wien bridge oscillator distorted output

Posted on Feb 6, 2014

try another op amp. I could be changes in the input bias current that is causing a strange voltage drop across the 10k resistors. The LM358 is not really a high quality op amp it`s the diodes in the feedback loop. that`s a poor choice of limiter for a sine wave oscillator. usually wien bridge oscillators use a slow nonlinear element for maintainin

wien bridge oscillator distorted output
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g a constant signal, such as an incandescent lamp or a fet driven by a rectified and filtered portion of the output signal. I have to agree that the main reason for the `hump` is because of the diodes. The diodes have a relatively sharp IV curve so although they do limit the gain, they do so very abruptly and this shows up as distortion on the output. This of course assumes that the frequency of operation is within the limit that the op amp can easily handle. First is to increase the output voltage so the hump isnt as significant relative to the total amplitude. This means increasing the gain and making sure the power supply voltage is high enough. Second, you can soften the two diode curves by placing a resistance in series with them. You then work the diodes plus series resistance against a bigger resistance value (bigger than 10k) so you still get automatic gain adjustment. Say you start with 20k in series with the diodes, then maybe 50k in parallel and adjust the impedance of the other two resistances in the negative feedback network to provide approximately the same gain (but maybe a bit higher as above). Once the diode curves are softened the gain change wont be as abrupt and should provide for a cleaner output. So really all you would be doing is placing a resistance in series with the two diodes, then adjusting the impedance of the other negative feedback elements (going higher) so they can still work effectively...

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