This means that virtually no current passes through it the positive voltage is applied to the cathode. This page describes varactor diode basics and varactor diode applications. The junction capacitance of diodes varies with the amount of reverse bias. Discrete semiconductor products diodes variable capacitance varicaps, varactors are in stock at digikey. It may also be used to produce generation of frequency modulation. When a forward bias voltage is applied, the electric current flows, as a result the depletion region becomes negligible, which is undesirable. In this way it is obvious that it is being used as a variable capacitor rather than a rectifier. Write down all circuit equations and simplify as much as possible 2. Some of the more common specialpurpose diodes are i zener diode ii lightemitting diode led iii photodiode iv tunnel diode v varactor diode and vi shockley diode. The form of junction in the diodes has a major impact on the properties and performance. Use the diode equation for that state to solve the circuit equations and find i. The varactor diode or varicap diode is shown in circuit diagrams or schematics using a symbol that combines the diode and capacitor symbols. There are two types of fm modulators direct and indirect. The junction capacitance of varactor diode varies linearly with applied voltage.
Varactor diode free download as powerpoint presentation. Nominal varactor capacitances are typically available from a few picofarads to several hundred picofarads. The varactor diode was named because of the variable reactor or variable reactance or variable capacitor or variable capacitance property of these diodes. One of the most major applications for varactors are in tuning circuits, where they function to modulate or in simple terms, vary fm waves so that we get our different fm channels, so that you can change to different stations the varying of fm waves to produce different fm channels is called fm modulation.
Download as ppt, pdf, txt or read online from scribd. A number of specific types of diodes are manufactured for specific applications in this fast developing world. In addition to being referred to as varicaps, varactors are also known as voltagevariable capacitors and tuning diodes. Varactor diode working, characteristics and its applications. Diodes and transistors university of california, berkeley. It is well known that the operation of the pn junction depends.
Some varactor diodes may be categorised as abrupt and hyperabrupt types these terms may sometimes be seen in the varcator data sheets the terms abrupt varactor diode and hyperabrupt varactor diode refer to the properties of the varactor diode junction. Characteristics of varactor diode varactor diode applications. Varactor diodesideal for vco, vcxo, voltage controlled filters and phase shifter products high quality factor abrupt varactor diodes plastic surface mount technology smt abrupt varactor diodes hermetic ceramic abrupt varactor diodes abrupt varactor diode chips wide tuning range hyperabrupt varactor diodes. It is a pn junction with a special impurity profile, and its capacitance variation is very sensitive to reversebiased voltage. A varactor diode is considered as a special type of diode that is widely used in the electronics industry and is used in various electronics applications. Varactor diode definition, symbol, construction and. Varactor diodes, which are sometimes referred to as varicap diodes, are used in electronic tuning systems to eliminate the need for moving parts. This is done to represent the effect of capacitance during operation. Recipe for solving diode circuits state of diode is unknown before solving the circuit 1. Varactor diodes are also referred to as varicaps or tuning diodes.
The function of the varactor diode is to store charges, so it is always operated in reverse bias condition. Its symbol is that of an ordinary diode, with a capacitor symbol next to it. However, in varactor diode, the cathode terminal is shown by the 2 plates of the capacitor. Microsemis prodiuct line inlcudes also step recovery diodes, harmonic generator varactors, impatt diodes and multiplier diodes.
Varactor diode is used for switching operation in the proposed antenna. A number of schematic symbols are used to represent a varactor diode in circuit diagrams. Increase in reverse bias of varactor diode increases the capacitance as shown in the figure below. Because the phase of the carrier is shifted, the resulting signal has a frequency which is. View a of figure 215 shows the varactor schematic symbol. The link to varactor diode calculator,pin diode,tunnel diode and gunn diode basics and applications are also mentioned. As a result, the width of depletion region increases and the capacitance decreases. Varactor diode is one kind of semiconductor microwave solidstate device and the applications of this diode mainly involve in where variable capacitance is preferred which can be accomplished by controlling voltage. Varactor diode varactor diode capacitance parameters are controlled by the method of doping in the depletion layer or the size and geometry of the diode construction. Even though the outcome of the variable capacitance can be shown by the normal pn.
Lets look into the construction, working of diode, characteristics and applications of varactor diode. The varactor is simply a diode, or pn junction, that is designed to have a certain amount of capacitance between junctions. In a varactor diode, these capacitance parameters are controlled by the method of doping near the pn junction and the size and geometry of the diodes construction. Download request datasheet the smv123x series of silicon hyperabrupt junction varactor diodes are designed for use in voltage controlled. Generation of frequency modulation varactor diode modulator.
