(57) A current mode bus coupler (10) for electromagnetically coupling a terminal unit,
i.e., an electronic subsystem, with a data bus cable (24) comprising a twisted wire
pair is disclosed. The current mode bus coupler (10) includes a planar coil (16),
upper and lower slotted planar shields (20 and 22) and a ferromagnetic core (12).
The planar coil 16 and planar shields (20 and 22) are formed in a sandwich (14) of
alternating dielectric and conductive layers. Apertures (36, 37 and 38) are formed
in the sandwich (14) for receiving the legs of the ferromagnetic core (12), and the
planar coil (16) spirals around one of the apertures (37). The ferromagnetic core
(12) has at least two legs, one of which is inserted into the aperture (37) around
which the planar coil (16) is formed. The ferromagnetic core (12) is disengagable
and disassemblable so that the core can be inserted in a loop formed by separating
the conductors of the twisted wire pair data bus. The planar shields (20 and 22) which
would be connected to a common ground form upper and lower layers of the sandwich
(14) and shield the planar coil (16) from external electromagnetic and electrostatic
fields. The upper planar shield (20) lies between the planar coil (16) and the twisted
wire pair data bus in which the ferromagnetic core (12) is inserted. The apertures
of the planar shields (20 and 22) are slotted (58 and 60) so that the shields, which
are conductive, do not form short circuits about the legs of the ferromagnetic core
(12). The sandwich (14) can include additional planar coils (18) formed about the
same (or other) aperture and connected in series by conductively plated through-holes
(48).
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