A rate 16/18 trellis code in conjuction with EPR4 signaling on magnetic recording channels and the associated time-varying Viterbi detector for the code are developed. We show that EPR4ML detection with the proposed 16/18 code can provide better performance than an 8/10 trellis coded PR4ML and a 16/17 EPR4ML detection.
A time varying MTR (Maximum Transition Run) code which enhances the minimum distance by controling the timing of PRML detector trellis was introduced. This code can be made in better than 8/9 rate. This method is different from MSN (Matched Spectral Null) code which is restricted in its power spectral density, and the scale of hardware is same as uncoded one because the code doesn't have the states of itself. We have made sure that when the time varying MTR E2PR4 Viterbi detector operated once in two time slot, it needed only 14 states. We confirmed the fundamental performance for magnetic recording and the hardware needed input signal quantized into 5 to 6 bits for the performance of bit error rate 10^<-5> by simulating. We also made sure this performance on magnetic disk apparatus.
We propose a new PRML algorithm for the digital recording systems with d≧1 channel code. First, the reproducing signals are equalized to the PR1 characteristic and detected 2-level bit-by-bit. Then the state transition path are limited to four. Using this limitation, we can realize Viterbi decoder for EPR4ML systems with only 2-state. The proposed decoder can be realized easily as high speed circuit with less circuit. The performance of this decoder is a little better than the conventional decoder.
Regarding recording channels as linear transmission channels, understanding of transmission characteristics in recording channels is very important for their precise equalization. We have considered a new method for measuring transmission characteristics and surface magnetic flux distributions in recording channels using periodical pulse waves. The method makes use of the symmetrical property of waves. The transmission characteristics and surface magnetic flux distributions in recording channels on a variety of magnetic tapes have been measured using this method.
A highly sensitive magnetic sensor and a nondestructive random access memory were developed by using giant magnetoresistive (GMR) effect. The GMR devices were constructed of a multilayered structure including spin-valve film and bias current line, and the device operation was controlled by magnetic field generated by the bias current. A new sensitive GMR sensor was developed by utilizing only the MR loop edge, in which the patterned spin-valve element exhibited the step shape MR loop. In the nondestructive memory, the information was stored as the spin-valve resistance. A low electric power consumption device was realized by the differential type memory.