Frequency modulation coding methods with reduced transition intervals

Abstract

There is provided a method of modulating a data bit series consisting of a first value (e.g. 1) and a second value (e.g., 0) whereby a transition as a state transition is caused so as to satisfy the following conditions of (a) to (d). (a) The transition at the boundary portion of the bit cell which is sandwiched by bits 0. (b) The transition at the central portion of the bit cell of bit 1. (c) Among an even number of the bits of 1 which are sandwiched by bits 0, the transition is inhibited at the central portion of each bit cell of the last two bits of 1 and the transition is caused at the boundary portion of these two bit cells of 1. (d) When at least one bit in a pattern which starts from the two bits of (01) appears at a location next to an even number of the bits of 1 subsequent to bit of 0, the transition is caused at the central portion of the bit cell of bit 0 between these two bits.

What is claimed is: 
     
       1. A method of modulating digital data of a data bit series consisting of bits within respective bit cells of predetermined length, and each having a first or second state whereby a state transition is caused to satisfy predetermined conditions, comprising the steps of: (a) causing the transition at a boundary portion of a bit cell which is bounded on either side by bits having said second state;   (b) causing the transition at a central portion of a bit cell of a bit having said first state, .[.unless there are.]. .Iadd.except each bit cell of the last two bits of .Iaddend.an even number of bits of said first state bounded on either side by bits of said second state .[.or unless a pattern formed of a bit of said first state and a bit of said second state occurs after an even number of bits of said first state follow a bit of said second state.].;   (c) determining an even number of bits having said first state which are bounded on either side by bits having said second state, .[.inhibiting the transition at a central portion of each bit cell of the last two bits having the first state,.]. and causing the transition at a boundary portion of said .Iadd.last .Iaddend.two bit cells .Iadd.of said even number of bits .Iaddend.having the first state; and   (d) determining when a pattern formed of a bit having said second state and a bit having said first state appears after an even number of bits having the first state follow a bit having the second state and causing the transition at a central portion of a bit cell of the bit having the second state in said pattern.   
     
     
       2. A method of modulating digital data .[.bits.]. .Iadd.of a data .Iaddend.series consisting of bits within respective bit cells of predetermined length and each having a first or second state whereby a state transition is caused to satisfy predetermined conditions, comprising the steps of: (a) causing the transition at a boundary portion of a bit cell which is bounded on either side by bits having said second state;   (b) causing the transition at a central portion of a bit cell of a bit having said first state, .[.unless there are.]. .Iadd.except each bit cell of the last two bits of .Iaddend.an even number of bits of said first state bounded by bits of said second state or unless a pattern of four bits formed of two bits of said first state bounded by bits of said second state occurs after an even number of bits of said first state that follows a bit of said second state;   (c) determining an even number of bits having said first state which are bounded on either side by bits having said second state.[., inhibiting the transition at a central portion of each bit cell of the last two bits having the first value.]. and causing the transition at a boundary portion of said last two bit cells .Iadd.of said even number of bits .Iaddend.having the first value; and   (d) determining when a pattern of four bits formed of two bits having said first state bounded by bits having the second state appears after an even number of bits having the first state .[.that follows.]..Iadd.follow .Iaddend.a bit having the second state and causing the transition at a central portion of a bit cell of the first bit having the second state in said pattern of four bits.   
     
     
       3. A method of modulating digital data of a data bit series consisting of bits within respective bit cells of predetermined length and each having a first or second state, whereby a state transition is caused to satisfy predetermined conditions, comprising the steps of: (a) causing the transition at a boundary portion of a bit cell which is bounded on either side by bits having said second state;   (b) causing the transition at a central portion of a bit cell of a bit having said first state, .[.unless.]. .Iadd.except each bit cell of the last two bits of .Iaddend.an even number of bits of said first state .Iadd.which .Iaddend.bounded .Iadd.on either side .Iaddend.by bits of said second state .[.or unless a two bit pattern of a bit of said second state and a bit of said first state follows an even number of bits of said first state that is after a bit of said second state.].;   (c) determining an even number of bits having said first state which are bounded on either side by bits having said second state.[., inhibiting the transition at a central portion of each bit cell of the last two bits having the first state,.]. and causing the transition at a boundary between said last two bit cells .Iadd.of said even number of bits .Iaddend.having the first state; and   (d) determining when a two-bit pattern formed of a bit having said second state and a bit having said first state appears after an even number of bits having the first state .[.that follows.]. .Iadd.follow .Iaddend.a bit having the second state and causing the transition at a central portion of a bit cell of the bit having the second state of the two-bit pattern. .Iadd.   
     
