JPH04315872A - Waveform equalizer - Google Patents

Abstract

PURPOSE:To obtain a waveform equalizer with small size and high performance by varying the gain of an amplifying means in accordance with the extent of the degradation of a regenerative signal and adjusting the extent of waveform expansion. CONSTITUTION:By an arithmetic circuit 10, a difference between the output signals of a peak detector 8 and a bottom detector 9 is calculated, by a comparator 11, a control signal varyig a reference voltage V2 is outputted to a reference voltage circuit 4 in accordance with the compared result of the difference and the reference voltage V3. In this case, by the circuit 11, the reference voltage V2 is varied in accordance with the difference between a peak value and a bottom value so that the extent of the waveform expansion is small when the degradation of the high band of frequency is small and the extent of the waveform exspansion is large whent the degradation of the frequency is large. By this configuration, the waveform equalizer capable of equalizing the waveform with high performance in spite of small size is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform equalization device for equalizing the waveform of a reproduced signal read from an information recording medium such as a magnetic disk or an optical disk.

0002

2. Description of the Related Art FIG. 7 is a circuit diagram showing a conventional waveform equalizer. In the figure, 15 is a matching resistor, 16 is a delay element that delays the signal by a certain time τ, 17 is an attenuator that adjusts the waveform equalization rate, and 18 is a differential amplifier. For example, a reproduced signal obtained by amplifying a signal read from an optical disk is input to the input terminal of the matching resistor 15 as a head amplifier output. Here, if the input signal waveform is represented by a time function f(t+τ) (τ is the delay amount of the delay element),
At the matching end a of the delay element, a sum signal of the input signal f(t+τ) and the reflected signal f(t−τ) from the open end b is obtained. This sum signal is expressed by the following equation.

f(t+τ)+f(t-τ)...(1) This sum signal passes through the attenuator 17, where it is multiplied by K and sent to the differential amplifier 1.
It is input to one terminal of 8. K is the attenuation rate of the attenuator 17. Furthermore, the signal f(t) via the delay element 16 is input to the other side terminal of the differential amplifier 18 . Therefore, the output of the differential amplifier 18 is f(t)-K/2{f(t+τ)+f(t-τ
)}...(2) A modified signal is obtained for the original input signal f(t+τ). Furthermore, as a result, the transfer function H(ω) of the above waveform equalizer is generally given by the cosine H(ω)∝1-2Kcosωτ (4), assuming that f(t)=A sinωt...(3) Becomes a function. Therefore, by adjusting the attenuation factor K of the attenuator 17, it is possible to obtain an output signal whose waveform is optimally equalized with respect to the input signal. FIG. 8 is a diagram showing the relationship between the frequency and waveform equalization rate of the above-mentioned waveform equalizer, and the attenuation rate K=0
．． This is the equalization characteristic when 5.

0004

SUMMARY OF THE INVENTION However, the conventional waveform equalization device described above has the following problems. (1) Since the traveling wave and reflected wave of the delay element are used,
The waveform is distorted due to the input impedance of the differential amplifier. (2) If the input waveform from the input signal source is not symmetrical, depending on the delay amount of the delay element and the phase relationship of the input signal, waveform equalization cannot be performed independently on the left and right output signals of the delay element. However, the application of waveform equalization has the opposite effect, and the performance of the device cannot be improved. (3) In general, a waveform equalization circuit using a cosine equalization or transversal filter requires a delay circuit including a plurality of delay elements, and these delay elements are relatively expensive. This not only increases the cost of the device, but also makes it difficult to downsize and integrate in terms of mounting space. (4) Since the characteristics of the waveform equalization amount are determined by the initially set circuit constants, it is not possible to follow variations in the characteristics due to head variations, disc variations, or changes in ambient conditions. (5) When playing a disc at a constant rotation speed, the recorded pit length differs depending on the information recording position in the radial direction on the disc, so the playback signal recorded on the inner circumference is better than that on the outer circumference. The high frequency deterioration caused by intersymbol interference is greater than that of the recorded reproduction signal. Therefore, in a CAV disc, it is not possible to follow changes in the reproduced signal due to differences in address positions. (6) Since this is a means of emphasizing the high frequency band, disc noise, laser noise, etc. are emphasized and the S/N deteriorates, contrary to the improvement of waveform interference, and the probability of occurrence of extra pulses that cause errors increases. Increase. (7) The reproduced signal amplitude level also decreases due to waveform equalization,
S/N deteriorates.

