Which are the key assumptions of the ideal op-amp model used in basic analysis?

Which are the key assumptions of the ideal op-amp model used in basic analysis?

• A. Infinite open-loop gain, infinite input impedance, zero output impedance, and zero input current
• B. Finite open-loop gain, finite input impedance, nonzero output impedance, and nonzero input current
• C. Infinite input current with finite impedance
• D. Zero gain with finite input impedance

Answer: (A)

In the ideal op-amp model used for basic analysis, four properties are assumed. The open-loop gain is infinite, the input impedance is infinite, the output impedance is zero, and there is zero current into the input terminals. With infinite gain, any tiny difference between the two input voltages is driven to make the output respond accordingly, so under negative feedback the inputs sit at almost the same voltage—a virtual short. Infinite input impedance means almost no current flows into the input pins, so the source isn’t loaded. Zero output impedance means the output can drive a load without losing voltage, behaving like an ideal voltage source. Zero input current follows from the infinite input impedance, so input currents are neglected in basic analysis. These assumptions simplify the behavior to focus on how the feedback network sets the output.

In the ideal op-amp model used for basic analysis, four properties are assumed. The open-loop gain is infinite, the input impedance is infinite, the output impedance is zero, and there is zero current into the input terminals. With infinite gain, any tiny difference between the two input voltages is driven to make the output respond accordingly, so under negative feedback the inputs sit at almost the same voltage—a virtual short. Infinite input impedance means almost no current flows into the input pins, so the source isn’t loaded. Zero output impedance means the output can drive a load without losing voltage, behaving like an ideal voltage source. Zero input current follows from the infinite input impedance, so input currents are neglected in basic analysis. These assumptions simplify the behavior to focus on how the feedback network sets the output.