Asynchronous digital threshold detector for a digital data storage channel
AssigneeInternational Business Machines Corporation
InventorsSteven R. Bentley, Robert A. Hutchins, Constantin M. Melas, Pantas Sutardja
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Abstract
A zero-crossing detector for asynchronous detection of threshold transitions in a digitally sampled signal waveform. The Asynchronous Digital Threshold Detector (ADTD) receives a digitized self-clocking data readback waveform and provides the relative location of a zero-crossing within the sample period where it occurs. The digital output, which is useful for recovering data and clock signals, is in a digital form that can be used directly by a certain class of asynchronous digital phase detector systems. The ADTD is entirely digital and can be embodied in a low power configuration using CMOS technology.
Claims35
A method for asynchronous detection of the time t of a threshold transition in a signal waveform having a data clock rate F.sub.d, said method comprising the steps of:
- (a) sampling said signal waveform at a first clock rate R.sub.s =2F.sub.d equal to the reciprocal of a first sampling interval T.sub.s to create a plurality of digital sample signals {S} representing a series of instantaneous values of said signal waveform including an i.sup.th sample signal S.sub.i and the preceding adjacent sample signal S.sub.i-1 where i is a nonzero positive integer;
- (b) creating a detection signal responsive to a signal difference between said sample signal S.sub.i and said sample signal S.sub.i-1 ;
- (c) doubling said first sampling interval T.sub.s to create a second sampling interval T.sub.d =2T.sub.s equal to the reciprocal of said data clock rate F.sub.d ;
- (d) creating a first digital signal corresponding to that half of said second sampling interval T.sub.d in which said detection signal is located;
- (e) creating a second digital signal by interpolating between said sample signal S.sub.i and said sample signal S.sub.i-1, wherein said second digital signal represents an estimate of the location t/T.sub.s of said threshold transition within an i.sup.th said first sampling interval T.sub.s ;
- and
- (f) combining said first and second digital signals to create a third digital signal representing the location t/T.sub.d of said threshold transition within a contemporaneous said second sampling interval T.sub.d.
An Asynchronous Digital Threshold Detector (ADTD) for detecting the time t of a threshold transition in a signal waveform having a data clock rate F.sub.d, said ADTD comprising:
- input means for accepting a plurality of digital sample signals {S} at a transfer rate F.sub.s =2F.sub.d representing a sequence of instantaneous values of said signal waveform;
- transition detection means coupled to said input means for assembling an adjacent pair of said digital sample signals (S.sub.i, S.sub.i-1) and creating a detection flag DF.sub.i responsive to a sign difference between said adjacent pair of digital sample signals (S.sub.i, S.sub.i-1);
- decimation means coupled to said transition detection means for reducing said transfer rate F.sub.s of said sample signals from 2F.sub.d to said data clock rate F.sub.d ;
- and
- time generator means coupled to said decimation means for interpolating said threshold transition time t within an interval T.sub.d equal to the reciprocal of said data clock rate F.sub.d and for creating a digital signal representative of the ratio t/T.sub.d of said threshold transition time t to said interval T.sub.d.
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 a signal waveform having a data clock rate F.sub.d equal to the reciprocal of a data clock interval T.sub.d and having transitions through a first threshold, said data being recovered in said channel, an Asynchronous Digital Threshold Detector (ADTD) comprising:
- input means for accepting a plurality of digital sample signals {S} at a transfer rate F.sub.s =2F.sub.d representing a sequence of instantaneous values of said signal waveform;
- transition detection means coupled to said input means for assembling an adjacent pair of said digital sample signals (S.sub.i, S.sub.i-1) and creating a detection flag DF.sub.i responsive to a sign difference between said adjacent pair of digital sample signals (S.sub.i, S.sub.i-1);
- decimation means coupled to said transition detection means for reducing said transfer rate F.sub.s of said digital sample signals from 2F.sub.d to said data clock rate F.sub.d ;
- and
- time generator means coupled to said decimation means for interpolating said threshold transition time t within an interval T.sub.d equal to the reciprocal of said data clock rate F.sub.d and for creating a digital signal representative of the ratio t/T.sub.d of said threshold transition time t to said interval T.sub.d.
In an optical Pulse Width Modulated (PWM) storage device recording channel wherein digital data stored as a series of signal transitions in said optical medium are read by sensing said transitions to create a signal waveform having a data clock rate F.sub.d equal to the reciprocal of a data clock interval T.sub.d and having transitions through a first threshold, said data being recovered in said channel, an Asynchronous Digital Threshold Detector (ADTD) comprising:
- input means for accepting a plurality of digital sample signals {S} at a transfer rate F.sub.2 =2F.sub.d representing a sequence of instantaneous values of said signal waveform;
- transition detection means coupled to said input means for assembling an adjacent pair of said digital sample signals (S.sub.i, S.sub.i-1) and creating a detection flag DF.sub.i responsive to a sign difference between said adjacent pair of digital sample signals (S.sub.i, S.sub.i-1);
- decimation means coupled to said transition detection means for reducing said transfer rate F.sub.s of said digital sample signals from 2F.sub.d to said data clock rate F.sub.d ;
- and
- time generator means coupled to said decimation means for interpolating said threshold transition time t within an interval T.sub.d equal to the reciprocal of said data clock rate F.sub.d and for creating a digital signal representative of the ratio t/T.sub.d of said threshold transition time t to said interval T.sub.d.
In a data storage tape drive magnetic recording channel wherein digital data stored as a series of signal transitions in said magnetic tape are read by sensing said transitions to create a signal waveform having a data clock rate F.sub.d equal to the reciprocal of a data clock interval T.sub.d and having transitions through a first threshold, said data being recovered in said channel, an Asynchronous Digital Threshold Detector (ADTD) comprising:
- input means for accepting a plurality of digital sample signals {S} at a transfer rate F.sub.s =2F.sub.d representing a sequence of instantaneous values of said signal waveform;
- transition detection means coupled to said input means for assembling an adjacent pair of said digital sample signals (S.sub.i, S.sub.i-1) and creating a detection flag DF.sub.i responsive to a sign difference between said adjacent pair of digital sample signals (S.sub.i, S.sub.i-1);
- decimation means coupled to said transition detection means for reducing said transfer rate F.sub.s of said digital sample signals from 2F.sub.d to said data clock rate F.sub.d ;
- and
- time generator means coupled to said decimation means for interpolating said threshold transition time t within an interval T.sub.d equal to the reciprocal of said data clock rate F.sub.d and for creating a digital signal representative of the ratio t/T.sub.d of said threshold transition time t to said interval T.sub.d.
Dependencies are inferred from the claim text.