description about varactor diode....

1. Topic: Varactor Diode
Name: Abdul Mohiz
Roll No: CS-15-41

2. o A varactor is a diode that always works /operates
in reverse bias and is doped to maximize the
inherent capacitance of depletion region.
o The Depletion region act as a capacitor di-electric
because of its non conductive characteristic.
o The P and N region are conductive and acts as the
capacitor plates.

3. Capacitance varies with reverse voltage

4. Basic
Operation
Recall that
capacitance is
determined by the
parameters of plate
area (A), dielectric
constant
( ), and plate
separation (d), as
expressed in the
following formula:

5. Basics
Varactor Diode are
also referred to as
Varicaps or
Tuning Diodes
and they are
commonly Used in
Communication
Systems.

6. Information About Varactor Diode
A tuning diode, also
known as a varactor
diode, variable
capacitance diode,
varicap diode or variable
reactance diode, is a
diode that has a variable
capacitance which is a
function of the voltage
that is impressed on its
terminals.
Tuning / varactor diodes
are operated reverse-
biased, and therefore no
current flows. However,
since the thickness of
the depletion zone
varies with the applied
bias voltage, the
capacitance of the diode
can be made to vary.
The symbol of varactor
diode is shown in the
figure. The varactor
diode symbol consists of
the capacitor symbol at
one end of the diode
that represents the
variable capacitor
characteristics of the
varactor diodes.

7. Defining Varactor Diode

9. Meaning of Varactor

11. In general, it looks like a normal PN- junction diode
in which one terminal is termed as the cathode and
the other terminal is termed as anode. Here, varactor
diode consists of two lines at one end (cathode end of
normal diode) that indicates the capacitor symbol.

12. P-N JUNCTION:

13. Operation :
Varactors are operated in a reverse-biased state, so
no DC current flows through the device. The
amount of reverse bias controls the thickness of
the depletion zone and therefore the varactor's
junction capacitance. Generally, the depletion
region thickness is proportional to the square
root of the applied voltage, and capacitance is
inversely proportional to the depletion region
thickness. Thus, the capacitance is inversely
proportional to the square root of applied voltage.
All diodes exhibit this variable junction
capacitance, but varactors are manufactured to
exploit the effect and increase the capacitance
variation.

15. Usage

16. Characteristic

18. Varactor Diode Example

19.  The body plotters show the frequency response at 0V
and 20V reverse bias.
 The center of the 0V bias response curve is at 553.64
KHz and the center of the 20V bias response curve at
1.548 MHz

20. Any Questions
About Varactor
Diode