This invention relates to sinusoidal oscillators, and more particularly to a feedback-type oscillator employing a linear operational amplifier (op amp) connected in a unity-gain configuration.
Sinusoidal oscillators are basic building blocks in electronic equipments of all kinds. In the conventional feedback-type oscillator, positive feedback is provided to sustain oscillation through a frequency-determing r-c network such as a Wien bridge, and negative feedback is provided to control the gain of the op amp and adjusted so as to exactly make up for the loss of signal in the frequency-selective network, thus making overall loop gain equal 1. A thermistor or other voltage-sensitive non-linear attenuator is used in one of the feedback paths to stabilize the oscillator.
The main difficulty in designing an oscillator of the type described above to be variable in frequency is getting reasonably constant loop gain. To achieve fairly constant positive feedback over a wise frequency range usually requires either an extraordinarily sensitive gain-control system or an elaborate tuning scheme, requiring for example awkward dual ganged variable resistors or capacitors. In any case such an oscillator uses a large number of parts and may require delicate adjustment for optimum performance.