Inverting Op-Amp (1): Virtual Ground Explained

Inverting Op-Amp (1): Virtual Ground Explained

by Vincent Chang

Formal & Physical Sciences Engineering & Technology TJFElectronics engineeringTJFCElectronics: circuits and components
🎙 Vincent Chang 👥 2K 📅 January 25, 2021 ⏱ 12 min 👁 452 📄 tutorial 🧭 2026-08-17
Available in: English (current) Français

Keywords

virtual groundinverting amplifierclosed-loop gaininput resistanceideal op-amp

Summary

This tutorial introduces the inverting operational amplifier configuration, focusing on the concept of virtual ground. The instructor, Vincent Chang, begins by reviewing the ideal op-amp characteristics: infinite input resistance, zero output resistance, and infinite open-loop gain. He then explains that in a closed-loop configuration with negative feedback, the voltage at the inverting input equals that at the non-inverting input, creating a virtual short. Since the non-inverting input is grounded, the inverting input becomes a virtual ground. Using this concept, he derives the closed-loop gain as -R2/R1, emphasizing the phase inversion. He also calculates the input resistance, which equals R1, and highlights a trade-off: achieving high gain requires a large R2/R1 ratio, but high input resistance requires a large R1, leading to conflicting design goals. The video concludes by summarizing these key points and encouraging designers to consider this trade-off.

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Critical Evaluation

Value of the Information & Strength of the Argument

The video provides a solid foundational explanation of the inverting op-amp, with clear derivations based on ideal assumptions. The argumentation is logical and step-by-step, making it easy to follow. The instructor effectively uses the virtual ground concept to simplify circuit analysis. The discussion of the trade-off between gain and input resistance adds practical value for designers. However, the video does not address non-ideal effects or alternative configurations, limiting its depth.

Scientific Rigor, Source Quality, Title Accuracy

The scientific rigor is high for an introductory tutorial; the derivations are mathematically sound and consistent with standard textbooks. The instructor’s credentials lend credibility. The title accurately describes the content. No external sources are cited, but the material is well-established knowledge. The video is self-contained and does not reference specific publications, which is acceptable for a tutorial.

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Title / Content Match

The title accurately reflects the content, focusing on the virtual ground concept in the inverting op-amp configuration.

Quality & Reliability

8/10

The video provides a clear, step-by-step derivation of the inverting amplifier's gain and input resistance using ideal op-amp assumptions. The instructor is an experienced educator with a PhD in Electrical Engineering. The content is accurate and well-structured, though it lacks citations to external sources.

Key Moments

Markers derived by PSI from the transcript: the creator did not define chapters.

Contribution & Novelties

The video offers a clear pedagogical explanation of the virtual ground concept, which is fundamental to op-amp analysis. It emphasizes the trade-off between gain and input resistance, a key design consideration. The step-by-step derivations are valuable for beginners.

Pour aller plus loin :

  • Operational amplifier — Provides comprehensive background on op-amps, including ideal characteristics and various configurations.
  • Negative feedback — Explains the principle of negative feedback, which is essential for understanding virtual ground.
  • Virtual ground — A dedicated article on the virtual ground concept, offering further insights.

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Radar Profile

The radar profile shows high scores in quality and reliability, with moderate scores in quantity and technical depth. This indicates a focused, accurate tutorial that may not cover advanced topics but is solid for its intended audience.

Reliability 8/10