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Fast Synchronizing Phase Locked Loop

IP.com Disclosure Number: IPCOM000080481D
Original Publication Date: 1973-Dec-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Malone, DJ: AUTHOR [+2]

Abstract

A phase-locked oscillator (PLO) is used to provide a write clock, which is synchronous to the rotational speed of a disk. A variable-frequency oscillator (VFO) is used to clock the data. The VFO may also be locked to the PLO when it is not clocking data.

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Fast Synchronizing Phase Locked Loop

A phase-locked oscillator (PLO) is used to provide a write clock, which is synchronous to the rotational speed of a disk. A variable-frequency oscillator (VFO) is used to clock the data. The VFO may also be locked to the PLO when it is not clocking data.

The PLO is locked to servo synchronization pulses which are provided by track following electronics. The VFO is locked to the read data. The input data rates to each are significantly different, the PLO being much lower which places restrictions on sync times.

The purpose of the four speed PLO is to combine the function of the two loops into one multigain loop. One problem that is solved with this concept is the sync requirement for the PLO, which can be virtually eliminated. This results in a faster turnaround when switching from read to write. This is achieved by relying on the frequency being held in the filter and by using a counter preset operation.

By using the described method switching from read to write can be provided while using one phase-locked loop and not suffer the long sync time that normally would be required.

In a binary data processing circuit, data is fed to a VFO single-shot 10 and to a data latch 12 through a select data circuit 34. The outputs of the single-shot 10 and latch 12 are compared in a phase comparator 16, and a positive or negative error signal is developed and applied to current sources 18a or 18b, respectively. The corrected signal is passed...