Hiroki Kuribayashi

New Equalizer to Improve Signal-to-Noise Ratio

Signal-to-noise ratio (SNR) of an optical memory disc deteriorates as the recording density increases. The authors have coped with this problem and developed a new equalizer which can improve the SNR by boosting higher frequency components on the readout signal without increasing the inter-symbol interference (ISI). The authors measured the jitter values on a prototype disc applying the new equalizer. The disc had a capacity of 15 Gbytes, a track pitch of 0.37 µm and a minimum pit length of 0.25 µm. An optical head with a second harmonic generation (SHG) blue laser with a wavelength of 430 nm and an objective lens with a NA of 0.6 was used. As a result, it was confirmed that the new equalizer could improve not only the SNR but also the tilt margins. Furthermore, the correlation between the jitter and the bit error rate observed on a conventional equalizer was found unchanged even with the new equalizer.

25 GB Read-Only Disk System using the Two-Dimensional Equalizer

In order to achieve a higher density disk system, we applied a two-dimensional equalizer along with a limit equalizer to an optical disk drive system which has an objective lens with a numerical aperture of 0.85 and a thin transparent cover layer of 0.1 mm thickness. Consequently we realized the 25 GB read-only disk system with sufficient margins against disk tilt and defocus. The two-dimensional equalizer is composed of a cross-talk cancel system and a tangential adaptive equalizer, and could prevent deterioration due to inter-symbol interference and cross-talk from adjacent tracks. Using the limit equalizer could prevent deterioration due to disk noise. By measuring the jitter with the limit equalizer, which has an ability to expand the system margin almost equivalent to that of the Viterbi decoder, we could evaluate the disk quality for standardization and verification.

Signal Processing for 15/27 GB Read-Only Disk System

In order to realize 15/27 GB read-only disk systems using blue laser, new signal processing is required. The technology of large-scale integrated circuits has advanced considerably. Hence we can use a complicated circuit with a big gate size without increasing the system cost significantly when we fabricate the blue laser disk system. We have realized the 15/27 GB system using the two-dimensional equalizer and the limit equalizer. The two-dimensional equalizer was composed of the cross-talk cancel system and the asymmetry compensation type tangential adaptive equalizer. And could improve the deterioration due to the inter symbol interference and the cross-talk from the adjacent tracks. The limit equalizer could improve the deterioration due to the disk noise. Using these signal-processing systems, we could reduce the bottom jitter by more than 3% and expand the tilt margin.

Analysis of prediction level setting in PRML decoding on Blu-ray disc system

In the application of the PRML decoding to the optical disk system, an asymmetry of a reproduced signal deteriorates the decoding performance. We investigated the relation of the prediction level setting and the PRML decoding performance. When the average level of the input signal was adjusted to the center of the prediction level, the margins was deteriorated little, even if there is a signal asymmetry. We found that the PRML decoding has a good tolerance to the signal asymmetry by using a simple circuit structure.

Cross-talk Canceller for Wobbling Signal

We have developed a cross-talk canceller for a wobbling signal (WCTC). The WCTC cancels cross-talk in the wobbling signal using three push-pull signals reproduced from three adjacent tracks. Furthermore, push-pull tracking offset, caused by a shift of an objective lens, is detected from a balance between cross-talk from an inner track and that from an outer track. It is experimentally confirmed that the WCTC effectively reduces cross-talk and can detect the tracking offset.

Analysis of the Crosstalk in a High-Density Optical Disc System

A crosstalk canceler has been proposed in order to readout a signal from a high-density optical disc. We have confirmed by the computer simulations that a crosstalk canceler is highly useful technology. Furthermore, we have calculated the readout margins of the high-density optical disk system applying a blue laser, a crosstalk canceler and some other signal processing methods.

A CMOS front-end LSI with a CTC for Blu-ray disc system

A CMOS front-end LSI for the Blu-ray disc system including a crosstalk canceller, an adaptive tangential equalizer, a limit-equalizer, a Viterbi decoder was developed. It contains about 1M gates and operates up to 3/spl times/ speed and performs to improve tolerances of the system.

Tolerance of 3 beam cross-talk canceller

The next-generation digital versatile disc (DVD) is required to have a capacity of 15 Gbytes so that it can store high-definition television signals for two hours or longer. To achieve the capacity, we developed a 3 beam cross-talk canceller (CTC) which uses two sub-beams positioned on adjacent tracks to cancel cross-talk components. The sub-beam positions are varied due to a grating adjustment error, a radial deviation of a track and a wavelength change of a laser diode. Since the sub-beam offset deteriorates signals reproduced from the adjacent tracks, it might degrade a performance of the CTC system. The tolerance of the CTC system against the sub-beam offset should be discussed for practical use. We measured the performance of the CTC system when the sub-beam positions were shifted. As a result, we confirmed that the CTC system has sufficient margin against the sub-beam offset.