There are many designs for small fm transmitters but they have some problems. Presented here is a lowpower fm transmitter with varactor diode tuning using surfacemount devices smd that will be received with a standard fm radio. Varactors are used as voltagecontrolled capacitors. There are different types of diodes are available in the market based on the working principle and characteristics such as tunnel diodes, zener diodes, constantcurrent diodes, varactor diodes, photodiodes, laser diodes, etc. As a result, when c 2 is connected in series with the lower capacitance of. What is varactor diode, how varactor diode works, electronic devices. Varactor diode d 1 is connected in series with capacitor c, across the tuned circuit. 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. These diodes provide the variable resistance in the parallel resonance circuit. Varactor diode nyamador enock seth university of mines and technology umat, tarkwa computer science and engineering 14 twitter. Application of varactor diode used in electronic tuning circuits. It always works in reverse bias condition and is a voltagedependent semiconductor device.
Lets look into the construction, working of diode, characteristics and applications of varactor diode. Mouser is an authorized distributor for many varactor diode manufacturers including diodes inc. Varactor diode working, structure and applications reverse bias. Laser diode construction, working and its applications. Some of the more common specialpurpose diodes are i zener diode ii lightemitting diode led iii photo diode iv tunnel diode v varactor diode and vi shockley diode. A varactor diode circuit for indirect fm is shown in figure 3. Another fm modulator which is widely used in transistorized circuitry uses a voltagevariable capacitor varactor. Voltage control oscillators are used extensively in transmission and receiving circuits in communication. And youll note here in the diagrams that are used to define this device, here we have a diode and heres a capacitor and theres an arrow indicating that it is variable. Varactor diode modulator is a semiconductor diode having a variable junction capacitance. Here you will learn how the varactor diode acts as a variable capacitor and how. Varactor diode is known by several names as varicap, voltcap, voltage variable capacitance or tunning diode. Varactor diodes help in achieving frequency modulation.
Varactor diode definition, symbol, construction and. Its symbol is somewhat similar to the symbol of a normal diode. Varactor diode is a type of diode whose internal capacitance varies with respect to the reverse voltage. Even though the variable capacitance effect can be exhibited by the normal diodes pn junction diodes, but, varactor diodes are preferred for giving the desired capacitance changes as they are special types of diodes. The disadvantage of this varactor diode modulator is that is uses a two terminal device. The l 1 and c 1 represent the tuned circuit of the carrier oscillator. There is a small voltage drop across the diode terminals when current flows through a diode. However, a small variation is seen in the symbol of a zener diode which is shown by the bends at the two ends of the vertical line. Varactor diode construction the varactor diode is made up of the ptype and ntype semiconductor. Please view our large selection of varactor diodes below. They provide a method of varying the capacitance within a circuit by the. First, you need an audio amplifier to get enough modulation. Varactor diode it is a diode that always operates in reverse bias it is also called as varicap, tuning or voltage variable capacitor diode.
Now junction capacitance is optimized in a varactor diode and is used for high frequencies and switching applications. The value of c 2 is made very large at the operating frequency so that its reactance is very low. The word varicap is originated from the combination of word variable and capacitor. In a pn junction a very thin depletion region acts as an insulator of the o rder of 5. In electronics, a varicap diode, varactor diode, variable capacitance diode, variable reactance diode or tuning diode is a type of diode designed to exploit the voltagedependent capacitance of a reversebiased pn junction. Because the phase of the carrier is shifted, the resulting signal has a. Varactor diodes are commonly found in communication equipment where electronic tuning is a necessity. Varactor diode is the one which works on the principle of variation in capacitance by changing the width of the depletion region of pn junction.
A number of specific types of diodes are manufactured for specific applications in this fast developing world. Varactor diodes are widely used within many rf designs. What is varactor diode how varactor diode works electronic. The figure below, represents the diffused structure of a zener diode. Light emitting diode led working principle duration. Fm transmitters and phase locked loops in radio, television sets and cellular telephone. This page describes varactor diode basics and varactor diode applications. It uses gallium arsenide doped with elements such as selenium, aluminium, or silicon to produce p type and n type semiconductor materials. Varactor diode explained working, specifications and applications of varactor diode duration.
