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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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