Dual detector read channel with semi-soft detection

Abstract

An apparatus for detecting data within a signal having both data and noise is disclosed herein. The apparatus includes means for receiving first samples of an input signal, a first detection unit and a second detection unit. The first detection unit processes the first data samples to create a first bit signal, a second bit signal and a probability related signal. The second detection unit includes first and second modification units and a selection unit. The first and second modification units separately modify the first data samples based on the first and second bit signals, respectively, to create first and second error signals, respectively. The selection unit selects one of the first and second bit signals based on the first and second error signals and a threshold signal.

What is claimed is:  
     
         1 . An apparatus for detecting data within a signal having both data and noise, said apparatus for use in a data storage system, comprising: 
 means for receiving first data samples of an input signal;    a first detection unit for processing said first data samples to create a first bit signal, a second bit signal, and a probability related signal;    first and second modification units for separately modifying said first data samples based on said first and second bit signals, respectively, to create first and second error signals, respectively; and    a selection unit for selecting one of said first and second bit signals based on said first and second error signals and a threshold signal.    
     
     
         2 . The apparatus of    claim 1   , further comprising: 
 a multiplexer for processing said signal selected by said selection unit.    
     
     
         3 . The apparatus of    claim 1   , wherein: 
 said first and second modification units each include cancellers for subtracting cancellation values from said first data samples.    
     
     
         4 . The apparatus of    claim 3   , wherein: 
 said first and second cancellers include a random access memory (RAM) for storing said cancellation values.    
     
     
         5 . The apparatus of    claim 1   , wherein: 
 said first and second error signals are squared error sums that are accumulated over a predetermined number of bit times.    
     
     
         6 . The apparatus of    claim 1   , wherein: 
 said selection unit includes a subtracter for determining a difference between said first and second error signals.    
     
     
         7 . The apparatus of    claim 6   , wherein: 
 said selection unit includes a comparator for comparing said difference to said probability related signal.    
     
     
         8 . The apparatus of    claim 1   , wherein: 
 said first detection unit includes a pair of decision feedback equalizers.    
     
     
         9 . The apparatus of    claim 1   , wherein: 
 said first bit signal and said second bit signal represent two possible detected data strings for the first data samples.    
     
     
         10 . The apparatus of    claim 1   , wherein: 
 said threshold signal is calculated using said probability related signal.    
     
     
         11 . The apparatus of    claim 10   , wherein: 
 said probability related signal is approximately proportional to a log likelihood that bits of the first bit signal are accurate.    
     
     
         12 . An apparatus for detecting data in an input signal having data and noise, said apparatus for use in a data storage system, comprising: 
 first means for performing hard detection on said input signal, wherein said first means does not use a probability related signal to perform said detection;    second means for performing soft detection on said input signal, wherein said second means compares a first probability related signal to a second probability related signal to facilitate detection of said data in said input signal; and    means for selecting one of said first means and said second means for providing a detected data output signal.    
     
     
         13 . The apparatus of    claim 12   , wherein: 
 said second means includes first and second canceller units for modifying said input signal.    
     
     
         14 . The apparatus of    claim 13   , wherein: 
 said first means includes a pair of decision feedback equalizers.    
     
     
         15 . The apparatus of    claim 14   , wherein: 
 said second means includes a latch for latching a quality value with a flag signal indicating a low detection probability.    
     
     
         16 . The apparatus of    claim 14   , further comprising: 
 means for generating a flag based on said input signal, wherein said means for selecting is responsive to said flag.    
     
     
         17 . A data detection apparatus for use in a data storage system, comprising: 
 means for receiving an input signal having a data component and a noise component;    means for detecting said data component of said input signal, said means for detecting being capable of operating in a soft detection mode and a hard detection mode; and    means for generating a select signal for selecting either said soft detection mode or said hard detection mode for said means for detecting, wherein said means for generating is responsive to said input signal.    
     
     
         18 . The apparatus of    claim 17   , wherein: 
 said means for generating compares an amplitude derived from said input signal to a threshold value.    
     
     
         19 . The apparatus of    claim 17   , wherein: 
 said means for detecting, while in said hard detection mode, does not use a probability related value to perform detection on said input signal.    
     
     
         20 . The apparatus of    claim 19   , wherein: 
 said means for detecting, while in said soft detection mode, compares a first probability related value to a second probability related value.