Book Analog Interfacing to Embedded Microprocessors
Rf + R3 R1 + R2
Substituting into the basic opamp equation:
V1 ¥ R2 ( Vo - V2)R3
Vo = Av Ê - + V2ˆ
Ë R1 + R2 Rf + R3 ¯
Expanding and solving for Vo:
V1RfR2 + V1R2R3 - ( V2RfRL + V2RfR2)
Vo = Av
R1Rf + R2R3 + R2Rf + R2R3 + AvR3R1 + AvR2R3
Dividing the right fraction by Av/Av and allowing Av to be very large:
V1R2Rf + V1R2R3 - ( V2RfRL + V2RfR2)
Vo =
R1R3 + R2R3
V1 ¥ R2 Ê Rf ˆ Rf
= 1+ - V2
R1 + R2 Ë R3 ¯ R3
If R2 = RF and R1 = R3, then we get:
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