FT in transistor Опции

[Sara00]

hello my friends
i searched a lot in the internet and i couldn't find my answer.could you tell me what is exactly FT do in transistor?
what are the formula that join ft to another transistor elements for designing an oscillator or mixer?
if good book tell me more i will appreciate you.
Thanks

[Sara00]

Thanks dr
in university we read that Ai=Beta in common emitter( Electronic 1)
and read that |Ai|=ft/f (Electronic 3)

now voltage gain in common emitter can be varied by determine the resistor network.before oscillation Ai=Beta and after that when we inject high frequency it changed to equal |Ai|=ft/f ?am i right?

they are the same?or different?

what book you suggest to know more?

because i designed and works with a collpits oscillator with 2n3904 but it works frequency below 3Mhz and doesn't work at higher frequency when i changed the collpits capacitors and inductor

Сообщение отредактировал Sara00 - Apr 29 2012, 15:04

[proxi]

in university we read that Ai=Beta in common emitter( Electronic 1)
and read that |Ai|=ft/f (Electronic 3)

Witch university?
Beta is static ( for DC only ) parameter. It`s base current gain to collector. It is close to H21 ( gain at some kilohertz) . In fact here are a lot books concerning basic H and Y transistors parameters in english . Usable frequencies for the BJT transistors amplifiers is the band with working f up to ft/10 and for oscillators up to ft/2, preferable bellow ft/5. For hi frequencies are usable S par also.
Here is Collpits ( in russian емкостная трехточка ) oscillator simulation with BC 337 ft=100MHz and crystal. It works @ 10MHz.
Where are you from. How I understood the English isn`t your first language. Somewhere from Asia? China? Or eastern Europe?

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