Method and apparatus for signal-eye tracking in digital transmission systems

Apparatus for use in a digital transmission system wherein the digital signal has n signal levels which form n-1 aligned signal-eyes, where n has an integer value of at least two, said apparatus characterized by

• means (e.g., 102, 104, 109) for forming first samples, regeneration samples and second samples of the digital signal, each regeneration sample is formed at a regeneration sampling time which occurs within said signal-eyes, each of said first samples is formed at a first sampling time which precedes said signal-eyes and one of said regeneration samples, each of said second samples is formed at a second sampling time which succeeds said signal-eyes and said one of said regeneration samples, each of said first, regeneration and second samples having an amplitude that represents the amplitude of the digital signal at the respective sampling time relative to a reference level which passes through one of said signal-eyes,
• detection circuit means (e.g., 604, 605 and 607) for comparing the amplitude of each of said first samples with the amplitude of said one of said regeneration samples and generating a first comparison signal therefrom,
• detection circuit means (e.g., 605, 606 and 608) for comparing the amplitude of each of said second samples with the amplitude of said one of said regeneration samples and generating a second comparison signal therefrom, said first and second comparison signals having a difference therebetween,
• means (e.g., 117) for averaging the difference between said first and said second comparison signals to form an error signal, and
• means (e.g., 201) responsive to said error signal for aligning said regeneration sampling time with a predetermined position within said signal-eyes.

A method of tracking in time the n-1 aligned signal-eyes formed by n signal levels of a digital signal, where n has an integer value of at least two, characterized by the steps of

• forming (e.g., 102, 104, 109) first samples, regeneration samples and second samples of the digital signal, each regeneration sample is formed at a regeneration sampling time which occurs within said signal-eyes, each of said first samples is formed at a first sampling time which precedes said signal-eyes and one of said regeneration samples, each of said second samples is formed at a second sampling time which succeeds said signal-eyes and said one of said regeneration samples, each of said first, regeneration and second samples having an amplitude that represents the amplitude of the digital signal at the respective sampling time relative to a reference level which passes through one of said signal-eyes,
• comparing (e.g., 604, 605, 607) the amplitude of each of said first samples with the amplitude of said one of said regeneration samples and generating a first comparison signal therefrom,
• comparing (e.g., 605, 606, 608) the amplitude of each of said second samples with the amplitude of said one of said regeneration samples and generating a second comparison signal therefrom, said first and second comparison signals having a difference therebetween, and
• averaging (e.g., 117) the difference between said first and said second comparison signals to form an error signal which varies with the movement of said signal-eyes relative to said regeneration sampling time.

A method of generating an adaptive timing signal for use in regenerating a digital signal having n signal levels which form a series of n-1 signal-eyes in time, where n has an integer value of at least 2, characterized by the steps of

• forming (e.g., 102, 104, 109) first samples, regeneration samples and second samples of the digital signal, each regeneration sample is formed at a regeneration sampling time which occures within said signal-eyes, each of said first samples is formed at a first sampling time which precedes said signal-eyes and one of said regeneration samples, each of said second samples is formed at a second sampling time which succeeds said signal-eyes and said one of said regeneration samples, each of said first, regeneration and second samples having an amplitude that represents the amplitude of the digital signal at the respective sampling time relative to a reference level which passes through one of said signal-eyes,
• comparing (e.g., 604, 605, 607) the amplitude of each of said first samples with the amplitude of said one of said regeneration samples and generating a first comparison signal therefrom,
• comparing (e.g., 605, 606, 608) the amplitude of each of said second samples with the amplitude of said one of said regeneration samples and generating a second comparison signal therefrom, said first and second comparison signals having a difference therebetween,
• averaging (e.g., 117) the difference between said first and said second comparison signals to form an error signal, and
• varying said regeneration sampling time in response to said error signal to align said regeneration sampling time with a predetermined position within said signal-eyes.