Inverting Amplifier

The inverting amplifier configuration is shown in Fig. 1.9.

  

Figure 1.9: Inverting Amplifier

Equating V⁺=V^- and realizing the V⁺ is grounded means that V^-=0. Since the ideal op-amp draws no current ($R_{in}=\infty$) , Kirchoff's laws give I_s=-I_f. Since $I_{s}=\frac{V_{in}}{R_1}$ and $I_{f}=\frac{V_{out}}{R_f}$,then algebra yields the inverting op-amp gain A_inv:

$$A_{inv}= \frac{V_{out}}{V_{in}}= \frac{-R_f}{R_1}$$ (14)