JP2870060B2 - Encoding method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoding method applied to recording and reproducing digital data on a recording medium such as an optical disk.

[Conventional technology]

When digital data is recorded on a recording medium such as an optical disk or a magnetic tape, as shown in FIG.
An NRZ at which the level becomes low at "0" and an NRZI at which the waveform is inverted at the center of the bit cell at "1" are known.
In the case of NRZ, the level of the recording waveform or its edge corresponds to data information, and in the case of NRZI, the edge of the recording waveform corresponds to data information.

In the case of magnetic recording / reproduction, a reproduction waveform is taken out as a differential waveform by a magnetic head. In the case of an optical disk, since a DC component can also be reproduced, a reproduced signal having a slightly reduced recording waveform shown in FIG. 4 can be obtained. In the reproduction waveform of this optical disk, in the case of NRZ, a DC threshold level is set, and data is decoded from the relationship between the threshold and the reproduction level. In the case of NRZI, edge information was obtained from the zero cross of the waveform obtained by differentiating the reproduced waveform twice, and the data was decoded.

[Problems to be solved by the invention]

In an optical disk reproducing apparatus, the level of a reproduced signal fluctuates due to a tracking error, a focus error, a skew between the optical axis of the read light from the optical pickup and the disk surface, and the like. Therefore, when the threshold value for the reproduced signal or the waveform obtained by the second differentiation is fixed, there is a problem that the reproduced data cannot be correctly decoded. For this reason, it is necessary to perform a process of detecting the level fluctuation of the reproduced signal and changing the threshold level in accordance with the detected level fluctuation.

Conventionally, the envelope of the playback signal is frequency discriminated,
The level fluctuation of the reproduction signal was detected from the frequency discrimination output. However, in the conventional configuration, the configuration of the detection circuit is complicated, and since the detection circuit is configured by an analog circuit, there is a problem in the implementation of an IC and a problem of temperature drift occurs.

Therefore, an object of the present invention is to enable the threshold value to be correctly set in accordance with a reproduced signal with a simple digital circuit configuration,
As a result, it is an object of the present invention to provide an encoding method for recording on which data can be accurately decoded on the reproducing side.

[Means for solving the problem]

According to the present invention, data having a specific value on a recording waveform obtained at the time of reproduction is allocated to a fixed bit position R for each predetermined period, corresponding to a data sequence recorded on a recording medium by a predetermined modulation method. An encoding method comprising: detecting a reproduction level at a fixed bit position R based on a clock synchronized with reproduction data from a recording medium; and normalizing a reproduction signal level based on the detected reproduction level. It is.

[Action]

Fixed bit position R of the data sequence to be recorded and reproduced
Can be known on the playback side. On the reproducing side, the level of the fixed bit position R is detected, and a threshold value TH is formed according to the detected level. The threshold TH and the reproduction signal are compared in level, and the data is decoded. Since the setting of the threshold value TH is appropriately performed according to the level fluctuation of the reproduction signal, the decoding is correctly performed.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes an input terminal to which a reproduction signal reproduced from an optical magnetic disk by an optical pickup is supplied.

This reproduced signal is supplied to the A / D converter 2 and is converted into, for example, 8-bit digital data. An output signal of the A / D converter 2 is supplied to a digital subtraction circuit 3 and a delay circuit 4. The delay circuit 4 delays data for a period of one bit cell. The output signal of the delay circuit 4 is supplied to the subtraction circuit 3. In the subtraction circuit 3, the output signal of the delay circuit 4 is subtracted from the output signal of the A / D converter 2, and the subtraction output is supplied to the comparison circuit 5. The subtraction circuit 3 generates an absolute value of the subtraction output.

The comparison circuit 5 has a threshold value from the threshold value determination circuit 6.
TH is supplied. The comparison circuit 5 compares the level of the subtraction output with the threshold value, and forms a high level when the subtraction output is greater than the threshold value TH and a low level when the subtraction output is smaller than the threshold value TH. Is done. This comparison output is taken out to the output terminal 7 as reproduction data.

This embodiment is a case of the NRZI recording modulation method,
In the data recorded on the magneto-optical disk, a two-bit pattern of "00" is inserted at a fixed bit position R every predetermined period. By detecting the 2-bit reproduction level at the bit position R, the threshold value TH is determined from the detected output.

The output signal of the A / D converter 2 is supplied to a latch 8, and the output of the latch 8 is supplied to a threshold value determination circuit 6. The subtraction output of the subtraction circuit 3 is supplied to the latch 9, and the output of the latch 9 is supplied to the threshold value determination circuit 6. The threshold value determination circuit 6 determines an appropriate threshold value TH from the values latched by the latches 8 and 9, and outputs the appropriate threshold value TH to the comparison circuit 5. A latch pulse P2 is supplied from the timing generation circuit 10 to these latches 8 and 9.

