Phase Shift Oscillator Design

Thread Starter

artmaster547

Joined Jan 6, 2016
410
Hi
I have a design task of creating a Phase Shift Oscillator with a frequency of 5kHz, which I have done now (using a 3 stage RC ladder network and an inverting operation amplifier (with gain of 29)), as an extension to this I would like to remove unwanted frequencies from this circuit, which are visible when viewing a FFT (fast fourier transform) any tips/guidance/circuit topologies in order to add to this oscillator would be much appreciated .

I personally would also love to know how could I adjust the oscillation so that it occurred between two voltage this more out of curiosity
Thanks
Sunday
 

Jony130

Joined Feb 17, 2009
5,089
Do you have any circuit automatic gain control circuit for amplitude stabilization? And do you build this oscillator in real life?
 

Thread Starter

artmaster547

Joined Jan 6, 2016
410
Do you have any circuit automatic gain control circuit for amplitude stabilization? And do you build this oscillator in real life?
Hi at the moment this is in the simulation phase of design I am using a software called: LT Spice. That's interesting that you bring up automatic again control circuit I currently do not have this in my design will this assist in creating what I am after? Do you know any examples of topology for this?
 

Thread Starter

artmaster547

Joined Jan 6, 2016
410
may I ask exactly what I am doing wrong should I only have one voltage input at rails? I connect the negative rail to ground? Also still unsure where to progress from there in order to remove unwanted harmonics as they will still be present I understand? Is this what you mentioned about automatic gain? Do you use a JFET for this?
 

atferrari

Joined Jan 6, 2004
3,570
I think this is the correct file
Your power supplies are a weird "pulse" pulse instead of a steady DC value (the usual way). There is clipping as you were told already.

Some time ago when playing with different circuits I used this among many. Warning: I know there is a better (and proper way) to make the oscillator start in the simulator. I used brute force.

Just in case be sure you do not confuse circuits with op amps powered with dual supply (+/- voltages) and those powered with a single polarity supply as below. In this case, you set Vref = +V/2.
 

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Thread Starter

artmaster547

Joined Jan 6, 2016
410
Your power supplies are a weird "pulse" pulse instead of a steady DC value (the usual way). There is clipping as you were told already.

Some time ago when playing with different circuits I used this among many. Warning: I know there is a better (and proper way) to make the oscillator start in the simulator. I used brute force.

Just in case be sure you do not confuse circuits with op amps powered with dual supply (+/- voltages) and those powered with a single polarity supply as below. In this case, you set Vref = +V/2.
Hi thank you for providing this resource and some more explanation about supplies this aids a lot with my understanding. I understand the staggered approach of using buffers between the RC stages has an effect on the loading. Upon analysising the FFT of the this circuit I can see that that are still quite a lot of unwanted frequencies, in order to remove this should I be using filters or is there a more elegant approach I can be taken I have seen with Wein Bridge Circuits in a lot cases they employ diodes, or in others they employ JFet's but have not seen such additions to Phase Shift circuits which is why I'm having some difficulty
 

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Thread Starter

artmaster547

Joined Jan 6, 2016
410
Your power supplies are a weird "pulse" pulse instead of a steady DC value (the usual way). There is clipping as you were told already.

Some time ago when playing with different circuits I used this among many. Warning: I know there is a better (and proper way) to make the oscillator start in the simulator. I used brute force.

Just in case be sure you do not confuse circuits with op amps powered with dual supply (+/- voltages) and those powered with a single polarity supply as below. In this case, you set Vref = +V/2.
also what method would you use in order to make the oscillation occur between two voltages i.e. V max: 4V and V min: 1V
 

atferrari

Joined Jan 6, 2004
3,570
To shift the signal, (if the amplitude is already what you need) I would add a voltage in Vref that would bring it up as much as you need.

Anyway, as jony130 suggested, download that .pdf and try some of those circuits, if at all possible with the same pair of R & C values. LTSpice is good to become familiar with the basics.
 

Thread Starter

artmaster547

Joined Jan 6, 2016
410
To shift the signal, (if the amplitude is already what you need) I would add a voltage in Vref that would bring it up as much as you need.

Anyway, as jony130 suggested, download that .pdf and try some of those circuits, if at all possible with the same pair of R & C values. LTSpice is good to become familiar with the basics.
OK yes thank you, if I did need to change the amplitude however what should I do?
 
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