Patent ID: 7317408

Claim:
A digital modulation apparatus for converting input source data to an NRZI format modulated code having a limited run length, comprising: modulated code generating means of generating a plurality of candidate modulated codes with respect to the source data, the plurality of candidate modulated codes being candidates for the modulated code; DSV change calculating means of calculating a degree of a change in a DSV of a modulated code sequence when each of the plurality of candidate modulated codes generated by the code generating means is selected as the modulated code; modulated code determining means of comparing the degrees of changes in the DSVs calculated by the DSV change calculating means with each other, and determining that one of the plurality of candidate modulated codes generated by the modulated code generating means, the one causing the degree of a change in the DSV to be relatively small, should be used as the modulated code; and modulated code selecting means of selecting one of the plurality of candidate modulated codes generated by the code generating means, the one corresponding to a result of determination by the code determining means, and outputting the selected candidate modulated code as the modulated code.