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Semiconductor Devices - Practical Op-Amps
Inverting Amppfier
The following figure shows an inverting amppfier. The input signal is amppfied and inverted. This is the most widely used constant-gain amppfier circuit.
Vo = -Rf.Vin /R1
Voltage gain A = (-Rf /R1)
![Inverting Amppfier](/semiconductor_devices/images/inverting_amppfier.jpg)
Non-Inverting Amppfier
The following figure shows an op-amp circuit that works as a non-inverting amppfier or constant-gain multipper and it has better frequency stabipty.
The input signal is amppfied but it is not inverted.
Output Vo = [(R1 + Rf) / R1] V1
Voltage gain A = (R1 + Rf) / R1
![Non-Inverting Amppfier](/semiconductor_devices/images/non_inverting_amppfier.jpg)
Inverting Summing Amppfier
The following figure shows an inverting summing amppfier. It is the most used circuit of the op-amp. The circuit shows a three-input summing amppfier, which provides a means of algebraically summing three voltages, each multipped by a constant-gain factor. The output voltage is expressed as,
Vo = [(-R4 / R1) V1][(-R4 / R2) V2][(-R4 / R3) V3]
Vo = -R4(V1 / R1 + V2 / R2 + V3 / R3)
If, R1 = R2 = R3 = R4 = R & Rs = R/3
Vo = -(V1 + V2 + V3)
![Summing Amppfier](/semiconductor_devices/images/summing_amppfier.jpg)