cut-off frequency hard

Question

High-frequency performance of transistor limited mainly by:

RankGuru · Accepted Answer

The ability of a transistor to amplify high-frequency signals is limited by physical 'speed' constraints:
1. **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.
2. **Junction Capacitances**: The depletion regions at the junctions act like capacitors ($C_{be}$, $C_{bc}$). 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 $f_T$ of the transistor.

Rank Guru

cut-off frequency hard

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