5.1 The Inverting Amplifier

The primary function of an inverting amplifier is to amplify the input signal and invert its sign, creating a 180-degree phase difference between the input and output.

• How it works: The non-inverting (+) terminal is connected to ground (0V). Due to the virtual short, the inverting (-) terminal is also at 0V. The current flowing through the input resistor R1 is V_i / R1. Since no current flows into the op-amp’s input terminal, this same current must flow through the feedback resistor Rf. This creates an output voltage of V_0 = – (V_i / R1) * Rf.
• Gain Formula: V_0 / V_i = -(Rf / R1)

5.2 The Non-Inverting Amplifier

The primary function of a non-inverting amplifier is to amplify the input signal without changing its sign or phase.

• How it works: The input signal V_i is applied directly to the non-inverting (+) terminal. Because of the virtual short, the voltage at the inverting (-) terminal is also V_i. This voltage is determined by the voltage divider formed by Rf and R1, so V_i = V_0 * (R1 / (R1 + Rf)).
• Gain Formula: V_0 / V_i = 1 + (Rf / R1)

5.3 The Voltage Follower

The voltage follower is a special case of the non-inverting amplifier. Its purpose is to produce an output voltage that exactly follows the input voltage, acting as a buffer.

• How it works: The input V_i is applied to the non-inverting (+) terminal, and the output is connected directly back to the inverting (-) terminal. The virtual short ensures that V_0 (at the inverting terminal) is equal to V_i (at the non-inverting terminal).
• Gain Formula: V_0 / V_i = 1

The power of these simple configurations unlocks a vast world of more advanced electronic circuit design.