They are commonly used in voltage-controlled oscillators, parametric amplifiers, and frequency multipliers. The junction is made of gold or aluminum and n-type silicon. They are often used in pairs to switch between two different RF sources such as the VHF and UHF bands in a television tuner by supplying them with complementary bias voltages. Generally, the depletion region thickness is proportional to the square root of the applied voltage, and capacitance is inversely proportional to the depletion region thickness. https://creativecommons.org/licenses/by-sa/3.0 This reduces the overall capacitance and the capacitance range by half, but has the advantage of reducing the AC component of voltage across each device and has symmetrical distortion should the AC component possess enough amplitude to bias the varicaps into forward conduction. It is necessary to have the value of r to be very high. For example the 1N5461 Varactor Diode only changes its capacitance from 6.8pF to 6.94pF, over rated temperature. When designing tuning circuits with varicaps it is usually good practice to maintain the AC component of voltage across the varicap at a minimal level, usually less than 100 mV peak to peak, to prevent changing the diode capacitance too much, which would distort the signal and add harmonics. This can be accomplished by placing a DC blocking capacitor with a capacitance about 100 times greater than the maximum capacitance of the varicap diode in series with it and by applying DC from a high impedance source to the node between the varicap cathode and the blocking capacitor as shown in the upper left circuit in the accompanying diagram. The symbol of tunnel diode is as shown below. The DC bias voltage must be blocked from entering the tuned circuit. Maximum reverse bias voltage is usually between 5 and 7 Volts, before the avalanche process starts conducting. Varicap (7642 views - Electronics & PCB Engineering) 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 voltage-dependent capacitance of a reversed-biased p–n junction. It uses the region between the p-side and n-side of the diode where electrons and holes balance each other. In this case four diodes are used, via a dual package for the tank / bandpass filter and a dual package for the local oscillator. Varactor diodes are also termed as varicap diodes, in fact, these days they are usually termed as varactor diodes.Even though the variable capacitance effect can be exhibited by the normal diodes (P-N junction diodes), but, varactor diodes are preferred for giving the desired capacitance changes as they are special types of diodes. These circuit configurations are quite common in television tuners and electronically tuned broadcast AM and FM receivers, as well as other communications equipment and industrial equipment. This is called the depletion zone. The varicap was developed by the Pacific Semiconductor subsidiary of the Ramo Wooldridge Corporation who received a patent for the device in June 1961. Phase-locked loops are used for the frequency synthesizers that tune many radios, television sets, and cellular telephones. In this way it is obvious that it is being used as a variable capacitor rather than a rectifier. Symbol: Name: Description: Diode: Diode allows current flow in one direction only (left to … Size of this PNG preview of this SVG file: I, the copyright holder of this work, hereby publish it under the following licenses: Add a one-line explanation of what this file represents. By changing the amount of reverse voltage, the size of the depletion zone changes. 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