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Forum: Analog Circuits How to adjust RC oscillator circuit frequency?


von Lernend B. (Company: KAI Electro Semiconductor Inc.) (lernend05)


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Hello folks,
Recently I am working on RC oscillator circuit according to here 
(source: 
https://www.kynix.com/Blog/What-are-Oscillator-Types-Example-with-Diagrams.html), 
but I had problems with adjusting frequency. I can adjust frequency but 
it effects amplitude too (amplitude is changing while adjusting 
frequency), how can i separate these two variables ? I mean, when I am 
adjusting frequency, I want to amplitude remains same, and also for 
amplitude too. By the way I am using this circuit: (Ignore the opamp 
circuit, it is converting sinusoidal wave into square wave.)

Any idea of it? Thank you in advance.

von Cartman (Guest)


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Thats quite easy.

Use a ceramic adjustment tool for the frequency and
another tool for the voltage.
Determine the correlation between frequency change and
voltage change vs. voltage control and frequency control.
With this you will be able to adjust your circuitry to
the final values in one step.

von Lothar M. (Company: Titel) (lkmiller) (Moderator)


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Lernend B. wrote:
> I can adjust frequency but it effects amplitude too (amplitude is changing
> while adjusting frequency), how can i separate these two variables ?
Simple answer: you can't.

Or a little bit longer: you can, but you must add much more parts into 
your schematic to keep the oscillator sinusodial AND to stabilize the 
amplitude of the output signal.
So the first step is: generate a sine signal.
Second step is:  stabilize it to a stable amplitude.
And the last step is: amplify it to the desired output swing.

Thats why real world signal generators are more expensive compared to 
some C, R and a transistor.

> Any idea of it?
Whats the actual problem?

: Edited by Moderator
von Lutz V. (lvw)


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Lernend B. wrote:
> Hello folks,
> Recently I am working on RC oscillator circuit according to here
> (source:
> 
https://www.kynix.com/Blog/What-are-Oscillator-Types-Example-with-Diagrams.html),
> but I had problems with adjusting frequency.
> ..........................
> Any idea of it? Thank you in advance.

I think, for a real helpful answer, we need some more information:

* What is the required tuning range (frequency)?
* What is the required amplitude range?
* Is it allowed to vary two components in parallel?
* Are you required to use the shown circuitry (phase shift principle 
with a BJT)?

You should know that there are many different and versatile oscillator 
circuits (more than mentioned in the referenced paper), which - probably 
- are more suitable for your needs....

: Edited by User

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