Shogo Miyanabe

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.

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.