Op-amp differential amplifier is given in figure bellow.

Simulate op-amp differential amplifier.

Input in op-amp is already realized as differential amplifier with discrete components. Voltage gain from inverting input to the output is the same as voltage gain from non-inverting input to the output, but with different sign. Overall voltage difference gain is almost infinite for op-amp without negative feedback. It means that input range is zero if there is no negative feedback. For that purpose negative feedback with resistors R_{1} and R_{2} is set. By using superposition theorem, we have

and

By combining upper two equations and having following condition satisfied:

we obtain:

i.e. upper circuit operates as an analog op-amp differential amplifier, with much wider range for input signals V_{1} and V_{2} comparing to differential amplifier with discrete components. If additional condition

is fulfilled, both analog inputs V_{1} and V_{2} has the same input impedance. CMRR factor of op-amp differential amplifier is highly dependent of how well resistors R_{1}, R_{2}, R_{3} and R_{4} are matched. Better version of op-amp differential amplifier is with three op-amps, scheme known as op-amp instrumentation amplifier.

Go to op-amp differential amplifier.

**External links:**

Op-amp Differential Amplifier on electronics-tutorials

## Leave a Reply