Transistor problem

Discussion in 'Homework Help' started by nahid5692001, Mar 8, 2011.

  1. nahid5692001

    Thread Starter New Member

    Mar 8, 2011
    5
    0
    Hello,

    I need some assistance with a HW problem. The specifications are to be these below for transistor:

    input voltage is given
    gain is high
    input resistance high
    output resistance low

    i know this cannot be done with just one transistor. how many are need? and what configuration do you think?

    im thinking a CB with a CC. The CB will output high gain and CC will output gain = 1 so all gain will come from CC, so we can control that with resistors. The CC works well with input and output resistances.

    What do you guys think?

    Regards
    Nanja
    Bangalore, India
     
  2. nahid5692001

    Thread Starter New Member

    Mar 8, 2011
    5
    0
    Hello,
    Can anyone push me in the right direction?

    Appreciate it.
    Regards
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Post the specific amplifier design goal values and show some attempt at your working - then you will probably receive some helpful responses.
     
  4. nahid5692001

    Thread Starter New Member

    Mar 8, 2011
    5
    0
    I just want to know if my theory is correct. Those are the requirements and with my understanding i should use a CB cascaded with a CC.

    I just want to know if i am correct on this via my specs.
     
  5. nahid5692001

    Thread Starter New Member

    Mar 8, 2011
    5
    0
    Here is one of my attempts:

    Please view the image.
     
    • hw1.jpg
      hw1.jpg
      File size:
      141.1 KB
      Views:
      33
  6. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    You have been asked for a high input resistance, but you have chosen a common-base input stage.

    The common-base configuration has the lowest input resistance.

    Think again. What sort of input stage is needed?
     
  7. nahid5692001

    Thread Starter New Member

    Mar 8, 2011
    5
    0
    hello,
    your absolutely right. i need to switch what i have now. so the CC can be first then the CB. this will work because rout is low and CB has low.

    how about that?
     
  8. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    The output impedance of a common-base stage is not low. Also, the common-base stage will put a heavy load on the common-collector input stage, so that its input impedance would not be particularly low.

    I think the best thing for you to to would be to write a table of the characteristics of each of the three configurations, so that you are clear about them. If there are things you are not sure of, check up with your study texts or use the internet.

    You may find that the ideal solution to this problem requires more than two transistors.
     
Loading...