = Output current of stage 1.

    Input voltage = Input current * input impedance

    Steve.
     
  3. moliver777

    Thread Starter New Member

    Aug 13, 2007
    2
    0
    Thanks very much.

    Anyone know how the overall input and output impedances are gained?

    Basically I need to compress a large number of those elements to just one element with one input z, one output z, and one gain.
     
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