Varactor Diode: Know Definition, Working, Formula, Uses

Varactor Diode: Know Definition, Working, Formula, Uses

Varactor Diode

Varactor Diode allow you to select from various doping profiles, spanning all commonly used concentration profiles, from hyperabrupt, over abrupt to linear. The corresponding characteristic of the diode is calculated and displayed.

In practice, theoretical doping profiles as assumed by the simulation program can be obtained only with difficulty. Complicated diffusion processes cause non-constant concentration-dependent diffusion coefficients and therefore result in deviations from the ideal dopings. Diodes are usually manufactured with complex technologies such as multiple diffusion or multiple implantation.

Symbol of Varactor Diode:

The diagram below shows that the symbol for the varactor diode is identical to that of the PN-junction diode. A diode has two terminals: anode and cathode. The diode is at one end of the symbol, while the capacitor’s conducting plates are represented by two parallel lines on the other. The space between the plates reveals the dielectric.

Operation of Varactor Diode:

The varactor diode’s role is to store charges, hence it is always operated in reverse bias mode. When a forward bias voltage is supplied, electrical current flows. As a result, the depletion region diminishes, which is undesirable.

A p-n junction diode’s junction capacitance is inversely proportional to its depletion layer width. In other words, if the width of the depletion layer is reduced, the capacitance increases, and vice versa. So, if we want to raise a varactor diode’s capacitance, we should reduce the reverse bias voltage.

It causes the breadth of the depletion layer to shrink, resulting in increased capacitance. Similarly, raising reverse bias voltage should reduce capacitance. The ability to obtain multiple capacitance values simply by adjusting the voltage supplied is the main advantage of a varactor diode over a standard variable capacitor.

Notations Used In The Varactor Formula:

  • Cj represents the diode capacitance.
  • C represents the diode capacitance when the device is unbiased.
  • V represents the applied voltage.
  • Vb represents the barrier voltage at the junction.
  • m is the material-specific constant, K is a constant equal to one, and F is the highest operating frequency.
  • f represents the operational frequency.

Varactor Diode Characteristics:

Varactor diodes are typically operated under reverse bias conditions, so there is no conduction. They are voltage-controlled capacitors, often known as varicap diodes, however the term varactor is commonly used.

Variable Capacitance Characteristics:

Normal diodes exhibit variable capacitance, while varactor diodes are recommended for giving the necessary capacitance fluctuations. The diodes are specially designed and produced to allow for large capacitance variations across a wide range. Varactor diodes are classified according to the qualities of the diode junction.

Varactor Diode Applications:

The following sections describe some of the applications of varactor diodes.

  • They are used in RF design to adjust capacitance inside a circuit using control voltage. It gives them a unique capacity, which is why varactor diodes are employed in the radio frequency business.
    These diodes are utilized in a variety of circuits and have two major uses.
  • FR filters – Filters may be tuned using varactor diodes. Front-end receiver circuits may require tracking filters, which are enabled to track the frequency of incoming signals.
    Voltage-controlled oscillators (VCOs) are utilized in a variety of applications, with the most common being oscillators within a phase-locked loop. VCOs are found in practically every wireless receiver and radio.

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