Capacitive diodes (varactor) - definition
Capacitive diodes (varactor) - definition
A Capacitive Diode (varactor) is a specialised semiconductor element whose main function is to vary capacitance depending on the voltage applied in the forward direction. Unlike standard Diodes, it is not used as a rectifier, but as a non-linear voltage-controlled capacitor. Its operation is based on changing the width of the depleted layer of the p-n junction, which acts as the dielectric of the capacitor.
As the breakdown voltage increases, the thickness of the depleted region increases, leading to a decrease in the capacitance of the junction. This phenomenon is used in electronic circuits for precise frequency control, modulation and tuning of resonant circuits. The capacitive characteristics of the varactor are non-linear, which allows dynamic tuning of the parameters of filters, generators and phase shifters in real time.
Varactors are widely used in high-frequency technology, especially in RF and microwave circuits, where their small size and high speed of response to voltage changes allow applications in modern communication systems. A suitably designed semiconductor structure and doping process influence the range of adjustable capacitance, loss and parameter stability as a function of temperature.
Due to its operation in the inverting state, the capacitive diode is characterised by a very low leakage current and high input impedance, which makes it useful in high Q systems. Typical materials used in the manufacture of varactors are silicon and gallium arsenide, which enable a wide operating bandwidth and low dielectric losses.
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