help bjt amplifier cascade and AO

Discussion in 'Homework Help' started by albertgil1989, Apr 21, 2010.

  1. albertgil1989

    Thread Starter New Member

    Nov 13, 2009
    Hello, sorry my bad english
    I am From Venezuelan
    I need help

    I need to know if this circuit comprising an operational amplifier that generates a factor of 3.125 to its output can be replaced by a transistor configured in two stages in cascade.
    they entered the operational amplifier circuit has an input c which varies from 0 400 millivolts, is captured by the AO and multiply it by 3.125, I want to do the same but with 2N2222 transistors or other you suggest or recommend me p
    ero basically be like this in the image, the gain is going to determine this factor, then I have to design this circuit with a gain of 3.125 I understand that but the problem is that when various input output falls please help as I am Venezuelan and part of the world that we are half overdue Help me please. I put the images attached
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    A gain of 3.125 is very low, and can easily be achieved with a two stage amplifier. A single stage BJT amplifier would do the job. Presumably you want two stages in cascade to eliminate the phase inversion you get from a single stage BJT amplifier.

    If you want an accurate gain of 3.125, that will take some trial-and-error with those component values which determine the overall cascade amplifier gain.

    The advantage of the operational amplifier is that you can achieve a known gain with greater ease by a simple selection of input and feedback resistors. Using 1% resistor tolerances in the OA case will give a notional gain tolerance of 2%.

    Perhaps I should ask - why do you want to substitute a discrete 2-stage BJT amplifier for a single operational amplifier stage?