The basic inverting amplifier configuration using an op-amp with input impedance Z1 and feedback impedance Zf .

**Sign
Changer (Phase Inverter)**

The
basic inverting amplifier configuration using an op-amp with input impedance Z1
and feedback impedance Zf . If the impedance Z1 and Z f are equal in magnitude° and phase, then the closed loop voltage gain is -1, and the
input signal will undergo a 180 phase shift at the output. Hence, such circuit
is also called phase inverter. If two such amplifiers are connected in cascade,
then the output from the second stage is the same as the input signal without
any change of sign. Hence, the outputs from the two stages are equal in
magnitude but opposite in phase and such a system is an excellent paraphase
amplifier.

**Scale
Changer:**

Referring
the above diagram, if the ratio Z_{f} / Z_{1} = k, a real
constant, then the closed loop gain is – k, and the input voltage is multiplied
by a factor –k and the scaled output is available at the output. Usually, in
such applications, Z_{f} and Z_{1} are selected as precision
resistors for obtaining precise and scaled value of input voltage.

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