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## Re: Op-amp transfer function help

 Subject: Re: Op-amp transfer function help John Popelish Sun, 06 Aug 2006 19:51:26 -0400 sci.electronics.basics
 ```Wayne wrote: ``````Hello Group, I need some tips on the deviration of a transfer function for an op-amp circuit that is in "Troubleshooting Analog Circuits" by Bob Pease, pg. 95. I do not want anyone to solve it for me; rather, I would like a sanity check on my loop equations that I am coming up with using Mesh Analysis to determine the transfer function...and...if there is an easier way. Once I get the loop equations, that leaves me with three equations and a big ass determinant to deal with. There must be an easier way and/or something that I am missing. A single resistor between the terminals shouldn't cause this much trouble :-( I am assuming clockwise for all currents in each window and analyzing clockwise as well. The loop equations I am coming up with are: Loop1: Vin - I1(R3+R4) + (I2*R3) + (I3*R4) = 0 Loop2: Vin + (I1*R3) - I2(R1 + Rb + R3) + (I3*Rb) = 0 Loop3: -(I1*R4) - (I2*Rb) + I3(R4 + Rb + R2) = Vo Mr. Pease states that the transfer function is: Vout/Vin = (1 + R2/R1) + ((R2 + R4)/Rb) Link to circuit: http://kingcosmos.bravehost.com/circuit.GIF `````` ```If you are simplifying by assuming an ideal opamp, you assume infinite gain, so Vin - must equal Vin +, in order to eliminate a saturated output. ``` ```
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