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Rise times and fall times of fast transistors seem way too long

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In the data sheet of a 400 MHz transistor I found fall time = 60 ns. Clearly these are contradictory specifications
- trise and tfall should be at least an order of magnitude shorter.
Should I believe that fT is specified correctly? (e.g. 2SA2088FRAT106Q transistor).
 

Hi,

400MHz is for small signal (non saturated) analog mode....where the gain = 1
60ns is for large signal, saturated, switching mode.

Two completely different situations.

Klaus
 
Apart from the difference between saturated switching and small signal amplifier operation, do you understand the meaning of fT? It's the frequency where the small signal current gain would drop to unity.
 

fT of an unloaded transistor, or one in a 50 ohm ideal
test setup and rise/fall times with a spec load, 10-90%
are not at all the same condition.

Fall time is drive current and (load+Miller) capacitance.
 

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