| CPC H03H 7/427 (2013.01) [H01P 1/20 (2013.01); H01P 3/08 (2013.01); H03H 7/0115 (2013.01); H03H 1/0007 (2013.01)] | 8 Claims |

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4. A signal transmission circuit comprising:
a common mode filter comprising:
a substrate having a first surface, a second surface and a plurality of through holes, wherein the first surface and the second surface are opposite to each other, and the plurality of through holes each pass through the first surface and the second surface;
a first conductive layer disposed on the first surface of the substrate;
a ground layer disposed on the first surface of the substrate and spaced from the first conductive layer;
two conductive lines disposed on the second surface of the substrate, wherein one end of each of the two conductive lines is electrically connected to the first conductive layer through one of the plurality of through holes;
two passive components electrically connected to the ground layer and the first conductive layer; and
a second conductive layer disposed on the first surface of the substrate and spaced from the first conductive layer and the ground layer,
wherein another end of each of the two conductive lines is electrically connected to the second conductive layer through another one of the plurality of through holes, and
two differential-signal lines disposed on the second surface of the substrate and located between the two conductive lines.
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