Data readers

Abstract

A data reader arranged to produce a signal on reading a data holding medium ( 4 ), said data reader comprising processing circuitry ( 8 ) arranged to process said signal, said processing circuitry including a filter ( 14 ) having a variable cut-off frequency (F c ), a velocity signal generator ( 23 ) arranged to produce a signal ( 21 ) corresponding to the velocity of the data holding medium ( 4 ), and a processor ( 22 ), said processor ( 22 ) being arranged to read the velocity signal ( 21 ) and set the cut-off frequency (F c ) of the filter ( 14 ). The data reader is generally arranged to be incorporated into a tape drive ( 2 ) arranged to be used as a computer data storage device.

1 . A data reader arranged to produce a signal on reading a data holding medium, said data reader comprising processing circuitry arranged to process said signal, said processing circuitry including a filter having a variable cut-off frequency, a velocity signal generator arranged to produce a signal corresponding to the velocity of the data holding medium, and a processor, said processor being arranged to read the velocity signal and vary the cut-off frequency of the filter in substantially linear relation to variations in the velocity signal on the basis of data generated during a calibration process of only the particular data reader.  
   
   
       2 . A data reader according to  claim 1  wherein the velocity signal generator comprises a read head arranged to produce said velocity signal on reading a data holding medium.  
   
   
       3 . A data reader according to  claim 2  wherein said read head is arranged to read markers on said data-holding medium in order to produce said velocity signal.  
   
   
       4 . A data reader according to  claim 1  wherein said processor is arranged to determine the frequency of said velocity signal in order to vary said cut-off frequency of said filter.  
   
   
       5 . A data reader according to  claim 1  wherein said processor is arranged to vary said cut-off frequency of said filter by referring to a look up table, the values of which look up table were generated during the calibration process.  
   
   
       6 . A data reader according to  claim 1  wherein said processor includes an output register arranged such that the contents of said register controls said filter cut-off frequency.  
   
   
       7 . A data reader according to  claim 6  wherein a Digital to Analogue Converter (DAC) is provided within said processing circuitry and is arranged to produce an analogue signal to control said filter cut-off frequency.  
   
   
       8 . A data reader according to  claim 7  wherein said DAC is arranged to have input thereto the value that is contained in said output register of said processor.  
   
   
       9 . A data reader according to  claim 8  wherein said filter is arranged to have an increased gain in the region of said cut-off.  
   
   
       10 . A data reader according to  claim 1  arranged to cause the velocity of said data-holding medium to be varied over any velocity within a predetermined range.  
   
   
       11 . A data storage device incorporating a data reader according to  claim 1 .  
   
   
       12 . A data storage device according to  claim 11  wherein a buffer is provided and arranged to receive data sent to said device.  
   
   
       13 . A data storage device according to  claim 12  wherein said data reader is arranged to cause the velocity of the data-holding medium to be varied according to the amount of data present in the buffer.  
   
   
       14 . A data storage device according to  claim 13  that is arranged to receive magnetic tapes wherein said magnetic tape provides said data-holding medium.  
   
   
       15 . A method of reading data from a data-holding medium to produce an output signal, the method comprising determining the velocity of the data holding medium and varying the cut-off frequency of a filter in substantially linear relation to variations in the velocity of the data holding medium on the basis of data generated during a calibration process of only the particular data reader.  
   
   
       16 . A method according to  claim 15  including consulting a look up table to vary the cut-off frequency.  
   
   
       17 . A method according to  claim 16  in which the values in the look up table are set by the calibration process.  
   
   
       18 . A method according to  15  in which the filter is arranged to provide gain to a signal fed thereto in a region of said appropriate cut-off frequency.  
   
   
       19 . A method according to  claim 15  in which the processor utilises a clock signal generated by a read head to determine the velocity of the data-holding medium.