Talk:Wien bridge oscillator

message: Need to add a schematic (or several) -- I'll get to it shortly Madhu 03:23, 21 February 2005 (UTC)
thread_title:  Schematic 

message: the link to the other schematic, supposedly in spanish, is broken.  —Preceding unsigned comment added by 172.213.91.54 (talk) 20:16, 14 April 2008 (UTC)
thread_title:  Link broken 

message: I think the explanation of the cause of the nonlinear resistance of the light bulb is misleading.  The actual cause of the nonlinearity is that the power dissipation in the filament is proportional to the square of the current P = i2R.  I would think that the large nonlinear increase in power radiated away from the filament with temperature due to the Stefan-Boltzman law would tend to reduce the temperature rise of the filament, thus reducing the nonlinearity.  --ChetvornoTALK 17:30, 10 July 2009 (UTC)
replies: text: All you need to make a sine wave are an LC and an excitation source.  If you solved a few differential equations you would discover sinusoids are very common.  Tape an LED to a bicycle wheel and watch it's locus as the wheel rolls - another sinusoid!  Zen-in (talk) 05:31, 29 July 2011 (UTC)
replies: text: Well, LC oscillator is clear but RC one is the problem. The big question is (was:), "How does a sine wave conceive in the humble RC circuit?" Differential equations will show sinusoids in detail but will not answer this question. The LED example is very attractive; I will carry out it to explain to my grandson what a sinusoide is:) Circuit dreamer (talk, contribs, email) 06:16, 29 July 2011 (UTC)
replies: text: In actual fact the led on a bicycle wheel will trace out a curate cycloid not a sinusoidal curve. Dmcq (talk) 16:49, 5 August 2011 (UTC)

text: A sine wave is the time-wise representation of a single frequency.  If you just have one RC you can only have one frequency.   Another question though is: If you haven't been able to grasp this basic concept then why are you editing this page?  Zen-in (talk) 16:38, 30 July 2011 (UTC)
replies: text: I have begun editing this page to find out the answer to this basic question:) And as you can see, I have managed to find it... The next question is, "Why does the circuit oscillate exactly at the Wien network resonant frequency? Is this really true?" If you (and Grlx) can, help me to find the answer. Circuit dreamer (talk, contribs, email) 21:21, 30 July 2011 (UTC)
replies: text:  Adding your WP:OR damages the article. Editing an article is not an opportunity to find answers; editing an articles requires consulting actual sources -- not one's own thoughts about the material or some blogger's ramblings. I don't have the time to fix this. Glrx (talk) 23:19, 30 July 2011 (UTC)
replies: text: Oh, but this was only a joke! Can you joke at all? Otherwise the topic is extremely serious and difficult for understanding. Circuit dreamer (talk, contribs, email) 04:19, 31 July 2011 (UTC)

text: Just revert C-F's edits.  There's no point in trying to edit what he has written.  We aren't his secretaries.  Zen-in (talk) 05:09, 31 July 2011 (UTC)
replies: text: The sorry fact that you cannot understand the simple truth about this clever circuit does not mean that it should be removed. Circuit dreamer (talk, contribs, email) 06:42, 31 July 2011 (UTC)
thread_title: Is explanation of operation of light bulb gain control correct?

