High-Frequency Response of MOSFET Common-Source Amplifier (2): Open-Circuit Time Constant

Item: High-Frequency Response of MOSFET Common-Source Amplifier (2): Open-Circuit Time Constant
Rating: 4
Author: PostSingularity Institute

by Vincent Chang

Formal & Physical Sciences Engineering & Technology TJFElectronics engineering TJFCElectronics: circuits and components

🎙 Vincent Chang 👥 2K 📅 July 13, 2021 ⏱ 17 min 👁 1K 📄 tutorial 🧭 2026-08-17

Available in: English (current) Français

Keywords

MOSFETcommon-source amplifierhigh-frequency responseopen-circuit time constantMiller effect

Summary

This video is the second part of a series on the high-frequency response of MOSFET common-source amplifiers, focusing on the open-circuit time constant method. The instructor, Vincent Chang, begins by reviewing the high-frequency analysis methodology, including the equivalent circuit with capacitors Cgs and Cgd. He then explains the open-circuit time constant method step by step: setting the input signal to zero, calculating the open-circuit resistances seen by each capacitor, and summing the time constants to estimate the upper 3-dB frequency. The main challenge is finding the resistance seen by Cgd, which involves a voltage-controlled current source. The instructor encourages solving this by inspection, using the resistance reflection rule (ro + (1+mu)Rs) and introduces the concept of mu = gm*ro. He demonstrates how to simplify the circuit and derive the expression for R2o. The method is presented as a quick estimation technique for amplifier bandwidth. The video ends with a preview of the next lecture on Miller’s theorem. The tutorial is aimed at students and engineers in analog IC design, with a focus on intuitive understanding and practical application.

178 words

Critical Evaluation

Value of the Information & Strength of the Argument

The video provides valuable insights into the open-circuit time constant method, a standard technique for estimating the bandwidth of amplifiers. The instructor’s approach of teaching analysis by inspection is particularly valuable, as it helps students develop intuition for circuit analysis. The argumentation is solid, with clear step-by-step reasoning and a practical example. The instructor also encourages active learning by asking viewers to pause and solve a problem, which enhances engagement. The method is well-established in the field, and the explanation is accurate, though it could benefit from more formal derivations for completeness.

Scientific Rigor, Source Quality, Title Accuracy

The scientific rigor is high, as the method is a standard textbook technique in analog IC design. The instructor, with 30 years of experience, provides accurate explanations. However, no specific sources are cited in the video or description, which limits the ability to verify claims independently. The title accurately reflects the content, and the video is well-structured. The description mentions the instructor’s credentials, adding credibility. Overall, the content is reliable, but the lack of explicit references is a minor weakness.

187 words

Title / Content Match

The title accurately reflects the content, which focuses on the open-circuit time constant method for high-frequency response of a common-source amplifier.

Quality & Reliability

8/10

The content is a well-structured tutorial by an experienced educator, providing a clear methodology and encouraging analytical insight. The method is standard in analog IC design, and the explanation is accurate, though it lacks formal derivations and references.

Key Moments

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

Contribution & Novelties

The video offers a unique pedagogical approach by teaching the open-circuit time constant method through analysis by inspection, which is often not emphasized in textbooks. This helps students develop a deeper understanding of circuit behavior. The instructor’s method of using the resistance reflection rule to simplify the calculation of R2o is a valuable shortcut. The video also encourages active learning by prompting viewers to solve problems independently.

Pour aller plus loin :

Miller effect — Relevant to the next lecture and understanding the alternative method.
Common-source amplifier — Provides background on the amplifier configuration.
Time constant — Fundamental concept used in the method.

103 words

Radar Profile

The radar profile shows high scores in quality and reliability, with moderate quantity and technical level. This indicates a focused, accurate tutorial that may not cover a broad range of topics but excels in depth and clarity.

Reliability 8/10