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All diodes exhibit this variable junction capacitance, but varactors are manufactured to exploit the effect and increase the capacitance variation. The figure shows an example of a cross section of a varactor with the depletion layer formed of a p–n junction.
In electronics, a step recovery diode (SRD, snap-off diode or charge-storage diode or memory varactor [a]) is a semiconductor junction diode with the ability to generate extremely short pulses. It has a variety of uses in microwave (MHz to GHz range) electronics as pulse generator or parametric amplifier .
The thickness of the depletion layer of a reverse-biased semiconductor diode varies with the DC voltage applied across the diode. Any diode exhibits this effect (including p/n junctions in transistors), but devices specifically sold as variable capacitance diodes (also called varactors or varicaps ) are designed with a large junction area and a ...
When a small voltage is applied across the electrodes, only a tiny current flows, caused by reverse leakage through the diode junctions. When a large voltage is applied, the diode junction breaks down due to a combination of thermionic emission and electron tunneling, resulting in a large current flow. The result of this behavior is a nonlinear ...
The classical varactor parametric oscillator consists of a semiconductor varactor diode connected to a resonant circuit or cavity resonator. It is driven by varying the diode's capacitance by applying a varying bias voltage. The circuit that varies the diode's capacitance is called the "pump" or "driver".
Various semiconductor diodes. Left: A four-diode bridge rectifier.Next to it is a 1N4148 signal diode.On the far right is a Zener diode.In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is conducting.
At high frequencies, the PIN diode appears as a resistor whose resistance is an inverse function of its forward current. Consequently, PIN diode can be used in some variable attenuator designs as amplitude modulators or output leveling circuits. PIN diodes might be used, for example, as the bridge and shunt resistors in a bridged-T attenuator.
The work of physicist W. W. Hansen was instrumental in the development of the klystron and was cited by the Varian brothers in their 1939 paper. His resonator analysis, which dealt with the problem of accelerating electrons toward a target, could be used just as well to decelerate electrons (i.e., transfer their kinetic energy to RF energy in a ...