Varactor Diodes, also known as "variable reactance diodes", are made byPN junctionWhen reverse bias occurs, the junction capacitance varies with the applied voltage.When the reverse bias voltage increases, the junction capacitance decreases. On the contrary, the junction capacitance increasesCapacitanceGenerally, it is small, the maximum value is tens of pF to hundreds of pF, and the ratio of maximum capacitance to minimum capacitance is about 5:1.It is mainly used for automatic tuning, frequency modulation, and phase modulation in high-frequency circuits, for example, as a variable capacitor in the tuning circuit of a television receiver.[1]
Chinese name
Varactor diode
Foreign name
Varactor Diodes
Alias
Variable reactance diode
Main parameters
Zero bias junction capacitance, zero bias voltage merit, etc
1. The function of varactor diode is to usePN junctionA semiconductor device based on the principle of variable capacitance between, which is used in high-frequency tuning, communication and other circuitsVariable capacitoruse.
Fig. 2 Varactor and reverse bias
Varactor diode belongs to reverse bias diode. Changing the reverse bias voltage on its PN junction can change the PN junctionCapacitance。The higher the reverse bias, the less the junction capacitance. The relationship between reverse bias and junction capacitance is nonlinear, as shown in Figure 2.
2. Diagram of relationship between capacitance value of varactor diode and reverse bias value:
(a) The capacitance decreases with the increase of reverse bias voltage;
(b) The reverse bias voltage decreases, resulting in an increase in capacitance.
The capacitance error range is a specified capacitance range of varactor diode.The data sheet will show the minimum, nominal and maximum values, which are often plotted on the graph.
working principle
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Varactor Diodes are a kind of special diodes.When the forward bias voltage is applied, a large amount of current is generated, and the depletion region of the PN junction becomes narrower, and the capacitance becomes larger, resulting in the diffusion capacitance effect;When the reverse bias voltage is applied, the transition capacitance effect will occur.However, since leakage current will be generated when forward bias is applied, reverse bias is applied in all applications.
Varactor diode, also known as voltage controlled varactor, is a semiconductor that changes the junction capacitance according to the voltage provided.In other words, as a variable capacitor, it can be used in resonance circuits and FM modulation circuits such as FM tuners and TV tuners.
In fact, we can regard it as aPN junctionWe think that if a reverse voltage V is added to the PN junction (the varactor diode is used in reverse), thenN-type semiconductorThe electrons inside are directed to the positive pole,P-type semiconductorThe holes inside are led to the negative pole, and then a depletion layer with neither electrons nor holes is formed. The width of the depletion layer is set to d, which changes with the change of reverse voltage V.In this way, as the reverse voltage V increases, the depletion layer d becomes wider and the diode capacitance C decreases (according to C=kS/d), while as the reverse voltage decreases, the depletion layer width d becomes narrower,diodeThe capacitance of becomes larger.The change of the reverse voltage V causes the change of the depletion layer, thus changing the junction capacity C of the voltage controlled converter.The goal was achieved.
Varactor diode is a semiconductor device based on the principle of variable capacitance between PN junctions. It is used as a variable capacitor in high-frequency tuning, communication and other circuits.
Varactor diode YesGlassThere are many packaging forms, such as enclosure packaging (glass packaging), plastic packaging (plastic packaging), metal enclosure packaging (gold packaging) and leadless surface packaging.Generally, small and medium power varactors are glass sealed, plastic sealed or surface sealed, while large power varactors are mostly gold sealed.Common varactor parameters.
Application and manufacturing process
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Manufacturing process
Most materials are silicon orGallium arsenidesingle crystal, and use epitaxyProcess technology。The larger the reverse bias voltage, the smaller the junction capacitance.The varactor diode has a series resistance related to the resistivity of the substrate material.Varactor diodes with different C and Vr characteristics shall be selected for different purposes, such as electrically regulated varactor diodes specially used for tuning resonant circuits, parametric varactor diodes suitable for parametric amplification, and power step varactor diodes used for frequency doubling and phase shifting in solid power sources.
Main purpose
be used forAutomatic frequency control(AFC) and small power diode for tuning are called varactor diodes.By applyingReverse voltage, make its PN junctionstatic electricityThe capacity changes.Therefore, it is used for automatic frequency control, scanning oscillation, frequency modulation and tuning.Generally, although silicon is usedDiffused diodeHowever, special diodes such as alloy diffusion type, epitaxial bonding type and double diffusion type can also be used, because these diodes have a large change rate of electrostatic capacity for voltage.The junction capacitance changes with the reverse voltage VR, replacingVariable capacitance, used as tuning circuit, oscillation circuit, phase-locked loop, commonly used in channel conversion and tuning circuit of TV tunerSilicon materialmake.
For tuning circuit
Fig. 3 Diode for tuning circuit
As shown in Figure 3, the reverse voltage of diode (D) will be changed by changing different R2, which will cause the capacitance of diode to change.Therefore, the parallel resonance can be adjusted by changing the resonant frequency of the varactor diodeBandpass filterThe full range of capacitance required in.
Other information
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Commonly used domestic varactor diodes are 2CC series and 2CB series. The following table shows the main parameters.
