Patent ID: 7016286

Claim:
A digital signal modulation method which generates a code word data group by repeating a number of times an operation for converting source data whose bit number is p (p is a positive integer) into code word data whose bit number is q (q is an integer larger than p), generates synchronous words at predetermined bit intervals, obtains code word series data by arranging said code word data group after said generated synchronous words, and obtains a signal to be supplied to a storage medium or a transmission medium by NRZI-converting said obtained code word series signal, said digital signal modulation method comprising: a first step of simultaneously generating a first synchronous word and a second synchronous word having respective numbers of times of inversion different from each other, by said NRZI conversion; a second step of generating said code word data group based on a run-length encoding method which restricts a run length in a predetermined range, generating first code word series data by arranging said generated code word data group after said first synchronous word, and generating second code word series data by arranging said code word data group after said second synchronous word; a third step of obtaining first direct-current component data concerning a direct-current component generated when NRZI-converting said first code word series data and obtaining second direct-current component data concerning a direct-current component generated when NRZI-converting said second code word series data based on said first and second code word series data generated at said second step; and a fourth step of comparing said first direct-current component data with said second direct-current component data, and selecting and supplying one having smaller direct-current component data from said first code word series data and said second code word series data.