message: ==== Some intuitive explanations ====
(copied from Electronic oscillator talk page)
... I will add to this discussion all RC oscillators (e.g., Wien bridge) that are a big challenge for human imagination. Why? Just because it is too hard for a mere mortal:) to imagine how the humble RC circuit can produce sine wave, how it can act as a "resonator" at all. Three years ago I managed to reveal how the more sophisticated LC circuit does this magic. Then I began thinking about how the humbler RC circuit could do it... and this was a big challenge for my imagination. Here are my intuitive achievements about the most general (philosophical:) idea behind RC oscillators. I have used, as usual, a figurative and colorful language to picture the circuit operation.
RC oscillators stay between relaxation and harmonic (LC) oscillators; they possess properties from the both. Like relaxation oscillators, they have only one storing element (capacitor) that continuously charges and discharges; it stores only one kind of energy (electric) that is wasted. Like LC oscillators, the storing element is connected in a positive feedback loop to sustain the oscillations; they produce "rounded", "smooth", sine waves... Let's see why and how.
Simply speaking, both the relaxation and RC oscillator consist of a voltage source (an amplifier) driving a capacitor through a resistor. To make the voltage across the capacitor wiggle, this source has somehow to change its polarity at the peaks of the halfwaves.
*In a relaxation oscillator, the amplifier output voltage stays constant (maximum or minimum, at one of the supply rails) until the capacitor charges/discharges. When voltage drop across the capacitor reaches the peak, the amplifier switches sharply (helped by the accelerating positive feedback) this voltage from the current to the other rail. As a result of this voltage jump, the shape of the relaxation oscillation is peaked, angular, not sine...
*In an RC oscillator (Wien bridge oscillator is a good example), the storing element (the grounded capacitor in the figure on the right) is connected in the positive feedback loop. (IMO) the loop gain has to be close to but yet a little more than unity. At these conditions, the amplifier output voltage is constantly a little higher than the voltage drop across the capacitor and the latter continuously charges. The capacitor voltage tries to reach the amplifier voltage that continuously shuns up because of the positive feedback. Figuratively speaking, the capacitor is "self-charging"; it "pulls up" itself (with the help of the supplied amplifier) like Baron Münchhausen escaping from a swamp by pulling himself up by his own hair:) If the loop gain was exactly unity, the amplifier output voltage would be equal to the voltage drop across the capacitor... no current, no voltage change, no wave... Another impressive analogy is a cage equipped with "antiweight". Imagine you are in the cage but some "joker" has increased slightly the antiweight and, of course, loosed the brakes:) As a result, to your great surprise, you will begin lift up just like the voltage across the capacitor... If the antiweight was equal to the cage weight, you will stay immovable.
When the capacitor voltage approaches the positive supply rail, the amplifier begins saturating; the loop gain begins decreasing and the voltage change looses its nerve. Finally, at the top of the halfwave, the amplifier does not amplify at all and the voltage stops changing; thus the upper sine peak. Now the grounded capacitor begins discharging through the parallel connected resistor (note there is no charging current from the amplifier output since the upper capacitor impedes it). The positive feedback helps this process as above (now the joker has decreased slightly the antiweight and you travel down:) Its voltage begins decreasing trying to reach the amplifier voltage that continuously shuns down. When the capacitor voltage approaches the negative rail, the amplifier begins saturating; the loop gain begins decreasing and the voltage slows its change. At the bottom of the halfwave, the amplifier does not amplify and the voltage stops changing; thus the bottom sine peak.
As a final conclusion, RC oscillations arise because of the slight positive feedback with dynamic loop gain (between peaks it is bigger than one; at the peaks it is exactly one). The shape of an RC oscillation is smooth (sinusoidal) since at the peaks of the halfwaves the amplifier output is saturated and does not change its voltage (just like an LC oscillator).
These were only my insights. I would be glad if you share and enrich them... Circuit dreamer (talk, contribs, email) 20:22, 28 July 2011 (UTC)
replies: text: All you need to make a sine wave are an LC and an excitation source.  If you solved a few differential equations you would discover sinusoids are very common.  Tape an LED to a bicycle wheel and watch it's locus as the wheel rolls - another sinusoid!  Zen-in (talk) 05:31, 29 July 2011 (UTC)
replies: text: Well, LC oscillator is clear but RC one is the problem. The big question is (was:), "How does a sine wave conceive in the humble RC circuit?" Differential equations will show sinusoids in detail but will not answer this question. The LED example is very attractive; I will carry out it to explain to my grandson what a sinusoide is:) Circuit dreamer (talk, contribs, email) 06:16, 29 July 2011 (UTC)
replies: text: In actual fact the led on a bicycle wheel will trace out a curate cycloid not a sinusoidal curve. Dmcq (talk) 16:49, 5 August 2011 (UTC)

