Wien Bridge Oscillator


Posted on Feb 6, 2014

It is one of the most popular type of oscillators used in audio and sub-audio frequency ranges (20 20 kHz). This type of oscillator is simple in design, compact in size, and remarkably stable in its frequency output. Furthermore, its output is relatively free from distortion and its fre ­quency can be varied easily. However, the maximum freque


Wien Bridge Oscillator
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ncy output of a typical Wien bridge oscillator is only about 1 MHz. This is also, in fact, a phase-shift oscillator. It employs two transistors, each producing a phase shift of 180 °, and thus producing a total phase-shift of 360 ° or 0 °. It is essentially a two-stage amplifier with an R-C bridge circuit. R-C bridge circuit (Wien bridge) is a lead-lag network. The phase`-shift across the network lags with increasing frequency and leads with decreasing frequency. By adding Wien-bridge feedback network, the oscillator becomes sensitive to a signal of only one particular frequency. This particular frequency is that at which Wien bridge is balanced and for which the phase shift is 0 °. If the Wien-bridge feedback network is not employed and output of transistor Q2 is fedback to transistor Q1 for providing regeneration re ­quired for producing oscillations, the transistor Q1 will amplify signals over a wide range of frequencies and thus direct coupling would result in poor frequency stability. Thus by em ­ploying Wien-bridge feedback network frequency stability is increased. This bridge circuit can be used as feedback network for an oscillator, provided that the phase shift through the amplifier is zero. This requisite condition is achieved by using a two stage amplifier, as illustrated in the figure. In this arrangement the output of the second stage is supplied back to the feedback network and the voltage across the parallel...




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