Decision feedback demodulator with phase and frequency estimation

In a decision feedback demodulator in which an estimated phase error for a current symbol from a stream of symbols is used in estimating data for said current symbol and in generating a measured phase error, and said estimated phase error is based upon measured phase errors from past symbols, a method for demodulating a received signal comprising steps of:

• a) recording said measured phase errors for at least 2N of said past symbols to provide at least 2N recorded phase errors, where N is an integer number;
• b) generating a recent phase error which is responsive to a first one of said at least 2N recorded phase errors;
• c) generating an old phase error which is responsive to a second one of said at least 2N recorded phase errors, said first one of said at least 2N recorded phase errors occurring more recently than said second one of said at least 2N recorded phase errors;
• d) finding a phase difference between said old and recent phase errors;
• e) generating an average phase error which approximates an average of said at least 2N recorded phase errors;
• and
• f) generating said estimated phase error in response to said phase difference and said average phase error.

A circuit for demodulating a received signal that has been modulated to convey discrete predetermined data codes in a stream of symbols, said circuit comprising:

• recording means for recording a plurality of measured phase errors, each of said plurality of measured phase errors corresponding to a difference, during one of said symbols, between an estimated modulation phase and a received phase exhibited between quadrature components of said received signal;
• a combination circuit, coupled to said recording means, for generating an average phase error which approximates an average of said plurality of measured phase errors;
• a first phase rotator, coupled to said recording means, for determining a phase change exhibited by at least a portion of said plurality of measured phase errors;
• a second phase rotator, coupled to said first phase rotator and said combination circuit, for determining an estimated phase error;
• and
• decision means, coupled to said second phase rotator and being responsive to said received signal, for generating said estimated modulation phase.