Tweaker's Asylum

• Re: What is unity gain in op amp? - Gepetto 14:47:04 05/05/02 (3)
  In Reply to: What is unity gain in op amp? posted by Bom on May 05, 2002 at 12:58:15:

  In simple terms:

  Unity gain op amps are compensated so they are stable even with the output directly wrapped around to the negative input in a non-inverting voltage follower mode or with Rf=Rin in an inverting configuration. These configurations have a gain of ONE or unity.

  Op amps that are not compensated for unity gain will be unstable in the unity gain follower mode or the inverting configuration where Rf=Rin.

  If an op amp states that it is stable for Av> =5 for example, Rf must be selected to be > = 5*Rin for it to operate in a stable manner.

  
  G.
  Crank it up...
  
  

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  • in op amp math: -1 = +2 - jcox 22:50:08 05/06/02 (2)
    In Reply to: Re: What is unity gain in op amp? posted by Gepetto on May 05, 2002 at 14:47:04:

    for stabiltity "noise gain" of circuit is what counts
    
    

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    • Re: in op amp math: -1 = +2 - Bom 07:17:32 05/07/02 (1)
      In Reply to: in op amp math: -1 = +2 posted by jcox on May 06, 2002 at 22:50:08:

      Thanks guys, so in replacing op amp, we have to choose the unity gain type. AM I right?
      
      

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      • unity-gain stable op amp "safer" as drop in, but... - jcox 08:11:10 05/07/02 (0)
        In Reply to: Re: in op amp math: -1 = +2 posted by Bom on May 07, 2002 at 07:17:32:

        devilish details:

        single 8-pin op amps may use pins 1,5, and/or 8 for offset adjustment and/or external frequency compensation -- not always the same pins and component values for different parts, compensation components are not compatable between op amp types and are removed by tweakers before substituting

        if you're looking at a single op amp with circuit connections to pins 1, 5, and/or 8 you've got know more before subtituing op amps

        dual 8-pin/quad 14-pin op amps don't have pins to spare for external compensation so unity-gain stable drop in replacements usually work, although replacing a decompensated ( min stable gain > 1) op amp with a unity-gain stable one may give up some performance
        
        

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