JPS5864604A - Dropout compensating device - Google Patents

Abstract

PURPOSE:To prevent malfunction originating from a dropout compensating circuit, and to perform normal servo locking, by decreasing the detection sensitivity of a dropout detection part during unlocking operation. CONSTITUTION:An unlocked state of a speed servo system 9 is detected by a lock detector 10 to turn on a switching element Q1, and a capacitor C2 is connected in parallel to the capacitor C1 of the time constant circuit 71 of a retriggerable MMV7. Therefore, the time constant of the MMV7 is greater during unlocking operation than in locking operation, so the pulse width of the MMV7 increases to decrease dropout detection sensitivity. Consequently, a sink chip level is never regarded as a dropout during the low-speed rotation of a spindle motor 11 while a spindle servo loop is turned off, thus preventing the generation of a dropout detecting signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dropout compensation device, and more particularly to dropout compensation @pupil in an information signal reproducing device.

In information playback devices such as video disc players,
Since dropouts occur due to dirt or damage to the recording medium, a dropout detection wheel weight is used to detect and compensate for dropouts in order to obtain high-quality reproduced images. FIG. 1 is a schematic block diagram of an example of this dropout detection device, in which a reproduced RF signal modulated by FMTI is inputted into a limiter 1 and converted into a pulse train signal, and then converted into a composite video signal by an FM detector 2. This detection output is inputted directly to the video switch 4 via the delay device 3 for 1 day (dark period equivalent to 1 horizontal line), and is selectively selected and reproduced by the switch 4 depending on the presence or absence of the dropout detection signal. Line output.

On the other hand, the reproduced RF signal passes through another limiter 5 and becomes the input (A) of a monostable multivibrator (hereinafter abbreviated as MMV) 6, and the pulse train output (B) of a constant time width of this MMV 6 is This is the trigger input for the retriggerable MMV7. The output (C) of the MMV 7 becomes a signal (D) whose terminal edge is stretched for a certain period of time by a pulse stretch circuit 8, and this is used as a dropout detection signal to control the video switch 4.

Figures 2 (A) to (D) show the signals (A) of each part of the circuit in Figure 1.
) to (D), and the reproduced RF signal is an FM signal, so the limiter output waveform is (A).
It has a pulse width corresponding to the composite video signal level as shown in FIG.

Therefore, MMV6 is used to make this output 1 (A) a signal (B) with a constant pulse width. This pulse train signal (
A retriggerable MM that is triggered, for example, at the rising edge of B)
The time constant of V7 is set to a value larger than the cycle of the reproduction RF signal corresponding to the video information signal. Therefore, the output has a waveform as shown in (C). That is, figure (A)
If dropout occurs during period (1), the retriggerable MMV 7 will not be triggered and will output at a low level. This low level output may be used as a dropout detection signal to control the switching of the video switch 4, but since the dropout disappears and the reproduction information is disturbed after a certain period of time, the pulse stretch circuit 8
The trailing edge of the output (C) of MMV7 is extended by a period II T 2 sufficient to make the period h bar. , this is taken as the detection signal (D).

In an information generation device having such dropout compensation @1, a speed f1[→1bo system is used to control the relative speed in the track contact direction between the recording track and the pickup, and the time axis of the reproduced signal is Variation removal is done. In video disc players, the so-called spindle servo system corresponds to this system, and the method for pulling in the servo loop is to increase the disc rotational speed in a so-called free rush state in which the loop is open, and when the rotational speed increases to a certain degree. The servo loop is turned on and the specified rotational speed is maintained from then on. For example, if 1800 rpm is used as this specified rotation speed, the rotation speed at which the spindle servo loop is turned on depends on the aging and temperature characteristics of the motor, the aging and temperature characteristics of the circuit components, and also the speed at which the spindle servo loop is turned on. 1 for disk detection etc.
200 to 150 (generally set to around 1 rpm). However, if the servo loop is turned on at such a rotation speed, the servo loop may malfunction and servo lock due to the following reasons. There is.

5- That is, 1200-1500rpm Te, RF double signal sync chip frequency is 7.6MHz Xl 200
/1800-5.06MHz ~7.6MHz xi
500/1800-6.3MHz 8 degrees,
This is within the range of 4.3 to 6.8 MH2 (at 1800 rotations), which is the dropout detection frequency of the dropout compensation circuit. This means that dropout compensation is performed even when dropout does not occur near the sync chip.

The repetition period (one day) of the synchronization signal during normal playback is 63.5 μ5 oct', but it is 1200 to 1500 rp-
So 63.5x1800/1500~63.5x180
Since the period is 0/1200 usec, which is longer than Atte, the replacement signal of the sync chip portion, that is, the compensation signal, by the signal passed through the 1H delay device 3 having a delay time of 63.5 μsec becomes a video signal.

FIG. 3 is a waveform diagram showing the dropout compensation operation in such a case. The waveform (d), which is the out detection waveform and corresponds to the signal (D) in FIG. This becomes a composite video signal for forming a reproduction horizontal synchronization signal. Therefore, the level is clamped by the level clamp circuit and the overall level is lowered, and the level is compared at the level indicated by the dashed line in the figure and the reproduced horizontal synchronization signal is separated, so the waveform as shown in (e) is obtained. becomes. Since this waveform (e) is the reproduction synchronization signal used to obtain the control signal for the spindle servo loop, its frequency has apparently increased, and due to interaction with the half H removal circuit, etc., the servo loop is When the rotational speed of the spindle servo reaches 1,200 to 1,500 rpm, it is determined that the rotational speed has apparently increased, and the servo is locked.