text: A sine wave is the time-wise representation of a single frequency.  If you just have one RC you can only have one frequency.   Another question though is: If you haven't been able to grasp this basic concept then why are you editing this page?  Zen-in (talk) 16:38, 30 July 2011 (UTC)
replies: text: I have begun editing this page to find out the answer to this basic question:) And as you can see, I have managed to find it... The next question is, "Why does the circuit oscillate exactly at the Wien network resonant frequency? Is this really true?" If you (and Grlx) can, help me to find the answer. Circuit dreamer (talk, contribs, email) 21:21, 30 July 2011 (UTC)
replies: text:  Adding your WP:OR damages the article. Editing an article is not an opportunity to find answers; editing an articles requires consulting actual sources -- not one's own thoughts about the material or some blogger's ramblings. I don't have the time to fix this. Glrx (talk) 23:19, 30 July 2011 (UTC)
replies: text: Oh, but this was only a joke! Can you joke at all? Otherwise the topic is extremely serious and difficult for understanding. Circuit dreamer (talk, contribs, email) 04:19, 31 July 2011 (UTC)

text: Just revert C-F's edits.  There's no point in trying to edit what he has written.  We aren't his secretaries.  Zen-in (talk) 05:09, 31 July 2011 (UTC)
replies: text: The sorry fact that you cannot understand the simple truth about this clever circuit does not mean that it should be removed. Circuit dreamer (talk, contribs, email) 06:42, 31 July 2011 (UTC)
thread_title:  How do RC oscillators produce sine wave? 

