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

[Dr.Drew]

C945 will work fine. In my YIG oscillator 3-9 GHz transistor with Ft=14 GHz is used and works fine. Voltage gain of transistor amplifier depends not only on Ft but on passive elemets values. Using Ft value one can calculate a current gain at present frequency which is Ft/f. Current gain at low frequencies is limited by DC gain h21e. Look at transistor amplifier books.
To oscillate amplifier gain must be greater than losses in loaded resonator in feedback. In GHz band losses are often 3-10 dB. So thansistor amplifier gain must be 7-13 dB with typical 3 dB margin. Required Ft will be at least 2 times greater than Fosc.