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Homework Help: Basic amplifier.

  1. May 11, 2007 #1
    Hello every body

    I am new members in here

    I hope you will eccept me as a good member

    I study electronic in college...

    I have got this task and I can't answer it

    The reason why because the tutor didn't explain to us how it's work ...

    he wan't us to answer it using the internet or other peaple to help ??

    so If any one don't mind helping me to answer it

    and explain to me how it work

    I will be very pleased to him

    You are provided with a single stage circuit and associated circuit diagrams, (Fig.2 below). With reference to the circuit briefly answer the following:


    1) Identify the circuit’s function.

    2) Using the circuit diagram component reference number briefly describe the operation of the circuit.

    thank you very much

    and I am waiting for the answer

    If anyone could help me !!!

    I would be very greatfull for him
  2. jcsd
  3. May 11, 2007 #2


    User Avatar

    Staff: Mentor

    Welcome to the PF, khalid. Homework and coursework questions need to be posted in the Homework Help forums here on the PF, and not in the general forums like the EE forum. I've moved your thread into the Homework Help forums.

    Also, an important PF rule is that you must show some of your own work before we can help you. We do not provide answers here on the PF, but we can provide tutorial help. So tell us what you know about the circuit....
  4. May 11, 2007 #3
    hi berkeman

    As you can see down this is the work I have done for those answer ??

    In analyzing the circuit, you would need to use Thevenin's Theorem for R1 and R2. You will also need to know basic transistor theory.

    Rth = R1 || R2
    Vth = 9*(22/104)

    Then you can locate the DC quiscent-point of the circuit via the BC108 transistor's characteristic curves. With an AC input before capacitor C1, the quiscent point will move along the load line and give a proportional voltage output at the common-emitter terminals, which is just the input signal amplified. Below is a general picture of what I am talking about:
    http://www.eng.cam.ac.uk/DesignOffice/mdp/electric_web/Semi/03144.png [Broken]

    This post was just meant to give you the general idea about what I have done
    . Also I will have to do a bit more research to understand the operation completely.

    Can any one help me please ???
    Last edited by a moderator: May 2, 2017
  5. May 11, 2007 #4


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    Staff: Mentor

    That's a better start. Now explain how R1, R2 and R4 set the bias for the NPN transistor. And then explain how R3, R4 and C3 set the gain through the amplifier. And explain the effects of C1, R1, R2, and C2 and R3 on the amplifier bandwidth. And using typical specs for a small-signal transistor like a 2N3904, draw the Ic vs. Vce curves like you show, with appropriate Beta gain considerations in the fan of lines, and draw the load line, and show how if varies with frequency.
  6. May 11, 2007 #5
    thank you very much Mr berkeman

    you realy make me happy

    that's very kind of you

    I'll do my best to answer it

    I will do what you told me

    thx again
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