Wien Bridge Oscillator with AGC and PLL

Gregory explains the circuit of a Wien Bridge Oscillator, that uses automatic gain control and a PLL architecture for amplitude and frequency stability.
The Wien bridge oscillator works by positive feedback excitation over a linear amplifier. Very high harmonic purity is accomplished by the passive feedback network and the linear operation.
Automatic gain control is need to sustain oscillation at a constant amplitude, preventing saturation or suppression of the signal.
The frequency stability of a normal Wien bridge oscillator is defined by the phase-slope of the feedback network. For this design, the desired output phase-noise improvement was accomplished by locking the linear oscillator in a PLL architecture.
Watch the video showing the circuit working:
kzbin.info/www/bejne/goaboYKPgdKnrtE
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[@AllElectronicsChannel]

Support the channel becoming a Patron patreon.com/allelectronics

[@andersonnobre5163]

Grande PROF. Eng.Greg!!!!Sou seu FÃ! !!!!THANK YOU for this GREAT electronic classes!

[@AllElectronicsChannel]

Thanks friend!!

[@soothcoder]

Very neat. PLL with no PLL chip. But you could always just make a oscillator where the crystal is in the feedback loop (Pierce oscillator). I was hoping you built it - would have been cool to see it run.

[@AllElectronicsChannel]

The reference oscillator is a Pierce one, using a CMOS gate!

How does this architecture compare with a crystal oscillator with a output filter to remove harmonics? Given the number of extra components needed for the wien-bridge, dual pll's, is the benefit in THD large enough to offset the extra complexity vs the simpler crystal oscillator plus filter?

[@AllElectronicsChannel]

It was a design exercise... probably a crystal oscillator followed by a crystal filter would generate an overall simpler and powerful architecture. I thinking on measuring the performance of this Wien bridge in the next video. What do you think ?

[@michelmorel9208]

I really like this lecture. Thank you very much. I would have appreciated seeing some scope shots to see the output sine wave and amplitude given a fixed supply voltage (because I built a standard Wien Bridge but my sine wave looked okay, but it was not a perfect sine wave so to compare really). Would it be difficult to include variable resistor to adjust the frequency without loosing the quality of the sine wave in this circuit or would this question require a complex setup? And when you spoke about locking phase, would this apply to a very low frequency such as 10Hz? Thank you again for teaching me about electronics.

[@AllElectronicsChannel]

I have another video showing it working, take a look! Frequency locking should work for lower frequencies...

[@iuri.castro]

Great content as always

[@_wave64_]

I'm sure there's a reason behind building this curcuit this way; on the other hand if I had to build a clean 100kHz source, I would definitely have made a shortcut and just cleared up the digital 100kHz output with a couple of high-Q tunable LC filters in order to get rid of the harmonic content

[@AllElectronicsChannel]

Yep!! This circuit was a design exercise, to play with raw analog stuff. Your design idea indeed is much better for real life usage!

[@sersheva]

Excellent video Gregory!, just a question, why after D1 rectifier is not necessary a capacitor to generate the dc proportional to AC signal? I understand that the complete job is done by the integrator with final LPF (R15 and C7). Maybe I am not understanding the principal job of that integrator.

[@AllElectronicsChannel]

Hi man! Thanksss. The capacitor is not needed because the pulsed (rectified waveform) already has the DC information. The integrator will average and extract it. You could argue that a capacitor would smoth the signal even more. True, but it also would add a pole to the loop, making it harder to tune/stabilize

[@sersheva]

@@AllElectronicsChannel thank you Gregory!! Nice explanation, I got it

[@vernonbosshard9317]

Do you have an image of the circuit for printing or downloading?

[@baghdadiabdellatif1581]

Great work. It seems that you have worked with Thales equipment

[@ruhnet]

Superb explanation! I have two questions: 1. you mention a couple times the oscillator going into saturation without proper amplitude limiting---that would effectively make the output a square wave as the op amp pushes the output up to the power rail voltage, correct? 2. What was the purpose originally of this design---or in other words what would be a practical use example where this particular oscillator design would be appropriate?

[@AllElectronicsChannel]

Thanks 1. Yep! 2. It was a design exercise. Analog circuit like these where found in THD meters.

