Miniaturized common mode filter

#1. Field of the Invention

#The present invention relates to a miniaturized common mode filter, and more particularly to a common mode filter with a greatly simplified design so that it can be manufactured very economically.

#2. Description of Related Arts

#FIG. 1 is an exploded perspective layer-by-layer view of a miniaturized common mode filter in accordance with the present invention;

#FIG. 2 is an exploded perspective layer-by-layer view of the miniaturized common mode filter of FIG. 1 showing how to electrically connect each layer;

#FIG. 3 is an exploded perspective view of adjacent layers in FIG. 1 showing a positive coil layout on a first substrate and a negative coil layout on a second substrate configured to form a non-overlapped pattern;

#With reference to FIGS. 1 and 2, a common mode filter in accordance with the present invention comprises multiple substrates (11-19). Each substrates (11-19) is defined with conductive through holes (110, 120) and coil patterns (111-191). Positive coils (111, 131, 151, 171, 191) and negative coils (121, 141, 161, 181) are formed on alternate substrates (11-19). After all the substrates (11-19) are stacked, each positive coil (111, 131, 151, 171, 191) is able to connect in a sequence via the first plurality of through holes (110) (as shown in FIG. 4). Similarly the negative coils (121, 141, 161, 181) are connected as a sequence via the second plurality of through holes (120). In order to clearly represent the multi-layered configuration of the common mode filter, the thickness of each substrate (11-19) is omitted from the drawing.

#Still with reference to FIG. 1, as an example, the common mode filter of the embodiment is made up of nine layers of substrates (11-19) that are sequentially designated with first to ninth substrates (11-19) hereinafter. The positive coils (111, 131, 151, 171, 191) are formed respectively on each of the odd-numbered substrate (11, 13, 15, 17, 19). Similarly, negative coils (121, 141, 161, 181) are formed respectively on each even-numbered substrate (12, 14, 16, and 18). On some of the multiple substrates, i.e. the first, second, eighth and ninth substrates (11, 12, 18 19), one end (112, 122, 182, 192) of each positive coil (111, 191) and each negative coil (121, 181) is used as an input/output terminal for connection to an external circuit (not shown).

#The purpose of the present invention is to alleviate the parasitic capacitance while the positive coils (111, 131, 151, 171, 191) stack up the negative coils (121, 141, 161, 181) without increasing the thickness of each substrate (11-19). Moreover, the common mode filter of the present invention still retains good differential mode characteristic impedance to provide superior impedance-matching performance. For this objective, the layout of the positive coils (111, 131, 151, 171, 191) is purposely configured to interlace with the negative coils (121, 141, 161, 181).