High Frequency Oscillators
High frequency oscillators (HFOs) are electronic devices that generate a continuous steady-state waveform at frequencies above a kilohertz. Typically, the frequencies of HF oscillators range from a few kilohertz up to a gigahertz or more. Such devices have been traditionally used in radios, television sets and other communication equipments like modems, but can also be used in instruments measuring electronic data, medical equipments for medical imaging and monitoring, digital signal processing (DSP) algorithms, microwave systems and others.
In electronics, the term oscillator is used to describe the device that generates a steady-state waveform at high frequencies. There are two types of oscillators: the transistor oscillator and the LC (inductance-capacitance) oscillator. The transistor oscillator uses transistors as active elements while the LC oscillator uses inductors and capacitors as passive elements.
The most important characteristic of an HFO is its frequency stability, which is usually measured with respect to a reference frequency such as a quartz crystal. Quartz crystals provide stability by storing energy and vibrating the crystal at a certain frequency. This vibration then acts as a frequency reference for the oscillator circuit since it is not affected by environmental influences such as temperature or supply voltage. Because of their storage ability and stability, these crystals are the most used components in digital and analog circuits.
The frequency of an oscillator is determined by adjusting the values of its components, mainly varactors (variable capacitors) or inductors, or by introducing feedback circuits. Negative feedback is usually used to reduce the oscillation frequency and positive feedback is used to increase it.
Low power applications usually require HF oscillators with low frequency stability, so a temperature-compensated oscillator can be used. These are circuits that are nearly constant over a wide temperature range as a result of special temperature compensation components such as thermistors.
For applications that require high frequency stability, such as frequency synthesizers and communications systems, crystal oscillators are used. These are circuits that use the quartz crystal to provide a precisely fixed frequency by using its physical characteristics. These oscillators are the most stable oscillators available, with an accuracy of around a few parts per million. This makes crystal oscillators the ideal choice for frequency sensitive electronics.
High frequency oscillators are a critical component in many electronic circuits. They are available in various forms and shapes, which makes them suitable for almost any application. The frequency stability and accuracy of the oscillator is an important factor in choosing the right device, and the desired frequency must be chosen to ensure that the oscillator meets the specific needs of the application.
