Cirrus Logic Inc.

Jim Graba

Paul M Romano

Louis Supino

William G Bliss

German S Feyh

Shuangxia Zhu

A sampled amplitude read channel for optical disk storage systems is disclosed comprising an all digital timing recovery circuit. The RF read signal from the read head is sampled asynchronous to the baud rate and the asynchronous sample values are interpolated to generate sample values that are substantially synchronous to the baud rate. A data detector, such as a Viterbi sequence detector, processes the synchronous sample values to generate an estimated binary sequence representing the recorded binary sequence. The timing recovery circuit comprises a baud rate estimator for estimating the baud rate relative to the sampling rate, wherein the estimated baud rate is used to initialize a timing recovery loop filter at the end of seek operations. The all digital timing recovery circuit and baud rate estimator enable the storage device to begin reading the user data immediately after a seek operation, rather than wait for the CLV servo loop to acquire the target spindle speed.

Sampled amplitude read channel employing a baud rate estimator for

A trellis sequence detector is disclosed for detecting a quadrature servo signal in optical disk storage devices. The quadrature servo signal is generated in discrete time and comprises two sinusoidal signals phase offset by 90 degrees. The sampling frequency of the quadrature signal is controlled relative to the track crossing velocity so as to produce a fixed number of samples per period of the sinusoid (i.e., per track crossing). In the embodiment disclosed herein, the sampling of the sinusoidal signals is controlled such that there are eight samples per track crossing. The eight samples are associated with a state transition diagram and corresponding trellis diagram which define the operation of a trellis sequence detector. The trellis sequence detector processes the actual samples of the quadrature signal to determine an estimated quadrature sequence closest to the actual samples of the quadrature signal. In this manner, spurious pulses in the actual quadrature signal are filtered out which significantly enhances the performance of the servo system.

Trellis sequence detector for detecting a quadrature servo signal in

In an optical disk storage device wherein user data is demodulated from a light beam reflecting off data pits in tracks of an optical disk storage medium, a quadrature seek signal is generated indicative of the light beam crossing tracks of the optical disk during a seek operation. The quadrature seek signal is generated from a discrete-time tracking error signal (TES) and a discrete-time RF baseband signal. The discrete-time TES is generated according to the mode of operation, compact disk (CD) or digital video disk (DVD). In CD mode the TES is generated as the difference between E and F tracking photodiodes, and in DVD mode the TES is generated using a discrete-time differential phase detector (DPD). To generate the discrete-time RF baseband signal, the RF data signal (generated as the sum A+B+C+D of a four quadrant photodiode) is sampled at the channel rate and the RF data samples passed through a discrete-time envelope detector. The envelope detector extracts a discrete-time RF baseband signal which represents the light beam's location with respect to a track centerline. The discrete-time TES and baseband signals are synchronized and converted into binary square waves which form a quadrature seek signal (four transitions per track) for counting track crossings and for determining the radial seek direction.

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Longmont, CO, United States of America

Jim Graba