message: (copied from Electronic oscillator talk page)
... I will add to this discussion all RC oscillators (e.g., Wien bridge) that are a big challenge for human imagination. Why? Just because it is too hard for a mere mortal:) to imagine how the humble RC circuit can produce sine wave, how it can act as a "resonator" at all. Three years ago I managed to reveal how the more sophisticated LC circuit does this magic. Then I began thinking about how the humbler RC circuit could do it... and this was a big challenge for my imagination. Here are my intuitive achievements about the most general (philosophical:) idea behind RC oscillators. I have used, as usual, a figurative and colorful language to picture the circuit operation.
RC oscillators stay between relaxation and harmonic (LC) oscillators; they possess properties from the both. Like relaxation oscillators, they have only one storing element (capacitor) that continuously charges and discharges; it stores only one kind of energy (electric) that is wasted. Like LC oscillators, the storing element is connected in a positive feedback loop to sustain the oscillations; they produce "rounded", "smooth", sine waves... Let's see why and how.
Simply speaking, both the relaxation and RC oscillator consist of a voltage source (an amplifier) driving a capacitor through a resistor. To make the voltage across the capacitor wiggle, this source has somehow to change its polarity at the peaks of the halfwaves.
*In a relaxation oscillator, the amplifier output voltage stays constant (maximum or minimum, at one of the supply rails) until the capacitor charges/discharges. When voltage drop across the capacitor reaches the peak, the amplifier switches sharply (helped by the accelerating positive feedback) this voltage from the current to the other rail. As a result of this voltage jump, the shape of the relaxation oscillation is peaked, angular, not sine...
*In an RC oscillator (Wien bridge oscillator is a good example), the storing element (the grounded capacitor in the figure on the right) is connected in the positive feedback loop. (IMO) the loop gain has to be close to but yet a little more than unity. At these conditions, the amplifier output voltage is constantly a little higher than the voltage drop across the capacitor and the latter continuously charges. The capacitor voltage tries to reach the amplifier voltage that continuously shuns up because of the positive feedback. Figuratively speaking, the capacitor is "self-charging"; it "pulls up" itself (with the help of the supplied amplifier) like Baron Münchhausen escaping from a swamp by pulling himself up by his own hair:) If the loop gain was exactly unity, the amplifier output voltage would be equal to the voltage drop across the capacitor... no current, no voltage change, no wave... Another impressive analogy is a cage equipped with "antiweight". Imagine you are in the cage but some "joker" has increased slightly the antiweight and, of course, loosed the brakes:) As a result, to your great surprise, you will begin lift up just like the voltage across the capacitor... If the antiweight was equal to the cage weight, you will stay immovable.
When the capacitor voltage approaches the positive supply rail, the amplifier begins saturating; the loop gain begins decreasing and the voltage change looses its nerve. Finally, at the top of the halfwave, the amplifier does not amplify at all and the voltage stops changing; thus the upper sine peak. Now the grounded capacitor begins discharging through the parallel connected resistor (note there is no charging current from the amplifier output since the upper capacitor impedes it). The positive feedback helps this process as above (now the joker has decreased slightly the antiweight and you travel down:) Its voltage begins decreasing trying to reach the amplifier voltage that continuously shuns down. When the capacitor voltage approaches the negative rail, the amplifier begins saturating; the loop gain begins decreasing and the voltage slows its change. At the bottom of the halfwave, the amplifier does not amplify and the voltage stops changing; thus the bottom sine peak.
As a final conclusion, RC oscillations arise because of the slight positive feedback with dynamic loop gain (between peaks it is bigger than one; at the peaks it is exactly one). The shape of an RC oscillation is smooth (sinusoidal) since at the peaks of the halfwaves the amplifier output is saturated and does not change its voltage (just like an LC oscillator).
These were only my insights. I would be glad if you share and enrich them... Circuit dreamer (talk, contribs, email) 20:22, 28 July 2011 (UTC)
replies: text: All you need to make a sine wave are an LC and an excitation source.  If you solved a few differential equations you would discover sinusoids are very common.  Tape an LED to a bicycle wheel and watch it's locus as the wheel rolls - another sinusoid!  Zen-in (talk) 05:31, 29 July 2011 (UTC)
replies: text: Well, LC oscillator is clear but RC one is the problem. The big question is (was:), "How does a sine wave conceive in the humble RC circuit?" Differential equations will show sinusoids in detail but will not answer this question. The LED example is very attractive; I will carry out it to explain to my grandson what a sinusoide is:) Circuit dreamer (talk, contribs, email) 06:16, 29 July 2011 (UTC)
replies: text: In actual fact the led on a bicycle wheel will trace out a curate cycloid not a sinusoidal curve. Dmcq (talk) 16:49, 5 August 2011 (UTC)

text: A sine wave is the time-wise representation of a single frequency.  If you just have one RC you can only have one frequency.   Another question though is: If you haven't been able to grasp this basic concept then why are you editing this page?  Zen-in (talk) 16:38, 30 July 2011 (UTC)
replies: text: I have begun editing this page to find out the answer to this basic question:) And as you can see, I have managed to find it... The next question is, "Why does the circuit oscillate exactly at the Wien network resonant frequency? Is this really true?" If you (and Grlx) can, help me to find the answer. Circuit dreamer (talk, contribs, email) 21:21, 30 July 2011 (UTC)
replies: text:  Adding your WP:OR damages the article. Editing an article is not an opportunity to find answers; editing an articles requires consulting actual sources -- not one's own thoughts about the material or some blogger's ramblings. I don't have the time to fix this. Glrx (talk) 23:19, 30 July 2011 (UTC)
replies: text: Oh, but this was only a joke! Can you joke at all? Otherwise the topic is extremely serious and difficult for understanding. Circuit dreamer (talk, contribs, email) 04:19, 31 July 2011 (UTC)

