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Best BJT of colpits osc. ?????????

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ahmed osama

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collipts oscillator

hi all

what are the best bjt for colpits osc. about 100 Mhz ???



does its Ft must be at least 10*100Mhz so about 1Ghz

thx all
bye
 

colpits

Something like BFR90 would be a good choice:
**broken link removed**

And the 10x factor is explained, to some extend, here:
The highest achievable value of the fundamental frequency f * in the chaotic Colpitts oscillator is about 10 times less than the threshold frequency fT of the employed transistor. Chaotic oscillations are extremely sensitive to the parasitic CB capacitance of the transistor ...
Click to expand...
Cited from:
**broken link removed**

Regards,
IanP
 

Hi
I used q2n3904 for collipts osc at 27 and 100 MHz
It worked fine for both.

its Ft is about 400 MHz from simulation and lab test

Thanks
 

haytham said:
Hi
I used q2n3904 for collipts osc at 27 and 100 MHz
It worked fine for both.

its Ft is about 400 MHz from simulation and lab test

Thanks
Click to expand...

what sim s/w did u used??? and does it gives the same freq. as the equ. say ??

and what about the period of the sim. how many cycle u left the sim. to work ??
 

SA Ahmed
I used Orcad 9. It was about four years ago
I remeber that the difference was not large and it was depending mainly on your good estimation of circuit parasitics and use of good transistor model.

Thanks
 

SA Ahmed

rwhat about the period of the sim. how many cycle u left the sim. to work ?
Click to expand...
?

it depends on your machine.

You should sample at least 10 times more than your frequency to get moderate accuracy. the more points you will take, the more accuracy u will get.

Simualtion time should allow u to see about 20 ~ 50 cycle. Also, the more time you could allow will refelct in your accuracy of making FFT for examoke because it counts on number of points.

That's all

Thanks
Haytham
 

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