The present invention was made to solve these problems, and its purpose is to provide a waveform equalization device that is small in size yet capable of performing waveform equalization with high performance. .

[0006]

[Means for Solving the Problems] Such an object of the present invention is to provide an amplifying means provided for waveform expansion of a reproduced signal read from an information recording medium, a means for adjusting the gain of the amplifying means, means for detecting the degree of deterioration of the reproduction signal due to waveform interference; and means for controlling the gain adjustment means based on the output of the detection means, the gain of the amplification means being adjusted according to the degree of deterioration of the reproduction signal. This is achieved by a waveform equalizer that is characterized by varying the waveform and adjusting the degree of waveform expansion.

[0007]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the waveform equalization device of the present invention.

In FIG. 1, reference numeral 1 denotes a waveform expansion circuit that expands the signal waveform of the input head amplifier output to an optimum value according to the degree of intersymbol interference. 2 is waveform expansion circuit 1
A comparison circuit that allows or prohibits the waveform expansion operation of the head amplifier, and outputs a signal that permits the waveform expansion operation to the comparison circuit 3 in the waveform expansion circuit 1 only when the amplitude level of the head amplifier output is greater than a predetermined reference voltage V1. . The comparison circuit 3 is a control circuit that compares the head amplifier output and the output voltage V2 of the reference voltage circuit 4 when receiving this operation permission signal, and outputs a gain control signal to the gain adjustment circuit 5 according to the comparison result. be. The gain adjustment circuit 5 is a circuit that adjusts the gain of the buffer amplifier 6 in accordance with a gain control signal, so that the head amplifier output is waveform-expanded to an optimum value by the buffer amplifier 6. In addition, in this example, as an information recording medium,
A magneto-optical disk is used, and a reproduced signal read from the disk is input to a buffer amplifier 6 as a head amplifier output.

7 is a switch element whose opening and closing are controlled by a gate signal to be described later; 8 is a peak detection circuit for detecting the peak value of the output reproduction modulation signal of the buffer amplifier 6; and 9 is a bottom detection circuit for detecting the bottom value thereof. be. The output signals of the peak detection circuit 8 and the bottom detection circuit 9 are each output to an arithmetic circuit 10, and the difference between both outputs is computed. This difference signal is output to the comparison circuit 11 as a signal representing the degree of intersymbol interference of the reproduced signal waveform. The comparison circuit 11 compares the difference voltage with a preset reference voltage V3.
and sends a control signal to the reference voltage circuit 4 according to the comparison result.
Output to. Therefore, the reference voltage V2 of the reference voltage circuit 4
is varied according to the differential voltage of the arithmetic circuit 10, so that the degree of waveform expansion in the waveform expansion circuit 1 is determined by the difference signal,
That is, it is controlled according to the degree of intersymbol interference.

FIG. 2 is a diagram showing the format of the magneto-optical disk used in this embodiment. Each sector is composed of a data area 12 and a preformat area 13, and each preformat area 13 has various types of information for each sector recorded in advance. Further, the data area 12 is an area where information can be freely recorded, erased, and reproduced. The preformat area 13 has sector marks S as shown enlarged in the figure.
M, a preamble serving as a reference signal for synchronization detection, a sector address, and a CRC for error detection. Generally, according to the ISO standard format, about 10-odd bytes of continuous signals with a minimum inversion interval (maximum repetition frequency) are recorded in the preamble area. Therefore, the reproduction signal of the preamble suffers the greatest deterioration in the high frequency characteristics caused by intersymbol interference. Therefore, in this embodiment, as shown in FIG. 2, the gate signal input to the switch element 7 is turned on in the preamble region, and at this time, deterioration of frequency characteristics due to intersymbol interference is detected and the deterioration is corrected. It is.

