Method and apparatus for encoding digital data

An apparatus for encoding an input bit stream into a stream of output code words according to variable-length encoding rules using a variable constraint length, wherein a maximum value N of the constraint length is equal to or greater than 2, and the output-code-word stream observes prescribed run length limiting rules RLL(d, k), “d” and “k” denoting a predetermined minimum run length and a predetermined maximum run length respectively, the apparatus comprising:

• first means for encoding every m-bit piece of the input bit stream into an n-bit output code word by referring to predetermined M encoding tables following the variable-length encoding rules, “m” and “n” denoting predetermined natural numbers respectively, M denoting a predetermined natural number equal to or greater than 2;
• second means for generating CDS (code word digital sum) values corresponding to respective n-bit output code words generated by the first means;
• third means for generating DSV (digital sum variation) control bits in response to the CDS values generated by the second means;
• fourth means for periodically inserting the DSV control bits generated by the third means into the input bit stream at intervals each corresponding to a prescribed number of successive bits;
• and
• fifth means for subjecting the input bit stream to variable-length encoding while implementing DSV control responsive to the inserted DSV control bits.

An apparatus for encoding an input bit stream into a stream of output code words according to variable-length encoding rules using a variable constraint length, wherein a maximum value N of the constraint length is equal to or greater than 2, and the output-code-word stream observes prescribed run length limiting rules RLL(d, k), “d” and “k” denoting a predetermined minimum run length and a predetermined maximum run length respectively, the apparatus comprising:

• first means for periodically inserting a first candidate DSV (digital sum variation) control bit being “0” into an original input bit stream to get first control-bit-added input data;
• second means for periodically inserting a second candidate DSV control bit being “1” into the original input bit stream to get second control-bit-added input data;
• third means for encoding every m-bit piece of the first control-bit-added input data into a first n-bit output signal by referring to a plurality of encoding tables following the variable-length encoding rules, “m” and “n” denoting predetermined natural numbers respectively;
• fourth means for encoding every m-bit piece of the second control-bit-added input data into a second n-bit output signal by referring to the encoding tables;
• fifth means for generating first CDS (code word digital sum) values corresponding to respective first n-bit output signals generated by the third means;
• sixth means for generating second CDS values corresponding to respective second n-bit output signals generated by the fourth means;
• seventh means for periodically generating a first DSV value in response to the first CDS values generated by the fifth means, the first DSV value corresponding to the first candidate DSV control bit;
• eighth means for periodically generating a second DSV value in response to the second CDS values generated by the sixth means, the second DSV value corresponding to the second candidate DSV control bit;
• ninth means for comparing the first and second DSV values generated by the seventh and eighth means with each other, and deciding which of the first and second DSV values is smaller in absolute value to get a smaller-absolute DSV value;
• tenth means for selecting one from the first and second candidate DSV control bits as a final DSV control bit which corresponds to the smaller-absolute DSV value;
• eleventh means for inserting the final DSV control bit into the original input bit stream to get final control-bit-added input data;
• and
• twelfth means for encoding every m-bit piece of the final control-bit-added input data into a final n-bit output signal by referring to the encoding tables;
• and
• thirteenth means for serially connecting final n-bit output signals generated by the twelfth means to get a stream of output code words.