JPH067426B2 - Auto slice circuit - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention can be used in a magnetic or optical recording device.
The present invention relates to an auto-slice circuit that waveform-shapes a signal (hereinafter, referred to as an RF signal) obtained by reading a digital signal recorded on a medium and restores the original digital signal.

Configuration of Conventional Example and Problems Thereof In recent years, an auto slice circuit has become important in an optical or magnetic recording / reproducing apparatus such as a compact disc.

A conventional auto slice circuit will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a conventional auto slicing circuit, in which 1 is a slicer, 2 is an integrating circuit, an input signal RF is input to a slicer 1, and an output of the slicer 1 is resistors R ₄ , R ₅ and a capacitor C. ₂ and the differential amplifier 21 are input to the integrating circuit 2. The output of the integrating circuit 2 is fed back to the slicer 1 via the resistor R ₂ .

The operation of the auto slice circuit configured as described above will be described below. R read from the recording medium
The F signal usually has a blunted waveform due to the frequency characteristics of the recording medium and the frequency characteristics of the reading head (magnetic head, photodetector, etc.). By passing this through the slicer 1, the original The digital signals (pulse signals of "0" and "1") were returned.

As this slicer, a two-input voltage comparator for comparing an input level with a predetermined level is generally used, but as another means, as shown in FIG. 1, the input level is compared with its operating point to obtain "0", A 1-input limiter amplifier that converts to a "1" signal can be used. Since there is no difference between the two operations as a slicer, an example using a limiter amplifier will be described below. Therefore, hereinafter, 1 is referred to as a limiter amplifier.

The DC potential of the RF signal fluctuates due to fluctuations in the drive system of the recording medium, dust scratches on the recording medium, etc. Therefore, negative feedback of the low frequency component is applied to the limiter amplifier 1 to limit it.
The operating point was always located at the center of the amplitude of the input RF signal.

Referring to FIG. 1 in order, the RF signal having a DC fluctuation component has its DC component cut by the capacitor C ₁ ,
Although it is added to the input of the limiter amplifier ₁ through the resistor R _1, the component having a frequency higher than the frequency substantially determined by C ₁ and R ₁ is not cut off, and still has a DC fluctuation component.

At the left end of FIG. 2 (a), an enlarged view of this RF signal by time extraction is shown. This RF signal is output by the limiter amplifier 1.
It is returned to the digital signal DS as shown in FIG. 2 (b).
The operating point of the limiter amplifier 1 at this time is shown by the line SL in the figure.

Signals that are magnetically or optically recorded generally have frequency characteristics of the device, so FM, MFM, 3PM, EFM that does not have a DC component.
Since a modulated signal such as is used, the output signal DS of the limiter amplifier 1 is passed through an integrator 22 composed of a resistor R ₄ and a capacitor C ₂ , and its output is the input digital signal D.
A signal having the DC fluctuation component is obtained centering on the voltage of 1/2 of the amplitude of S. When this is negatively fed back to the limiter amplifier 1 via the differential amplifier 21 having one end of the input connected to the constant voltage source VR having a half of the amplitude of the signal DS and the adding resistor R ₂ , the amplitude center of the RF signal is obtained. Is always a limiter amplifier 1
It comes to match the operating point of. For the sake of convenience, when the diagram is drawn such that the operating point of the limiter amplifier is changed to match the center of the RF signal, the slice level SL shown in FIG. 2 is obtained.
That is, the RF signal having a voltage higher than the slice level SL is converted into "1" of the digital signal DS, and the low signal thereof is converted into "0".

However, in the above configuration, the input RF
When a signal is dropped due to dust adhering to the medium, damage, etc., this is called dropout, but the slice level follows the input RF with a delay of a time constant t ₁ determined by the resistor R ₄ and the capacitor C _2. To do. Therefore, the RF during this t ₁
The signal is not sliced with the correct voltage, the output digital signal DS has an incorrect phase, and the clock signal to be reproduced from this also has a phase error, which prevents correct data reproduction.

The larger the time constant of auto slicing, the higher the slice level S
L is stable, and the digital signal SL after slicing has less jitter, but conversely, if dropout occurs, it takes a lot of time to recover, and there is a serious problem that the data during that time is erroneous. Was there.