They are an important component of radio frequency or rf applications. The capacitance of d 1, of course, is controlled by two factors. In fact, a typical varactor diode can vary from 60 pf at zero bias to 15 pf at 20 v. Variable capacitance varicap diode voltage variable capacitor vcc diode tuning diode variable reactance diode 4. For this reason, a varactor diode is sometimes called voltagecontrolled capacitor.
View and download powerpoint presentations on varactor diode ppt. Varactor diode is a pn junction diode whose capacitance is varied by varying the reverse voltage. Pin, schottky, varactor diodes brochure select diodes available from stock for prototype or high volume production skyworks solutions offers a select group diodes from our diverse rf diode offering in stock and ready for immediate design into your demanding applications. Usually either r 1 or r 2 is made variable so that the center carrier frequency can be adjusted over a narrow range. The figure below shows the symbolic representation of a varactor diode. Varactor diode is one of the many microwave semiconductor devices in use today. Varactor diode explained working, specifications and applications of varactor diode duration. The modulating signal varies the capacitance of the diode, which then changes the phase shift incurred by the carrier input and thus changes the phase of the output signal. A planar varactor tuned microstrip oscillator for ka band operation comprising a gaas gunn diode, a varactor diode, an impedance inverter microstrip line placing the varactor in shunt with the gunn diode, an impedance matching transformer connected from the output of the gunn diode to a load connection means, a source of negative bias potential for the varactor and a. The low resistance of these varactors makes them appropriate for highq resonators in wireless system vcos to frequencies over 10 ghz. The variation is achieved by applying a reverse bias. As a result these diodes are also referred to as varicaps, tuning diodes, voltage variable capacitor diodes, parametric diodes and variable capacitor diodes. When a reverse bias voltage is applied, the electrons from nregion and holes from pregion moves away from the junction. Pdf distortionfree varactor diode topologies for rf.
Operation it has a pn junction of semiconducting material and is always reverse biased. Varactor diode 1 varactor diode report by john paolo labaro 2 varactor diodealso known as varicap diodeis a device whose reactance can be varied in a controlled manner with a bias voltage. Before going to varactor diode, lets first take a look at the capacitor. In a normal pn junction diode, doping impurities are. Due to their remarkable properties, varactor diodes now find extensi,e use everywhere from the audio frequencies to the outer reaches of the extreme microwave frequencies. Essentially, it allows an electric current to flow in one. The time constant of the diode load of the discriminator is quite large, in the order of 100. Varactor diode or varicap diode working and applications. Distortionfree varactor diode topologies for rf adaptivity. We will learn more about its operation in the following sections.
Macoms gaas and silicon varactor tuning diodes provide broadband performance ranging from 10 mhz to 70 ghz. Select diodes include the most popular pin, schottky and tuning varactor diodes, readily available to ship in. Their mode of operation depends on the capacitance that exists at the pn junction when it is reverse biased. Lets look into the construction, working of diode, characteristics and applications of varactor diode authorstream presentation. Varactor diodes are commonly found in communication equipment where electronic tuning is a necessity. Basis of operation operates in reverse bias and this gives rise to three regions. Varactor diode operation the junction capacitance of diodes varies with the amount of reverse bias. Varactor diode construction, working, characteristics. A varactor diode is a semiconductor diode whose junction capacitance varies linearly with the applied voltage when the diode is reversebiased. Ppt varactor diode powerpoint presentation free to.
With careful manufacturing, however, the capacitance range can be increased to tentoone. So varactor diode should always be operated in reverse bias. Varactor diodes are specially designed to take advantage of this characteristic and are used as voltage controlled capacitors rather than traditional diodes. Its symbol is somewhat similar to an ordinary diode. However, if the applied reverse bias voltage is very low the capacitance will. Figure 1 shows how a varactor diode might be connected to demonstrate its operation. Us4574256a varactor tuned microstrip oscillator for ka.
Varactor diode or varicap diode working and applications a varactor diode is a pn junction. Their symbol is that of a diode placed directly next. In fig b, the bias on d 1 is set by the voltage divider which is made up of r 1 and r 2. Find powerpoint presentations and slides using the power of, find free presentations research about varactor diode ppt. Another fm modulator which is widely used in transistorized circuitry uses a voltagevariable capacitor varactor. These devices are commonly used in communication systems. At either end of the diode are the p and n regions. Varactor diode it is a diode that always operates in reverse bias it is also called as varicap, tuning or voltage variable capacitor diode. Mouser is an authorized distributor for many varactor diode manufacturers including diodes inc. The operation of these diodes is the subject of this document. Design of frequency reconfigurable antenna using varactor. One advantage is that the capacitance of a varactor diode can be changed just by changing the voltage across its terminals. The depletion region in a pn junction forms a barrier which separates the p ositive and negative charges on the opposite plates of a.
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