Next, the concrete operation of this embodiment will be explained. FIG. 3 is a waveform diagram of the reproduction signal in the preformat area. This reproduced signal has a sector mark SM at the beginning, followed by a preamble and an address, which are output in this order. In this case, as described above, the frequency characteristics of the preamble reproduced signal are degraded due to intersymbol interference, and the amplitude level is attenuated. Further, FIG. 4 is a signal waveform diagram showing the reproduced signal waveform input to the waveform expansion circuit 1 and the waveform equalized output signal waveform after waveform expansion. In FIG. 4, V0 is a potential corresponding to the amount of DC light obtained from the land portion of the magneto-optical disk, V1 is the reference voltage of the comparator circuit 2, and V2 is the reference voltage of the comparator circuit 3. Further, a and b shown in FIG. 4 are potentials corresponding to the amount of modulated light obtained by the groove shape of the magneto-optical disk.

When the scanning of the reproducing light beam shifts from the SM area to the preamble area, the gate signal becomes high level as described above, and the switch element 7 is turned on. Further, the reproduced signal shown in FIG. 3 is input to the buffer amplifier 6, the comparison circuit 3, and the comparison circuit 2 of the waveform expansion circuit 1. Comparison circuit 2 compares the amplitude level of the reproduced signal with reference voltage V1, and outputs a signal to comparator circuit 3 to permit operation when the amplitude level is greater than V1. When the comparator circuit 3 is allowed to operate, it compares the amplitude level of the reproduced signal with the reference voltage circuit 4.
A control signal corresponding to the comparison result is output to the gain adjustment circuit 5. Therefore, comparison circuit 3
outputs a control signal when the amplitude level of the reproduced signal is V
1 and smaller than V2. In this case, the input/output characteristics of the waveform expansion circuit 1 are nonlinear, and in other cases, the input/output characteristics are linear.

On the other hand, the output signal of the waveform expansion circuit 1 is outputted to a peak detection circuit 8 and a bottom detection circuit 9 through a switch element 7, and the peak value and bottom value of the reproduced modulation signal are respectively detected. The calculation circuit 10 calculates the difference between the peak value and the bottom value and outputs the difference value to the comparison circuit 11.The comparison circuit 11 compares the difference with the reference voltage V3 and sets the reference voltage V2 according to the comparison result. A control signal for varying the voltage is output to the reference voltage circuit 4. In this case, in the comparator circuit 11, when there is relatively little frequency deterioration in the high range and the difference between the peak value and the bottom value is relatively large, the level of the reference voltage V2 is changed toward the lower level V21 as shown in FIG. A control signal is output to make this happen. On the other hand, if the frequency deterioration in the high range is relatively large and the difference value is relatively small, the level of the reference voltage V2 is changed to the high level V2 as shown in FIG.
A control signal is output in order to vary in two directions. In other words, the reference voltage V2 is varied according to the difference between the peak value and the bottom value, such that when the frequency deterioration in the high range is small, the degree of waveform expansion is decreased, and when the frequency deterioration is large, the degree of waveform expansion is increased. . FIG. 5 shows the input/output characteristics of the waveform expansion circuit 1, and the characteristics change depending on the voltage level of the input head amplifier output to perform optimal waveform expansion processing. Note that the input/output characteristics become nonlinear for input signals that are higher than the reference voltage V1 and lower than V2, but in this case, the negative side gain of the buffer amplifier 6 increases according to the gain adjustment signal of the gain adjustment circuit 5. The frequency deterioration of the reproduced signal is corrected.

