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.
Referring the above diagram, if the ratio Zf / Z1 = 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, Zf and Z1 are selected as precision resistors for obtaining precise and scaled value of input voltage.