Wien Bridge Oscillator


Posted on Feb 5, 2014

This report entails the details on the principles and operation of an amplifier known as the Wien Bridge Oscillator. This oscillator was designed as part of a laboratory exercise, which unfortunately I did not get to participate in, therefore, this write will contain more discussion and thoughts on the theoretical aspect behind this model and vari


Wien Bridge Oscillator
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ous other types of amplifier models. It is crucial that when constructing an oscillator circuit that it consists of the following two sections: forward gain and positive( feedback= 1G †0. For) the essential oscillation to occur the Barkhausen criteria must be satisfied. A diagram of a basic oscillator circuit can be seen in figure 1. Figure 1 - Diagram including the negative feedback factor courtesy of Lab 3: Design, Construction & Test of a Variable Frequency Sinusoidal Oscillator instruction sheet Barkhausen criteria states that: The magnitude of the loop gain must be 1, the phase shift of the loop gain must be 0G‚ ° or 180G‚ ° plus an integer multiple of 360G‚ °. This criterion is necessary but not sufficient as it only deals with observation based upon a linear circuit. The conventional oscillator is created in order that its amplitude will be controlled when it starts oscillating. In order that a linear circuit may oscillate, the Barkhausen criteria must be met. That is, its loop phase must be one and the phase around the loop must be an integer multiple of 360 degrees. The linear oscillator theory does not explain how the oscillator starts up or the method of determining the amplitude as the linear oscillator can sustain any amplitude. The loop gain is initially larger than unity in practice. All circuits produce noise and a selected range of that noise will be close to the required frequency. The amplitude of the...




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