Apparatus and method for dual tone multifrequency signal detection
 A DTMF digit detecting method and apparatus includes signal state identifier (32) for identifying whether the received signal is in a DTMF-digit-detect state, a no-detect high-energy state, or a no-detect low-energy state, digit candidate identification processor (34) for identifying a digit candidate when the presence of a state other than the no-detect low-energy state is detected following a detection of the presence of the no-detect low-energy state for a first predetermined period of time, digit identifier (32) for identifying a DTMF digit corresponding to a sample group in a DTMF-digit-detect state, and valid digit identifier (34) for identifying a valid DTMF digit when at least a first predetermined number of sample groups are all in the DTMF-digit-detect state or in an allowable combination of states. An allowable combination of states exists provided the following conditions are met: (1) at least half of the first predetermined number of sample groups are in the DTMF-digit-detect state and correspond to the same DTMF digit; (2) no two sequential sample groups are in a state other than the DTMF-digit-detect state; and (3) no two sequential sample groups in the DTMF-digit-detect state correspond to one or more DTMF digits other than the DTMF digit corresponding to at least half of the first predetermined number of sample groups. 
Hughes Electronics
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H04Q H04Q
inventional inventional
Jie Shrirang
Chen Jangi