JPH0991877A - Signal reproducing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a suitable shaping circuit applicable to an optical disk signal reproducing circuit in which a smoothness and a quick converging speed of a threshold value are compatible with each other by providing a feedback loop of a comparator with a low pass filter and a sample-and-hold circuit. SOLUTION: A feedback loop of a comparator 12 is provided with a hold- sample-hold circuit(SHC) 16 of an output of LPF 14 via LPF 14 and a switch 17. By utilizing a time band of a VFO range in a sector format of a continuous servo tracking system according to the ISO Standards, keeping the switch 17 on to turn on the LPF 14 up to halfway in the VFO range to quickly converge a threshold value by feedback controls, the threshold value is held by the SHC 16. Thereafter, the switch 17 is turned off halfway in the VFO range and the threshold value is held to be smoothed. Consequently, the suitable shaping circuit applicable to an optical disk signal reproducing circuit is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal reproducing circuit, and more particularly to a waveform shaping circuit suitable for application to a signal reproducing circuit of an optical disk.

[0002]

2. Description of the Related Art Recording of data on an optical disc, such as a magneto-optical disc, is a thermal recording performed by irradiating a laser beam. Change. Due to this change in the shape of the recording magnetic domain, the center of the eye of the eye pattern of the reproduced RF signal is vertically shifted without being the center of the amplitude, and the deviation of the center of the eye deteriorates the error rate of the reproduced signal.

Further, in the reproduction RF signal, the low frequency component also fluctuates due to the fluctuation of the reflectance of the optical disk, the shift of focus, and the shift of the laser beam from the track center.

The above problems will be described below with reference to the reproduction signal processing system block circuit of the optical disk. FIG. 4 shows a block circuit of a general reproduction signal processing system of an optical disc. In FIG. 4, the signal detected by the photodiode PD of the optical pickup 1 is amplified by the reproduction amplifier circuit 2, and the reproduction output is input to the waveform equalizer 3. The reproduced RF signal corrected by the waveform equalizer 3 has an RF eye pattern (hereinafter referred to as an eye pattern) as shown in FIG.

Reproduced RF corrected by the waveform equalizer 3
The signal is shaped into a binary signal by the shaper 4 and converted into a pulse signal indicating the presence or absence of the signal. The pulse signal shaped by the shaper 4 is input to the phase comparator 6 and the discriminator 9 of the PLL circuit 5 which constitutes the synchronizing signal generator. The error signal of the phase comparator 6 is supplied to the VCO 8 through a low pass filter (LPF) 7. The VCO 8 generates a synchronization signal synchronized with the fundamental cycle of the pulse signal and supplies it to the discriminator 9.

The discriminator 9 detects whether or not there is a reproduction pulse signal in the center of the eye pattern, that is, determines whether the data is "0" or "1" in the central portion of the data, and the determined detection is made. The code string is decoded by the decoder 10 into a data bit string.

By the way, in the shaper 4, the reproduction R
In order to eliminate fluctuations in the low-frequency component of the F signal, the reproduced signal output is AC-coupled by a high-pass filter, and then the zero-crossing detection circuit determines whether the amplitude of the input signal is positive or negative. A method of converting to a pulse signal of "1" or "0" is known, but since a low frequency component offset occurs in this method, a shaping circuit as shown in FIG. 5 is used as a method of correcting this. Are known.

In FIG. 5, reference numeral 11 is a high-pass filter composed of a capacitor C1 and a resistor R1, and the waveform equalizer 3 is connected to the input terminal of the high-pass filter 11.
Of the peak output voltage of the comparator 12, which will be described later, through the resistor R1.
Is connected to the voltage source Vs.

Reference numeral 12 is a comparator, and the high-pass filter 1 is provided on the non-inverting input terminal side of the comparator 12.
The output signal of 1 is input. The output of the comparator 12 is a capacitor C3, a resistor R3 and an operational amplifier circuit 13
The signal is fed back to the inverting input terminal of the comparator 12 via a low-pass filter (LPF) 14 composed of.

Operational amplifier circuit 1 constituting the LPF 14
A voltage source Vs corresponding to ½ of the peak output voltage of the comparator 12 is connected to the non-inverting input terminal of 3.

Hereinafter, regarding the waveform shaping of the shaping circuit,
The operation will be described. The waveform of the reproduction RF signal is a sine wave, and the reproduction waveform and the threshold value (compare level) Vth are set to a state shown in FIG. In the waveform diagram, Vs is 1 of the output voltage of the comparator 12.
/ 2.

If the feedback loop of the LPF 14 is disconnected, the output voltage waveform of the comparator 12 does not have a duty of 50% as shown in FIG. 3B, but the feedback loop is closed and the LP
By passing F14, the feedback loop becomes | V
It operates so that s-Vth | = 0.

That is, the feedback is applied so that the average output of the comparator 12 becomes ½ of the peak voltage of the comparator output, so that the threshold value Vth at a certain point in time as shown in FIG. 3C. The instantaneous value becomes V _S or less, and finally Vth changes to the direction shown by the arrow and becomes Vs, the DC offset voltage is removed, and the output waveform of the comparator 12 stabilizes at a duty of 50%.

If the reproduced data is almost random when corrected by the shaping circuit, by comparing the centers of the eye patterns, the average voltage of the output of the comparator 12 becomes 1/2 of the peak voltage of the comparator output, and the reproduced waveform is Although it can be faithfully reproduced, it is necessary to smooth the threshold value Vth in order to improve the error rate. In order to smooth the threshold Vth, it is necessary to remove the low frequency component from the threshold Vth. Therefore, the cutoff frequency of the LPF 14 must be lowered.

