Operational Amplifier Fundamentals Unit 2 – The Inverting Amplifier
Since the op amp has high gain and feedback is provided, the inverting op amp terminal is
maintained at virtual ground.
For this circuit configuration, the inverting op amp terminal serves as the circuit summing point.
In the circuit shown, VO represents the action of an op amp. The junction VJ is maintained at
virtual ground (0V) because VO varies as VI varies.
Since VJ is held at virtual ground, it is also the circuit summing junction: VJ = VI - VO.
NOTE: Virtual ground and summing junction concepts will be extensively explored in this and
other units.
NEW TERMS AND WORDS
inverting amplifier - a circuit using an active device to amplify and invert (180-degree phase
shift) an input signal.
virtual ground - a circuit point that behaves like circuit common or has near zero potential with
respect to circuit common.
summing point - a node where two or more voltages or currents meet and algebraically combine.
phase shifted - the difference between two signals; measured in units of time or degrees.
Gain-bandwidth product - the product of the closed-loop gain of an op amp and its
corresponding closed-loop bandwith.