Here, this article discusses an overview of a varactor diode, that includes working, construction, applications, and. 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. And varactor diode plays a significant role in construction of voltage controlled. It is a device whose capacitance changes with the variation in the applied reverse bias potential. The link to varactor diode calculator,pin diode,tunnel diode and gunn diode basics and applications are also mentioned varactor diode is one of the many microwave semiconductor devices in use today they are manufactured with gallium arsenide. Ppt varactor diode powerpoint presentation free to. Varactor diode construction, working, characteristics. Fig b shows the basic concept of a varactor frequency modulator.
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. Varactor diode construction, working, characteristics, applications. The above figure shows a simplified construction of a laser diode, which is similar to a light emitting diode led. The symbol of the varactor diode is similar to that of the pnjunction diode. Varactor diode working, characteristics and its applications. May 08, 2020 working of varactor diode, zener diode, led, photo diode notes electronics and communication engineering ece notes edurev is made by best teachers of electronics and communication engineering ece. Varactor diode working, structure and applications reverse bias pn junction capacitance hd. Varactor diode or varicap diode working and applications.
Introduction varactor diode is a special type of pn junction diode, in which pn junction capacitance is controlled using reverse bias voltage. 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. Thus, in communication devices varactor diodes are significant. The varactor is simply a diode, or pn junction, that is designed to have a certain amount of capacitance between junctions. Soldering surface mounted devices is not so hard and actually is quite easy. View a of figure 215 shows the varactor schematic symbol. In the year 1940 at bell labs, russell ohl was working with a silicon crystal to find out its properties.
The junction in the varactor diode is formed by joining two semiconductors one ptype material and other ntype material. Varactor diode modulator electronics forum circuits. The junction capacitance of varactor diode varies linearly with applied voltage. There are two types of fm modulators direct and indirect. This document is highly rated by electronics and communication engineering ece students and has been viewed 608 times. A schottky diode, also known as a hot carrier diode, is a semiconductor diode which has a low forward voltage drop and a very fast switching action. In addition to being referred to as varicaps, varactors are also known as voltagevariable capacitors and tuning diodes. They are an important component of radio frequency or rf applications. Schottky diode working principle engineering tutorial.
A varactor diode is a pn junction diode that is especially operated in reverse biased mode. A varactor diode is the one which works on the principle of variation in capacitance by changing the width of the depletion region of pn junction. Microsemis prodiuct line inlcudes also step recovery diodes, harmonic generator varactors, impatt diodes and multiplier diodes. They are commonly used in voltagecontrolled oscillators. 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. Varactor diode is also sometimes referred to as varicap diode, tuning diode, variable reactance diode, or variable capacitance diode. Glass passivation is provided to create a shell that protects from corrosion. Even though i put the 1n4001 back in its drawer after i finished testing it last week i was able to retrieve the same diode for retesting. To learn how a varactor diode works, you need to first understand the working principle of a variable capacitor.
The variation is achieved by applying a reverse bias. Here you will learn how the varactor diode acts as a variable. Working of varactor diode, zener diode, led, photo diode. Varactor diodes are also termed as varicap diodes, in fact, these days they are usually termed as varactor diodes. We simplify information in a wide variety of categories. The varactor diode is manufactured in such as way that it shows better transition capacitance property than the ordinary diodes.
This video describes in detail, what is a varactor diode, structure of varactor diode and working of varactor diode. The diode whose internal capacitance varies with the variation of the reverse. One day accidentally when the silicon crystal which has a crack in it was exposed to the sunlight, he found the flow of current through the crystal and that was later called as diode, which was the beginning of the semiconductor era. Varactor diode definition, symbol, construction and working diode. Some of the more common specialpurpose diodes are i zener diode ii lightemitting diode led iii photo. A capacitor consists of two conducting surfaces separated by a nonconducting dielectric medium see figure below. At the base we have heatsink to moderate the temperature of the diode and for cooling purpose.
959 1340 203 788 547 643 247 729 621 1314 180 424 221 1223 779 419 285 1214 676 283 763 666 398 823 1181 833 844 1095 32 475 1220 814 894 1079 122 790 278 750 620 470 590 1388 469 92 379