Osamu Kawamae

A high speed signal processing for quadruple speed CD-ROM

A high speed digital signal processor for a quadruple speed CD-ROM has been developed. It has an enhanced error correction capability and a short defect recovery time. >

Random seed scrambling method for high density phase change optical discs

Repeatedly rewriting the same channel bit pattern at the same location on a phase-change optical disc usually causes the media to deteriorate. To prevent this, the random bit shift of 128-bit and the free polarity of NRZI-converted pulses were introduced into the DVD-RAM system. However, these measures cause difficulty in the timing control at writing starts and. complication of the control of circuits. So in this paper, a new scrambling method, the Random Seed Scrambling Method is proposed. In this method, the data is scrambled using a different seed each time the data is written, so the different data is over-written at the location each time. The method of random seed scrambling has a unique characteristic that the seed is not necessary to de-scramble the scrambled data. By using this method, the amount of the high density phase-change optical disc wear is reduced.

Adaptive signal processing method using PRML for high density optical disks

Numerous types of DVD recording equipment have emerged on the market, and there is much demand for such optical storage systems with high speed and large capacity for digital high definition broadcasts. However, it becomes difficult to maintain data reliability with increasing recording speed and density, because the signal to noise ratio degrades and recording control of the phase changed mark becomes difficult. To improve the error rate of reproduced data, PRML (partial response maximum likelihood) decoding is expected to be used. We have developed a more advanced method of PRML, where the difference of the reproduced waveform is analyzed and the PRML decoder is compensated. In this paper we report the analysis of the reproduced waveform and the effect of the developed PRML algorithm.