Transimpedance Amp report help

Discussion in 'Homework Help' started by smithe836, Jul 21, 2012.

  1. smithe836

    Thread Starter New Member

    Nov 22, 2011
    3
    0
    Hey, new here and looking for some help/ guidance.

    I need to write a report on transimpedance amplifiers and their importance.

    I need to include 1) An op amp with local feedback 2) A single transistor amp with local feedback and 3 ) A multi- transistor amp with global feedback.

    For each i need to include a description of the circuits, details on how component values are calculated, calculation of gain and input impedance and a simulation using electronics workbench.

    I really should be able to do this easily but find myself struggling to find any of the info i need and failing to understand what i do find, any advice/websites anyone could direct me to would be appreciated.

    Thank you
     
  2. smithe836

    Thread Starter New Member

    Nov 22, 2011
    3
    0
    I got the op amp done no problem after i realized I was using the wrong op amp in multisim. working on the transistor versions now, will likely post back soon.
     
  3. ramancini8

    Member

    Jul 18, 2012
    442
    118
    If you are looking for a transimpedance op amp you need a current feedback type op amp. Intersil had a good line of current feedback op amps. An emitter resistor in a common-emitter configuration yield curren feedback. Almost any direct coupled multi transistor configuration requires feedback. If you are having trouble with circuit configurations stay away from simulators because circuit configurations require brain power where simulators require relatively low level operators. I made a fortune fixing simulator designed circuits because the designers didn't understand the circuits.
     
  4. crutschow

    Expert

    Mar 14, 2008
    12,977
    3,220
    You don't need a current feedback type op amp to build a transimpedance (current-to-voltage) circuit. Any standard voltage feedback amplifier will work. The simplest design is just a single feedback resistor between the output and the minus input as shown in his simulation. The output voltage is then equal to the input current times the feedback resistor value.

    Simulators are a very good circuit design tool but can be misused like any other tool. I would never design a circuit without one. But it is a complex tool and the user needs a good understanding of circuits to obtain meaningful results and know how to interpret the odd results.
     
  5. smithe836

    Thread Starter New Member

    Nov 22, 2011
    3
    0
    I have attached a simulation.

    This amp seems to work for gains above 100 (value of Rf) and seems more accurate as the value of Rf increases.

    To get the circuit I

    Chose Ic to be 1ma
    Chose VCC to be 12V
    Set Ve to be 10% of VCC- 1.2v
    Re= Ve/Ic= 1.2k
    Rc= VCC/2Ic= 12k
    R2= 10Re= 12k
    R1= (Vcc-(Ve+0.7)/(Ve+0.7))R2
    Gain = Rf
    B= 1/Rf

    Can anyone tell me how to calculate the input impedance? Is it (R1+R2)/(R1R2)

    Also could anyone say which transistor configuration would be best to use to cascade it and apply global feedback with? I am looking at an emitter follower but am not having much success.
     
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