MOSFET Small-Signal Model (3): Internal Capacitances & High-Frequency Model

MOSFET Small-Signal Model (3): Internal Capacitances & High-Frequency Model

by Vincent Chang

Formal & Physical Sciences Engineering & Technology TJFElectronics engineeringTJFDElectronic devices and materials
🎙 Vincent Chang 👥 2K 📅 February 17, 2021 ⏱ 20 min 👁 733 📄 tutorial 🧭 2026-08-17
Available in: English (current) Français

Keywords

MOSFETsmall-signal modelinternal capacitanceshigh-frequency modelgate capacitance

Summary

This lecture, part of a series on MOSFET small-signal models, focuses on the internal capacitances and the high-frequency model. The instructor, Vincent Chang, begins by contrasting the low-frequency model (which neglects capacitances) with the high-frequency model. He then systematically introduces the four main internal capacitances: gate-to-source (Cgs), gate-to-drain (Cgd), source-to-body (Csb), and drain-to-body (Cdb). For each, he explains the physical origin: Cgs and Cgd arise from the gate-to-channel capacitance, with contributions from overlap capacitance due to manufacturing imperfections; Csb and Cdb are junction depletion capacitances. He provides formulas for these capacitances, including the two-thirds rule for the channel charge distribution. The lecture also discusses the gate-to-body capacitance (Cgb) and then presents a simplified high-frequency model, often used in common-source amplifiers, where the body is connected to the source, leading to a reduction in the number of capacitances. The instructor emphasizes the importance of this model for frequency response analysis and hints at a future lecture on bandwidth and unity-gain frequency.

160 words

Critical Evaluation

Value of the Information & Strength of the Argument

The video provides a solid foundational explanation of MOSFET internal capacitances, which is essential for understanding high-frequency behavior. The instructor uses a combination of physical intuition and mathematical formulations, making the content valuable for students. The argumentation is generally coherent, but some derivations are skipped or stated without proof, which may reduce the depth of understanding for some viewers. The use of diagrams and mapping to physical structures helps reinforce the concepts.

Scientific Rigor, Source Quality, Title Accuracy

The scientific rigor is moderate: the instructor is credible, but no external sources are cited, and the content relies on standard textbook knowledge. The title accurately reflects the content, and the video is well-structured. The lack of explicit references may be a limitation for those seeking to verify the information independently.

138 words

Title / Content Match

The title accurately reflects the content, which focuses on internal capacitances and the high-frequency small-signal model of MOSFETs.

Quality & Reliability

7/10

The content is presented by an experienced educator (Ph.D. in EE, 30 years teaching) and follows a logical structure. However, the video lacks explicit citations to external sources, and the presentation is informal with some digressions. The technical derivations are stated without full proof, relying on the instructor's authority.

Key Moments

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

Contribution & Novelties

This video provides a clear and structured explanation of MOSFET internal capacitances, bridging the gap between device physics and circuit analysis. It emphasizes the physical origins of each capacitance and offers a simplified model for practical use. The instructor’s teaching experience is evident in the pedagogical approach.

Pour aller plus loin :

81 words

Radar Profile

The radar profile shows a balanced performance with high scores in technical level and information quality, but slightly lower in quantity and reliability due to the lack of external references. This indicates a focused, technically sound tutorial that could benefit from additional supporting sources.

Reliability 7/10