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Automatic Level Control of Wien Bridge oscillator

IP.com Disclosure Number: IPCOM000168511D
Original Publication Date: 2008-Mar-26
Included in the Prior Art Database: 2008-Mar-26

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In order to control the amplitude of an oscillator's output, there are different methods presently known. One of the methods is using a variable resistance to modify the negative feedback's factor of the oscillator and therefore the amplitude of the oscillation. This variable resistance is controlled by a comparator which compares the amplitude of the oscillator with a defined reference voltage. A disadvantage of this method is its limitation due to complexity. It is mostly appropriate for applications of low power fully integrated oscillators only. A second method is using two diodes in order to inject or retrieve the current of the oscillator's feedback loop. By adding a resistance between the negative and the positive feedback loop, a voltage difference is generated at the amplifier input which results in an increased or decreased amplitude at the oscillator's output. However, the additional resistance modifies the transfer function of RC elements and therefore changing the oscillation frequency and the loop gain. Another problem of this method is the start-up of the oscillator by a certain feedback factor equal 3, but due to complexity of the RC's function it is also difficult to start the oscillation with a positive feedback.