Differential circuit and layout method for the same

A differential circuit comprising:

• a semiconductor package comprising two terminals connecting to the semiconductor package through two packaged leads in the semiconductor package;
• a first differential signal trace comprising a first parallel section and a first unparallel section connecting the first parallel section to a terminal of the semiconductor package;
• a second differential signal trace comprising:
• a second parallel section parallel to the first parallel section, and having a length equal to the first parallel section;
• a second unparallel section connecting to the second parallel section;
• an equalizing section connecting second unparallel section to the another terminal of the semiconductor package, the total length of the equalizing section, the first unparallel section and the packaged lead connected to the corresponding terminal being equal to the total length of second unparallel section and the packaged lead connected to the another corresponding terminal.

A layout method for a differential circuit, comprising:

• laying out a first differential signal trace on a circuit board with an electronic element, the first differential signal trace comprising a first parallel section and a first unparallel section connected the first parallel section to the electronic element;
• laying out a second unparallel section and an equalizing section of a second signal trace on the circuit board, and the equalizing section connecting to the electronic element to the second unparallel section;
• measuring the length of the first unparallel section and a total length of the second unparallel section and the equalizing section of the second differential signal trace;
• modifying the length of the equalizing section to make the total length of the second unparallel section and the equalizing section equal the length of the first unparallel section;
• laying out a second parallel section of the second differential signal trace on the circuit board parallel to the first parallel section, and the second parallel section connected to the second unparallel section;
• measuring the length of the first parallel section and the length of the second parallel section of the second differential signal trace;
• modifying the length of the second parallel section equal to the length of the first parallel section.