Correction !!!!

Discussion in 'Homework Help' started by Nice, Jun 13, 2009.

  1. Nice

    Thread Starter Member

    Jun 13, 2009
    19
    0
    Hi Guys

    How can I have an amplifier with :

    1- High gain
    2- High input resistance
    3- Low output resistance

    Is it important to use multistage amplifier ??
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    67
    How high is the gain?

    What is the maximum operating frequency?
     
  3. Nice

    Thread Starter Member

    Jun 13, 2009
    19
    0
    The input signal is 10mV

    and the needed gain is 40V/V

    The frequency is 1000Hz= 1khz
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    67
    You can use an op amp in this case with good results.
     
  5. Nice

    Thread Starter Member

    Jun 13, 2009
    19
    0

    I should use BJT's or MOSFET's only !!!:(
     
  6. Nice

    Thread Starter Member

    Jun 13, 2009
    19
    0
    Thank you for your response
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
    67
    Then you have to build a common emitter amplifier with a gain of 40V/V and then fed its output to the input of an emitter follower to achieve low output impedance.
     
  8. bertus

    Administrator

    Apr 5, 2008
    17,121
    3,001
    Hello,

    So you need a gain of 40 V/V.
    What input resistance is required?
    What output resistance is required?

    Greetings,
    Bertus
     
  9. Nice

    Thread Starter Member

    Jun 13, 2009
    19
    0

    Rin > 40k

    Rout < 1k
     
  10. Nice

    Thread Starter Member

    Jun 13, 2009
    19
    0

    Can you please show me the connection

    because I tried this configuration (CE-CC) in the PSpice & the gain is approximately = 1 :(
     
  11. Nice

    Thread Starter Member

    Jun 13, 2009
    19
    0
    Thank you guys..I appreciate what you are doing
     
  12. bertus

    Administrator

    Apr 5, 2008
    17,121
    3,001
    Hello,

    That could be made with a two stage amplifier.
    At the input a mosfet for the high input resistance and gain.
    Afther that an emmitter follower for the low output resistance.

    Greetings,
    Bertus
     
  13. mik3

    Senior Member

    Feb 4, 2008
    4,846
    67
    The gain of a CC is about 1.

    The gain of a CE depends on Rc and Rin.
     
  14. Nice

    Thread Starter Member

    Jun 13, 2009
    19
    0

    Also CE will give a high gain & input resistance !!!
     
  15. Nice

    Thread Starter Member

    Jun 13, 2009
    19
    0
    The rule says:

    The gain of a multistage amplifier is the gain product of each BJT
     
  16. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    9,454
    912
    So simply make a CE transistor with a gain of 40 followed by a CC transistor that has a gain of 1. The CE transistor has a high input impedance and the CC transistor has a low output impedance.
     
  17. mik3

    Senior Member

    Feb 4, 2008
    4,846
    67
    This is true about the voltage gain.

    For the current gain you cannot simply multiply the individual current gains.
     
  18. Nice

    Thread Starter Member

    Jun 13, 2009
    19
    0

    You are absolutely right..
     
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