Attached file appears to be good, but after navigation I did not find it a lotI don't think there is a set ratio rule. You can see here which explains rather
well. The aim is an impedance transform, to get the impedance at the tap (low impedance) to become a
higher impedance at the top of C1 (connected to the base) for the frequency in question.
Depends on the gain of the transistor but generally you want C3 to swamp Cbe by factor of 10 since it changes the most with drive and temp. If you are going to load output at emitter then you want C2 to swamp out variation in load capacitance.
If you are AC grounding collector it is actually better to tie ground side of C2 to collector. You then don't go through the collector bypass cap.
With selected C2 & C3 then Cc is selected to maximize Q of tank for the given coil inductance/Q while maintaining enough loop gain for reliable startup.
(1) How much the ratio C2/C1 should be in order to start oscillations?
(2) If the output signal is taken from emitter through a suitable capacitor, how will be the feedback path to the base if the transistor?
(3) We all know that there is a stray capacitance came of external connections and the internal capacity of the transistor itself. If I use a 2n3904 transistor which has the following data:
...
My question is how much capacitance I should add to the series C1 and C2?
(4) Are there any effects from Cc cap on the oscillation frequency?
First comment: Operating the oscillator near transistor fT limit makes the oscillator calculation rather difficult and less intuitive. To understand the basic circuit relations, a medium frequency oscillator (e.g. 1 MHz) is better suited.
In a low and medium frequency oscillator, C2 is mainly determing the resonance frequency and C1 can be larger by a factor of 50 or 100. As in your circuit, Cc will be set to a large value that doesn't affect the oscillation frequency.
Besides C1 to C2 ratio, the characteristic impedance of the resonant circuit is the other parameter that can be varied. It should be considerably larger than the emitter follower output impedance as well as smaller than the base node load impedance.
1 - Why did you choose this ratio for C2/C1 = 0.5?
2 - How will feedback path from emitter to base?
3 - How was stray capacitance value calculated using the 2n3904 transistor datasheet?
4 - How the capacity divider works? i.e how it matching the impedances between low emitter and high base?
5-What relationship of loaded Q to this ratio (C2/C1)?
I do not want to understand howo scillator works , because dozens of books and hundreds of articles talking about it and I'm sick of them
I want to design one
I want clear answers and specific, and not the words of not fattening nor of hunger.
I think it is a common emitter, What is your guide on it common-base configuration?Are you asking about feedback in common-base configuration?
Good pointYour component values are small. Oscillations will be in the RF range. High internal capacitance in a transistor can limit high-frequency response. You must determine how to choose a transistor on that basis.
Can you help me or at least the the guideline method of calculating resistance through B-E of my circuit? Are you mean (1/gm) orA smaller capacitor exhibits greater voltage swings, with less current (as compared to a large capacitor). As to impedance matching between C1's reactance and resistance through B-E, they may or may not be equal at the oscillation frequency.
Of course it is Clapp typeNow for some other questions that at least one of your colleagues will ask:
'Is this a Colpitts type or a Clapp type?'
What is your answer?
No, it starts oscillating on its own reliably at power up.'Does your circuit start oscillating on its own reliably at power up, or does it need a kick, or shock, or some instigation?'
What is your answer?
According to multisim.10 simulator it takes less than 2ms.'How much time goes by until oscillations are continuous?'
What is your answer?
I'll leave BradtheRad respond to you.1.) Contrary to BradtheRad, I think your circuit is working in common collector (CC) configuration, and not in common base (CB) configuration.
Although your analysis was terrific and entered my brain, but I want you to know that you can use voltage-divider common emitter configuration which has a voltage gain much larger than 1. All you have to do is to designe this configuration and then add to it the resonance circuit with little of settings it will oscillate soon.2.) This leads to a certain problem during explanation of the oscillation condition which requires a loop gain equal to or slightly larger than unity. Normally, the gain of the active device is larger than unity and, thus, only a portion of the output signal is fed back in order to fulfill the loop gain requirement. However, here in CC configuration the transistor gain is slightly smaller than unity. Therefore, the signal that is fed back to the base must be larger than the signal at the emitter node. Therefore, something similar to "signal up-transformation" takes place: It is easy to recognize that the voltage at the top of the tank circuit (base node) will be larger than between both capacitors (which is the input of the feedback path). But this signal at the base node must be only slightly larger than at the emitter node (because the transistor gain is only slightly lower than unity).
Here you come back and say it is common base (CB) configuration as BradtheRad said!!!!!!4.) For a better understanding of the circuit's function it is sometimes convenient to use the "virtual ground" principle to modify the visual appearance of the circuit - without modifying its basic properties.
In this case, create a pure ac equivalent circuit by suppressing all elements (resistors) which are necessary to dc bias the transistor only but do not contribute to the oscillation frequency.
Then, ground the base and all elements which were connected to the base (and, of course, lift the ground at the collector). Now you have an equivalent circuit in CB configuration. Now you easily can identify the feedback path between collector and emitter and you can simulate the loop gain (watch the restrictions and requirements for loop gain measurements!).
Fortunately the text books don't need to be rewritten.In view of this I must concede that sammy555's configuration is a common collector.
Here you come back and say it is common base (CB) configuration as BradtheRad said!!!!!!
Fortunately the text books don't need to be rewritten.
In the circuit in post 6 the transistor is connected in common collector configuration, also known as emitter follower.
Input is to the base, output is from the emitter. There is feedback from emitter to base to make it oscillate.
Common emitter means input to base, output from collector.
Common base means input to emitter, output from collector.
In this circuit, the collector is connected directly to the battery. There is no output there.
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