Summary Difference (or differential) amplifiers

DIFFERENCE AMPLIFIER OR SUBTRACTOR

 Derive the out put voltage equation :




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 Difference (or differential) amplifiers are used in various
applications where there is a need to amplify the difference
between two input signals.
 This is a device that amplifies the difference between two
inputs but rejects any signals common to the two inputs.
 Considering the op amp circuit shown in Figure above:
 There is no current that passes through the op amp
terminals(i.e Inverting and Non Inverting).Hence the
current is zero at the two terminals, and
 Va = Vb

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 Calculating the voltage at the non inverting terminal using
voltage divider rule:
 When resistors R1 = R3 and R2 = R4
 Vb = [R2 / R1 + R2] V2 ….Using Voltage Divider Rrule

 Hence, Va = Vb = [R2 / R1 + R2] V2. ……………(i)

 Current (I1) : Flowing from V1




 Current (I2) : Through feedback resistor



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