In the digital electronic circuits, one of the basic essential devices is diodes. A diode consists of two terminals. These two terminals connected to the supply results in conduction. The way the terminal sare connected makes it classified as a forward-biased diode or reverse-biased diode. In forward bias, the diode allows the current to flow through it. During reverse bias, it blocks the flow of current. This reverse biasing is used in the case of the varactor diode. Based on the characteristics of voltage and current and the requirement the diodes are classified as Tunnel diode, Zener diode, and so on.
What is a Varactor Diode?
A diode that is known for the varying capacitance by the application of reverse voltages is defined as a varactor diode. Usually, diodes don’t go well during reverse bias conditions. But this varactor diode is a special classification of diode which operates well with reverse voltages.
Varactor Diode Basics
As the purpose of this diode is to vary the value of capacitance hence the other name for this diode is a volt cap or varicap. It has taken special care during manufacturing so that in comparison to the normal diodes it is known well for transition capacitance. The functionality of this diode is dependent on the voltage.
Like basic P-N junction diode, it is a combination of p-type and n-type material. based on the usage of the regions of p-type and n-type are made using gallium arsenide or silicon material. The usage of material can be decided based on the frequencies. If the diode has to operate for low frequencies silicon is preferred otherwise for higher frequency gallium arsenide is used.
In similar to P-N junction diode the varactor diode symbol consists of two terminals known as cathode and anode. Where anode is the positive side of the terminal and the cathode will be negative.
Varactor Diode Working
To understand the functionality of varactor diode one should know the capacitor.
- The capacitor is one of the electronic components. The purpose of it is to store the charge.
- It is designed by using two parallel plates that are conducting by nature and separated by the medium of the dielectric.
- The equation of the capacitance is
c = ε A / W
- From the above equation, it is determined that the area of the capacitor is directly proportional to the value of the capacitance.
Variable capacitance leads to the origination of the varactor diode. A varactor diode works as follows:
- A basic diode consists of p-type and n-type materials which are considered as the conducting plates.
- The region of depletion is considered to be the dielectric.
- The region of depletion is an important factor in determining the value of capacitance. Hence this concept is similar to that of a capacitor.
- The increment or decrement in the region of depletion is proportional to the applied reverse voltage.
- If the reverse voltage applied increases the region of depletion increases and vice-versa.
- Based on the applied values of reverse voltages the capacitance can be varied.
Here the varactor diode is designed such that to store the charges rather than to conduct. The conduction is possible by the application of forwarding voltages. Because of the application of the forward value of potential diminishes the region of depletion. This is the reason for varactor diodes are preferred working with reverse voltages. The change in the value of capacitance obtained is measure in terms of picofarads (pF).
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Varactor Diode Characteristics
The characteristics of varactor diodes are:
- The increase in reverse voltages increases the value of capacitance.
- The functionality of the diode is dependent on the reverse biased mode of the diode.
- These are available in compact sizes.
- The noise produced in this kind of diodes is less in comparison with the other diodes.
- These diodes are considered to be more reliable.
The varactor diode applications are:
- In the arena of RF design where the capacitance can be varied with the application o controlled voltage, these diodes are used.
- The applications like tuners in FR filters these diodes are preferred. These are placed at the front of the filters to detect the frequency obtained from the incoming signals.
- The voltage-controlled oscillator utilizes such kinds of varactor diode circuits.
- The parametric amplification circuits use these diodes.
Because of the varying capacitance technique involved in it based on certain values of voltages the highly applicable areas of such diodes are Tuners and frequency modulators. Even in the harmonics generation, these variable capacitance diodes are preferred.
Please refer to this link for Choosing resistor values for diodes.
1). What is the use of a varactor diode?
The concept of change in the capacitance due to the application of a variable range of voltages has been proven to be very beneficial in RF industries. In the applications of tuners, these diodes are used.
2). What is Schottky diode used for?
A Schottky diode is work son low voltages. It is also known as barrier diode. These kinds of diodes are used in mixers, radiofrequency applications as well as a rectifier in terms of power applications.
3). What is the difference between a Schottky diode and the normal diode?
A normal diode is nothing but a basic version of a P-N diode. The difference between a normal and the Schottky diode is the formation of the junction. In a normal diode, the junction is formed at P and N types semiconductor. The junction is formed at N-type and the metal plate for Schottky diodes.
4). Which diode is used in the rectifier?
By considering the type of rectification the diodes are chosen. For the rectification of power, the Schottky diodes or the power diodes are used. Whereas for the signals rectification purpose a signal diode or the small point contacting diodes are used.
5). Why the PIN diode is faster?
A PIN diode consists of p-type and n-type semiconductor material along with it a region called intrinsic is sandwiched between them. Although it is lower in terms of rectification the presence of this region makes the functionality of the PIN diode is faster.
A varactor diode is useful for real-time applications in digital electronics. Basing on the properties of the junction these varactor diodes are categorized. Further, many special types of diodes are used for various applications. Can you tell for tuning circuits which type of diode is used?