Object of the invention An object of the present invention is to have a dropout detection circuit for detecting such dropout, and by holding the slice level by the detection output, it is possible to perform recovery very quickly after dropout. At the same time, it is an object of the present invention to provide an auto-slicing circuit that can minimize the error period of data.

The auto slicing circuit of the present invention has a limiter amplifier for adding an input signal and an output signal of an integrating circuit, and digital "1" or "0" depending on whether the input signal is higher or lower than a predetermined level. A slicer that outputs the output signal of the slicer, the integration circuit that returns a difference signal between a DC component obtained by integrating the output signal of the slicer and a predetermined level to the slicer, and a dropout detection that detects that the input signal is interrupted. Circuit, and switch means for holding the output of the integrator circuit constant by the detection output of the dropout detector circuit, the integrator circuit is configured to feed back the output of the negative phase amplifier to the input side with an integrating capacitor. The switch means is configured by using an integrator of integration type, and the input side of the integrator is connected to a constant voltage source so that the output of the integrator circuit is connected. The are those configured by including switches connected so as to hold constant, thereby, those which can quickly perform recovery after the dropout.

Description of Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a circuit diagram of an auto slice circuit according to an embodiment of the present invention. In FIG. 3, 1 is a limiter amplifier which is a slicer, 2 is an integrating circuit, 3 is a dropout detection circuit, and SW is a switch means.

The operation of the auto slicing circuit of the present embodiment having the above configuration will be described below.

First, the input RF signal is applied to the limiter amplifier 1 through the DC blocking capacitor C ₁ and the adding resistor R ₁ to be converted into a digital signal DS.

The DC fluctuation component included in the digital signal DS is extracted by the complete integration circuit including the resistors R ₄₁ , R ₄₂ , the capacitor C ₂ and the amplifier 21, and is passed through the adding resistor R ₂ .
A negative period is applied to the input side of the limiter amplifier 1, and feedback is applied so that the midpoint of the amplitude of the RF signal coincides with the operating point of the limiter amplifier 1.

On the other hand, the input RF signal is also input to the dropout detection circuit 3, the detection signal DO is output only during the period when RF is stopped, and the hold switch SW is turned on.

The configuration of the dropout detection circuit 3 is a well-known technique in which an input RF signal is detected and a comparator detects that the level of the envelope is lower than a predetermined value. The dropout detection level is set so that the detection signal is not output when the RF level is slightly decreased due to a small scratch or the like and the RF level is not interrupted.

Immediately before the dropout occurs, the differential amplifier 21 applies the feedback output voltage to the limiter amplifier 1 so that the voltage at its plus input terminal becomes equal to that at its minus input terminal. The positive input terminal of the differential amplifier 21 is supplied with a voltage half the amplitude of the digital signal DS from the reference voltage source VR. If the auto-slice circuit operates properly, the reproduced digital signal DS is originally a signal that does not include a DC component, so the long-term average of its duty is 50%, and the output voltage obtained by integrating this is equal to the reference voltage VR. Should do. The integrating circuit of the resistors R ₄₁ and R ₄₂ and the capacitor C ₂ averages the duty for a long time, and the output voltage is applied to the mine input terminal of the differential amplifier 21. The output of the differential amplifier 21 works so as to cancel the DC fluctuation component of the input RF signal.

When dropout occurs and the detection signal DO is output, the switch SW is closed and the reference voltage VR is also applied to the minus input terminal side of the differential amplifier 21 through the resistor R ₄₂ . Since the internal resistance of the reference voltage VR is sufficiently lower than that of the resistor R ₄₁ , both inputs of the differential amplifier 21 have the same voltage VR and the output voltage is held. The time constant of this hold is approximately A times R ₄₂ × C ₂ when the open loop gain of the differential amplifier 21 is A, and even a normal operational amplifier has a DC gain of about 100 dB, so a small time constant (R _{Even with 41} × C ₂ ), it is possible to hold with extremely high precision.

When the dropout ends and the RF signal recovers, the output of the dropout detection circuit 3 stops, the switch SW turns off, and the original feedback loop is formed. Since the held potential is the correct slice level immediately before, the auto slice circuit starts to reproduce the original digital signal DS without delay at the same time as the recovery of RF.

