Wien bridge with smoothed sine wave output

LvW

Joined Jun 13, 2013
1,752
What is "poor bandwidth".
The filter has a slower rolloff than a Salen-Key filter but it has the same rolloff slope and high frequency attenuation.
I think, when we are speaking about the attenuation characteristics of a bandpass, the term "poor bandwidth" is identical to a pretty large bandwidth.

Regarding "high frequency attenuation": No, I think you are not correct.
Comparing two bandpass functions with Q=0.5 (maximum value for the circuit under discussion) and Q=10 we can easily convince ourself that with Q=10 we have app. 20..25dB more high frequency attenuation.

The following formula shows how the transfer functions magnitude depends on frequency (w) as well Q (center frequency at w=1 rad/s, gain normalized to unity):

|H(jw)|=1/SQRT[1+(w+(1/w))²Q²]
 
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LvW

Joined Jun 13, 2013
1,752
Wien Bridge - a crossing of the river Danube (Donau)?
If you think of the original meaning of "bridge" as a measurement circuit, as in Wheatstone bridge, then if one element is a thermistor or a filament lamp, or a pair of diodes, then no oscillator fits the original definition. You can't measure anything when your reference is variable!
If redrawn then the JLLH circuit can be just as much a bridge as all the others. There are now two op-amps, but both have the non-inverting input grounded, so it is essentially amplifying the difference between the two sides of the bridge.
You are, of course, correct about the poles - now that I have drawn the phase plot. I got confused by the zero at the origin (knew there was a zero somewhere).
Probably we should just call it a Wien oscillator?
OK - when I see the redrawn circuit I agree to you - it is possible to verify a "bridge" topology.
 
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