A.H.J. Immink

Two-dimensional optical storage

With storage capacities increasing much faster than data rates, fast read-out of content is becoming a bottleneck for the convenient use of optical storage devices. Two-dimensional optical storage (TwoDOS) is a new concept that solves this data-rate problem by using a multi-spot parallel readout system. In addition, the storage capacity is increased with a factor of at least 2. Using the same read-out physics as in the Blu-ray disc standard, single layered 12 cm discs with capacities up to 50 GB have been read out successfully at bit-rates as high as 560 Mbit/s. Basic pillars of TwoDOS are advanced signal processing and disc mastering techniques, and a proper design of the optical path.

Refinements of Multi-Track Viterbi Bit-Detection

In optical storage, data can be arranged on the disc in a meta-spiral consisting of a large number of bit-rows with a small track-pitch. Successive revolutions of the meta-spiral are separated by a narrow guard band. For high storage densities, such a system results in severe 2-D inter-symbol interference. In the multi-track Viterbi algorithm (MVA) of Krishnamoorthi and Weeks, the complex problem of 2-D bit-detection is broken down into a number of smaller bit-detection problems on sets of adjacent bit-rows called stripes. We improve the bit error rate (bER) performance of such a 2-D bit-detector via a number of measures such as: 1) weighing of the separate contributions to the branch metrics from each bit-row in a stripe and 2) inclusion of an additional contribution to the branch metrics from a bit-row adjacent to a stripe. In addition, we reduce the computational complexity by varying the number of bit-rows per stripe during successive iterations of the MVA, and through the use of local sequence feedback.

Two-Dimensional Optical Storage

Two-dimensional optical storage aims at increasing the data capacity and data rate for a given physical read-out system. It uses parallel read-out in combination with advanced signal-processing. Experimental results results on read only memory (ROM) discs are presented that proof the concept. Laser beam recorded discs proof the concept, and electron beam recorded disc show the feasibility at real physical parameters for a density at 35 GB with ample tilt margins.

Near minimum bit-error rate equalizer adaptation for PRML systems

Receivers for partial response maximum-likelihood systems typically use a linear equalizer followed by a Viterbi detector. The equalizer tries to confine the channel intersymbol interference to a short span in order to limit the implementation complexity of the Viterbi detector. Equalization is usually made adaptive in order to compensate for channel variations. Conventional adaptation techniques, e.g. LMS, are in general suboptimal in terms of bit-error rate. In this paper we present a new equalizer adaptation algorithm that seeks to minimize bit-error rate at the Viterbi detector output. The algorithm extracts information from the sequenced amplitude margin (SAM) histogram and incorporates a selection mechanism that focuses adaptation on particular data and noise realizations. From a complexity standpoint, the algorithm is as simple as the conventional LMS algorithm. Simulation results, for an idealized optical storage channel, confirm a substantial performance improvement relative to existing adaptation algorithms

Near-Minimum Bit-Error Rate Equalizer Adaptation for PRML Systems

Receivers for partial response maximum-likelihood systems typically use a linear equalizer followed by a Viterbi detector. The equalizer tries to confine the channel intersymbol interference to a short span in order to limit the implementation complexity of the Viterbi detector. Equalization is usually made adaptive in order to compensate for channel variations. Conventional adaptation techniques, e.g., LMS, are, in general, suboptimal in terms of bit-error rate (BER). In this paper, we present a new equalizer adaptation algorithm that seeks to minimize the BER at the Viterbi detector output. The algorithm extracts information from the sequenced amplitude margin (SAM) histogram and incorporates a selection mechanism that focuses adaptation on particular data and noise realizations. The selection mechanism is based on the reliability of the add compare select (ACS) operations in the Viterbi detector. From a complexity standpoint, the algorithm is essentially as simple as the conventional LMS algorithm. Moreover, we present a further simplified version of the algorithm that does not require any hardware multiplications. Simulation results, for an idealized optical storage channel, confirm a substantial performance improvement relative to existing adaptation algorithms.

