Patent ID: 7397289

Claim:
A skew adjusting apparatus for adjusting a skew between a positive-side differential signal and a negative-side differential signal in differential signals inputted from an outside device via outside transmission lines; comprising: a positive-side transmission line for propagating said positive-side differential signal inputted to an input end; a negative-side transmission line for propagating said negative-side differential signal inputted to an input end; a plurality of differential comparators connected with said positive-side and negative-side transmission lines so that a positive wiring length from the input end of said positive-side transmission line to one of the differential comparators and a negative wiring length from the input end of said negative-side transmission line to the one of the differential comparators are different from each other, the plurality of differential comparators receiving said positive-side differential signal and said negative-side differential signal; and a selecting section for selecting a signal outputted by said differential comparators by which a skew between the positive-side line from an output terminal of said positive-side differential signal in said outside device to the one of said differential comparators and the negative-side line from an output terminal of said negative-side differential signal in said outside device to the one of said differential comparators is minimized, wherein the positive-side transmission line comprises the input end, which is to be connected to the outside device and receives differential signals from the outside device, and a non-input end which is another end of the positive-side transmission line and receives no differential signals from the outside device, and the negative-side transmission line comprises the input end which is to be connected to the outside device and receives differential signals from the outside device and a non-input end which is another end of the negative-side transmission line and receives no differential signals from the outside device, the skew adjusting apparatus further comprising an adjusting signal output section for supplying an adjusting differential signal to the non-input end of said positive-side transmission line and to the non-input end of said negative-side transmission line, wherein the selecting section selects a combination of said positive-side junction and said negative-side junction that minimize said skew based on said adjusting differential signal reflected from end pads of the outside transmission lines, wherein the outside device is to be connected to the end parts.