Coded data generation or conversion – Digital code to digital code converters – To or from run length limited codes
Reexamination Certificate
2002-07-30
2003-12-16
Tokar, Michael (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from run length limited codes
C341S050000, C341S058000, C341S094000, C341S102000, C341S103000, C341S107000
Reexamination Certificate
active
06664904
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for recovering data to be decoded, and more particularly to a method for recovering nT run length limited (RLL) constrained data to be decoded to user data. The present invention also relates to a device for recovering nT RLL constrained data.
BACKGROUND OF THE INVENTION
Computer storage systems (such as optical, magnetic, and the like) record digital data onto the surface of a storage medium, which is typically in the form of a rotating magnetic or optical disc, by altering a surface characteristic of the disc. The digital data serves to modulate the operation of a write transducer (write head) which records binary sequences onto the disc in radially concentric or spiral tracks. When reading this recorded data, a read transducer (read head), positioned in close proximity to the rotating disc, detects the alterations on the medium and generates a sequence of corresponding pulses in an analog read signal. These pulses are then detected and decoded by read channel circuitry in order to reproduce the digital sequence.
Detecting and decoding the pulses into a digital sequence can be performed by a simple peak detector in a conventional analog read channel or, as in more recent designs, by a discrete time sequence detector in a sampled amplitude read channel. Discrete time sequence detectors are preferred over simple analog pulse detectors because they compensate for intersymbol interference (ISI) and are less susceptible to channel noise. Consequently, discrete time sequence detectors increase the capacity and reliability of the storage system. There are several well known discrete time sequence detection methods including discrete time pulse detection (DPD), partial response (PR) with Viterbi detection, maximum likelihood sequence detection (MLSD), decision-feedback equalization (DFE), enhanced decision-feedback equalization (EDFE), and fixed-delay tree-search with decision-feedback (FDTS/DF).
When transmitting data or, for example, storing data on a magnetic disk, optical disk, magneto optic disk, or other storage medium, the data is modulated so as to make it suitable for the transmission or storage. An nT run length limited (nT RLL) code is known as one of such modulating codes, wherein T is the bit interval of a channel bit series (storage waveform series) and nT is the minimum inversion interval. In other words, nT RLL encoding constrains to n the minimum number of “0” or “1” consecutive bits appearance before inverting to bit “1” or “0”.
Please refer to
FIG. 1
which is a partial functional block diagram illustrating a conventional optical pickup device. An analog read signal V outputted from a pickup head is processed by a signal processing device that includes a variable gain amplifier
10
, an analog-to-digital converter
11
, a retiming system
12
and a gain control feedback device
13
. The variable gain amplifier
10
adjusts the amplitude of the analog read signal V, and an analog filter (not shown) provides initial equalization toward the desired response as well as attenuating aliasing noise. The analog-to-digital converter
11
asynchronously samples the equalized analog read signal from the analog filter at a time interval T. The asynchronous sample values are applied to the gain control feedback device
13
through and to the retiming system
12
for adjusting the amplitude of the analog read signal V and the frequency and phase of the asynchronous sample values, respectively. The retiming system
12
thus generates synchronous samples Xn. The synchronous samples Xn are then input into a discrete time sequence detector
14
, such as a maximum likelihood (ML) Viterbi sequence detector, which detects an estimated binary sequence Bn from the synchronous sample values. A 3T RLL decoder
15
, such as a table mapping demodulator, decodes the estimated binary sequence Bn from the sequence detector
14
into estimated user data.
According to the 3T RLL encoding format, essentially single and double repetitive bits are not allowed, i.e. a minimum of three consecutive bits of “0”s or “1”s is required. Hence, when the binary sequences 111
—
010
—
111 and 000
—
101
—
000 appear, the binary sequences will be automatically corrected into 111
—
000
—
111 and 000
—
111
—
000, respectively, thereby recovering the bit data. However, when the following situation happens, it is troublesome to recover data correctly. Please refer to
FIG. 2
which is a diagram illustrating the waveform of the analog read signal V, the synchronous sample value sequence Xn and the estimated binary sequence Bn. A preset level Vr is used to determine corresponding high or low levels of the sampling values of the synchronous sample value sequence Xn so as to obtain the estimated binary sequence Bn. For the sample values of the sequence Xn larger than Vr, the corresponding bit values thereof are determined to be “1”s, and on the contrary, the bit values are “0”s for those sampling values smaller than the preset value Vr. Hence, when the estimated binary sequence Bn is 111
—
1001
—
111 as shown in
FIG. 2
, it is sure that there is an error in the sequence Bn because of its origination from the 3T RLL encoding format. The binary sequence Bn is supposed to be either 111
—
0001
—
111 or 111
—
1000
—
111. According to the conventional method, however, it cannot determine which sequence is the correct data.
Therefore, the purpose of the present invention is to develop a method and a device for recovering the correct nT RLL constrained data to deal with the above situations encountered in the prior art.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and a device for recovering nT run length limited (RLL) constrained data to be correctly decoded in an nT RLL decoder.
According to an aspect of the present invention, there is provided a method for recovering a data required to have n consecutive and repetitive “0” and “1” bits. The data is obtained by converting a sample value sequence into a binary sequence according to a preset value and the data having n−1 consecutive first-level bits and two second-level bits immediately adjacent to two end bits of the n−1 consecutive first-level bits, respectively. The method corrects one of the two second-level bits, which has a corresponding sample value closer to the preset value than the other, into another first-level bit to obtain n consecutive first-level bits.
In an embodiment, the first-level bit is bit “1” and the second-level bit is bit “0”.
In another embodiment, the first-level bit is bit “0” and the second-level bit is bit “1”.
For example, the preset value can be zero.
For example, n can be equal to 3.
According to another aspect of the present invention, there is provided a device for recovering a data including n−1 consecutive first-level bits with two second-level bits immediately adjacent to two end bits of the n−1 consecutive first-level bits to a data including n consecutive first-level bits. The device includes a first storing device for storing an analog signal sequence including n sample values, a second storing device for storing a binary sequence that is converted from the sample value sequence according to a preset value so as to include the n−1 consecutive first-level bits with the two second-level bits, and a comparative bit detector electrically connected to the first and second storing devices, and correcting one of the two second-level bits in the second storing device, which has a corresponding sampling value in the first storing device closer to the preset value than the other, into another first-level bit to obtain n consecutive first-level bits.
According to a further aspect of the present invention, there is provided a data-recovering device for recovering nT RLL constrained data that is to be used in an nT RLL decoder. The data-recovering device includes a first storing device for storing a sampling value sequence including a plurality of sample values, a second storing device for storing a binary sequence
Mar William
Wen Luke
Madson & Metcalf
Nguyen Linh Van
Tokar Michael
Via Optical Solution, Inc.
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