Adaptation and timing recovery for two-dimensional optical storage

This paper discusses several issues related to adaptation and timing recovery for two-dimensional (2D) optical storage. In the TwoDOS format bits are stored on a 2D hexagonal lattice which is formed by recording multiple bit rows with a fixed phase relation in a so-called broad spiral or meta-spiral. Besides a large increase in data rate by reading out with multiple spots, also a density increase by a factor of two compared to Blu-ray Disc is targeted. To increase the storage density, 2D signal processing is proposed including 2D PRML detection in the form of a stripe-wise Viterbi detector. This detector introduces an increasing detection delay when going from the outer rows towards the center of the broad spiral. For fast control loops in a decision-directed mode, special measures are needed to avoid instability due to this delay. Another issue is the large span of the 2D inter-symbol interference at higher densities and tilt, leading to a large 2D equalizer. Furthermore, in case the broad spiral is recorded with a multiple-pass mastering technology (e.g. for ROM TwoDOS discs), write-channel imperfections such as time-varying lattice distortion require independent timing recovery on each row within the broad spiral.

Two-dimensional optical storage: high-speed read-out of a 50 GByte single-layer optical disc with a 2D format using lambda=405 nm and NA=0.85

With ever increasing storage capacities, long read-out times of content are becoming a bottleneck for the convenient use of optical storage devices. Two-dimensional optical storage (TwoDOS) is a new concept that solves this data-rate problem through parallel read-out. Furthermore, an increase of at least a factor of 2 in storage capacity is achieved by exploiting a two-dimensional format. The advantages offered by TwoDOS are obtained without the need of changing the physics of the read-out system. Using Blu-ray Disc optics, single-layered 12 cm discs with capacities up to 50 GByte have been read out successfully. Signal level and error analysis show the feasibility of a further capacity increase. Also, bit-rates as high as 700 Mbit/s during read-out have been reached. All this is achieved by applying advanced signal processing and advanced disc mastering techniques and the proper design of the optical path.

A 16 b accurate CMOS laser driver IC with 500 mA output current and 1.5 ns rise time

A CMOS laser driver IC combines two 500 MHz 250 mA driver DACs with on-board digital write strategy generator and PLL to achieve 2 ns timing resolution. An embedded laser power control algorithm with analog monitor diode pre-processing compensates for laser temperature variations and aging.

GEN04-6: Near Minimum-BER all-Adaptive Partial Response Equalization For High Density Recording Systems

In order to reduce the implementation complexity of maximum likelihood sequence detectors (MLSD), equalized maximum likelihood receivers are often used. This consists of employing an equalizer to transform the channel response to a short target response to which the Viterbi detector is matched. Existing equalizer and target adaptation schemes are often based on the minimum mean-square error (MMSE) criterion which is not always optimal in terms of detection bit-error rate at the Viterbi detector output. In this paper we consider minimum bit-error rate joint adaptation of equalizer and target response and present a practical adaptation algorithm that achieves near minimum bit-error rate performance. Our new equalizer and target adaptation scheme shows significant performance improvements in the presence of channel nonlinearities and media noise when compared to MMSE adaptation schemes. This is very promising for high density recording systems that are mainly hampered by media noise and channel nonlinearities. Moreover, from a complexity standpoint, the proposed algorithm is comparable to the MMSE-based algorithms.

GEN04-5: Data-Dependent Noise Estimation in Digital Recording Systems

In high-density recording systems performance is largely determined by noise, n general different noise sources are present, where each source has direct impact on the overall performance. Therefore the characterization of a noise source provides insightful information about the recording system. In general noise characterization involves the choice of an appropriate stochastic model for it and furthermore the estimation of the parameters of the selected stochastic model. The characterization results can be used as diagnostic information to evaluate existing recording systems and they play an important role in state of the art bit-detection techniques. In these techniques the estimated stochastic parameters are used as side information to improve the detection reliability. For this reason an accurate estimation is very important. The estimation algorithm proposed in this paper, achieves a high estimation accuracy for systems where both data-dependent media noise and correlated additive noise are present. This algorithm makes use of the difference in data-dependency between the two noise sources to jointly estimate the stochastic parameters of the two noise sources.