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SIZE ENHANCEMENT FOR R-F CHOKES

IP.com Disclosure Number: IPCOM000006471D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2002-Jan-07
Document File: 3 page(s) / 111K

Publishing Venue

Motorola

Related People

Stephen Einbinder: AUTHOR [+2]

Abstract

Recent developments in R-F chokes have seen a drastic reduction in the size of chip coils. Hybrids require smaller and smaller components and many of our designs are limited by the size of a chip inductor. One unfortu- nate limitation is that higher values of inductances are not available in the smaller physical sizes. The smaller inductor coils may be used as chokes at lower frequen- cies by taking advantage of the self resonance of a capac- itor placed in parallel with the inductor. This shifts the anti-resonant frequency downward. Unfortunately, sim- ply placing a chip capacitor in parallel does not yield any size advantage. (See Figure 1). There is a much more compact way to accomplish the same result.

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MOTOROLA INC. Technical Developments Volume 15 May 1992

SIZE ENHANCEMENT FOR R-F CHOKES

by Stephen Einbinder and Reginald Barnes

  Recent developments in R-F chokes have seen a drastic reduction in the size of chip coils. Hybrids require smaller and smaller components and many of our designs are limited by the size of a chip inductor. One unfortu- nate limitation is that higher values of inductances are not available in the smaller physical sizes. The smaller inductor coils may be used as chokes at lower frequen- cies by taking advantage of the self resonance of a capac- itor placed in parallel with the inductor. This shifts the anti-resonant frequency downward. Unfortunately, sim- ply placing a chip capacitor in parallel does not yield any size advantage. (See Figure 1). There is a much more compact way to accomplish the same result.

  Another way to accomplish this effect is to print a narrow "Gap" capacitor underneath the choke. The capacitor is an interdigital thin metal gap capacitor printed directly on the substrate across the chip coil's pads. This capacitor effectively lowers the anti resonant frequency of the coil by adding capacitance across the inductor's

pads without taking up ani more space. The inductor is essentilly stacked on top Of a capacitance. This tech- nique allows us to use thefsmaller chip inductor at the lower frequency without g&g up any space. The new area sizes are compared in &ure 1.

  A coil cral? 50x80.220 nh coil was chosen to dem- onstrate the effect of the brinted interdigit...