On the other hand, there is a demand for the threshold value Vth to converge quickly, and for this reason, the cutoff frequency of the LPF 14 must be increased. However, the LP
When the cutoff frequency of F14 is increased, an unnecessary low frequency component remains in the threshold value Vth input to the comparator 12, and the threshold value Vth1 having an unsmooth waveform as shown in FIG. 2D. As a result, the output of the comparator 12, that is, the edge of the data detection window is blurred as shown in FIG. 2D, and the width of the data detection window becomes narrower.

As described above, the shaping circuit cannot simultaneously meet the demands for smoothness of the threshold and rapid convergence of the threshold.

[0017]

In view of the above-mentioned problems, the present invention provides a shaping circuit suitable for application to a signal reproducing circuit of an optical disk, which can achieve both smoothness of threshold value and convergence speed of threshold value. In point.

[0018]

A signal reproducing circuit of the present invention,
A reproduction signal that has become an eye pattern and a threshold value signal that detects the center of the eye pattern are input, and a comparator that compares the threshold value signal and the reproduction signal, and the threshold value input terminal of the comparator, A low pass filter provided in a feedback loop for feeding back the output of the comparator and a sample hold circuit for sampling and holding the output of the low pass filter are provided. The cut-off frequency of the low-pass filter is set to a high value so that its output is rapidly converged, and V in the sector format of the ISO standard continuous servo tracking system is set.
In the time zone of the FO region, the output of the low-pass filter is sampled and held for each sector.

[0019]

EXAMPLE A signal reproducing circuit for an optical disk includes a PLL circuit 5 for generating a synchronizing signal as described above.
(FIG. 4). Then, the VC of the PLL circuit 5
O8 supplies a sync signal having a detection window width equal to the basic period of the recording signal to the discriminator 9, and the sign of the pulse detected by the shaper 4 based on the sync signal is "1" or "0". Are identified.

In order to lock the PLL circuit 5, the optical disc is pre-formatted as a sector format of the ISO (International Organization for Standardization) standard continuous servo tracking system as shown in FIG. V
A continuous data pattern called FO in which the PLL is easily locked is recorded. Note that, here, the VFO region and other parts required for the present invention are shown in a simplified manner.

According to the present invention, by utilizing the time zone of the VFO area, the LPF having a high cutoff frequency set to a midway point of the VFO area is fed back to rapidly converge the threshold value, and then the threshold value is set. The value is sampled and held to obtain a smooth threshold value, and data is extracted.

In FIG. 1A, a sample hold circuit 16 including a buffer 15, a capacitor C2 and a resistor R2 is connected to the output side of the LPF 14 of the feedback loop via a switch 17. Then, the output of the sample hold circuit 16 is input to the inverting input terminal of the comparator 12 as a threshold value.

Here, the cutoff frequency of the LPF 14 is set high, that is, the time constant is set small, and the output change of the LPF 14 is increased to start up rapidly.
Speed up the threshold convergence.

Then, the switch 17 is turned on for each sector of the ISO standard so that the LPF having a high cut-off frequency is obtained.
Feedback is applied at 14 to rapidly converge the threshold, and the sample hold circuit 16 holds the threshold. After that, the switch 17 is turned off, the feedback loop is cut off, and the hold value of the sample hold circuit 16 is set to the threshold value, whereby the threshold value can be smoothed.

As described above, with the sample-hold pulse as shown in FIG. 1C, the switch 17 is turned on up to the middle of the VFO area, and the threshold value is rapidly converged, whereby the eye pattern is converged. The threshold can be quickly tracked to the center of.

On the other hand, by turning off the switch 17 in the middle of the VFO area and holding the threshold value, data can be extracted with a smooth threshold value. FIG.
2A shows a smooth threshold value Vth2, and FIG. 2B shows the data detection window. The edges of the data detection window are not blurred, and as a result, the detection window is not narrowed. The error rate can be reduced.

[0027]

According to the present invention, by setting the cutoff frequency of the low-pass filter high, the threshold value can be converged quickly, and by sampling and holding the threshold value, a shaping circuit that can obtain a smooth threshold value can be provided. realizable. When applied to a signal reproduction circuit of an optical disk, a shaping circuit that can quickly follow the threshold value to the center of the eye pattern can be realized by only partially changing the configuration of the low pass filter and adding a sample hold circuit. it can.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a shaping circuit according to the present invention and an explanatory diagram thereof.

FIG. 2 is an operation waveform diagram of the present invention and a conventional example.

FIG. 3 is another operation waveform diagram of the conventional example.

FIG. 4 is a block circuit diagram of a reproduction system of an optical disc.

FIG. 5 is a block circuit diagram of a conventional shaping circuit.

[Explanation of symbols]

12 comparator 14 low-pass filter with high cutoff frequency 16 sample and hold circuit

Claims (3)

[Claims] 1. A comparator for inputting a reproduced signal having an eye pattern and a threshold signal for detecting the center of the eye pattern and comparing the threshold signal with the reproduced signal, and a threshold of the comparator. A signal reproducing circuit comprising: a low-pass filter provided in a feedback loop for feeding back the output of the comparator to a value input terminal; and a sample-hold circuit for sample-holding the output of the low-pass filter. 2. The signal reproducing circuit according to claim 1, wherein the cutoff frequency of the low pass filter is set high.
A signal reproduction circuit characterized by rapidly converging its output. 3. The signal reproducing circuit according to claim 2, wherein the IS
A signal reproducing circuit characterized in that the output of the low-pass filter is sampled and held for each sector in the time zone of the VFO area in the sector format of the O standard continuous servo tracking system.