Topic: Analog Circuits
Which of the following conditions must hold true for the virtual ground assumption to be valid in an op-amp circuit?
- A. The op-amp must have infinite input impedance and zero output impedance
- B. The op-amp must be operated in open-loop mode
- C. Negative feedback must be present and the op-amp should be operating in the linear region
- D. The op-amp should have a very low gain
Answer: C. Negative feedback must be present and the op-amp should be operating in the linear region
Explanation: The virtual ground concept assumes the voltage difference between the inverting and non-inverting input terminals is zero. This happens because the op-amp has very high open-loop gain; to maintain a finite output voltage (operating in the linear region), the differential input must be virtually zero. This requires negative feedback to stabilize the output and keep it from saturating.