Method and apparatus for DC restoration in digital receivers

In a digital communication system between a local receiver and between a plurality of remote data sources, each source selectively generating a digitally modulated signal having X predetermined amplitude levels, said remote sources providing a short preamble signal immediately pror to the transmission of one of said digitally modulated signals, said preamble signal characterized by a coding that produces multiple cycles of equal amplitude level excursions in said receiver, a process for removing any dc offset voltage, V.sub.off, in said receiver from said digitially modulated signal, said process comprising the steps of:

• periodically converting said digitially modulated signals into a digitally formatted signal at a repetition interval T;
• digitally processing said digitally formatted signal for generating a dc offset voltage at time intervals nT, where n is an integer, said dc offset voltage being equal to
• V.sub.off n+1=V.sup.n +(1/.alpha.)V.sub.e n,
• where:
• V.sup.n =the offset voltage at time nT;
• V.sub.e n=the offset voltage at time nT as measured by the voltage difference between said digitally formatted signal and the closest normalized coding level;
• and
• .alpha.=a predetermined number,
• such that at time n=1, V.degree., the initial offset voltage, is set equal to the average amplitude level during at least one of said multiple cycles during said preamble period;
• and
• periodically converting said digital V.sub.off into an analog V.sub.off signal;
• and,
• summing said analog V.sub.off signal with said digital modulated signal prior to said first converting step so as to subtract out the unwanted dc offset voltage from said digital modulated signal.

In a digital communication system between a local receiver and between a plurality of remote data sources, each source selectively generating a digitally modulated signal having X predetermined amplitude levels, said remote sources providing a short preamble signal immediately prior to the transmission of one of said digitally modulated signals, said preamble signal characterized by a coding that produces multiple cycles of equal amplitude level excursions in said receiver, a process for removing any dc offset voltage, V.sub.off, in said receiver from said digitially modulated signal, said process comprising the steps of:

• periodically converting said digitally modulated signals into a digitally formatted signal at a repetition interval T;
• digitally processing said digitally formatted signal for generating a dc offset voltage at time intervals nT, where n is an integer, said dc offset voltage being equal to
• V.sub.off n+1=V.sup.n +(1/.alpha.)V.sub.e n,
• where:
• V.sup.n =the offset voltage at time nT;
• V.sub.e n=the offset voltage at time nT as measured by the voltage difference between said digitally formatted signal and the closest normalized coding level;
• and
• .alpha.=a predetermined number,
• such that at time n=1, V.degree., the initial offset voltage, is set equal to the average amplitude level during at least one of said multiple cycles during said preamble period;
• and
• periodically summing said V.sub.off signal with said digitally formatted signal prior to said digitally processing step so as to subtract out the unwanted dc offset voltage from said digital modulated signal.