1. An apparatus for converting a sequence of m-bit information words into a modulated digital signal, where m is an integer, the apparatus comprising input means for receiving the sequence of m-bit information words, m-to-n bit converter means for converting the sequence of m-bit information words into a sequence of n-bit codewords, where n is an integer larger than m, the sequence of codewords forming the modulated signal, which signal comprises bit cells having a first signal value and bit cells having a second signal value, determining means for determining a coding state related to a digital sum value at the end of a modulated signal portion, which digital sum value denotes for said modulated signal portion a running value of a difference between the number of bit cells having the first signal value and the number of bit cells having the second signal value, the m-to-n bit converter means comprising selection means for selecting for the conversion a code word from a set of codewords that depends on the coding state, at least one of the digital sum values determining a first and a second coding state, the first and second coding state being determined in response to the information word that corresponds to the previous codeword, wherein the apparatus is adapted to form a modulated signal satisfying the requirement that the number of consecutive bit cells in the modulated signal having the same signal value does not exceed 7.
1. An apparatus for converting a sequence of m-bit information words into a modulated digital signal, where m is an integer, the apparatus comprising input means for receiving the sequence of m-bit information words, m-to-n bit converter means for converting the sequence of m-bit information words into a sequence of n-bit codewords, where n is an integer larger than m, the sequence of codewords forming the modulated signal, which signal comprises bit cells having a first signal value and bit cells having a second signal value, determining means for determining a coding state related to a digital sum value at the end of a modulated signal portion, which digital sum value denotes for said modulated signal portion a running value of a difference between the number of bit cells having the first signal value and the number of bit cells having the second signal value, the m-to-n bit converter means comprising selection means for selecting for the conversion a code word from a set of codewords that depends on the coding state, at least one of the digital sum values determining a first and a second coding state, the first and second coding state being determined in response to the information word that corresponds to the previous codeword, wherein the apparatus is adapted to form a modulated signal satisfying the requirement that the number of consecutive bit cells in the modulated signal having the same signal value does not exceed 7. 5. An apparatus as claimed in claim 1, the apparatus further comprising sync word generator means for generating a sync word for a block of p consecutive code words in the modulated signal, the sync word generator means being adapted to generate said sync word from the following set of available sync words: 11100011111110, 10100011111110, 01100011111110, 11000100000001, 01011100000001, 10011100000001, and 00011100000001 the sync word generator means being adapted to select one of the sync words in dependence upon the coding state.