Sigma-delta digital FM demodulator

A method of frequency demodulation comprising the steps:

• receiving a frequency modulated signal;
• indicating time of occurrence for chosen transitions in said frequency modulated signal;
• generating an anticipated time of occurrence for each of said chosen transitions, said generation of an anticipated time of occurrence being a function of an accumulated error value;
• measuring a cycle error for each of said anticipated times of occurrence relative to the corresponding times of occurrence;
• incorporating said cycle errors into said accumulated error value;
• and
• deriving a frequency of said frequency modulated signal as a function of a selected series of said anticipated times of occurrence.

A device producing a representation of frequency of a signal, the device comprising:

• means receiving a frequency signal and indicating times of occurrence of given chosen conditions in said frequency signal, the relative time of occurrence among said given chosen conditions representing frequency of said frequency signal;
• means generating anticipated times of occurrence for said given chosen conditions;
• means comparing an indication of time of occurrence for said given chosen condition with the associated anticipated time of occurrence and producing a representation of error in the anticipated time of occurrence relative to the indicated time of occurrence;
• and
• means collecting from said comparing means said representation of error and incorporating said errors into an accumulated error, said generating means selecting each anticipated time of occurrence as a function of said accumulated error.