A Sine wave oscillator or a Wien bridge oscillator can be made variable by using two frequency determining parts that are varied simultaneously at high tracking accuracy.
High quality tracking potentiometers or variable capacitors are, however, expensive and difficult to obtain. To avoid having to use such a component, this oscillator was designed to operate with a single potentiometer.
The output frequency, fo, is calculated from fo = 1/(2pi.RC.rootAlpha) where R=Rz=Rz=R4=Rs, C=Ci:C2, and a=(P1+R1)R. Preset P2 allows adjusting the overall amplification such that the output signal has a reasonably stable amplitude (3.5 Vpp max.) over the entire frequency range.
The stated components allow the frequency to be adjusted between 350 Hz and 3.5 kHz. Other frequency ranges are readily defined with the aid of the above formula, although it should be noted that the upper frequency limit is determined mainly by the gain-bandwidth product of the opamps Type OP-221 and TLC272.
The current consumption of the oscillator depends on the type of opamp used. The following values were measured: OP-221: 0.5 mA; TLC272: 2mA; TLO72: 2mA. The construction of the oscillator should present very few problems since a readymade circuit board is available through our Readers Services.
Circuit diagram of a sine wave oscillator is shown below:
High quality tracking potentiometers or variable capacitors are, however, expensive and difficult to obtain. To avoid having to use such a component, this oscillator was designed to operate with a single potentiometer.
The output frequency, fo, is calculated from fo = 1/(2pi.RC.rootAlpha) where R=Rz=Rz=R4=Rs, C=Ci:C2, and a=(P1+R1)R. Preset P2 allows adjusting the overall amplification such that the output signal has a reasonably stable amplitude (3.5 Vpp max.) over the entire frequency range.
The stated components allow the frequency to be adjusted between 350 Hz and 3.5 kHz. Other frequency ranges are readily defined with the aid of the above formula, although it should be noted that the upper frequency limit is determined mainly by the gain-bandwidth product of the opamps Type OP-221 and TLC272.
The current consumption of the oscillator depends on the type of opamp used. The following values were measured: OP-221: 0.5 mA; TLC272: 2mA; TLO72: 2mA. The construction of the oscillator should present very few problems since a readymade circuit board is available through our Readers Services.
Circuit diagram of a sine wave oscillator is shown below:
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