As described above, according to the present embodiment, the dropout detection signal fixes the input of the integrator circuit to a predetermined voltage to keep the output voltage constant. A quick circuit is realized.

Next, another embodiment of the present invention will be described with reference to the drawings.

FIG. 5 is a circuit diagram of an integrating circuit of an auto slice circuit according to another embodiment of the present invention. In FIG. 5, 21 is a differential amplifier, SW is a switch, and a resistor R
_The configuration is such that the input of the integrator composed of ₄ and the capacitor C ₂ is opened by the dropout detection signal DO.

The operation of the auto-slice circuit of this embodiment configured as described above will be described below. The slicer and dropout detection circuit is similar to that of the embodiment shown in FIG. The configuration of the integrating circuit 2 is the same as that of the integrating circuit 2 shown in FIG. 1 except for the switch SW.

When dropout occurs, the switch SW is opened by the dropout detection signal DO, and the input impedance of the amplifier 21 is sufficiently high.
The DC component of F remains held in the capacitor C ₂ , and the output of the integrating circuit 2 is held constant.

As described above, according to this embodiment, by opening the input of the passive integrator composed of the resistor R ₄ and the capacitor C ₂ , the DC component of the input signal immediately before dropout is held in the capacitor. , The output of the integrating circuit is kept constant, and hence the slice level is kept constant.

Although the predetermined voltage VR represents the voltage source symbol in the above embodiment, the voltage source is not limited to the battery, and any voltage source capable of equivalently supplying the predetermined voltage may be used. For example, it is possible to use a resistance circuit that generates a predetermined voltage by a resistance division circuit from a power supply that supplies electric power for the entire circuit.

EFFECTS OF THE INVENTION As is clear from the above description, the present invention is configured to detect a dropout and hold the slice level at the immediately preceding value. Therefore, recovery after loss of an RF signal due to dropout or the like is performed. The excellent effect that is performed very quickly is obtained. Due to the effect, loss of reproduced data is suppressed to a minimum, and when an error correction device or the like is used in combination, a very excellent effect that the capability of the error correction device can be sufficiently exhibited is obtained.

Further, when a perfect integrating type integrator is used as the integrator as in the embodiment of FIG. 3, the DC gain is very large, and the jitter of the digital signal after auto-slicing is suppressed to a very small level. If you connect a clock extraction circuit to this,
It is possible to reduce the jitter of the extracted clock sufficiently.
The operation of the playback device can be kept very stable. Moreover, since the gain of the amplifier (21) is applied to the holding time constant,
A very large time constant can be easily realized, and a very good holding characteristic can be realized.

Further, the integrator is composed of only passive elements, and the switch means is configured so as to hold the slice level by cutting off the connection between the resistor (R ₄ ) and the capacitor (C ₂ ) as shown in FIG. As a result, the effect that the slice level can be held without depending on the variation of the amplifier (21) is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a conventional auto slice circuit, FIG. 2 is a timing chart of signals for explaining the operation of the conventional auto slice circuit, and FIG. 3 is a diagram of an auto slice circuit according to an embodiment of the present invention. FIG. 4 is a signal timing diagram for explaining the operation of the embodiment of the present invention, and FIG. 5 is a circuit diagram showing another example of an integrating circuit which can be used in the present invention. 1 ... Slicer (limit amplifier), 2 ... Integrator circuit,
3 ... Dropout detection circuit, 21 ... Differential amplifier,
22 ... integrator, SW ... switch means.

Claims (1)

[Claims] 1. A slicer having a limiter amplifier for adding an input signal and an output signal of an integrating circuit, the slicer outputting digital "1" or "0" depending on whether the input signal is higher or lower than a predetermined level. The integration circuit for feeding back a difference signal between a direct current component obtained by integrating the output signal of the slicer and a predetermined level to the slicer, a dropout detection circuit for detecting that the input signal is interrupted, and a dropout thereof. Switch means for holding the output of the integration circuit constant by the detection output of the detection circuit, wherein the integration circuit is a perfect integration type integrator that feeds back the output of the negative-phase amplifier to the input side with an integration capacitor. The switch means is connected so that the input side of the integrator is connected to a constant voltage source and the output of the integrator circuit is kept constant. Auto slice circuit characterized by comprising, including switches.