Title: Varactor Diode or Varicap Diode Working and Applications
1Varactor Diode or Varicap Diode Working and
Applications
2Varactor Diode or Varicap Diode Working and
Applications
Introduction
- A Varactor diode is a P-N junction diode that
changes its capacitance and the series resistance
as the bias applied to the diode is varied. The
property of capacitance change is utilized to
achieve a change in the frequency and/or the
phase of an electrical circuit. Lets we have an
overview of a varactor diode, that includes
working, construction, applications and
characteristics.
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3Varactor Diode or Varicap Diode Working and
Applications
What is a Varactor Diode?
- Varactor diode is a one kind of semiconductor
microwave solid-state device. - Varactor diodes are also named as Varicap diodes.
- The outcome of the variable capacitance can be
showed by the normal P-N junction diodes. - These diodes are chosen for giving the desired
capacitance changes as they are special types of
diodes. - Varactor diodes are specifically fabricated and
optimized such that they permits a high range of
changes in capacitance.
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4Varactor Diode or Varicap Diode Working and
Applications
What is a Varactor Diode?
- The symbol of the Varactor diode looks like a
common PN- junction diode. - It includes two terminals namely the cathode and
the anode. - At one end this diode is inbuilt with two lines
that specifies the capacitor symbol.
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5Varactor Diode or Varicap Diode Working and
Applications
Different Types of Varactor Diodes
- The different types of Varactor diodes are
available in the market such as
- Hyperabrupt Varactor diode.
- Abrupt Varactor diode.
- Gallium-arsenide Varactor diode.
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6Varactor Diode or Varicap Diode Working and
Applications
Abrupt Varactor Diodes
- Abrupt varactor diodes are the more commonly used
for of diode. - Abruptness of the junction is governed by the
doping concentration and also the profile. - For an abrupt varactor diode the doping
concentration is held constant, i.e constant
doping level as far as reasonably possible. - The abrupt varactor exhibits an inverse square
law C-V function.
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7Varactor Diode or Varicap Diode Working and
Applications
Abrupt Varactor Diodes
- This provides for an inverse fourth law frequency
dependence. - In applications where a linear dependence is
required, a lineariser is needed. - It additional circuitry that may be an additional
burden for some applications, not only in terms
of circuitry. - It slower response speed caused by the lineariser.
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8Varactor Diode or Varicap Diode Working and
Applications
Hyperabrupt Varactor Diodes
- Hyperabrupt junctions provide a C-V curve that
has an inverse square law curve over at least
some of the characteristic. - This provides a narrow band linear frequency
variation. - The hyperabrupt junction gives a much greater
capacitance change for the given voltage change. - The advantages of the hyperabrupt varactor come
at a cost as there is a substantial reduction in
Q when compared to abrupt varactor diode. - The hyperabrupt diodes are generally only used at
lower microwave frequencies - up to a few GHz at
most.
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9Varactor Diode or Varicap Diode Working and
Applications
Working of a Varactor Diode
- To know the Varactor diode working principle.
- We must know the function of capacitor and
capacitance. - Let us consider the capacitor that comprises of
two plates alienated by an insulator.
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10Varactor Diode or Varicap Diode Working and
Applications
Working of a Varactor Diode
- The capacitance of a capacitor is directly
proportional to the region of the terminals. - The region of the terminals increases the
capacitance of the capacitor increases. - When the diode is in the reverse biased mode.
- Where the two regions of P-type and N-type are
able to conduct and thus can be treated as two
terminals.
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11Varactor Diode or Varicap Diode Working and
Applications
Working of a Varactor Diode
- The depletion area between the P-type N-type
regions can be considered as insulating
dielectric. - The volume of the depletion region of the diode
varies with change in reverse bias. - If the reverse voltage of the diode is increased,
then the size of the depletion region increases. - If the reverse voltage of the Varactor diode is
decreased, then the size of the depletion region
decreases. - By changing the reverse bias of the diode the
capacitance can be changed.
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12Varactor Diode or Varicap Diode Working and
Applications
Characteristics of Varactor Diode
- The characteristics of Varactor diode have the
following
- These diodes significantly generate less noise
compared to other diodes. - The cost of these diodes is available at lower
and more reliable also. - These diodes are very small in size and very
light weight. - There is no useful when it is operated in forward
bias.
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13Varactor Diode or Varicap Diode Working and
Applications
Characteristics of Varactor Diode
- In reverse bias mode, Varactor diode enhances the
capacitance as shown in the graph below.
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14Varactor Diode or Varicap Diode Working and
Applications
Applications of Varactor Diode
- The applications of Varactor Diode mainly involve
within the RF design arena. - In this article, we are discussing about the
couple of applications of Varactor diodes. - To illustrate how these diodes can be used in a
practical. - The capacitor in a practical circuit can be
changed with the Varactor diode.
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15Varactor Diode or Varicap Diode Working and
Applications
Applications of Varactor Diode
- It is necessary to make sure the tune voltage
that is, the voltage necessary to set the diode
capacitance. - To ensure that this diode is not influenced by
the bias voltage in the circuit. - By using voltage control technique in the diode
circuit, changing capacitance can be offered.
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16Varactor Diode or Varicap Diode Working and
Applications
Voltage Controlled Oscillators
- Consider the circuit of VCO designed by using
varactor diode D1. - The oscillator can be allowed by changing the
D1diode. - The capacitor C1 is used to stop the reverse bias
for the varactor diode. - Neglects the diode getting short circuited
through the inductor. - The diode can be adjusted by applying bias
through an R1 resistor (isolating series
resistor).
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17Varactor Diode or Varicap Diode Working and
Applications
Voltage Controlled Oscillators
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18Varactor Diode or Varicap Diode Working and
Applications
RF Filters
- The varactor diodes can be used in the RF filters
to tune. - In the receive front end circuits, tracking
filters may be crucial. - Varactor diodes allow the filters to follow the
frequency of the incoming received signal which
can be restricted using a control voltage. - Usually, this is offered by microprocessor
control through the DAC.
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19Varactor Diode or Varicap Diode Working and
Applications
Choosing the Right Tuning / Varactor Diode
- Check its Power Dissipation (225 mW, 300 mW, 330
mW), - Check its Minimum Breakdown Voltage (12 V, 14 V,
25 V, 30 V) - Check its Nominal Diode Capacitance (2.8 pF, 22
pF, 33 pF, )
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20Varactor Diode or Varicap Diode Working and
Applications
Advantage of Using Varactor Diode
- Tuning circuits to replace the old style variable
capacitor tuning of FM radio. - Small remote control circuits.
- Tank circuits of receiver or transmitter for
auto-tuning as in case of TV. - Signal modulation and demodulation.
- Adjusting bridge circuits.
- Adjustable bandpass filters.
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21Varactor Diode or Varicap Diode Working and
Applications
Applications Of Varactor Diodes
- These diodes can be used as frequency modulators
and RF phase shifters. - These diodes can be used as frequency multipliers
in microwave receiver. - These diodes are used to change the capacitance
in tank LC circuits.
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22Varactor Diode or Varicap Diode Working and
Applications
Conclusion
- The varactor diode is also called a varicap,
tuning or voltage variable capacitor diode, is
also a junction diode. In this presentation we
have seen its working, construction, applications
and characteristics.
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