Can I build a transimpedance amplifier with a NPN transistor?

Discussion in 'General Electronics Chat' started by richiechen, Mar 31, 2012.

  1. richiechen

    Thread Starter Member

    Jan 1, 2012
    93
    0
    Dear All

    Could I ask a silly question?
    I know that almost most Transimpedance Amplifier is built with OpAmp.

    However, why not use a transistor?

    Thank you very much. Any thoughts are welcome.

    Richie
     
  2. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    You can, but it won't be a particularly good one.
     
    richiechen likes this.
  3. richiechen

    Thread Starter Member

    Jan 1, 2012
    93
    0
    Thank you Steve!

    Could you please explain the drawbacks a little?

    Thank you
    Richie
     
  4. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    I've never tried to make one with a bipolar transistor, but I would imagine the simplest way is to inject current into the base with a voltage on the emitter. Then a resistor on the collector with a voltage on top of the resistor will allow proper biasing.

    One drawback is that it will only work for one direction of the current.

    Another drawback is that the current gain of the transistor will be sensitive to temperature and current and can be nonlinear. Also, it will vary from transistor to transistor.

    I'm sure there are other drawbacks, depending on the exact voltages you need on input and output, and whether you are doing AC or DC coupling.

    Also, output impedance will be high.
     
    Last edited: Mar 31, 2012
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Here are one and two transistor transimpedance amps. Obviously, in order to get an acceptable operating point, I had to add a DC bias current.
     
    Last edited: Apr 1, 2012
    Randy Parsons likes this.
Loading...