Differential amplifiers

Discussion in 'The Projects Forum' started by ShaunManners, Jun 6, 2008.

  1. ShaunManners

    Thread Starter Active Member

    Feb 16, 2008
    72
    1
    Hi All,

    I have been reading about differential amplifiers and I am unsure about something...

    When using negative feedback, a voltage divider is used between ground and the output with the centre of the divider going to the inverting input of the op-amp... which will amplify the input on the noninverting input according to the ratio of the divider.. thats fair enough...

    the bit I don't understand is that when you want a differential amp, you have to add another divider on the noninverting input too... why cant you connect one input to what would be the ground of the divider and the other to the noninverting input?

    I'm probably being really stupid here!

    Cheers
    Shaun
     
  2. Caveman

    Active Member

    Apr 15, 2008
    471
    0
    Fundamentally, you can, but the output will not be purely differential. It will have the input that is connected to what would be the ground of the divider added to the differential result. Get it?

    When you connect it the other way, it cancels out this effect.
     
  3. ShaunManners

    Thread Starter Active Member

    Feb 16, 2008
    72
    1
    I think I'm starting to see what you are saying... I think I'll go and sleep on it ;)

    Thanks for your reply.

    Cheers
    Shaun
     
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