PRML decoder for processing different channel codes with reduced hardware

A partial response maximum likelihood decoder comprising:

• a branch metric calculator for receiving an input bit sequence having a multi-level multi-state characteristic precoded in a particular channel code and producing a set of branch metrics corresponding in number to amplitude levels which the input bit sequence assumes;
• add/compare/select (ACS) circuitry including a plurality of ACS circuits, a plurality of adders and a plurality of unit delay elements connected respectively to the ACS circuits and the adders;
• first selector circuitry for selectively coupling the branch metrics to said ACS circuitry according to a channel code indication indicating a type of said particular channel code and second selector circuitry for selectively feeding path metrics back to the ACS circuitry according to the channel code indication, so that when said particular channel code is of a first type, the ACS circuits and the associated unit delay elements combine to produce a first path indication and most recent path metrics from the branch metrics and previous path metrics, and when said particular channel code is of a second type, the ACS circuits, the adders and the associated unit delay elements combine to produce a second path indication and most recent path metrics from the branch metrics and previous path metrics;
• and
• a path memory responsive to said first and second path indications and said channel code indication for producing an output bit sequence.

A partial response maximum likelihood decoder comprising:

• a branch metric calculator for receiving an input bit sequence having a multi-level multi-state characteristic precoded in a particular channel code and producing a set of branch metrics corresponding in number to amplitude levels which the input bit sequence assumes;
• add/compare/select (ACS) circuitry including a plurality of ACS circuits, a plurality of adders and a plurality of unit delay elements connected respectively to the ACS circuits and the adders, said ACS circuitry being arranged to respond to a channel code indication indicating a type of said particular channel code such that, when said particular channel code is of a first type, ones of said ACS circuits perform normal ACS functions and remainder ones of the ACS circuits perform add functions, and the normal-functioning ACS circuits, the add-functioning ACS circuits, the adders and the associated unit delay elements combine to produce a first path indication and most recent path metrics from the branch metrics and previous path metrics, and when said particular channel code is of a second type, the ACS circuits, the adders and the associated unit delay elements combine to produce a second path indication and most recent path metrics from the branch metrics and previous path metrics;
• and
• a path memory responsive to said first and second path indications and said channel code indication for producing an output bit sequence.

A playback system comprising:

• means for recovering an input bit sequence from a recording disc in which the bit sequence is recorded in a particular channel code so that the bit sequence has a multi-level multi-state characteristic and recovering a channel code indication indicating a type of said particular channel code;
• a branch metric calculator for receiving said input bit sequence and producing a set of branch metrics corresponding in number to amplitude levels which the input bit sequence assumes;
• add/compare/select (ACS) circuitry including a plurality of ACS circuits, a plurality of adders and a plurality of unit delay elements connected respectively to the ACS circuits and the adders, the ACS circuitry being arranged to respond to a channel code indication indicating a type of said particular channel code such that, when said particular channel code is of a first type, the ACS circuits and the associated unit delay elements combine to produce a first path indication and most recent path metrics from the branch metrics and previous path metrics, and when said particular channel code is of a second type, the ACS circuits, the adders and the associated unit delay elements combine to produce a second path indication and most recent path metrics from the branch metrics and previous path metrics;
• and
• a path memory responsive to said first and second path indications and said channel code indication for producing an output bit sequence.

A playback system comprising:

• means for recovering an input bit sequence from a recording disc in which the bit sequence is recorded in a particular channel code so that the bit sequence has a multi-level multi-state characteristic and recovering a channel code indication indicating a type of said particular channel code;
• a branch metric calculator for receiving said input bit sequence and producing a set of branch metrics corresponding in number to amplitude levels which the input bit sequence assumes;
• add/compare/select (ACS) circuitry including a plurality of ACS circuits, a plurality of adders and a plurality of unit delay elements connected respectively to the ACS circuits and the adders;
• first selector circuitry for selectively coupling the branch metrics to aid ACS circuitry according to a channel code indication indicating a type of said particular channel code and second selector circuitry for selectively feeding path metrics back to the ACS circuitry according to the channel code indication, so that when said particular channel code is of a first type, the ACS circuits and the associated unit delay elements combine to produce a first path indication and most recent path metrics from the branch metrics and previous path metrics, and when said particular channel code is of a second type, the ACS circuits, the adders and the associated unit delay elements combine to produce a second path indication and most recent path metrics from the branch metrics and previous path metrics;
• and
• a path memory responsive to said first and second path indications and said channel code indication for producing an output bit sequence.

A playback system comprising:

• means for recovering an input bit sequence from a recording disc in which the bit sequence is recorded in a particular channel code so that the bit sequence has a multi-level multi-state characteristic and recovering a channel code indication indicating a type of said particular channel code;
• a branch metric calculator for receiving said input bit sequence and producing a set of branch metrics corresponding in number to amplitude levels which the input bit sequence assumes;
• add/compare/select (ACS) circuitry including a plurality of ACS circuits, a plurality of adders and a plurality of unit delay elements connected respectively to the ACS circuits and the adders, said ACS circuitry being arranged to respond to a channel code indication indicating a type of said particular channel code such that, when said particular channel code is of a first type, ones of said ACS circuits perform normal ACS functions and remainder ones of the ACS circuits perform add functions, and the normal-functioning ACS circuits, the add-functioning ACS circuits, the adders and the associated unit delay elements combine to produce a first path indication and most recent path metrics from the branch metrics and previous path metrics, and when said particular channel code is of a second type, the ACS circuits, the adders and the associated unit delay elements combine to produce a second path indication and most recent path metrics from the branch metrics and previous path metrics;
• and
• a path memory responsive to said first and second path indications and said channel code indication for producing an output bit sequence.