     
       4.  A method of demodulating an input signal into digital data, in which the input signal is a data bit series at a bit clock rate consisting of bits within respective bit cells, each having a first or second state, the input signal having been modulated to have state transition satisfying the conditions of: (a) causing the transition at a boundary portion of a bit cell that is bounded on either side by bits having said second state; (b) causing the transition at a central portion of a bit cell of a bit having said first state except each bit cell of the last two bits of an even number of bits of the first state bounded on either side by bits of said second state; (c) determining an even number of bits having said first state that are bounded on either side by bits having said second state and causing the transition at a boundary portion of said last two bit cells of said even number of bits having said first state; and (d) determining when at least one pattern formed of a bit having said second state and a bit having said first state appears after an even number of bits having said first state follow a bit having said second state and causing the transition at a central portion of a bit cell of the bit having said second state in said pattern; the method of demodulating comprising the steps of: (e) detecting said state transition in said input signal;   (f) detecting whether respective positions of said transitions are at said central or boundary portions of said bit cells and producing a detection signal indicating that said transitions are at said central portions of said bit cells to that said transitions are at said boundary portions of said bit cells; and   (g) decoding said dection signal according to the conditions with which said input signal was modulated and producing said digital data. .Iaddend. .Iadd.5. A method of demodulating an input signal into digital data, in which the input signal is a data bit series at a bit clock rate consisting of bits within respective bit cells, each having a first or second state, the input signal being modulated to have state transitions satisfying the conditions: (a) causing the transition at a boundary portion of a bit cell that is bounded on either side by bits having said second state; (b) causing the transition at a central portion of a bit cell of a bit having said first state except each bit cell of the last two bits of an even number of bits of said first state bounded by bits of said second state or unless a pattern of four bits formed of two bits of said first state bounded by bits of said second state occurs after an even number of bits of said first state that follows a bit of said second state; (c) determining an even number of bits having said first state which are bounded on either side by bits having said second state and causing the transition at a boundary portion of said last two bit cells having said first state; and (d) determining when a pattern of four bits formed of two bits having said first state bounded by bits having said second state appears after an even number of bits having said first state follow a bit having said second state and causing the transition at a central portion of bit cell of the first bit having said second state in said pattern of four bits; the method of demodulating comprising the steps of:   (e) detecting said state transition in said input signal;   (f) detecting whether respective positions of said transitions are at said central or boundary portions of said bit cells and producing a detection signal indicating that said transitions are at said central portion of said bit cells or that said transitions are at said boundary portions of said bit cells; and   (g) decoding said detection signal according to the conditions with which said input signal was modulated and producing said digital data. .Iaddend. .Iadd.6. A method of demodulating an input signal into digital data, in which the input signal is a data bit series at a bit clock rate consisting of bits within respective bit cells, each having a first or second state, the input signal being modulated to have state transitions satisfying the conditions: (a) causing the transition at a boundary portion of a bit cell which is bounded on either side by bits having said second state; (b) causing the transition at a central portion of a bit cell of a bit having said first state except each bit cell of the last two bits of an even number of bits of said first state that are bounded on either side by bits of said second state; (c) determining an even number of bits having said first state that are bounded on either side by bits having said second state and causing the transition at a boundary portion of said last two bit cells of said even number of bits having said first state; and (d) determining when a two-bit pattern formed of a bit having said second state and a bit having said first state appears after an even number of bits having the first state follow a bit having the second state and causing the transition at a central portion of a bit cell of the bit having the second state of the two-bit pattern; the method of demodulating comprising the steps of:   (e) detecting said state transitions in said input signal;   (f) detecting whether respective positions of said transitions are at said central or boundary portions of said bit cells and producing a detection signal indicating that said transitions are at said central portions of said bit cells or that said transitions are at said boundary portions of said bit cells; and   (g) decoding said detection signal according to the conditions with which said input signal was modulated and producing said digital data. .Iaddend.