This amplifier uses both inverting and non-inverting inputs with a gain of one to produce an output equal to the difference between the inputs. It is a special case of the differential amplifier. You can also choose the resistances to amplify the difference.

This amplifier uses both inverting and non-inverting inputs with a gain of one to produce an output equal to the difference between the inputs. It is a special case of the differential amplifier. You can choose the resistances to get an amplification of one.

The behavior of most configurations of op-amps can be determined by applying the "golden rules". For the difference amplifier, the voltage at the non-inverting input is , so by the voltage rule that voltage also appears at point A.

Applying the current rule, the current into A must be zero, so

which for equal resistors becomes

The voltage at 3 is given by