Speech recognition circuit and method

A speech recognition circuit comprising:

• a circuit for providing state identifiers which identify states corresponding to nodes or groups of adjacent nodes in a lexical tree, and for providing scores corresponding to said state identifiers, the lexical tree comprising a model of words;
• a memory structure for receiving and storing state identifiers identified by a node identifier identifying a node or group of adjacent nodes, said memory structure being adapted to allow lookup to identify particular state identifiers, reading of the scores corresponding to the state identifiers, and writing back of the scores to the memory structure after modification of the scores;
• an accumulator for receiving score updates corresponding to particular state identifiers from a score update generating circuit which generates the score updates using audio input, for receiving scores from the memory structure, and for modifying said scores by adding said score updates to said scores;
• and
• a selector circuit for selecting at least one node or group of adjacent nodes of the lexical tree according to said scores.

A method of speech recognition, comprising

• providing state identifiers which identify states corresponding to nodes or groups of adjacent nodes in a lexical tree, the lexical tree comprising a model of words;
• providing scores corresponding to said state identifiers;
• receiving and storing state identifiers identified by node identifiers identifying a node or group of adjacent nodes in a memory structure;
• looking up said memory structure to identify particular state identifiers;
• reading of the scores corresponding to the state identifiers;
• receiving score updates corresponding t6 particular state identifiers from a score update generating circuit which generates the score updates using audio input;
• modifying said scotes by adding said score updates to said scores;
• writing back of the scores to the memory structure after modification of the scores;
• and
• selecting at least one node or group of adjacent nodes of the lexical tree according to said scores.

A speech recognition circuit comprising:

• lexical memory containing lexical data for word recognition, said lexical data comprising a lexical tree data structure comprising a model of words;
• means for accessing a state model corresponding to each phone or each group of phones in the lexical tree;
• a content addressable memory for storing content addressable data for each phone or group of phones, including states corresponding to said phone or group of phones, and for storing an address value for each said phone or group of phones;
• a RAM configured to store accumulated scores for each said phone or group of phones, the accumulated scores being addressable by said address value′ for each said phone or group of phones;
• means to obtain scores that each of a plurality of frames of an audio signals corresponds to each of a plurality of said states;
• a counter to sequentially search for each said state in the content addressable memory, to obtain the corresponding address value if the state is found in the content addressable memory;
• means to use said address value to access an accumulated likelihood and an accumulator to add said likelihood to the accumulated likelihood;
• means to use the phones or groups of phones with the highest accumulated scores to obtain a plurality of next phones from the lexical tree which correspond to the next phone;
• and
• output means for outputting a lexical tree path of highest likelihood.

A speech recognition apparatus comprising:

• a lexical tree having a corresponding state model;
• means for obtaining scores of an audio input corresponding to each of a plurality of states in said state model;
• a content addressable memory for storing a marker indicating a part of the lexical tree, and one or more states associated with said part of the lexical tree;
• a random access memory addressable by the CAM output, to output accumulated scores for states corresponding to said parts of the lexical tree;
• adder means for adding likelihood to said accumulated likelihood, to be stored back in the RAM.

A speech recognition apparatus, comprising:

• a CAM-RAM arrangement for storing records including pointers to a lexical tree, and accumulative scores for states within the lexical tree;
• input means for obtaining scores that an audio frame corresponds to a particular state in the lexical tree;
• an accumulator for calculating the updated scores and modifying the records in the CAM-RAM accordingly;
• output means for outputting a path of highest likelihood in the lexical tree.

A speech recognition method comprising:

• storing state identifiers which identify states corresponding to nodes or groups of adjacent nodes in a lexical tree, and scores corresponding to said state identifiers in a memory structure, the lexical tree comprising a model of words and the memory structure being adapted to allow lookup to identify particular state identifiers, reading of the scores corresponding to the state identifiers, and writing back of the scores to the memory structure after modification of the scores;
• repeating the following sequence of steps for each of a plurality of incoming frames of an audio signal:
• obtaining score updates corresponding to the likelihoods that said frame of the audio signal corresponds to each of a plurality of said states;
• accessing said memory structure to obtain scores, updating the scores by adding score updates to the scores, and writing back the updated scores to the memory structure;
• determining if scores for states furthest on in the lexical tree correspond to a significant likelihood, and if so, then accessing the lexical tree to determine the next set of possible states;
• and
• storing the next set of possible states and said scores of significant likelihood in the memory structure.

A speech recognition circuit comprising:

• a circuit for providing state identifiers which identify states corresponding to phones or groups of adjacent phones in a lexical tree, and for providing scores corresponding to said state identifiers, the lexical tree comprising a model of words;
• a memory structure for receiving and storing state identifiers and phone instance identifiers uniquely identifying instances of phones or groups of phones in the lexical tree;
• said memory structure being adapted to allow lookup to identify particular state identifiers, reading of the scores corresponding to the state identifiers, and writing back of the scores to the memory structure after modification of the scores;
• an accumulator for receiving score updates corresponding to particular state identifiers from a score update generating circuit which generates the score updates using audio input, for receiving scores from the memory structure, and for modifying said scores by adding said score updates to said scores;
• and
• a selector circuit for selecting at least one phone instance identifier according to said scores.