Therefore, it is an object of the present invention to provide a dropout compensation device that prevents malfunctions caused by the dropout compensation circuit in the non-lock operation aspect of the relative speed servo system between the pickup and the recording track and enables normal servo lock. It is to provide.

The dropout compensation device according to the present invention is characterized in that the dropout compensation operation is stopped when the relative velocity servo system between the pickup and the recording track is unlocked.

According to a preferred embodiment, the detection sensitivity of the dropout detector is reduced during non-lock operation, and as a result, the dropout compensation operation is cut off.

The present invention will be explained below using the drawings. FIG. 4 is a block diagram of an embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same reference numerals. The functions and interactions of the blocks 1 to 8 are exactly the same as those in FIG. 1, and their explanation will be omitted. In this example, when the spindle servo system 9 is not locked, the lock detector 10 detects this and turns on the switching element Q1, and connects the capacitor C2 in parallel to the capacitor C1 of the time constant circuit 71 of the retriggerable MMV7. It is intended to do so. Therefore, when the lock is not locked, the time constant of MMV7 is R1・(C+
+02>, which is larger than R1 and C1 when locked, so the pulse width of MMV7 increases, resulting in a decrease in dropout detection sensitivity. Therefore, by appropriately setting this time constant, when the spindle motor 11 rotates at a low speed (1200 to 15
00rp-), the sync tip level is no longer mistakenly regarded as a dropout. Generation of the dropout detection signal shown in FIG. 8(C) is prevented. Therefore, the lock-in operation of the spindle servo becomes normal.

In other words, in this embodiment, the reproduced RF signal frequency is -
In a device configured to generate a dropout detection signal when the servo is not locked, the cocoon value station wave number is lowered in order to lower the detection sensitivity when the servo is not locked.

FIG. 5 is a partial circuit diagram of another embodiment of the present invention;
Parts equivalent to those in the figure are indicated by the same reference numerals.

-〇 In this example, the threshold value of the detection frequency is made smaller when the servo is not locked than when the servo is locked in order to reduce the detection sensitivity, but the training frequency when the servo is not locked is changed to the motor 11. The rotation speed is changed according to the rotation speed.

For this purpose, the capacitance value of the time constant determining capacitor C2 of the MMV 7 is continuously changed by the voltage output proportional to the rotation speed by the FG (# wave number generator) 12 provided for detecting the rotation speed of the motor 11. ing. A variable capacitance diode can be used as this capacitor C2. Similar to FIG. 4, switching element Q+ is used to connect capacitor C2 in parallel with capacitor C+ only when the lock is off.

As another embodiment of the present invention, although not particularly shown, the dropout detection output (D) in FIG. 1 may be turned off to stop the dropout compensation operation when the servo lock detector detects a non-lock state. Alternatively, the switch 4 may be made inactive.

10- Like the soft soil, according to the present invention, the timing of switching the spindle servo system from the 7 re-run state to loop-on and #I4 control is extremely free, and the servo system is not disturbed by the dropout compensation circuit.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional dropout compensation device.
2 and 3 are waveform diagrams of various parts for explaining the operation of the blocks in FIG. 1, and FIGS. 4 and 5 are circuit block diagrams of the embodiment of the present invention. Explanation of symbols of main parts 3...1H delay device 4...Video switch 7...Retriggerable MMV 9...Speed servo system 10...・Servo lock detector 71... Time constant circuit output representative Universal Pioneer Co., Ltd.
Patent Attorney Ryo Muramotohiko 11- Procedural Procedure...Author (Method) May 17, 1980 Commissioner of the Patent Office Tono 1, Indication of the Case 1982 Patent Application No. 164406 2, Name of the Invention Dropout Compensation Wheel 3. Relationship with the case of the person making the amendment Patent applicant address: 1-4-1 Meguro, Meguro-ku, Tokyo Name:
Universal Pioneer Co., Ltd. 4, Agent 〒1
04 Address: 4-1-17-6 Tsukiji, Chuo-ku, Tokyo Subject of amendment Clear application form Kazuaki Kazuaki

Claims (1)

[Scope of Claims] (1) A dropout compensating device in an information reproducing apparatus having a speed servo means for controlling the relative speed of a recording track and a pickup in a tangential direction, the dropout compensating device comprising: The device is characterized by being configured to stop the bulge-out compensation operation. (2) The apparatus according to claim 1, further comprising a dropout detection means, and the detection sensitivity of the dropout detection means is reduced when the speed servo means is in an unlocked state. (3) The dropout detection means is configured to detect the frequency of the RF signal reproduced by the pickup and generate a dropout detection signal when this frequency is less than a predetermined threshold, and the dropout detection means is configured to detect the frequency of the reproduced RF signal by the pickup and generate a dropout detection signal when the frequency is below a predetermined threshold. 2. The apparatus according to claim 2, wherein the predetermined steel wire frequency of the dropout detection means is lowered during operation. (4) The dropout detection means has a retriggerable monostable multivibrator triggered by a regenerated RF signal, and is configured to greatly control the time constant of the retriggerable monostable multivibrator when the speed servo means is in an unlocked state. 4. The device according to claim 3, characterized in that: