Design of Rc Phase Shift Oscillator Using Fet
Welcome to EDAboard.com
Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
- Forums
- Analog Design
- Analog Circuit Design
You should upgrade or use an alternative browser.
FET Based Phase Shift Oscillator
- Thread starter Mehrzud
- Start date
- Status
- Not open for further replies.
- #1
I need help with design of a FET based wien bridge oscillator and simulate it using pspice. Any suggestion?
- #2
Hi
I need help with design of a FET based wien bridge oscillator and simulate it using pspice. Any suggestion?
Yes. My suggestion is that you specify your question a little bit deeper.
Just for a start, you can always search for it on the web.
Get some ideas what you're dealing with (what is it? how it's workin?). That's my suggestion 
- #3
Can anyone help with parameters and how to get the desired results?
f=1/(2*pi*R*C*√6)
|A|=gm*RL
RL=(RD*rd)/(RD+rd)
- #4
Your schematic does not show a WIEN bridge oscillator.
It is a phase shift oscillator based on high pass elements - not the best choice.
The gain of the FET stage has to be at least G=-29.
Moreover, the load must contain also the input impedance of the cR-stages.
It is better to use an opamp.
- #5
1) You are right. It's a phase shift oscillator.
2) I have no problem with the op-amp one, the problem here is how to see the oscillation results in Pspice by using FET?
- #6
1) You are right. It's a phase shift oscillator.
2) I have no problem with the op-amp one, the problem here is how to see the oscillation results in Pspice by using FET?
What do you mean with "...to see the .......results in PSpice by using FET " ??
If the circuit is designed well you´ll see the results. Or did I misunderstand the question ?
- #7
The first RC phase-shift stage is supposed to be driven from a very low impedance, not the high resistance of the 10k drain resistor.
The very high value 10k drain resistor must be loaded by a much higher impedance, not the low impedance of the phase-shift stages.
- #8
What do you mean with "...to see the .......results in PSpice by using FET " ??
If the circuit is designed well you´ll see the results. Or did I misunderstand the question ?
I mean what the value of elements should be to see the oscillation in time domain analysis of PSpice?(maybe a sine wave)
- #9
I don't think a single FET will work in that circuit because its voltage gain is too low and its output impedance is too high.
- #10
Would you please suggest some changes while the main idea is unchanged? I mean a phase shift oscillator with just a single FET even with imaginary parameters(high gain, low output impedance).
- #11
Practically, having a RC chain charateristic impedance >> 10k would allow circuit operation. This seems possible with a FETs input impedance, not considering the disadvantages of a high impedance network.
However, I suggest to take LvW's doubts seriously. I fear, the circuits performance would be rather bad anyway.
- #12
I mean a phase shift oscillator with just a single FET even with imaginary parameters(high gain, low output impedance).
So you intent to create a circuit with "imaginary" behaviour ? High gain and low output impedance with a single FET seems to violate the physics.
You have to decide what you really want.
I think, in principle it could be possible to work with the phase shift principle and a single FET - however the design is very critical because it contains several parameters which have large tolerances (Rout of the FET, Gm of the FET). And in addition, all CR stages should be designed with a high input impedance (C small and R high).
And dont forget: the gain of the FET has to be larger than G=-29 !!
- #13
Hi LvW
What values do you offer?
- #14
Hi LvW
What values do you offer?
It isn´t so easy ! The circuit has to be designed carefully. Analog circuit design means to select parts and values out of an unlimited number of alternatives.
In your case: Which Fet ? Which transconductance ? Which output resistance ? Which bias scheme ? ........?
I am really not in a position to "offer" you something. Try different alternatives and find out via simulation if you find one set of parameters which satisfiy you.
Is it really an absolute requirement to use only one single FET ?
- #15
Yes, Just a single FET, no matter the amplitude of oscillation or it's frequency just a single FET.
It's something like a competition between friends!:|
- #16
The phase-shift oscillator will not oscillate if the transistor's gain is less than 29.
- #17
- #18
- #19
- #20
By the way I used Orcad 16.0.1 and the result was nothing even when I changed the gm parameter of J110 PSpice model. but the EWB version worked fine just with a change in transistor!
- Status
- Not open for further replies.
Similar threads
- Forums
- Analog Design
- Analog Circuit Design
- This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
Design of Rc Phase Shift Oscillator Using Fet
Source: https://www.edaboard.com/threads/fet-based-phase-shift-oscillator.127179/
Post a Comment for "Design of Rc Phase Shift Oscillator Using Fet"