Phase-locked loop for an electronic sectoring scheme for rotating magnetic memory

Abstract

In a rotating magnetic memory, a phase-locked loop tracks pulses derived from sector marks on means mechanically connected to rotate with the memory. The output frequency of the phase-locked loop, which is significantly higher by a factor of N than the frequency of the sector mark pulses, is cyclically counted down to divide each revolution of the memory into M equally time spaced sectors. Third and fourth order filtering in the phase-locked loop assures a high degree of precision and consistency in the sectoring.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: .[.1. Apparatus for electronically dividing a rotating memory into a whole number of equally time spaced sectors comprising: 
     
        cycles during each revolution of said memory..]. .[.3.  The combination defined in claim 1 including higher order low pass filtering than second order filtering of any correction voltage signal derived from phase comparison of said sector marks and said feedback signal..]. .[.4. The combination in claim 3 including: means for providing an index mark to rotate in unison with said sector marks,   means for detecting said index mark to produce an index pulse once per revolution of said memory, and   means for synchronizing said means for counting down cycles of said output signal, whereby division of each memory revolution into a whole number of equally time spaced sectors begins at the same point during each   
     
     
        revolution of said memory..]. .[.5.  Apparatus for generating a sector timing signal which divides one revolution of a rotating magnetic memory into a whole number of equally time spaced sectors comprising: a surface connected to rotate on the same axis with said memory, said surface having a plurality of equally spaced sector marks on a circle, the center of said circle being on said axis,   means for sensing said sector marks as they pass by a fixed point in space during each revolution of said memory to generate a continuous train of pulses at a frequency that is a function of the speed with which said memory revolves about said axis,   a phase-locked loop for producing output pulses at a higher frequency by a known factor, said phase-locked loop being connected to receive said continuous train of pulses, whereby the output pulses of said phase-locked loop are synchronized with said continuous train of pulses, and   means for counting down output pulses from said phase-locked loop to effectively divide the total number of output pulses produced during each revolution of said record medium into a whole number of equally spaced sectors thereby producing at the output of said count-down means a cyclic waveform having a period for each cycle equal to the time-space of each sector..]. .[.6. The combination in claim 5 including higher order low pass filtering than second order filtering of any correction signal derived from any phase error between said train of pulses generated from   
     
     
        said sector marks and a feedback signal in said loop..]. .[.7.  The combination of claim 6 including: means for providing an index mark to rotate in unison with said sector marks,   means for detecting said index mark to produce an index pulse once per revolution of said memory, and   means for synchronizing said means for counting down cycles of said output signal, whereby division of each memory revolution into a whole number of equally time spaced sectors begins at the same point during each revolution of said memory..]. .Iadd. 8. Apparatus for electronically dividing a rotating memory into a whole number of equally time spaced sectors comprising:   means mechanically connected to rotate in unison with said memory, said means being divided into a number of evenly spaced sectors by sector marks,   means for detecting said sector marks and generating a train of sector pulses at a frequency f ± Δf, where Δf represents the magnitude of fluctuations in frequency of the sector pulses due to fluctuations in the speed of revolution of said memory,   a phase-locked loop having an oscillator controlled by a correction signal for producing an output signal at a frequency significantly greater than said train of sector pulses by a known factor, said correction signal being so produced as to stabilize the loop in phase by continual phase comparison of said sector pulses with feedback pulses, said feedback pulses being produced by continually dividing cycles of said oscillator output signal by said known factor, said correction signal being proportional to the difference between a reference DC signal and a phase error signal produced by second order filtering of a signal derived from phase comparison of said sector pulses with feedback pulses,   means for third and fourth order filtering of said correction signal, and   digital means for continually dividing said output signal by a predetermined integer to produce a timing signal having a number of cycles equal to said whole number of equally time spaced sectors. .Iaddend. .Iadd. 9. Apparatus for generating a sector timing signal which divides one revolution of a rotating magnetic memory into a whole number of equally time spaced sectors comprising:   a surface connected to rotate on the same axis with said memory, said surface having a plurality of equally spaced sector marks on a circle, the center of said circle being on said axis,   means for sensing and sector marks as they pass by a fixed point in space during each revolution of said memory to generate a continuous train of sector pulses at a frequency that is a function of the speed with which said memory revolves about said axis,   a phase-locked loop having an oscillator controlled by a correction signal for producing output pulses at a frequency higher than the frequency of said sector pulses by a known factor, said phase-locked loop having a phase comparator connected to receive said continuous train of sector pulses for phase comparison with feedback pulses to produce said correction signal for any phase difference between said train of sector pulses and said feedback pulses, said feedback pulses being derived from said oscillator output pulses by said factor, said correction signal being proportional to the difference between a reference DC signal and a phase error signal produced by said comparator and filtered by a low-pass filter which provides second order filtering, whereby the output pulses of said phase-locked loop are synchronized in phase with said continuous train of pulses,   means for third and fourth order filtering of any correction signal derived from any phase error between said train or sector pulses generated from said sector marks and said feedback pulses, and   means for counting down output pulses from said phase-locked loop to effectively divide the total number of output pulses produced during each revolution of said record medium into a whole number of equally spaced sectors thereby producing at the output of said count-down means a cyclic waveform having a period for each cycle equal to the time-space of each sector. .Iaddend.