Operational Amplifier Fundamentals Unit 7 – The Difference Amplifier
UNIT 7 – THE DIFFERENCE AMPLIFIER
UNIT OBJECTIVE
At the completion of this unit, you will be able to describe the operation of a difference amplifier
by using a typical operational amplifier circuit.
UNIT FUNDAMENTALS
The difference amplifier shown is a two-input circuit that amplifies the difference between V1
and V2.
V1 is connected to the inverting side of U1, and V2 is connected to the noninverting side of U1.
When R1, R2, R4, and R5 are equal in value, the difference amplifier subtracts V1 and V2.
VO = V2 - V1
In practice, the input impedance for V1 equals the ohmic value of R1. The input impedance for
V2 equals the ohmic value of R2 + R4. A difference amplifier circuit combines the gain effect
from the inverting and noninverting resistor ratios.
For V1, VO equals -[V1 x (R5/R1)].
For V2, VO equals {V2 x [R4/(R2 + R4)]} x [1 + (R5/R1)].