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

Please help me

http://en.wikipedia.org/wiki/Gain%E2%80%93...uct#Transistors

а может здесь про константу фи тэ он же kT/q = 25.85 мВ
вот этот коэффициент там делает а остальные так


а это вообще круто

А причём тогда тут генераторы и миксеры? И вообще, причём тут миксеры?

Миксеры. Жильберты. Однотранзисторные с совмещенным гетеродином в старых Нейвах-Альпинистах. Балансные. В Дроздивере на 2Т610А. Всякие. Тут http://electronix.ru/forum/index.php?showt...t&p=1000851 - двухбалансный ОБ-ОЭ каждый транзистор. Ft еще как нужно было знать до всяких там спайсов.

Да причем... а о чем это вы

Here isn`t right place for help. You can ask somewhere on EDA board or something else.

Thanks all
i read the wikipeida before.but i asked many people about ft to choosing a transistor for desire job.for example if i want to create a collpits oscillator with 100Mhz frequency what transistor should i choose?what is the formula according the ft of transistor and my frequency?
could you help me ? its not very important to tell me in English.please tell me with your fresh language
its important to me to understand and know about electronics in RF environment

2SC3356=NE85633
For oscillators Fosc<Ft/2

Сообщение отредактировал Dr.Drew - Apr 29 2012, 12:10

Thanks dr.drew
as you see in many oscillator with frequency between 90-108 Mhz they use c945 with 150 ft,how it works fine?
does we have an equation that explain the formula between Voltage Gain and ft in colpitts oscillators?
because i asked somebody else but tell me that "current gain * BW product = fT "
but if i use emitter-common that Current gain is approximately 100 and for oscillate my circuit in 100Mhz i shoud use transistor with ft 10Ghz?!!!

Does any books tell me moe about designing collpits oscillator with all steps(such as choosing transistor , Capacitor , ....)? theory and experimental?

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.

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

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?

thanks a lot dear friend
could you tell me books that you assume can be useful for me(basic to professional)?
my main problem is we study only the mathematical of components and for transistor we only assume they are at linear statues.so i have a close eye to electronic telecommunication.
Please help me what can i improve my ability and knowledge in RF design(as i told basic to professional)
i love to read book so please suggest the best books that you like and enjoy with it

excuse me that i waist your time