Using Coaxial Line Elements as Inductors
●Introduction
■Coaxial line elements can be used below resonance to simulate high Quality factor (Q), temperature-stable, compact inductors. More precisely, shorted coaxial lines exhibit an inductive reactance when used below quarter-wave resonance, and approximate the behavior of an ideal inductance or coil over a limited frequency range. As the operating frequency approaches the Self-Resonant Frequency(SRF ) of the coaxial line element, the approximation is less valid.
■An exact equivalent circuit is complex and includes parasitic elements resulting from a transition from the printed wiring board to the interior of the coaxial line. In this Application Note, a first-order model includes only the ceramic coaxial line and an estimate of the inductance due to the physical length of the center conductor tab. The tab inductance appears in series with the coaxial line's input impedance. An ideal, loss-less transmission line is assumed to simplify the calculations. Minor corrections to part length may be evident from prototype circuit performance.
■Let the preferred inductive reactance at the design frequency (f0) be approximated by:
▲Z-input = Z0 tan(Θ)
■Where:
▲Z-input = Impedance at the coaxial line terminals ( Ω).
▲Z0= Coaxial line characteristic impedance (Ω).
▲Θ= 2ℓ/λg Coaxial electrical length (radians).
■The characteristic impedance(ZO) is established by the coaxial dimensions and the material dielectric constant(εr), as shown in Table 1. The cross-section width(W)and hole diameter(d) differ from final catalog part sizes by an allowance of 0.001 inches for conductor metallization thickness.
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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May 21, 2013 |
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202810A |
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176 KB |
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