A varactor diode is a semiconductor device whose capacitance can be varied by changing the reverse bias voltage. It contains a p-n junction with a specially designed impurity profile that makes its capacitance highly sensitive to changes in the reverse bias voltage. The capacitance is determined by the permittivity of the semiconductor material, the junction area, and the depletion width, which varies with the applied reverse voltage. Varactor diodes are widely used for applications like parametric amplification, mixing, and voltage-controlled tuning due to this voltage-dependent capacitance characteristic.

1. Varactor Diode
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2. VARACTOR DIODE
-Also known as Varicap Diode
-Is a device whose reactance can
be varied in a controlled manner
with a bias voltage.
-It is a p-n junction with a special impurity
profile, and its capacitance variation is
very sensitive to reverse-biased voltage.

3. Continuation Varactor Diode
-Are widely used in parametric
amplification, harmonic
generation, mixing, detection, and
voltage-variable tuning…
-It was established that there is a region
of uncovered charge on either side of
the junction that together the regions
makes up the duplication region and
define the depletion width Wd.

4. The transmission capacitance (Ct) established
by the isolated uncovered charges is determined
by
A
CT=
ε
______
Wd
Where ε is the permitivity of the
semiconductor materials, A the p-n junction
area and Wd the depletion width.

6. The characteristics of a typical commercially
available varicap diode.
C(pF)
C(0)
80
60
40
20
-2
-4
-6
-8
-10 -12 -14
0
(VR = applied reverse bias)
VR(V)

7. In terms of the applied reversed bias, the
transition capacitance is given approximately
CT =
K
(VT + VR)n
Where
K = constant determined by the semiconductor
material and construction technique
VT = knee potential
VR = magnitude of the applied reverse-bias potential
n = ½ for alloy junctions and ½ for
diffused junction

8. In terms of the capacitance at the zerobias condition C(0), the capacitance as a
function of VR.
CT(VR) =
C(0)
(1 + |
VR/VT|)n

9. The symbols most commonly used for the
varactor diode and a first approximation for its
equivalent circuit in the reverse-bias region.
CT = f (VR)
Rs
RR ≥ 1MΩ
(0.1 - 12Ω)
LS
(1 – 5nH)

10. This is an Example of Varactor Diode

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BLESS!!!