# RC phase shift oscillator

Discussion in 'The Projects Forum' started by Thevenin's Planet, Jun 16, 2010.

1. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
1
Hello fellas!

#1. I would like to know does the amplitude of the noise of the resistors and/or transistor should be known in order that my biasing be correct?
#1a. What is a good bias point for a frequency for 2-7 hertz?
#2. Do the transistor must be in Satuation mode for the oscillation to start?
#3. The sign Beta is use for the selection filter,does that designate the attenuation and output voltage?
#4. How do I calculate for the correct filter components for a selection frequency of 2-6 hertz?

Apr 5, 2008
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Hello,

You could take a look in the attached PDF from TI.

Bertus

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3. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
1
The PDF is very informative but its not answering my questions.The PDF from TI concentrate on the Ic op amp, where I am concentrating on a single 2n4401 transitor as amplifier, but it hinted toward the question.Such as :The phase shift oscillator is very depend upon the change in phase at the point where the phase shift is 180 degree.How do I calculate the three RC section for components to acheive (1+AB)=1 or more?Also the PDF says the rate of change of the phase with frequency ,delta angle/delta omega determines the the frquency stability.I assuming this is determined by the components of the three RC sections.Finally,It states that after the equation has been satisfyied according to Barkhausen criterion there are three modes that can take place. The one I became concern about was ,nonlinearity in satuation or cut off can cause the system to becone stable and lock-up at the power rail.Do this action has something to do with the components also? Mostly the e-books teaches about one pole calculations but not three.

Last edited: Jun 19, 2010

Apr 20, 2004
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Apr 26, 2005
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6. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
1
this is a queation I can not find in the NEET PDF,How do I Thevinize the output Collector voltage and the Rc resistor? There is this equation,that gives Fc,cut-off frquency,1/2pi(Rc+RL)C3.The Rc and RL is addition which indicates they are in series.The C3 is the output capacitor to the Rload.It is always said that the Rc and RL is in parallel in the a.c. mode.This calculation seems to have a lot to do with the gain across the load ,which will be the RC filter.
Assuming that the the parameter of the transistor has a voltage divider for base input, collector resistor and Emitter resistor and a output resistor.The statement was said ,"looking into the collector on the left side of the output capacitor with Rc grounded thevinize.This was not shown but the equation was the results of this thevenized process,1/2pi(Rc+RL)C3.

Apr 26, 2005
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