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What Is a Varactor Diode and Its Functionality?

Diodes are a staple of digital electronic circuits, serving to direct current in a single direction. This is done through a low resistance being implemented in one direction, while a high resistance deters flow in the other. In a forward bias diode, the polarity of the external voltage will oppose the built-in potential, causing current to flow through the p-n junction. However, some diodes will have an external voltage that is of the same polarity as the built-in potential, blocking the flow of current as per the reverse bias phenomenon. There are various types of diodes available on the market, each varying in their characteristics of voltage and current to accommodate different applications. Varactor diodes in particular are types that are known for their ability to take on the application of reverse voltages. As a diode type commonly found in various FR filters, parametric amplification circuits, and other assemblies, it can be beneficial to have a better understanding of its design.

 While most diodes are not very capable of handling reverse bias conditions, varactor diodes are a specialized classification that are designed for reverse voltages. When implemented within an assembly, the character diode varies capacitance values, earning it the nickname “volt cap.” As transition characteristics are very important for the standard functionality of the diode, manufacturers enact a high level of control during the production phase.

Like many types of diodes, the varactor diode is a combination of a p- and n-type material. Gallium arsenide or silicon are both commonly used for the p- and n-type regions, though the choice may vary based on the application in question and its frequencies. While silicon is best suited for low frequencies, higher frequencies will demand a material such as gallium arsenide. Alongside the p- and n-type materials, the varactor diode also contains a positive anode and a negative cathode.

Before one can understand the functionality of a varactor diode, they first must be familiar with capacitors. A capacitor is another common circuit element, and they serve to store electrical charges. With two parallel plates separated by a dielectric medium, energy can be stored. Generally, a capacitor’s capacitance value will be directly proportional to its area.

Varactor diodes are often separated from standard diodes in the fact that they store charges like a capacitor, rather than conduct them. This is achieved through their p- and n-type materials that serve as the conducting plates, and the dielectric is the region of depletion. To determine the applied reverse voltage, one can look at the increment or decrement value of the region of depletion. Furthermore, the region of depletion will increase or decrease alongside the applied reverse voltage value.

There are various beneficial qualities of varactor diodes, including their low noise, compact design, and reliability that surpass many other diode types. With their advantages, varactor diodes commonly find use as tuners and frequency modulators. If you have an application or operation that could benefit from the use of varactor diodes, we encourage you to begin the procurement process with AFR Enterprises.

AFR Enterprises is a leading supplier of varactor diodes, presenting customers access to a multitude of circuit elements and IT hardware that has been sourced from leading global manufacturers that we trust. With AS9120B, ISO 9001:2015, and FAA AC 0056B accreditation, we explore every avenue to guarantee top-quality parts that you can depend on with ease. As a part of our NO CHINA SOURCING pledge, all parts ship out alongside their applicable qualifying certifications and manufacturing trace documentation. Get in contact with a team member of ours today and see why customers continue to rely on AFR Enterprises for all their operational needs.


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October 18, 2021
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