In this way, the reference voltage V2 of the reference voltage circuit 4
is controlled according to the frequency deterioration of the reproduced signal, and the comparator circuit 3 outputs a control signal according to the level of the reference voltage V2 to the gain adjustment circuit 5. Thereby, in the gain adjustment circuit 5, when the frequency deterioration of the reproduced signal is large and the difference is small, the gain of the buffer amplifier 6 is adjusted so as to increase the degree of waveform expansion accordingly. Furthermore, if the frequency deterioration of the reproduced signal is small and the difference is large, the gain of the buffer amplifier 6 is adjusted accordingly to reduce the degree of waveform expansion. As described above, the gain of the buffer amplifier 6 is automatically controlled to an optimum value depending on the degree of frequency deterioration of the reproduced signal. The gain of the buffer amplifier 6 adjusted in this way in the preamble region is
The gain of that sector is fixed, and the scanning of the reproducing light beam shifts to the next address area. At this time, the gate signal is turned off and the switch element 7 is turned off.

Therefore, in the subsequent reproduction operation, waveform equalization processing is performed with the gain adjusted in the above preamble area, and the reproduction signal input to the waveform expansion circuit 1 is waveformed with the optimum gain according to the degree of frequency deterioration. Equalized. As a result, Figure 4
As shown by the broken line in , the degraded component of the reproduced signal is automatically expanded in waveform with a gain according to the degree of degradation, so the degradation can be effectively corrected and the degraded component of the reproduced signal can be restored to its original level. can. Note that when reproducing the next sector, the gate signal is turned on again in the preamble region of that sector, and the gain is adjusted in accordance with the frequency deterioration of the reproduced signal in the same manner as described above. In this embodiment, the gain is adjusted for each sector in this way, and waveform equalization is performed using the adjusted gain each time.

FIG. 6 is a block diagram showing another embodiment of the present invention. In the figure, reference numeral 14 denotes an address detection circuit that detects the address of the disk and controls the voltage level of the reference voltage V2 of the reference voltage circuit 4 in accordance with the address. Note that the other configurations of the waveform expansion circuit 1 and comparison circuit 2 are the same as those in the embodiment shown in FIG. In the address detection circuit 14, when the address data is on the inner circumferential side of the disk, the level of the reference voltage V2 is changed toward the high level V22 as shown in FIG. Further, when the address data is on the outer circumferential side of the disk, the reference voltage V2 is changed toward a low level V21. That is, the address detection circuit 14 increases the reference voltage V toward the inner circumference of the disk.
Control is performed so that the reference voltage V2 becomes higher and the reference voltage V2 becomes lower toward the outer circumference. Thereby, the gain of the buffer amplifier 6 is controlled by the comparator circuit 3 and the gain adjustment circuit 5 according to the address position on the disk. Therefore, the gain of the buffer amplifier 6 is higher toward the inner circumference of the disk and lower toward the outer circumference, so that the reproduced signal on the inner circumference can be waveform expanded with a higher gain, and the reproduced signal on the outer circumference can be waveform expanded with a lower gain. .

[0017] As described above, the CAV rotates at a constant rotation speed.
In a disk, high frequency deterioration due to intersymbol interference increases toward the inner circumference of the disk, but in this embodiment, the gain of the buffer amplifier 6 is controlled according to the address position, so the deterioration in high frequencies due to intersymbol interference is The degree of waveform expansion of the reproduced signal can be changed. Therefore, frequency deterioration of the reproduced signal can be automatically corrected according to the address position on the disk, and a good reproduced signal can be obtained regardless of the address position.

In general, in magnetic recording, there is waveform interference caused by the sum of nonlinear interference (pattern peak shift) of the magnetization reversal pattern itself that occurs during the recording process and linear interference that occurs during the reproduction process. On the other hand, in optical recording such as in an optical disk device, interference between pits does not occur in principle during the recording process, and interference occurs predominantly during the reproduction process. Further, if the data code conforms to 2,7 RLL, the interference phenomenon is more attenuation of the amplitude level of the interference waveform than a peak shift, and therefore the present invention is particularly effective for optical recording/reproducing devices.

