Electronics > Projects, Designs, and Technical Stuff

Analog circuit analysis discussion – Colpitts oscillator

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AnneRanch:
OK, gentlemen
apparently  my "spicy" initial comment did not take.

Please read my posts.
I have no issues with the circuit oscillating.

However I cannot keep up with "adjust this  and that" posts here, do my stuff and "honey-dooes".

I have modified , annotated the TI circuit to match the book and changed some values.
Attached.

Perhaps I need to post SPECIFIC questions to get the discussion going in direction I was initially after.

From the TI book -
they determine the ratio of C2 / C3 experimentally as .47
from that I get the real combined value of C2/C3  - standard Colpitts calculation for oscillator frequency


Then there is a lengthy calculation involving C1
They use the initial C2C3 /C2+C3 AKA standard frequency value....

My question is - where did the C1 calculation come from and WHAT is the function of C1?

Cheers












ledtester:

--- Quote from: AnneRanch on September 17, 2019, 05:54:03 pm ---Please read my posts.

--- End quote ---
We are reading your posts.


--- Quote ---Perhaps I need to post SPECIFIC questions to get the discussion going in direction I was initially after.

--- End quote ---

That's always a good thing to do on an internet forum.


--- Quote ---From the TI book -

--- End quote ---

What TI book???


--- Quote ---My question is - where did the C1 calculation come from and WHAT is the function of C1?

--- End quote ---

I don't see a C1 designation on anything you've posted in this thread.

AnneRanch:
My question is - where did the C1 calculation come from and WHAT is the function of C1?

Per TI
C1 is AC bypass of R2  C1 = 300 pf  - value chosen to avoid self resonant frequency near 90 MHz 

duak:
Curiouser & curiouser...  I'm also having trouble with the reference designators, the Spice model & your questions.  Is the schematic posted mayhaps not what is desired?

Also, the schematic looks oddly like a regenerative receiver. ie., antenna on the left, headphone on the right and a control that will vary emitter current.

MagicSmoker:
The OP doesn't deserve help, I've concluded. Not only because the questions asked are nonsense (re: the non-existent C1), but mainly because of this gem of a thread: https://www.eevblog.com/forum/repair/464-delayed-sweep-switch-worn-out/

Keep demanding we help you for free and see where that gets you.

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