[@artemdavinci]

Precession of the signal phase of any of the generators leads to an increase in the voltage at the output of the phase detector. How then is the frequency stabilized? I understand that it is necessary to implement a scheme in which the advance of the phase of the target signal would lead to a decrease in the voltage on the gate of the field-effect transistor. And if the phase of the target signal is delayed, it would lead to an increase in the voltage on the gate of the field-effect transistor.

[@AllElectronicsChannel]

The XOR generates exactly what you said. Vcc/2 when 90 degree aligned, higher or lower voltage if delayed or advanced.

[@artemdavinci]

@@AllElectronicsChannel Then there must be a constant 90 degree phase shift to allow the pulse width to shift after the XOR. Did I understand correctly?

[@leomartihart]

Gregory muy buen diseño! que span de frecuecia tiene este oscilador? saludos! Leo

[@AllElectronicsChannel]

Hi Leo! This is a single fixed frequency design.

[@igorb4650]

Cool video! Would be awesome to see result in real life

[@smartups1]

Can we set frequency 50 or 60 HZ ?

[@argcargv]

In theory you could by simply increasing the capacitance. You would need to increase the capacitance in the Wein bridge to about 2 microfarad. But you would need to be careful to select a good quality capacitor to get good linear behavior. You would need to use a film capacitor to get good linear behavior. For the frequency locking you would either need to use a lower frequency crystal or add more divider stages to get to the 50-60 hz reference. You probably would need to increase the capacitance used in the integrator for the AGC and AFC loops to keep things stable.

[@AllElectronicsChannel]

Nice!

[@vladimirfrolov1440]

My GOOD, author is genius. I will try to build a schema with real components.

[@AllElectronicsChannel]

🙏🏼🙏🏼😁😁

[@peatmoss4415]

Holy Mackerel !, that was so good! I'm just a hobbyist but I followed that just fine. I see where the light bulb is replaced by the parallel RC combination circuit in the middle of your diagram. I took inspiration from your video... kzbin.info/www/bejne/iKCkiXt-nc94ea8

[@AllElectronicsChannel]

Beautiful man!

[@rovhalgrencparselstedt8343]

That should not work, as a Wien Bridge Oscillator relies on the two rc networks to be identical for oscillation to occur, most say the two has to be within a few ohms or less for oscillation to occur, or atleast to keep any sorta phase noise/THD to a minimum. Also the WBO is one of, if not THE the most frequency stable sinewave oscillator out there, so having the pll is kinda redundant/pointless unless you're shooting for frequency standard like accuracy + you can achieve the amplitude stabilization with nothing more than a couple of diodes in series/parallel arrangement to set a voltage level where the gain becomes unity, no need for the entire peak detector and servo amp combo. The diode stabilization basically goes in place of the light bulb in a light buld stabilized WBO, while its not as stable as with a light bulb, its heaps cheaper and easier than trying to locate a suitable light bulb. The advantage and appeal of the WBO is that it is one of the few, if not THE only true self starting sinewave oscillator that only need one opamp. Most others need two or more and have nowhere near as low THD as most/all of those are just square wave oscillators with wave shaping circuits to approximate a sinewave, or resonant filters that ned a trigger signal to kickstart oscillation. Though the disadvantage and reason we rarely if ever see the WBO used in practice and instead live with slightly worse THD, or use some DDS based system is difficulty to vary the frequency as you need to change both resistors or capacitors in the positive feedback network simultanously, most commonly you change the capacitors with a multi position rotary/push button array switch as there are no dual gang potentiometers in existance that track closely enough to be useable in a WBO for continous frequency adjustment over any sorta range, so its really only implemented as a fine control of a few Hz or up to a few tens of Hz at most to keep a dual gang pot in a range where the tracking of the two is close enough to remain fairly identical.

[@AllElectronicsChannel]

And it works 😁

[@mr1enrollment]

the weakness is no actual circuit with waveforms,...

[@AllElectronicsChannel]

Have another video on the channel, take a look!

[@PsyPhi25]

I found your voice to be so harsh and irritating that I couldn't watch the video.

[@AllElectronicsChannel]

Thanks for loving the content!