Frequency Response of Amplifiers (2): Open-Circuit Time Constant Method

Item: Frequency Response of Amplifiers (2): Open-Circuit Time Constant Method
Rating: 4
Author: PostSingularity Institute

by Vincent Chang

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

🎙 Vincent Chang 👥 2K 📅 June 4, 2023 ⏱ 10 min 👁 890 📄 tutorial 🧭 2026-08-17

Available in: English (current) Français

Keywords

open-circuit time constantfrequency responseamplifier3dB frequencyMOSFET

Summary

The video is a tutorial on the open-circuit time constant method for estimating the upper 3dB frequency of amplifiers. It begins with a review of the mid-band voltage gain of a common-source MOSFET amplifier, then explains that high-frequency behavior is dominated by internal parasitic capacitors while low-frequency behavior is affected by external coupling and bypass capacitors. The method is presented in four steps: (1) set the input signal to zero, (2) for each capacitor, open-circuit the others and find the resistance seen by that capacitor, (3) sum the time constants (C_i * R_io), and (4) take the inverse of the sum to get the upper 3dB frequency. The instructor emphasizes that the key step is finding the open-circuit resistances. The method is approximate, not exact. The video is concise and suitable for students familiar with basic amplifier analysis.

138 words

Critical Evaluation

Value of the Information & Strength of the Argument

The video provides a clear and structured explanation of the open-circuit time constant method, which is a valuable tool for quick estimation of amplifier bandwidth. The argumentation is logical, with each step justified. However, the video does not delve into the theoretical derivation or limitations of the method, and it lacks examples with numerical values. The instructor’s experience adds credibility, but the content is more instructional than analytical.

Scientific Rigor, Source Quality, Title Accuracy

The video does not cite specific sources, but the method is well-established in electronics textbooks. The title accurately reflects the content. The instructor’s credentials are mentioned in the description, but no external references are provided. The presentation is clear, but the lack of formal citations and the simplified treatment of the method limit its scientific rigor.

139 words

Title / Content Match

The title accurately reflects the content: the video explains the open-circuit time constant method for estimating the upper 3dB frequency of amplifiers.

Quality & Reliability

7/10

The video presents a standard method (open-circuit time constant) with clear step-by-step explanation. The instructor is experienced, but the video lacks formal citations and rigorous derivations. The method is well-known and correctly applied, but the presentation is simplified.

Key Moments

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

Contribution & Novelties

The video provides a clear pedagogical explanation of the open-circuit time constant method, which is a standard technique in analog circuit design. It breaks down the method into four simple steps, making it accessible to students. The main contribution is the step-by-step walkthrough, though it does not offer new insights beyond textbook material.

Pour aller plus loin :

Open-circuit time constant method — Provides a formal definition and derivation.
Frequency response — General concept of frequency response in systems.
MOSFET amplifier — Background on the amplifier topology used in the example.

91 words

Radar Profile

The radar profile shows a balanced performance across all dimensions, with slightly higher scores in quality and technical level, indicating a solid but not exceptional educational content.

Reliability 7/10