Asynchronous sampling digital detector system for magnetic and optical recording channels

In a channel having a data clock rate F.sub.d equal to the reciprocal of a data clock interval T.sub.d, a digital phase detector for detecting, in an analog signal waveform, one or more signal waveform crossings through a first threshold, said detector comprising:

• input means for accepting said analog signal waveform;
• sampling clock means having a sampling clock rate F.sub.s equal to the reciprocal of a sampling interval T.sub.s ;
• sampling means coupled to said input means and said sampling clock means for creating a plurality of first digital signals each representing a sample value of said signal waveform over one said sampling interval;
• filtering means coupled to said sampling means for creating a plurality of second digital signals each representing a value of an equalized and filtered version of said analog signal waveform over said one sampling interval;
• threshold-crossing detecting means coupled to said filtering means for detecting each said waveform threshold-crossing and for creating a third digital signal representing the phase of said each waveform threshold-crossing relative to said one sampling interval
• amplitude qualifying means coupled to said filtering means for creating one or more digital flags representing the qualification and polarity of said each waveform threshold-crossing where said qualification is responsive to the slope of said signal waveform relative to a second threshold.

In a Direct Access Storage Device (DASD) magnetic recording channel wherein digital data stored as a series of signal threshold-crossings in said DASD are read by sensing said crossings to create an analog signal waveform having a data clock rate F.sub.d equal to the reciprocal of a data clock interval T.sub.d and having crossings through a first threshold, said data being recovered in said channel, an Asynchronous Sampling Digital Detector (ASDD) comprising:

• input means for accepting said analog signal waveform;
• sampling clock means having a sampling clock rate F.sub.s equal to the reciprocal of a sampling interval T.sub.s ;
• sampling means coupled to said input means and said sampling clock means for creating a plurality of first digital signals each representing a sample value of said analog signal waveform over one said sampling interval;
• filtering means coupled to said sampling means for creating a plurality of second digital signals each representing a value of an equalized and filtered version of said analog signal waveform over said one sampling interval;
• threshold-crossing detecting means coupled to said filtering means for detecting each said waveform threshold-crossing and for creating a third digital signal representing the phase of said each waveform threshold-crossing relative to said one sampling interval;
• and
• qualifying means coupled to said filtering means for creating one or more digital flags representing the qualification and polarity of said each waveform threshold-crossing where said qualification is responsive to the slope of said analog signal waveform relative to a second threshold.

In an optical Pulse-Width-Modulated (PWM) storage device recording channel wherein digital data stored as a series of signal threshold-crossings in said optical medium are read by sensing said threshold-crossings to create an analog signal waveform having a data clock rate F.sub.d equal to the reciprocal of a data clock interval T.sub.d and having crossings through a first threshold, said data being recovered in said channel, an Asynchronous Sampling Digital Detector (ASDD) comprising:

• input means for accepting said analog signal waveform;
• sampling clock means having a sampling clock rate F.sub.s equal to the reciprocal of a sampling interval T.sub.s ;
• sampling means coupled to said input means and said sampling clock means for creating a plurality of first digital signals representing a sample value of said analog signal waveform over one said sampling interval;
• filtering means coupled to said sampling means for creating a plurality of second digital signals each representing a value of an equalized and filtered version of said analog signal waveform over said one sampling interval;
• threshold-crossing detecting means coupled to said filtering means for detecting each said waveform threshold-crossing and for creating a third digital signal representing the phase of said each waveform threshold-crossing relative to said one sampling interval;
• and
• qualifying means coupled to said filtering means for creating one or more digital flags representing the qualification and polarity of said each waveform threshold-crossing where said qualification is responsive to the slope of said analog signal waveform relative to a second threshold.