text: Just revert C-F's edits.  There's no point in trying to edit what he has written.  We aren't his secretaries.  Zen-in (talk) 05:09, 31 July 2011 (UTC)
replies: text: The sorry fact that you cannot understand the simple truth about this clever circuit does not mean that it should be removed. Circuit dreamer (talk, contribs, email) 06:42, 31 July 2011 (UTC)
thread_title:  Some intuitive explanations 

message: I have extracted the "philosophical" text below from a TI material. There are valuable thoughts there that can be useful for this page. See for example the third alternative: "(iii) The system stays linear and reverses direction, heading for the opposite power rail. This produces a sine-wave oscillator." Please, discuss why "the system reverses direction". Circuit dreamer (talk, contribs, email) 11:01, 31 July 2011 (UTC)
thread_title:  Interesting TI material 

message: This is essentially Schilling and Belove's analysis, if I take out the word "non-linear" in the description of the negative feedback.  Constant314 (talk) 04:35, 18 August 2011 (UTC)
thread_title:  Background:High-gain differential amplifier with positive feedback 

message: It could still use some references, but it looks essentially correct.Constant314 (talk) 13:33, 19 August 2011 (UTC)
replies: text: Yes, it is still disputed. Lead paragraph is wrong (in more ways that 2 != 3). Section omits goals of frequency stability, low distortion, (wide freq range, advantage of RC over LC at audio,) and operation of the lamp. (CD demoted amp control as a minor feature, but it's really the major idea; without the lamp, the oscillator is poor.) Vague info about why circuit oscillates; if you know Barkhausen you get it; if you don't.... Omits the sharp phase transfer. No direct mention of null/notch oscillator (compare twin-T). My intention with the hat note was to delete the whole section. You've been rescuing the diff amp portion. I have trouble with the "two partial feedbacks"; I haven't checked your reference; CD quoted TI for the two feedbacks; it is not a great explanation (if such a view is useful or important, then where's Mason's gain formula with the two loops?); two feedbacks is a disguised version of low gain w/positive feedback explanation. The low gain single ended explanation is the simple RC oscillator and not the WBO. I deleted the negative resistance version. Glrx (talk) 15:50, 19 August 2011 (UTC)
replies: text: It would be fine with me to remove the second explanation.  The first description includes the op-amp's gain explicitly where as the second explanation just absorbs the opamp gain into the "low gain amplifier".Constant314 (talk) 18:57, 19 August 2011 (UTC)
replies: text: On second thought, the low gain amplifier approach is useful precisly because it hides the op-amp gain, leaving a second order system that is easy to apply root locus analysis to the poles.Constant314 (talk) 18:01, 21 August 2011 (UTC)

text: Regarding Barkhausen.  I believe it is usually correct, but sometimes it indicates that a system is unstable when it is not.  In that case you can apply the Nyquist criteria which is both necessary and sufficient to predict instability.Constant314 (talk) 18:01, 21 August 2011 (UTC)
thread_title:  Is factual accuracy backgroud section still disputed? 

message: Barkhausen stability criterion has an orphan ref to 
*. URL leads to 56MB conference proceedings download.
Criticizes some textbooks. Article states that steady state oscillators must be nonlinear; linear oscillator is a fiction. Article talks about shifting poles. States an energy balance for the wandering poles. The ref does a classification of oscillators and uses WBO. Make WBO with nonlinear amp a Class I; with nonlinear diode feedback a Class II. Claims that when the ideal diff amp is replaced with a real op amp, the nonlinearities of the real op amp dominate the diode circuit. He cites to Strauss, but does not really address the Meacham/Hewlett bridge design.
I'd criticize the ref on a number of issues. Glrx (talk) 17:37, 25 August 2011 (UTC)
thread_title:  Oscillator classification 

message: Is there a standard English pronunciation for this oscillator? Properly, it should be a "Veen" from the German, but I've heard it as "Wine" and "Ween". Glrx (talk) 15:36, 26 August 2011 (UTC)
thread_title:  Pronunciation 

