Performance of serially concatenated turbo coding systems using various RLL codes is evaluated along with that of PRML systems. Error rates of these systems are experimentally estimated by an actual R/W channel using a spinstand with a double-layered perpendicular medium. The experimental results show that EPR3ML and E^2PR3ML systems give the best performance among PRML systems and PR1 system provides the best performance among RLL coded serially concatenated turbo coding system. Results also show that 32/33(0, 6)code exhibits the best performance among RLL codes.
Media noise of perpendicular magnetic recording media was investigated by statistical approach. An analysis in association with a Lorentzian correlation function and a numerical simulation with Voronoi cell modeling were used. A proportional relation between cluster size and noise voltage was confimed in contrast to a calculation considering cross-track correlation length only that shows less dependency. Size variation of the clusters increased noise voltage. Fine fluctuation of transition line was dramatically suppressed by averaging effect of finite readback track width, therefore, experimental result of the relatively large cluster size was considered to be caused by some real magnetic irregularity.
The transition position jitter which is one of the dominant source of the medium noise in double-layered perpendicular magnetic recording media corresponds to the noise power spectrum. The average transition waveform gives the discrete signal spectrum. The CN ratio for the Fourier spectrum of the waveform with the transition jitter was compared with that of the measured spectrum in order to estimate the jitter value. Applying the jitter estimation method to a Co-Cr-Nb-Pt double-layered perpendicular magnetic recording medium, the jitter value was suggested to be small.
Double layer perpendicular recording media employing highly square CoPtCrO recording layer with low noise granular structure and multi-layered [FeAlSi/C]n soft underlayer have been developed. Dynamic performance test revealed that the double layer CoPtCrO perpendicular exhibited the high output signal and the high resolution recording performance at the same time. Signal decay test also indicated the superior thermal stability.
As a high density approaches on optical disk receding, we have developed PR(3, 4, 4, 3)ML system on 8-16 modulation code under d=2 condition and implemented for PRML Digital Read Channel System LSI. When PRML is applied to optical disk, some issues apprise. These issues have solved by improving adaptive equalization system and PLL system. As a result, the improvement for play back characteristic and tilt margin for 0.2 degree were verified on the actual optical disk drive. This system LSI has introduced into 4.7GB DVD-RAM drive. Also this PRML system will be very effective way to achieve higher density on optical recording.
Applying PRML signal processing method has enabled SuperDisk, one of the major high capacity floppy disk drive format, to increase the linear density. As a result, the capacity of SuperDisk has increased from 120MB to 240MB. This high density recording technology also contributes to develop "FD32MB", which can store 32MB on traditional floppy disk. Furthermore, we have developed system LSI by integrating read channel, servo, controller and SRAM into one chip. This analog digital mix one chip system LSI will be able to make the product with lower cost, less components and less power consumption.
Limits in estimating reproduced waveforms at high linear recording density and density response curves by superposing reproduced isolated pulses are studied. First, a method of averaging measured isolated pulses from an MR head on a spin-stand tester by cross-correlation is described. Then, reproduced waveforms at high linear recording density are simulated by superposition of the averaged reproduced isolated pulses and compared with the measured ones. The results show that the estimable limitation in the superposition method exists at some high linear density, since the measured isolated pulses include noise. It is also shown that the density response curves can be correctly estimated by this method, even when amplitude asymmetry between positive and negative isolated pulses exists up to that limited linear density.