What is a Low frequency oscillator?

A low frequency oscillator is a device that generates a relatively low frequency signal. The definition of the word "low frequency" itself varies depending on the field in which it is used, but the specifications of low frequency oscillators as commercially available equipment range from a few Hz to several hundred kHz. By using an oscillator circuit, it is possible to generate an AC signal with a specific frequency, and it generally plays the role of generating a reference signal in tests using frequency signals.

The principle of low frequency oscillators lies in the technology of generating stable frequency signals based on oscillation circuits. The commonly known Hartley-type and Colpitts-type oscillation circuits based on LC resonant circuits have wavelength restrictions, making it difficult to generate low-frequency waveforms. Therefore, low frequency oscillators use RC type (or CR type) oscillation circuits.

RC type oscillators include Wien bridge circuits, bridged T-type circuits, and state variable type circuits. Oscillation can be obtained in all of these by adjusting the amount of feedback of the amplifier. Among them, the Wien bridge circuit is very famous and widely used because it is a simple circuit and only requires one amplifier.

On the other hand, state variable type circuits are characterized by the ability to obtain a sine wave and two-phase output with lower distortion. A variable resistor or varicap (variable capacitor) may be used to control the frequency. Another example of a method for determining the frequency is step variable using fixed resistors and capacitors.

However, it is difficult to obtain a sine wave with a constant amplitude using only an RC oscillation circuit, so a device to control the amplitude is usually required. For example, there are methods to adjust the amount of feedback using elements such as light bulbs and thermistors whose resistance changes depending on the applied voltage, and methods to build an electronic circuit that detects the output voltage and adjusts the amount of feedback.

Application of Low frequency oscillator

The most common use of low-frequency oscillators is when analyzing the frequency characteristics of audio equipment. Electronic devices for communication using frequency signals almost always use high frequency (RF), and familiar low frequencies become sound waves, so acoustic devices are the mainstream circuits that use low frequency signals.

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