Programming instructions

Diodes
Multisim Component Reference Guide 3-18 ni.com
3.11 Varactor Diode
The varactor is a type of
pn-junction diode with relatively high junction capacitance when
reverse biased. The capacitance of the junction is controlled by the amount of reverse voltage
applied to the device, which makes the device function as a voltage-controlled capacitor.
The capacitance of a reverse-biased varactor junction is found in the following way:
where:
C
T
= the total junction capacitance
ε = permittivity of the semiconductor material
A = the cross-sectional area of the junction
W
d
= the width of the depletion layer
The value of
C
T
is inversely proportional to the width of the depletion layer. The depletion
layer acts as an insulator (called the dielectric) between the
p-type and n-type materials.
Varactor diodes are used in place of variable capacitors in many applications.
C
T
ε()
A
W
d
-------
=
ComponentRef.book Page 18 Thursday, December 7, 2006 10:12 AM