Cut-off Frequency Hard
High-frequency performance of transistor limited mainly by:
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About This Question
- Subject
- physics
- Chapter
- semiconductor electronics
- Topic
- cut-off frequency hard
- Difficulty
- Hard
- Year
- 2025
Solution
Correct Answer:
Carrier transit time and junction capacitances
The ability of a transistor to amplify high-frequency signals is limited by physical 'speed' constraints:
- Transit Time: It takes a finite amount of time for charge carriers to diffuse across the base. If the input signal changes faster than this time, the output cannot track the input accurately.
- Junction Capacitances: The depletion regions at the junctions act like capacitors (Cbe, Cbc). These capacitors take time to charge and discharge, causing a phase lag and reducing the gain at high frequencies. These effects define the cut-off frequency fT of the transistor.
This hard difficulty physics question is from the chapter semiconductor electronics, covering the topic of cut-off frequency hard. It appeared in the 2025 exam.
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