초록 ▼

The invention is a modulation system that encodes symbols in accordance with a modulation code which, for a given communications channel, produces a signal that at the decoder includes maximized sample timing information in each encoded symbol. For systems that use PLLs to control a sample timing cl

The invention is a modulation system that encodes symbols in accordance with a modulation code which, for a given communications channel, produces a signal that at the decoder includes maximized sample timing information in each encoded symbol. For systems that use PLLs to control a sample timing clock, the sample timing information is the average or squared slope. The modulation code used for a given system is selected based on the target response h(x) of the associated communications channel, such that h (x)*rk exceeds a predetermined threshold value, where “*” represents convolution and rk is a modulation code symbol. To reduce the bit overhead, or code rate, the inventive modulation system provides more modulation code symbols at the start of a data block, or sector, when system jitter is expected to be relatively high in response, for example, to the movement of a read head. The system then includes fewer modulation code symbols later in the block, when the system jitter associated with a read or receive operation is reduced. The system thus provides sufficient timing information to minimize PLL jitter.

대표청구항 ▼

1. A system for encoding data, the system including:A. a communications channel that modifies multiple-bit symbols; and B. a modulation code encoder that encodes the data to produce multiple-bit modulation code symbols rk that are provided to the communications channel, the encoder encoding the data

1. A system for encoding data, the system including:A. a communications channel that modifies multiple-bit symbols; and B. a modulation code encoder that encodes the data to produce multiple-bit modulation code symbols rk that are provided to the communications channel, the encoder encoding the data in accordance with a modulation code that for a given code rate produces symbols that, after modification by the communications channel, include maximized bit timing information. 2. The system of claim 1 wherein the modulation code encoder produces the modulation code symbols that after manipulation by the communications channel are associated with average squared slopes that exceed the average squared slopes of other symbols of the same length.3. The system of claim 1 whereina. the target function is h(x); and b. the modulation encoder produces the modulation code symbols rk for which an average squared value of rk convolved with a first derivative of h(x) exceeds a predetermined threshold value. 4. The system of claim 2 whereina. the communications channel includes a magnetic medium for retaining the multiple-bit symbols in multiple-symbol blocks; and b. the modulation encoder produces the modulation code symbols that are to be recorded in predetermined locations within the blocks, the locations being selected based on a profile of system jitter associated with receiving or retrieval operations, with more locations selected for portions of the block that are associated with relatively large system jitter and fewer locations selected for portions of the block associated with less system jitter. 5. The system of claim 1 further includingB. an error correction encoder that encodes data bits to produce m bit error correction code symbols; and C. the modulation encoder encodes selected m-bit data and error correction code symbols to produce m+1 bit modulation code symbols, the encoder associating a given m-bit symbol with one of the 2m (2m+1)-bit symbols that after manipulation in accordance with a target function associated with the communications channel has an average squared slope above a predetermined threshold value. 6. The system of claim 5 wherein the modulation encoder encodes all of the data and error correction code symbols.7. The system of claim 5 wherein the modulation encoder encodes the data and error correction code symbols that correspond to selected locations within a block for recording.8. The system of claim 7 wherein the predetermined locations are selected based on a profile of system jitter associated with receiving or retrieval operations, with more locations selected for portions of the block associated with relatively large system jitter and fewer locations selected for portions of the block associated with less system jitter.9. A system for producing bit timing information, the system including:A. a communications channel with a target response; B. a modulation encoder for encoding multiple-bit symbols in accordance with a modulation code that produces modulation code symbols rk that after modification by passing through the communications channel are associated with maximized timing information; C. a decoder for taking samples of the modulation code symbols after the symbols have passed through the communications channel, the decoder i. comparing the amplitudes of the samples with amplitudes of corresponding generated waveforms and producing an amplitude error signal, ii. multiplying the amplitude error signal by the slopes of the corresponding generated waveforms and producing a phase error signal, and iii. using the phase error signal to drive into synchronism with the bits of the modulation code symbols a clock that controls the taking of the samples. 10. The system of claim 9 wherein the decoder estimates the bit values of signal samples and generates the waveforms based on the estimates.11. A method of recording symbols in blocks of a magnetic storage medium, the method including:A. determining a profile of system jitter associated with reading a recorded block; B. determining locations in the block for modulation code symbols by selecting a relatively closely spaced locations for the modulation code symbols in portions of the block that in the profile are associated with relatively large system jitter and selecting locations for the modulation code symbols that are more spaced apart in portions of the block that in the profile are associated with relatively small system jitter. C. encoding symbols associated with the selected locations in accordance with a modulation code to produce corresponding modulation code symbols; and D. recording the modulation code symbols in the associated selected locations. 12. The method of claim 11 wherein the encoding step includes encoding in accordance with a modulation code that produces symbols that, after being read from storage, include maximized bit timing information.13. The method of claim 12 wherein the encoding step produces modulation code symbols that, after being read from storage, have average squared slopes above a selected threshold value.14. The method of claim 12 further including the steps ofE. reading the block; F. sampling the modulation code symbols; G. assigning estimated bit values to the samples; H. generating waveforms that correspond to the estimated bit values; I. comparing amplitudes of the samples and the corresponding waveforms to produce an amplitude error signal; J. multiplying the amplitude error signal by the slope of the corresponding waveform to produce a phase error signal; and K. using the phase error signal to drive a clock that controls the timing of the taking of the sample into synchronism with the bits of the modulation code symbols. 15. A modulation code for encoding m-bits to produce (m+t)-bit code symbols, the code for use with a system that includes a communications channel that modifies code symbols, the code being generated by selecting from a possible 2m+t symbols the 2m symbols that when modified by the channel result in symbols with maximized bit timing information.16. The modulation code of claim 15 wherein the maximized timing information is average squared slope of the code symbols as modified by the channel.17. The encoding system of claim 15 whereina. the channel modifies symbols in accordance with a target function; and b. the modulation code includes code symbols that when modified by convolving with the target function have average squared slopes that are greater than the averaged squared slopes associated with the symbols that are not part of the code. 18. An encoding system including:A. a communications channel that modifies (m+t)-bit code symbols; and B. an encoder that encodes m bits to produce the (m+t)-bit code symbols that are provided to the communications channel, the encoder encoding the m bits in accordance with a code that has as symbols the 2m symbols of the possible 2m+t symbols that when modified by the channel have more bit timing information than the symbols that are not part of the code. 19. A modulation code for encoding m-bits to produce (m+t)-bit code symbols, the code for use with a system that includes a communications channel that modifies code symbols in accordance with a target function, the code being generated by selecting from a possible 2m+t symbols the 2m symbols that when convolved with the target function result in symbols with maximized bit timing information.20. A modulation code for encoding m-bits to produce (m+t)-bit code symbols, the code for use with a system that includes a communications channel that modifies code symbols in accordance with a target function, the code being generated by selecting from a possible 2m+t symbols the 2m symbols that when convolved with the target function result in symbols with sharper bit transitions than the (m+t)-bit symbols that are not selected.