message: There are some new schematic on commons (see Hungarian version)hu:Wien-hidas oszcillátor  --Duhos (talk) 14:21, 24 January 2012 (UTC)
replies: text: There was also a simple schematic in the article. --Netpilots (talk) 01:57, 5 March 2015 (UTC)
thread_title:  Schematic 

message: 1. "Meacham proposed a bridge oscillator to address those problems."
This sentence starts the section and it's disconnected. It should say what it's referring to. I assume it refers to the information contained in the the previous section.
2. "LC versus RC oscillator".
I don't see any inductor anywhere.
3. "The Wien bridge does not require equal values of R or C. At some frequency, the reactance of the series R2–C2 arm will be an exact multiple of the shunt R1–C1 arm. If the two R3 and R4 arms are adjusted to the same ratio, then the bridge is balanced."
It's impractical to expect the reader to follow without a schematic. There should be an image next to the text.
4. "Another analysis, with particular reference to frequency stability and selectivity, will be found in Strauss (1970, p. 671) and Hamilton (2003, p. 449)."
Why "will" and not "is"?
5. "-1.5±(sqrt(5)/2)"
This should be replaced by the actual equation (I'm not sure how to do this).
6. It would be nice to have an introductory sentence to explain what H(s) is.
7. The circuit talks about positive feedback with the R1-C1-R2-C2 components. I seem to understand negative feedback is also introduced with Rb-Rf. What is positive and negative about it? I know feedback has somewhat variable if not vague and standard definitions for positive and negative.
8. Reference "Meacham, L. A. (October 1938), "The Bridge Stabilized Oscillator" (PDF), Bell System Technical Journal 17 (4): 574–591, doi:10.1002/j.1538-7305.1938.tb00799.x. Frequency and amplitude stabilization of an oscillator with no tube overloading. Uses tungsten lamp to balance bridge." is pointing to nowhere.
ICE77 (talk) 19:12, 31 July 2015 (UTC)
thread_title:  Questions and comments 

message: The diode-limited schematic does not have enough low-level gain. At low amplitude, the gain will be about 2 (40k/20k), but the bridge needs at least 3. At high amplitude, the gain falls to about 1.5 (30k/20k). Taking the output at the 10k resistor is also a little odd. Glrx (talk) 16:24, 25 September 2015 (UTC)
replies: text: The output is odd, but that's the way it was in the book.  Just to vet it, I did run a SPICE sim and taking the output as shown has a little less distortion than taking it directly from the opamp, so I guess the source knew what he was doing.  The low level gain with the 1K pot all the way to one side is 1 + (30.1 + 10 +1)/19.8 = 3.076, just barely enough.  Constant314 (talk) 21:11, 25 September 2015 (UTC)
replies: text:  Ooops. My mistake for NI gain.... Glrx (talk) 22:16, 25 September 2015 (UTC)
thread_title:  Not enough low-level gain 

message: I do not think that there is anything incorrect in this section and indeed I derive the same result.  I have no intetion of deleting it.  But, there is no reference anywhere in the article for the operation of the Wien bridge oscillator when R1 ≠ R2 or C1 ≠ C2.  I thought the preceeding section attributed to Schilling and Belove covered it, but I checked; it turned out that they use the same R1=R2=R and C1=C2=C assumptions as everybody else.  I hope someone can find a reference.Constant314 (talk) 21:30, 27 September 2015 (UTC)
thread_title:  Frequency determining network section needs reference 

message: I hope someone can provide a reference.  I am working from memory.  I read somewhere that the Wien bridge oscillator has low phase noise and good frequency stability because the root locus plot crosses the imaginary axis at a right angle.  That means the frequency of oscillation isn't modulated by small perturbations of the gain.  Anybody got a reference? Constant314 (talk) 14:04, 10 October 2015 (UTC)
thread_title:  Root Locus and phase noise