Varicap schematic symbol

A varicap diode, varactor diode or tuning diode is a type of diode used in electronic circuits. Image File history File links Varicap_symbol. ... Image File history File links Varicap_symbol. ... Types of diodes closeup, showing silicon crystal In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... The field of electronics comprises the study and use of systems that operate by controlling the flow of electrons (or other charge carriers) in devices such as thermionic valves (vacuum tubes) and semiconductors. ... An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, and switches. ...

Applications

Varactors are commonly used in parametric amplifiers, parametric oscillators and voltage-controlled oscillators as part of phase-locked loops and frequency synthesisers.It is principally used as a voltage-controlled capacitor, and its diode function is secondary. A parametric oscillator is a simple harmonic oscillator whose parameters (its resonant frequency and damping ) vary in time in a defined way This equation is linear in . ... A voltage-controlled oscillator or VCO is an electronic circuit that uses amplification, feedback, and a resonant circuit to generate a repeating voltage waveform. ... In electronics, a phase-locked loop (PLL) is a closed-loop feedback control system that generates and outputs a signal in relation to the frequency and phase of an input (reference) signal. ... A frequency synthesizer is an electronic system for generating any of a range of frequencies from a single fixed timebase or oscillator. ... Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ...

Operation

Internal structure of a varicap

Operation of a varicap

Varactors are operated reverse-biased so no current flows , but since the width of the depletion zone varies with the applied bias voltage, the capacitance of the diode can be made to vary. Generally, the depletion region width is proportional to the square root of the applied voltage; and capacitance is inversely proportional to the depletion region width. Thus, the capacitance is inversely proportional to the square root of applied voltage. Image File history File links Varactor. ... Image File history File links Varactor. ... Image File history File links Varactor_function. ... Image File history File links Varactor_function. ... Reverse-biased usually refers to how a diode is used in a circuit. ... In semiconductor physics, the Depletion Zone or Depletion layer is a nonconductive region within a conductive, doped semiconductor material where the charge carriers have been swept away. ... In mathematics, a square root of a number x is a number whose square (the result of multiplying the number by itself) is x. ... Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential. ...

All diodes exhibit this phenomenon to some degree, but specially made varactor diodes exploit the effect to boost the capacitance and variability range achieved - most diode fabrication attempts to achieve the opposite.

Non diode varicaps

Not all varactors are formed by diodes. In CMOS processes, varactors can be formed by placing a heavily positively-doped region (called an P+ implant) inside a lightly negatively-doped region (called an n well.) The capacitance of these junctions behaves similarly to that of an NMOS transistor, which has an N+ implant inside a lightly positively-doped region (called a p well) - which also forms a P-N junction device. Static CMOS Inverter Complementary-symmetry/metal-oxide semiconductor (CMOS) (see-moss, IPA:), is a major class of integrated circuits. ...

External links

• Learning by Simulations Calculation of the characteristics of a varactor diode for various doping profiles
• [1] Trimless IF VCO: Part 1: Design Considerations from Maxim.