Browse Prior Art Database

Quantized Phase Detector for a Magnetic Disk Storage System

IP.com Disclosure Number: IPCOM000046914D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Goretzki, JA: AUTHOR [+3]

Abstract

Most magnetic disk files require a phase-locked oscillator to synchronously decode the data pulses which have been written on the disk. Digital processing and synchronous decoding occur after the amplification of data signals read from the disk. "Data windows" are used to determine the length of the magnetic domains which have been recorded on the disk. The phase-locked loop (PLL) continuously synchronizes the oscillator with the received data pulses. Because of the limited control loop bandwidth, the PLL will average the time between received data pulses while accommodating any variations in spindle speed. The PLL functions much like an electronic tachometer, placing precisely centered data windows around the circumference of the disk.

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Quantized Phase Detector for a Magnetic Disk Storage System

Most magnetic disk files require a phase-locked oscillator to synchronously decode the data pulses which have been written on the disk. Digital processing and synchronous decoding occur after the amplification of data signals read from the disk. "Data windows" are used to determine the length of the magnetic domains which have been recorded on the disk. The phase-locked loop (PLL) continuously synchronizes the oscillator with the received data pulses. Because of the limited control loop bandwidth, the PLL will average the time between received data pulses while accommodating any variations in spindle speed. The PLL functions much like an electronic tachometer, placing precisely centered data windows around the circumference of the disk. These data windows determine the time period in which the system looks to see if a "one" or a "zero" has been recorded at the location. Ideally, a phase-locked loop is used to synchronize an oscillator to another continuously appearing signal. In the case of a data stream read from a disk file, the occurrence of data pulses is dependent on the data which was recorded and there is no way of predicting whether or not a pulse will occur during the next interval. The common technique for overcoming this program is to delay the data pulse by exactly one-half the duration of the data window so that it is known whether or not the data pulse will occur in the next interval. While this is a satisfactory solution from the technical standpoint, it requires a very precisely timed delay element. Such elements are expensive and do not lend themselves well to incorporation in large-scale integrated circuits. In Fig. 1, flip-flop 1 is triggered by the leading edge of the data pulse read from the disk. The output Q1 is connected to the input of Delay 1 to provide a delayed output Q2. The delayed output Q2 resets flip-flop 1 and drives the input of Delay 2. AND gate 3 combines Q1 and Q2 to provide signal A. AND gate 2 combines the o...