Characteristics of varactor diode

The below graph illustrates the relation between the magnitude of reverse bias voltage p-type and n-type layers of a varactor diode, and the magnitude of junction capacitance. They are voltage controlled capacitor and sometimes known as varicap diodes although the word varactor is widely used.

Variable capacitance effect is shown by a normal diode, but the varactor diode is preferred for providing required capacitance changes. The diodes are uniquely optimized and also manufactured such that they enable high range changes in the capacitance device. A varactor diode is categorized based on the properties of a diode junction.

The characteristics of the varactor diode have the following:
  • These diodes are significantly generated less noise compared to other diodes
  • The cost of these diodes is available at lower or more reliable also
  • These diodes are very small in size and very lightweight compared to other diodes
  • There is no use when it is operated in forwarding bias
  • In reverse bias mode, this diode enhanced the capacitance as shown in the graph below

Characteristics of a varactor diode

tunnel diode symbol

The tunnel diode is a highly doped semiconductor device, that is is highly conductive, heavily doped PN junction diode in which the current induces because of the tunneling. The symbol of a tunnel diode is shown in the figure given below. The n-type material emits the electrons and is named as the cathode while P-type material act as the electrons and hence it called as the anode.

tunnel diode symbol

Characteristics of tunnel diode

Forward bias condition:
Under the forward bias condition, the immediate conduction occurs in the diode because of heavily doped conduction happen in the diode. The current in the diode reached the maximum current that diode reached a maximum value of Ip and when the voltage applied is Vp across it. The current value is decreased when more amount of voltage is applied. And it current keep decreasing unit it reaches a minimum value. This minimum value of current is called as the valley current Iv. The tunnel diode and normal PN junction diode characteristics are different from each other.
Characteristics of the tunnel diode
Reverse bias condition: 
Under the reverse bias condition, the tunnel diode act as a back diode or backward diode. In reverse bias condition, the empty state on the n side aligned with the filled state on the p side. The electron will tunnel through a potential barrier. Because of its high doping concentration tunnel diode acts as an excellent conductor.

The graph above shows that A to point of B the value of current decreases with the increases in voltage. So from figure A to B, the graph shows the negative resistance region of the tunnel diode, This region shows the most important property of the diode. Here in this region shown in, the tunnel diode produces the power instead of absorbing it.

Advantages and disadvantages of Tunnel diode

One of the main reason for the early success of the tunnel diode was its high speed of operation and the high frequencies it could handle. Here this post gives information about the advantages and disadvantages of the Tunnel diode to know more detailed about it.

Advantages of tunnel diode:
  • Low cost
  • Low noise
  • High speed
  • Fabrication is also very simple
  • Fast response
  • Moderate in operation
  • Low power
  • Longevity
  • Ease of operation
  • Environmental immunity
  • Insensitive to nuclear radiation
Disadvantages of tunnel diode:
  • The voltage range, which can be operated properly in around 1 volt or below
  • Being two terminal device, it provides no isolation between output and input circuit
  • The power output levels of tunnel diode are restricted to only a few milliwatts because the applied DC potential must be less than bandgap potential of the diode

Advantages and disadvantages of varactor diode

The diode whose internal capacitance varies with the variation of reverse voltage such type of diode is known as the varactor diode. The varactor diode always works in reverse bias and it is voltage dependent semiconductor device. It is used in storing the charge. Here this article gives information about the advantages and disadvantages of varactor diode to know more detailed about it.

Advantages of varactor diode:
  • It generates less noise as compared to other PN junction diode
  • The power loss due to noise is low 
  • It is portable due to the small size and  also a lightweight
  • Reliability
  • It is economical
  • Low cost
  • It has a small size 
  • It is reliable you can use it to vary a capacitance
Disadvantages of varactor diode:
  • These diodes are specially designed to work in the reverse biased mode. Hence they are not useful when operating them in the forward bias mode

Varactor diode applications

The applications of the varactor diode are mainly used in involve within RF design arena. It mostly used in frequency modulations or tunning circuit where the value of capacitance determines the output modulations frequency. Some of the applications of the varactor diode are listed below:
  • Automatic frequency controller wherein varactor diode is used to set LO signal
  • It is used in a variable resonant tank LC circuit
  • It is used in the electronic application
  • High-frequency radios
  • Frequency modulator
  • RF phase shifter
  • Frequency multiplier
  • It is used radio receiver for tunning the circuit
  • Parametric amplifier
  • Bandpass filters
  • Voltage controlled oscillators
  • Ultra-high-frequency television sets
  • Harmonic generators
  • Frequency control circuits
  • Voltage control oscillator is widely used in receiving and transmitting circuit in the field of communication
  • It can be used in high-frequency areas like Tv tunning and FM radio operations and frequency modulations

Tunnel diode application

Applications of tunnel diode:
  • Tunnel diode can be used as a switch, oscillator, and amplifier
  • It is used as an ultra high-speed switch
  • It shows a fast response
  • It is used as an ultra 
  • It is used as a high-frequency component
  • Tunnel diode acts as a logic memory storage device
  • It can be used as FM receiver since it is a low current device it is not used more
  • It can be used in modern military equipment
  • It can be used as a microwave oscillator at a frequency of about 10 GHz
  • It is used in nuclear magnetic resource machine
  • It can be used in satellite communication equipment
Practical application of tunnel diode:
  • The tunnel diode is mostly used as a relaxation oscillator circuit
  • It can be used microwave oscillator, which has the frequency above than 10 GHz
  • It can be used as an amplifier
  • It is used as a whenever high switching is needed mostly in control system because it has a switching time of the nanoseconds or picoseconds
  • It is used in satellite communication types of equipment
  • It is used as a memory storage device
  • It is used in nuclear magnetic resource machine
  • It is also used in the military type of equipment like sonars and radars
  • It has a small inductance, capacitance, and also it has negative resistance for that reason it is used in microwave oscillator and relaxation oscillator