AN-112: Single Resistor Control Wien Bridge Oscillator Frequency
Frequency control can be added to the conventional Wien bridge circuit by adding an op amp inverter (A1 in the diagram). the low power OP-221 dual works well in this circuit. The center frequency is 1/R1C1 multiplied by variable term 1/√α. The inverter gain is 1/α where α is a nominally unity.
The center frequency is given by:
This circuit adds tuning capability to the Wien bridge Oscillator circuit.
Figure 1.
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