Limited Wien-Bridge Oscillator Amplitude

amplifieroscillator

I've already seen a similar question but the circuit was a little bit different.
My question is simple: how do I calculate the maximum amplitude of the oscillation at Vo, as a function of the resistors present here?

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Thank you all!

Best Answer

For such a diode-stabilized WIEN oscillator you always have various options. One option you have shown with two equal resistors R22 in the parallel path. Here is my approach for dimensioning the circuit and for finding the output amplitude:

1.) For a safe start of oscillation we require (for example): (1+R22/R1)=3.2 with R22/R1=2.2

2.) During oscillations we have (Rd=statice diode resistance): [(R22+Rd)||R22]/R1=2

3.) From both equations we can eliminate R22 - and after some manipulations we get: Rd=1.98R1.

4.) Selecting R1=1kohm we have R22=2.2kohm and Rd=1.98kOhm

5.) Using a typical diode characteristic we find for Rd=19.8kohm a value of Vd=419mV and a current Id=0.02115mA.

6.) These values (Vd and Id) are the maximum values (ud,max and id,max) for the diode during the oscillation amplitude. The corresponding voltage across the resistor R22 (which is in series with the diodes) is R22*id,max=2.2*0.02115=0.0465V.

7.) Therefore the total voltage across the series connection (diodes-R22) is 0.0465+0.419=465.5mV. This value is identical to Vout*2/3.

8.) Result (oscillator amplitude): Vout,max=(3/2)*465.5=698.3mV( Simulation result: Vout,max=730 mV)

UPDATE/EDIT: Due to a simple calculation error I have corrected the above given values.

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