Inductor quality factor

Q(quality factor) A figure of merit that defines how close a coil comes to functioning as a pure inductor. High Q describes an inductor with little energy loss resulting from resistance. Q is found by dividing the inductive reactance of a device by its resistance. 

The inductance of rectangular spiral inductors is about 20% higher compared to the circular inductor with the same dimensions whereas the quality factor is higher for circular inductors. 

Coil designs are usually not optimized for line width and, subsequently, smallest outline, because their quality factor is influenced by the line width, adversely. On the other hand, wide lines cause high parasitic capacitances, thus, reducing the self-resonance frequency. In particular, the crossing conductor has a major impact. The lowest stray capacitance is achieved by a high wire-bond loop (Figure 9.27). Countless design combinations are available for each inductor. It has to be decided which coil parameter, besides the... 

The quality factor is frequency dependent and is applicable to lumped coils only (Figure 9.62). Inductors that are not small compared to the signal wavelength reveal line transformation effects. The resulting quality factor derived from measured S-parameters appears to be negative. 

Quality factor for the lumped three-dimensional inductor according to Figure 9.59. 

Eased on tiie system specification, a filter schematic is developed. A first sensitivity analysis (influence of component tolerances on the function) should be made to verify the manufacturability in general. Another technology-independent method uses typical parasitics, which are added to tiie schematic (e.g., capacitor with parasitic inductance or quality factor of an inductor). Eoth methods help to decide which filter type will perform best if several schematic structures are available. 

A microwave cavity is a special type of resonator, which consists of a closed metal stmcture that confines electromagnetic fields in the microwave region of the spectram. The stmcture is either hollow or filled with dielectric material. It acts similarly to a resonant circuit with extremely low loss at its frequency of operation, which results in quality factors up to the order of 10, compared to 10 for circuits made with separate inductors and capacitors at the same frequency. They are used in oscillators and transmitters to create microwave signals, and as filters to separate a signal at a given frequency from other signals, in microwave ovens. 

A resonator is characterized by a transfer function showing a narrow frequency bandwidth. In its simplest expression, it can be represented by a circuit consisting of three elements in series, an inductor L, a capacitor C and a resistor R, the latter reflecting the damping of the system. The important parameters are the resonance frequency fo in the absence of damping and the quality factor Q ... 

Active filter A type of device composed of a combination of passive and active (amplifying) components. Frequently, the latter are transistors or operational amplifiers that require an external power supply to work. Active components commonly have high Q, and achieve resonance without the use of inductors. The Q value (goodness factor) is used to measure the quality of a filter. Thus, a filter has a high Q if it selects or rejects a narrow range of frequencies compared with its center frequency. Other filters that can be included into this class are ... 

The main geometrical parameters of a coplanar spiral inductor are the strip width (W), the spacing between adjacent turns (S), the internal radius (Rmt), the number of turns (Nt), the spacing to the surrounding coplanar ground plane (Sg), and the metal thickness (VetaO- A relevant frequency-dependent parameter to measure the overall electrical quality of an inductor is the Q factor obtained when one port is shorted the higher the Q factor is, the better the device electrically behaves. The second parameter, often measured to evaluate inductors, is the self-resonance frequency. A selfresonance occurs when the inductive reactance of the device is equal to the parasitic capacitive reactance between the inductor and the substrate, i.e., if Q = 0. 

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