Varactor Diode Capacitance Formula: Equation and Calculator

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the reason for a device to possess negative resistance characteristic?

Emitter potential reduces and any further increase in IE shows a reduction in RB1.

In what region does a device reach saturation with an additional increase in Emitter current?

Saturation region.

What are the applications of UJT (Unijunction Transistor)?

Thyristor triggering, controlling DC voltage, overvoltage detection, measurement of magnetic flux, relaxation oscillator circuitry.

What is a Varactor Diode?

A diode whose internal capacitance varies with the reverse voltage. Signup and view all the answers

In what bias does a Varactor diode operate?

Reverse bias. Signup and view all the answers

Why is the Varactor diode considered voltage-dependent?

The output of the diode depends on the input voltage. Signup and view all the answers

What is the expression for the capacitance of a varactor diode?

𝑪𝑻 = ∈𝑨 𝑾 Signup and view all the answers

How does the capacitance of a varactor diode change with an increase in the p-type region?

The capacitance increases. Signup and view all the answers

What happens to the depletion region of a varactor diode as the reverse bias voltage increases?

The depletion region increases. Signup and view all the answers

What are two advantages of using a varactor diode compared to other diodes?

<ol> <li>Produces less noise. 2. Less costly and more reliable.</li> </ol> Signup and view all the answers

Why are varactor diodes operated under reverse bias?

To ensure the depletion region stores charge consistently. Signup and view all the answers

Why should the depletion region of a varactor diode be kept small to increase the storage capacity of charge?

The depletion region acts as a dielectric of the capacitor. Signup and view all the answers

What is the formula for the total Inter-base resistance RBB in the circuit?

RBB = RB1 + RB2 Signup and view all the answers

What is the equation to calculate the voltage at point A when a voltage VBB is applied between the two base terminals B1 and B2?

VA = VBB × (RB1 + RB2) Signup and view all the answers

What is the intrinsic stand-off ratio denoted by and what is its value range?

Intrinsic stand-off ratio denoted by η, with a value less than 1. Signup and view all the answers

What happens to the diode when no Emitter voltage is supplied to the circuit?

The diode gets reverse biased. Signup and view all the answers

What is the barrier potential value for a diode made of silicon semiconductor?

0.7 V Signup and view all the answers

What is the Emitter potential that puts the diode in forward biased condition known as?

Peak point voltage denoted by Vp. Signup and view all the answers

What is the main function of a photodiode?

Convert light energy into electric current Signup and view all the answers

Describe the construction of a photodiode.

It is a type of semiconductor device with a PN junction and an intrinsic layer between the p and n layers. Signup and view all the answers

How are photodiodes operated?

In reverse bias mode Signup and view all the answers

What happens when light illuminates the PN junction of a photodiode?

Covalent bonds are ionized, generating electron-hole pairs. Signup and view all the answers

Explain how electron-hole pairs are produced in a photodiode.

Electron-hole pairs are formed when photons with energy more than 1.1eV hit the diode. Signup and view all the answers

What happens to electron-hole pairs when they enter the depletion region of a photodiode?

They move away from the junction due to the built-in electric field. Signup and view all the answers

What is another name for a Schottky diode?

Schottky Barrier diode Signup and view all the answers

How does the forward voltage drop of a Schottky diode compare to a P-N junction diode?

Less forward voltage drop than P-N junction diode Signup and view all the answers

What type of junction is formed when aluminum or platinum metal is joined with an N-type semiconductor?

Metal-semiconductor junction Signup and view all the answers

What is the depletion layer formed between a metal and n-type semiconductor in a Schottky diode known as?

Schottky barrier Signup and view all the answers

In what type of applications are Schottky diodes widely used?

Radio frequency (RF) applications Signup and view all the answers

What characteristic of Schottky diodes makes them very useful in high-speed switching power circuits?

Can switch on and off much faster than P-N junction diode Signup and view all the answers

Study Notes

Negative Resistance and Saturation

A device possesses negative resistance characteristic to increase its current with a decrease in voltage.
A device reaches saturation with an additional increase in Emitter current in the active region.

Unijunction Transistor (UJT)

Applications of UJT include thyristors, oscillators, and pulse generators.

Varactor Diode

A Varactor diode is a type of diode that operates as a voltage-dependent capacitor.
It operates under reverse bias.
The capacitance of a Varactor diode is expressed as C = εA / (d - Δd), where ε is the permittivity of the semiconductor, A is the area of the p-n junction, d is the width of the depletion region, and Δd is the change in the width of the depletion region.
The capacitance of a Varactor diode decreases with an increase in the p-type region.
As the reverse bias voltage increases, the depletion region of a Varactor diode widens.
Advantages of using Varactor diodes include high capacitance and low losses.
Varactor diodes are operated under reverse bias to take advantage of the voltage-dependent capacitance.
The depletion region of a Varactor diode should be kept small to increase the storage capacity of charge.

UJT Circuit

The total Inter-base resistance RBB in the circuit is given by the formula RBB = R1 + R2.
The voltage at point A when a voltage VBB is applied between the two base terminals B1 and B2 is given by the equation VA = (R2 / (R1 + R2)) * VBB.
The intrinsic stand-off ratio is denoted by η and has a value range of 6 to 12.

Diode Characteristics

When no Emitter voltage is supplied to the circuit, the diode is said to be in cut-off mode.
The barrier potential value for a diode made of silicon semiconductor is approximately 0.7 V.
The Emitter potential that puts the diode in forward biased condition is known as the knee voltage.

Photodiode

The main function of a photodiode is to convert light into an electrical signal.
A photodiode consists of a PN junction diode with a transparent window to allow light to illuminate the PN junction.
Photodiodes are operated under reverse bias.
When light illuminates the PN junction of a photodiode, electron-hole pairs are produced.
Electron-hole pairs are produced in a photodiode when photons interact with the semiconductor material.
When electron-hole pairs enter the depletion region of a photodiode, they are separated by the electric field, resulting in a flow of current.

Schottky Diode

Another name for a Schottky diode is a hot carrier diode.
The forward voltage drop of a Schottky diode is lower compared to a P-N junction diode.
A Schottky diode is formed when aluminum or platinum metal is joined with an N-type semiconductor.
The depletion layer formed between a metal and n-type semiconductor in a Schottky diode is known as the Schottky barrier.
Schottky diodes are widely used in high-speed switching power circuits due to their fast switching times and low forward voltage drop.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Learn about varactor diodes, their symbol, working principle under reverse bias, and the expression for capacitance calculation. Explore how the capacitance of a varactor diode is determined based on the permittivity, area, and width of the depletion region.

Varactor Diode Capacitance Equation

Choose a study mode