Resonant capacitive coupler

Details Resonant capacitive coupler Resonant capacitive coupler

2000-03-09

2001-11-13

Bettendorf, Justin P. (Department: 2817)

Wave transmission lines and networks

Coupling networks

Nonreciprocal gyromagnetic type

C333S260000

Reexamination Certificate

active

06317011

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to circuit interconnection arrangements, and relates specifically to capacitive couplers.
BACKGROUND OF THE INVENTION
The recent proliferation of, and resulting stiff competition among, wireless communications products have led to price/performance demands that are difficult to meet with conventional technologies. The demands placed on radio-frequency interconnections between printed wiring boards (PWBs), and between printed wiring boards and other devices, such as antennas and filters, are no exception. Such interconnections are usually made via coaxial connectors and cables. These interconnections are expensive in terms of both the cost of the parts and the costs of manufacturing and assembly.
An alternative way of making interconnections is via capacitive coupling. A capacitive coupler is formed by two metallic parts that are a part of, or are directly connected to, the transmission lines of the components that are to be coupled, and that are positioned in close proximity to each other. One typical configuration takes the form of gap-coupled microstrip lines, where two parallel conductors, formed on the same layer of a PWB, almost but not quite abut each other or extend for a distance past each other in close proximity, whereby the adjacent edges (ends or sides) of the two conductors form a capacitor. Another typical configuration takes the form of broadside-coupled microstrip lines, where two parallel conductors, formed on adjacent layers of a PWB, extend for a distance over each other, whereby the adjacent faces of the two conductors form a capacitor. The capacitance, and consequently the size of the parts forming the capacitor, must be large enough to provide a low-impedance connection. To increase the capacitance, the adjacent edges or faces of the two conductors may be made wider than the remainder of the two conductors. However, even at wireless radio-frequencies (e.g., 0.8-3.5 GHz), the required size of the parts that form the capacitor is prohibitively large for many applications. Moreover, the parts must be positioned very close together, and therefore cannot bridge a considerable distance, e.g., the distance between PWBs.
SUMMARY OF THE INVENTION
This invention is directed to solving these problems and disadvantages of the prior art. According to the invention, a resonant capacitive coupler is used for coupling signals having a certain frequency between conductors of two physically separate components, such as substrates (e.g., printed wiring boards), that are separated by an air gap. According to a first embodiment of the invention, the coupler has a first conductive element adapted for placement in proximity to a conductor of a first one of the substrates to form therewith a capacitor having a capacitive impedance at the signal frequency, and a second conductive element connected to the first element and adapted for spanning the air gap and connecting to a conductor of a second one of the substrates. The second element has an inductive impedance that substantially equals the capacitive impedance at the signal frequency, whereby the impedances substantially cancel each other out and the coupler resonates at the signal frequency. According to a second embodiment of the invention, the coupler has a pair of first conductive elements each adapted for placement in proximity to a conductor of a different one of the substrates to form a capacitor therewith, and a second conductive element adapted for spanning the air gap and connected to the pair of first conductive elements. The capacitors have a combined capacitive impedance and the second element has an inductive impedance that substantially equals the combined capacitive impedance at the signal frequency, whereby the impedances substantially cancel each other out and the coupler resonates at the signal frequency.
According to another aspect of the invention, an electronic device that comprises a first substrate carrying a first conductor of signals and a second substrate physically separated from the first substrate by an air gap and carrying a second conductor of the signals further comprises the resonant capacitive coupler which spans the air gap and couples the signals between the first and the second conductors.
The resonant capacitive coupler provides a simple, inexpensive, low-loss interconnection between conductors on separate substrates. The design of the coupler presents a very-low series impedance to the signals and thereby allows it to bridge wide gaps between substrates while using a much smaller capacitance than would otherwise be needed if conventional capacitive coupling was employed. The coupler further lends itself to use with “drop-in” system components that require minimum assembly, such as a structure where one or both of the “substrates” are sheet metal parts and the coupler is formed as a tab integral with one of these parts.
These and other advantages and features of the invention will become more evident from the following description of illustrative embodiments of the invention considered together with the drawing.


REFERENCES:
patent: 5689216 (1997-11-01), Sturdivant
patent: 5861754 (1999-01-01), Ueno et al.
patent: 5936841 (1999-08-01), Kantner et al.
patent: 5958030 (1999-09-01), Kwa
patent: 6184833 (2001-02-01), Tran

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