Versatile phase-locked loop for read data recovery
AssigneePertec Corporation
InventorAshok K. Desai
Life of this patent
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Abstract
A clock pulse generating system is disclosed for recovery of read data from magnetic record media comprised of a phase-locked loop for tracking data pulses. The loop employs simple digital logic gates for phase error detection, third-order filtering for the transient phase and frequency error reduction and a voltage controlled oscillator (VCO) comprised of a capacitor charged by current from a voltage controlled current source, voltage threshold detection means, and means responsive to the threshold detection means to quickly discharge the capacitor. The VCO includes a flip-flop at its output to produce a square-wave feedback signal to the phase detection gates and to a data recovery circuit.
Claims10
In a binary magnetic record recovery system, a phase-locked loop responsive to a train of read pulses for generating reference pulses for use in data recovery comprising:
- voltage controlled means responsive to a corrective phase error signal for producing two square wave feedback signals at the frequency of said train of read pulses when a known cyclic pattern of recorded pulses are being read back, one feedback signal being 180.degree. out of phase with the other,
- first coincidence gating means for comparing said train of read pulses with the phase of said one feedback signal by transmitting an output signal of a predetermined binary level only during the period of each feedback signal cycle that both are at a selected binary signal level,
- second coincidence gating means for comparing said train of data pulses with the phase of said other feedback signal by transmitting an output signal of said predetermined binary level only during the period of each feedback signal cycle that both are at said selected binary signal level,
- first and second low pass filter means for separately filtering said output signals of said first and second coincidence gating means, and
- differential amplifying means for producing said corrective phase error signal proportional to the difference between output signals of said first and second low pass filtering means connected to a pair of differential input terminals of said amplifier.
In a system for reading magnetically recorded binary data, a phase-locked loop for generating local reference pulses for use in data recovery comprising:
- a voltage controlled means responsive to a corrective voltage signal for producing two square wave feedback signals 180.degree. out of phase,
- first gating means having two input terminals and one output terminal for translating pulses from one input terminal thereof to said output terminal while one of said two feedback signals present at the other input terminal is of the same predetermined binary voltage level as pulses at said one input terminal, whereby pulse-width modulation of pulses translated is achieved as a function of phase difference between pulses at said two input terminals,
- second gating means having two input terminals and one output terminal for translating from one input terminal thereof to said output terminal while the other one of said two feedback signals present at the other input terminal is of the same predetermined binary voltage level as pulses at said one input terminal, whereby pulse-width modulation of pulses translated is achieved as a function of phase difference between pulses at said two input terminals,
- means for coupling read pulses to said one input terminal of each of said first and second gating means,
- first means for second order low-pass filtering pulses at said output terminal of said first gating means,
- second means for second order low-pass filtering pulses at said output terminal of said first gating means,
- differential means for forming a difference signal between the outputs of said first and second filtering means, and
- means for coupling said difference signal as said corrective voltage signal to said voltage control means.
Dependencies are inferred from the claim text.