The timing generation circuit 10 also generates a clock P1 for the A / D converter 2. These clock P1 and latch pulse P2 need to be synchronized with the reproduced data. PLL1
1 forms a clock synchronized with the reproduction data, and supplies this clock to the timing generation circuit 10. A reproduction output of a pit for a clock formed at a predetermined position on the track is supplied to the PLL 11. The fixed bit position R is determined based on the timing of the clock pit.

The operation of one embodiment of the present invention will be described with reference to FIG. FIG. 2A shows the recorded data, which is
In the case of NRZI, it is recorded on the magneto-optical disk as the waveform shown in FIG. 2B. A fixed bit position R is provided for each predetermined number of bits of the recording data.
Bits are arranged. The reproduction signal shown in FIG. 2C corresponding to the recording waveform is supplied to the input terminal 1.

In the timing generation circuit 10, the clock shown in FIG.
P1 is formed, and the reproduced signal is A / D-converted by the clock P1. Accordingly, a digital output having a level between 0 and 255 is generated from the A / D converter 2 as shown in FIG. 2E. The output signal of the A / D converter 2 is delayed by the delay circuit 4 to obtain a delayed output shown in FIG. 2F. Subtraction circuit 3
Then, the signal of FIG. 2F is subtracted from the signal of FIG. 2E,
A subtraction output shown in FIG. 2G is formed as an absolute value.
This subtraction output is compared with a threshold value TH indicated by a one-dot chain line in a comparison circuit 5, and as shown in FIG. 2, reproduced data corresponding to the recorded data is decoded. However, the waveform in FIG. 2 represents data in NRZ.

In the timing generation circuit 10, a latch pulse P2 shown in FIG. 2H is formed. In the latch circuit 8, the level of the bit position R of the output signal (FIG. 2E) of the A / D converter 2 is latched by the latch pulse P2. In addition, the latch circuit 9
Then, the level of the bit position R of the output signal (FIG. 2G) of the subtraction circuit 3 is latched by the latch pulse P2.

The threshold value determining circuit 6 determines the level of the threshold value TH from the outputs of the latch circuits 8 and 9. The reason why the 2-bit bit position R is provided in the case of NRZI is to prevent a level transition from occurring in the bit position. When determining the threshold value TH, the outputs of the two latch circuits 8 and 9 are referred to in order to utilize the fact that the 2-bit pattern is "00". For example, for the first value obtained by adding 127 of the digital value to the average value of the output of the latch circuit 8, the value of (k <
By adding the value obtained by multiplying the coefficient k in 1), the threshold value TH is obtained.
Is formed. Various other methods for determining the threshold value are also possible.

The present invention is different from the embodiment and can be applied to the NRZ method. In this case, the bit position R is set to one bit as shown in FIG. 3, and "0" data is arranged in the bit position R. In the case of NRZ, the value of the bit position R is detected on the reproduction side, and a threshold value TH of a level that follows a change in this value is formed.

When recording digital data, the original M-bit data is converted into an N (> M) -bit code in order to reduce the DC component and facilitate self-clocking (M-
N) Transforms are often used. The present invention relates to (M-
N) The present invention is also applicable to a recording / reproducing system that uses conversion as channel coding. In this case, bit position R
"0" or "00" can be used also as a connection bit between the converted codes.

Further, the length of the fixed bit position may be longer than in the above example.

〔The invention's effect〕

According to the present invention, since data whose position and value are defined corresponding to a recording waveform in a predetermined modulation method (NRZ, NRZI, etc.) are arranged to form an area where no edge appears, a threshold adapted to a modulation signal is provided. A value can be set, and the use of existing data such as a combination bit as data at a fixed bit position has an advantage that the redundancy can be not increased.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a timing chart used for explaining the operation of one embodiment of the present invention, FIG. 3 is a waveform diagram used for explaining the case of NRZ, and FIG. FIG. 11 is a waveform diagram used for describing a conventional recording waveform. Description of main reference numerals in the drawings 1: input terminal of reproduced data, 3: subtraction circuit, 6: threshold value determination circuit, 7: output terminal, 8, 9; latch circuit.

Claims (1)

(57) [Claims] 1. A data having a specific value on a recording waveform obtained at the time of reproduction is allocated to a fixed bit position R at a predetermined period corresponding to a data sequence recorded on a recording medium by a predetermined modulation method. In addition, the reproduction level at the fixed bit position R is detected based on a clock synchronized with the reproduction data from the recording medium, and the level of the reproduction signal is normalized based on the detected reproduction level. Encoding method to be used.