Phase locked loop with compensation for loop phase errors

Claim 1

In a phase-locked loop circuit for use in a data recovery system of a rotating magnetic disk drive unit employing a phase encoded signal format and including a phase detector, a filter coupled to the output of the phase detector, an operational amplifier coupled to the filter and a voltage controlled oscillator coupled to the output of the operational amplifier, in which the phase detector compares an input signal with the output signal of the voltage controlled oscillator and provides a control signal to the voltage controlled oscillator, the improvement comprising: adjustable voltage means for supplying a voltage signal to said operational amplifier sized to offset phase errors caused by the components in said phase locked loop circuit, said adjustable voltage means comprising a positive supply voltage source, a negative supply voltage source and a potentiometer, said potentiometer having a movable arm connected to an input of said operational amplifier and a main leg connected at one end to said positive supply voltage source and at the other end to said negative supply voltage source.

Claim 3

A system for providing phase synchronism between a first signal and a second signal comprising: a. means for comparing the frequency of a reference signal with the frequency of a feedbak signal derived from said second signal to produce a first difference signal representing the frequency difference therebetwen; b. filter and amplifying means including a filter, an operational amplifier having low input offset voltage characteristics, adjustable voltage means for supplying an adjustable voltage signal sized to offset phase errors, said adjustable voltage means comprising a positive supply voltage source, a negative supply voltage source and a potentiometer, said potentiometer having a movable arm connected to a noninverting input of said operational amplifier and a main leg connected at one end to said positive supply voltage source and at the other end to said negative supply voltage source; c. switching means between said frequency comparing means and said filter and amplifying means for supplying said first frequency difference signal to said filter and amplifying means, said later means thereby providing a first control signal representing said frequency difference; d. oscillator means responsive to said first control signal for producing said second signal, the frequency of said second signal being controlled by said first control signal so that said frequency difference is minimized so that the frequency of said feedback signal derived from said second signal is in substantial synchronism with the frequency of said reference signal; e. means for comparing the phase of said second signal with the phase of said first signal to produce a second difference signal representing the phase difference therebetween; and f. means for actuating said switching means to supply said second phase difference signal to said filter and amplifying means and to prevent said first frequency difference signal from being supplied thereto when said substantial frequency synchronism has been achieved, said filter and amplifying means thereby providing a second control signal; g. said oscillator means being responsive to said second control signal so that said phase difference is minimized and the phase of said second signal is in substantial in-phase synchronism with the phase of said first signal.

Claim 4

A system for providing phase synchronism between a first signal and a second signal comprising: a. means for comparing the frequency of a reference signal with the frequency of a feedbak signal derived from said second signal to produce a first difference signal representing the frequency difference therebetwen; b. filter and amplifying means including a filter, an operational amplifier having low input offset voltage characteristics, adjustable voltage means for supplying an adjustable voltage signal sized to offset phase errors, said adjustable voltage means comprising a positive supply voltage source, a negative supply voltage source and a potentiometer, said potentiometer having a movable arm connected to a noninverting input of said operational amplifier and a main leg connected at one end to said positive supply voltage source and at the other end to said negative supply voltage source; c. switching means between said frequency comparing means and said filter and amplifying means for supplying said first frequency difference signal to said filter and amplifying means, said later means thereby providing a first control signal representing said frequency difference; d. oscillator means responsive to said first control signal for producing said second signal, the frequency of said second signal being controlled by said first control signal so that said frequency difference is minimized so that the frequency of said feedback signal derived from said second signal is in substantial synchronism with the frequency of said reference signal; e. means for comparing the phase of said second signal with the phase of said first signal to produce a second difference signal representing the phase difference therebetween; and f. means for actuating said switching means to supply said second phase difference signal to said filter and amplifying means and to prevent said first frequency difference signal from being supplied thereto when said substantial frequency synchronism has been achieved, said filter and amplifying means thereby providing a second control signal; g. said oscillator means being responsive to said second control signal so that said phase difference is minimized and the phase of said second signal is in substantial in-phase synchronism with the phase of said first signal.