![]() ![]() The RC network is connected in the positive feedback path of the amplifier and has zero phase shift a just one frequency. The other part, which forms the series and parallel combinations of R and C forms the feedback network and are fed back to the non-inverting input terminal (positive or regenerative feedback) via the RC Wien Bridge network and it is this positive feedback combination that gives rise to the oscillation. One part of the feedback signal is connected to the inverting input terminal (negative or degenerative feedback) via the resistor divider network of R1 and R2 which allows the amplifiers voltage gain to be adjusted within narrow limits. The output of the operational amplifier is fed back to both the inputs of the amplifier. ![]() The magnitude of the output voltage is therefore at its maximum and is equal to one third (1/3) of the input voltage as shown. The frequency value of the input waveform at which this happens is called the oscillators Resonant Frequency, ( ƒr).Īt this resonant frequency, the circuits reactance equals its resistance, that is: Xc = R, and the phase difference between the input and output equals zero degrees. So there must be a frequency point between these two extremes of C1 being open-circuited and C2 being short-circuited where the output voltage, V OUT reaches its maximum value. ![]() Likewise, at high frequencies, the reactance of the parallel capacitor, ( C2) becomes very low, so this parallel connected capacitor acts a bit like a short circuit across the output, so again there is no output signal. The above RC network consists of a series RC circuit connected to a parallel RC forming basically a High Pass Filter connected to a Low Pass Filter producing a very selective second-order frequency dependant Band Pass Filter with a high Q factor at the selected frequency, ƒr.Īt low frequencies the reactance of the series capacitor ( C1) is very high so acts a bit like an open circuit, blocking any input signal at Vin resulting in virtually no output signal, Vout. At the resonant frequency ƒr the phase shift is 0 o. The Wien Bridge Oscillator uses a feedback circuit consisting of a series RC circuit connected with a parallel RC of the same component values producing a phase delay or phase advance circuit depending upon the frequency. The Wien Bridge oscillator is a two-stage RC coupled amplifier circuit that has good stability at its resonant frequency, low distortion and is very easy to tune making it a popular circuit as an audio frequency oscillator but the phase shift of the output signal is considerably different from the previous phase shift RC Oscillator. The Wien Bridge Oscillator is so called because the circuit is based on a frequency-selective form of the Wheatstone bridge circuit. One of the simplest sine wave oscillators which uses a RC network in place of the conventional LC tuned tank circuit to produce a sinusoidal output waveform, is called a Wien Bridge Oscillator. In the RC Oscillator tutorial we saw that a number of resistors and capacitors can be connected together with an inverting amplifier to produce an oscillating circuit.
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