[0019]

[Effects of the Invention] As explained above, the present invention has the following effects. (1) Waveform distortion does not occur because waveform equalization is not performed using a traveling wave and a reflected wave by a delay element as in the conventional method. (2) Since no delay element is used, not only the cost can be reduced, but also the mounting space can be narrowed, and the circuit can be easily integrated. (3) Even if the input waveform is left-right asymmetric, the waveform equalization can be effectively performed without causing the opposite effect unlike the method using a delay line. (4) Since the degree of waveform expansion is automatically controlled according to the degree of intersymbol interference, it is possible to absorb variations in media and heads and changes in ambient conditions, and stable waveform equalization can be performed regardless of these factors. . (5) Since it is not a method that emphasizes high frequency components,
As the waveform of the reproduced signal is improved, noise does not increase. (6) Since the amplitude level of the reproduced signal does not decrease due to waveform equalization, the S/N ratio does not decrease. (7) Even if the reproduction signal is from a recording medium that rotates at a constant speed, by controlling the degree of waveform expansion according to the address position, high frequency deterioration due to intersymbol interference is corrected regardless of the address position. can do.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a waveform equalization device of the present invention.

FIG. 2 is an explanatory diagram showing the format of a magneto-optical disk used in the embodiment of FIG. 1;

FIG. 3 is a waveform diagram showing a reproduced signal in the format of FIG. 2;

FIG. 4 is a waveform diagram showing a comparison between a reproduced signal before waveform equalization and an output signal after waveform equalization in the embodiment of FIG. 1;

FIG. 5 is an input/output characteristic diagram showing the relationship between input signals and output signals of the embodiment of FIG. 1;

FIG. 6 is a block diagram showing another embodiment of the present invention.

FIG. 7 is a circuit diagram showing a conventional device.

FIG. 8 is an explanatory diagram showing waveform equalization characteristics of the conventional device.

[Explanation of symbols]

1 Waveform expansion circuit 2, 3, 11 Comparison circuit 4 Reference voltage circuit 5 Gain adjustment circuit 6 Buffer amplifier 7 Switch element 8 Peak detection circuit 9 Bottom detection circuit 10 Arithmetic circuit

Claims (5)

[Claims] 1. Amplifying means provided to expand the waveform of a reproduced signal read from an information recording medium, means for adjusting the gain of the amplifying means, and detecting the degree of deterioration of the reproduced signal due to waveform interference. and means for controlling the gain adjustment means based on the output of the detection means, the gain of the amplification means being varied according to the degree of deterioration of the reproduced signal,
A waveform equalization device characterized by adjusting the degree of waveform expansion. 2. The waveform equalization device according to claim 1, wherein the control means is permitted to perform a control operation when the amplitude level of the reproduced signal reaches a predetermined level. 3. The detection means includes means for detecting a peak value of the reproduced modulation signal, means for detecting a bottom value of the reproduction modulation signal, and a difference between the output of the peak value detection means and the output of the bottom value detection means. 2. The waveform equalization device according to claim 1, further comprising means for calculating the difference between the two and outputting the difference as a signal indicating the degree of deterioration of the reproduced signal. 4. The detection means operates when reproducing predetermined information repeatedly recorded on the recording medium, and the gain of the amplification means is set at any time based on the detection value obtained each time. 2. The waveform equalization device according to claim 1. 5. The information recording medium is a disk-shaped recording medium that rotates at a predetermined speed, and address information of the recording medium is detected, and the gain of the amplifying means is increased as the address position is closer to the inner circumference of the recording medium. 2. The waveform equalization device according to claim 1, further comprising means for controlling the waveform equalization device according to claim 1.