Which statement correctly describes the virtual ground concept at the inverting summing node?

Which statement correctly describes the virtual ground concept at the inverting summing node?

• A. The node is held at approximately 0 V by negative feedback.
• B. The node is at a fixed potential equal to one of the supply rails.
• C. The node has no effect on the output.
• D. The node is at a positive saturation when inputs are positive.

Answer: (A)

Virtual ground at the inverting summing node comes from the op-amp’s effort to make its two inputs equal when negative feedback is present. If the non-inverting input is grounded, the amplifier drives its output so that the inverting input sits near 0 V even though it isn’t physically connected to ground. This state is called a virtual ground: the node is at approximately 0 V, but it’s a high-impedance point with effectively no current entering the op-amp input. Because the input currents must sum at that node, all currents coming through the input resistors flow through the feedback resistor to the output. This relationship sets the output to enforce the zero-voltage condition at the node. In a single-input case, V_out = -(R_f / R_in) V_in; for multiple inputs, V_out = -R_f times the sum of (V_in_i / R_in_i). So the node is at approximately 0 V due to negative feedback and the grounded non-inverting input, not because it’s tied to a supply rail. The output adjusts to maintain that condition, and the node does influence the output through the feedback path. It’s not at a positive saturation under normal linear operation.

Virtual ground at the inverting summing node comes from the op-amp’s effort to make its two inputs equal when negative feedback is present. If the non-inverting input is grounded, the amplifier drives its output so that the inverting input sits near 0 V even though it isn’t physically connected to ground. This state is called a virtual ground: the node is at approximately 0 V, but it’s a high-impedance point with effectively no current entering the op-amp input.

Because the input currents must sum at that node, all currents coming through the input resistors flow through the feedback resistor to the output. This relationship sets the output to enforce the zero-voltage condition at the node. In a single-input case, V_out = -(R_f / R_in) V_in; for multiple inputs, V_out = -R_f times the sum of (V_in_i / R_in_i).

So the node is at approximately 0 V due to negative feedback and the grounded non-inverting input, not because it’s tied to a supply rail. The output adjusts to maintain that condition, and the node does influence the output through the feedback path. It’s not at a positive saturation under normal linear operation.