Digital supervisory audio tone detector

A method for selectively muting a radiotelephone by detecting a Digital Supervisory Audio Tone (DSAT) code contained in an input data stream, comprising the steps of:

• providing a first code, said first code being a predetermined one of either said received DSAT code or a reference code;
• providing a plurality of codes, said plurality of codes comprising a second code and a rotated second code, said second code being the non-selected one of said received DSAT code and said reference code;
• comparing said first code with said plurality of codes to provide a comparison signal for each code of said plurality of codes;
• evaluating said comparison signal to determine the number of differences between said first code and each code of said plurality of codes;
• providing a validity signal for said received DSAT code when said number of differences between said first code and any code of said plurality of codes is less than a predetermined value;
• and
• muting said radiotelephone if said validity signal is not provided and unmuting said radiotelephone if said validity signal is provided.

An apparatus for selectively muting a radiotelephone by detecting a received Digital Supervisory Audio Tone (DSAT) code contained in an input data stream, comprising:

• a first register operative to provide a first code, said first code being a predetermined one of either said received DSAT code contained in an input data streat or a reference code;
• a second register operative to provide a plurality of codes, said plurality of codes comprising a second code and a rotated second code, said second code being the non-selected one of said received DSAT code and said reference code;
• a first comparator opertive to compare said first code with said plurality of codes to provide a comparison signal for each code of said plurality of codes;
• a counter operative to provide a count signal indicative of the number of differences in said comparison signal for each code of said plurality of codes;
• a second comparator operative to provide a validity signal for said received DSAT code in response to said count signal being less than a predetermined value for any code of said plurality of codes;
• and
• means for muting said radiotelephone if said validity signal is not provided and for unmuting said ratiotelephone if said validity signal is provided.