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gain bandwidth product / op amps

Discussion in 'General Electronics Discussion' started by komalbarun, Aug 25, 2013.

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  1. komalbarun

    komalbarun

    67
    0
    Nov 25, 2011
    Hi all,
    1.How do we calculate gain-bandwidth product of an op-amp?

    like if :
    i have open loop gain Ao = 100,000.
    Bandwidth = unknown .
    Ao x unknown = ??

    2.what does frequency response, badwidth mean? how do these affect the output?

    3. What do we mean when we talk about unity gain in op-amps. Does it mean that gain=1?
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    1. You don't, you get it from the datasheet.
    2. GBP is the product of the gain and the frequency. Say it is 1 MHz. That means you will have unity gain at 1MHz, gain of 10 at 100KHz, gain of 100 at 10KHz etc.
    3. Yes.

    Bob
     
  3. komalbarun

    komalbarun

    67
    0
    Nov 25, 2011
    thnx a lot Bobk.

    There's still something i want to understant.

    cut off frequency = the frequency below which and above which output will not be as expected? that's how it seems to be after a lot of online reading xD.

    but, how do we get the -3dB?

    10 log 2 = 3 <--ok, i got it.
    10
    but:
    where does the 2 come from Oo?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,490
    2,831
    Jan 21, 2010
    The 2 comes from a factor of two -- a doubling or halving (in your case you are actually looking for 10 log 0.5).

    The the Log (base 10) part comes from the definition of a Bel and the fact that it's logarithmic and specifically log base 10.

    The 10 part comes from the fact that you want dB, not B.
     
  5. komalbarun

    komalbarun

    67
    0
    Nov 25, 2011
    Thx to both of you, things are much clearer now ^__^
     
  6. eman12

    eman12

    31
    0
    Aug 24, 2013
    Hi komalbarun,

    If I was you, I would try to take a look at the datasheet of "LM3886" Op-amp. It talks about GBP and give you an good example in this regard.
     
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