Golden Rules

When analyzing operational amplifiers, there are a few rules that need to be taken into consideration in order to solve circuits using KVL or KCL.

1. Because the output voltage does not depend on the output current, the output impedance equals zero.
2. The input impedance $i_{+}=i_{-}=0$.
3. When there is a negative feedback, both inputs have the same voltage. In other words, $V_{+}$ is equal to $V_{-}$.
4. When solving circuits using the nodal analysis, write node equations at $V_{+}$ and $V_{-}$, but not at $V_{o}$.

Sources

• Class Notes
• Ideal Op-amp
• Operational Amplifiers