# Wien Bridge Oscillator

Discussion in 'Electronics Homework Help' started by ahmed fathi, Nov 11, 2013.

1. ### ahmed fathi

10
0
Jun 25, 2013
Hello,

Does the oscillator (in the attachments) produce pure sine wave ?!

or Does the limiter circuit clip the output ?!

I couldn't understand the use of limter circuit or the difference between using a limiter circuit and using another op-amp with different Vcc & -Vcc for example if possible

I tried this circuit on proteus and it didn't work , but after some modifications to the connection of diodes and using a potentiometer as here

it gave sine wave for a range the Pot , and then became more squary for other ranges , I couldn't understand why either .

to summerize :: What is the exact effect of introducing the limiter ?!

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2. ### ahmed fathi

10
0
Jun 25, 2013
I reached some thing ... is the thing that happens that we determine the "MAXIMUM" Peak value for required sine wave for example , And then adjust the limiter circuit so that the gain below this value (Vy for example) makes AB Greater than one , while After this value makes AB Less than one ?!

and so , below this value the noise having the desired frequency gets enlarged , and its peak gets enlarged until peak reachs (Vy) then goes into the AB< 1 region so it tries to decay , hence entering the AB>1 region tries to increase and so on until saturation ?!

Is this plot correct ?!

http://i.imgur.com/JVucQma.png

3. ### duke37

5,364
772
Jan 9, 2011
A Wien bridge oscillator needs an amplifier with a gain of three. Less gain than this will not oscillate. More gain than this and the oscillation will grow until it is limited in some way.

The limiting will distort the sine wave so to get a good sine wave, the gain needs to be set just sufficient to oscillate with minimum limiting.

There must be limiting and many methods have been used to control gain, diode clipping, FET variable resistor, light bulb variable resistor. Usually sine purity is the objective rather than exact amplitude.