Inverting Amplifier

Gain = −Rf/Rin; the inverting input sits at a virtual ground.

Easy

Vin ──[ Rin ]──┬──[ Rf ]──┐
               │          │
              (−)         │
                  op-amp ─┴── Vout
              (+)
               │
              GND

Because $V_-$ is held at 0 V (virtual ground), the current through $R_{in}$ also flows through $R_f$ :

$A_v = -\frac{R_f}{R_{in}} \qquad Z_{in} = R_{in}$

Example: $R_{in}$ = 10 kΩ, $R_f$ = 47 kΩ → gain −4.7.

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