Patent ID: 7190728
Filing Date: 2007-03-13
Classification: H04L

Abstract:
1. A digital data transmission apparatus comprising: a data coding device operable to convert digital data into a signal level corresponding to a symbol that is assigned to the digital data in each symbol cycle as a prescribed unit cycle; a first digital filter having a first sampling cycle that is shorter than a unit cycle of a signal level string that has been obtained by said data coding device, and being operable to allow only predetermined frequencies to pass; a D/A converter operable to convert a digital data stream that has passed through said first digital filter, into an analog signal; a low-pass filter operable to eliminate folding distortion of said first digital filter from the analog signal that has been obtained by said D/A converter, the folding distortion being determined in the first sampling cycle; a differential driver operable to convert an output from said low-pass filter, into two signals having opposite polarities relative to a predetermined reference potential, and to input the two signals into a twisted pair cable; a differential receiver operable to receive transmission signals transmitted through the twisted pair cable, and to convert a difference in potential between two wires of the twisted pair cable into a signal; an A/D converter operable to convert the signal outputted from said differential receiver into a digital signal value in each second sampling cycle; a second digital filter operable to allow only a predetermined frequency band of a digital data stream that has been obtained by sampling with said A/D converter, to pass; and a level evaluator operable to evaluate a symbol value from a level of a signal in symbol timing, including a symbol in the signal, based on an output from said second digital filter, and to convert the symbol value into corresponding digital data, wherein said first and second digital filters both have low-pass characteristics, and said first digital filter has frequency characteristics of cutting off at least frequency data which are higher than a frequency band in which electromagnetic waves emitted from the respective two signals that pass through the twisted pair cable cancel each other out, thereby to eliminate emission of electromagnetic waves to outside the twisted pair cable.