In a channel having a data clock rate F.sub.d equal to the reciprocal of a data clock interval T.sub.d, a digital phase detector for detecting, in an analog signal waveform, one or more signal waveform extrema, said detector comprising:

• input means for accepting said analog signal waveform;
• sampling clock means having a sampling clock rate F.sub.s equal to the reciprocal of a sampling interval T.sub.s ;
• sampling means coupled to said input means and said sampling clock means for creating a plurality of first digital signals each representing a sample value of said analog signal waveform over one said sampling interval;
• filtering means coupled to said sampling means for creating a plurality of second digital signals each representing a value of an equalized and filtered version of said signal waveform over said one sampling interval;
• peak detecting means coupled to said filtering means for detecting each said waveform extremum and for creating a third digital signal representing the phase of said each waveform extremum relative to said one sampling interval;
• and
• amplitude qualifying means coupled to said filtering means for creating one or more digital flags representing the qualification and polarity of said each waveform extrema where said qualification is responsive to the amplitude of said signal waveform relative to a second threshold.

In a Direct Access Storage Device (DASD) magnetic recording channel wherein digital data stored as a series of signal transitions in said DASD are read by sensing said transitions to create an analog signal waveform having a data clock rate F.sub.d equal to the reciprocal of a data clock interval T.sub.d and having waveform extrema, said data being recovered in said channel, an Asynchronous Sampling Digital Detector (ASDD) comprising:

• input means for accepting said analog signal waveform;
• sampling clock means having a sampling clock rate F.sub.s equal to the reciprocal of a sampling interval T.sub.s ;
• sampling means coupled to said input means and said sampling clock means for creating a plurality of first digital signals each representing a sample value of said analog signal waveform over one said sampling interval;
• filtering means coupled to said sampling means for creating a plurality of second digital signals each representing a value of an equalized and filtered version of said analog signal waveform over said one sampling interval;
• peak detecting means coupled to said filtering means for detecting each said waveform extremum and for creating a third digital signal representing the phase of said each waveform extremum relative to said one sampling interval;
• and
• amplitude qualifying means coupled to said filtering means for creating one or more digital flags representing the qualification and polarity of said each waveform extremum where said qualification is responsive to the amplitude of said analog signal waveform relative to a second threshold.

A method for detecting analog signal waveform extrema in a recording channel, said channel having a sampling clock rate F.sub.s equal to the reciprocal of a sampling interval T.sub.s, said analog signal waveform containing data occurring at a synchronous data clock rate F.sub.d, where i is a nonzero positive integer, said method comprising the steps of:

• (a) sampling said analog signal waveform at the end of an i.sup.th said sampling interval to create an i.sup.th waveform sample S.sub.i, said sample S.sub.i having a sign .sub.Si ;
• (b) converting said waveform sample S.sub.i to a first digital signal representing the value of said waveform sample S.sub.i relative to said first threshold;
• (c) subtracting said first digital signal representing said waveform sample S.sub.i and a previous first digital signal representing a previous said waveform sample S.sub.i-1 from the (i-1).sup.th sampling interval to create a second signal D.sub.i having a sign d.sub.i, where said second signal D.sub.i represents an i.sup.th sample of the differentiated said analog signal waveform;
• (d) comparing the sign D.sub.i of said second digital signal D.sub.i with the sign d.sub.i-1 of a previous said second digital signal D.sub.i-1 representing the (i-1).sup.th sample of said differentiated analog signal waveform;
• (e) responsive to a difference between said sign d.sub.i and said previous sign d.sub.i-1, performing the steps of
• (e.1) interpolating the zero-crossing time t of said differentiated analog signal waveform within said i.sup.th sampling interval from said previous second digital signal D.sub.i-1 to said second digital signal D.sub.i,
• (e.2) creating a third digital signal representing said zero-crossing time t in said i.sup.th sampling interval, where said third digital signal also represents the time of an extremum in said analog signal waveform in said i.sup.th sampling interval, and
• (e.3) creating one or more digital flags representing the qualification of said analog signal waveform extremum at said time t in said i.sup.th sampling interval, where said qualification is responsive to an analog signal waveform amplitude that exceeds a second threshold.