JPS60212872A - Fm carrier wave reproducing signal correcting device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a black spot and stripe-like erroneous image information, by increasing the level of a high frequency section in the FM signal band of an FM carrier wave reproducing signal, restoring the zero-crossing point of FM carrier wave reproducing signals and correcting the duty. CONSTITUTION:FM carrier reproducing signals reproduced from a discoidal recording medium are inputted in a correcting circuit 50 by a video disk pickup circuit 1 and impressed upon a duty correcting circuit 11 after the level of a high frequency section in the FM signal band of the reproducing signals is increased by a high frequency correcting circuit 51. The FM carrier wave reproducing signals, whose duty is corrected at the circuit 11, are transferred to a demodulator circuit 20. Moreover, the circuit 51 is changed by a radial direction correcting circuit 13 so that the increased quantity of the level of the high frequency section in the FM signal band at the inner peripheral section of the disk becomes larger than that at the outer peripheral section. Therefore, black spots and stripe-like erroneous image information on a picture plane caused by the lack of the zero-crossing point of the FM carrier wave reproducing signals can be prevented and the duty correcting sensitivity can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides an FM signal suitable for use when demodulating a video signal recorded on a disc-shaped recording medium using the FM carrier wave recording format such as a video disc. The present invention relates to a carrier wave reproduction signal correction device.

Conventional configuration and its problems In the video disc recording and reproducing system, an FM signal is engraved on the disc in a spiral pattern with concavities and convexities. For example, in the case of VHD video disc format, recording is performed at a constant angular velocity, so FM
The information pits carved at a constant frequency within the frequency deviation of the carrier wave signal become shorter from the outer circumference to the inner circumference of the disk, and the information pits near the innermost circumference are used when recording FM signals on the disk. The length is extremely short, close to the spot diameter of the laser beam used, and the information pits cannot be formed optimally, and the formability of the disk with a stamper is still poor at the inner periphery. In particular, in the case of the v) ID video disc system, the width of the information pit that engraves the FM carrier signal on the inner circumference of the disc is smaller than the spot diameter of the laser beam. The FM carrier reproduced signal from the disc-shaped recording medium recorded in this state has a higher level in the high frequency part within the FM carrier signal band than the carrier signal before being recorded on the disc. is decreasing. Namely.

The level begins to decrease from the carrier frequency of the FM carrier signal or a frequency lower than that, and the level decreases more and more rapidly as the frequency increases. Furthermore, a duty shift at the zero crossing point of the FMi transmission signal also occurs. This tendency becomes more pronounced toward the inner circumference of the disk.

FIG. 1 is a block diagram showing an example of a video disk reproducing apparatus including a conventional FMM transmission reproduction signal correction circuit. In FIG. 1, a video disc binok asop circuit 1
An FM carrier wave reproduction signal is obtained from the disc-shaped recording medium. The duty of the FM carrier reproduction signal is corrected by a duty correction circuit 11 and applied to a frequency characteristic correction circuit 12 . The frequency characteristic of the frequency characteristic correction circuit 12 is based on the deviation of the FM carrier wave (for example, VH
For D video disc format, e, 1M1lz~7.9
The level at the center of the FM carrier wave is increased by the radial correction circuit 13 at the inner circumference of the disk, and the rate of increase is also the same at the outer circumference. The number is increasing compared to other countries. The duty correction circuit 11 and the frequency characteristic correction circuit 12 constitute an FMM transmission reproduction signal correction circuit 10.

FM corrected by the FMM transmission reproduction signal correction circuit 1o
The carrier wave reproduction signal is demodulated by 92M by the demodulation circuit 2o and transferred to the signal processing circuit 3o, where it is processed into a form suitable for being applied to the television receiver 40.

In the conventional configuration described above, the duty correction circuit 11 normally corrects the duty deviation of the FM carrier wave reproduction signal by the limiter effect (limiting or clipping of the signal) by a limiter circuit or a clip circuit. b changes) to perform duty correction. Also.

The frequency characteristic correction circuit 12 connected to the next stage of the duty correction circuit 11 is realized by, for example, a tuning circuit using collector peaking, and is
The level drop in the high frequency part within the M signal band is corrected.

The FM carrier signal f, M(t) is typically expressed as:

ZrM(t)=Acos(ω.t+m5lnω, t
:] (1) 2 people Σ Jk(m) cos (ω.+
ω, ) t , , −=, −(2) k=−, where ω is the amplitude of the signal, ω. carrier angular frequency.

ω is the modulation wave angular frequency 1m, which is the modulation index, and Jk (conversion) is the first type beso-seven function with respect to m.

In most cases, a small modulation index (m<1) is used for the FM disc transmission signal recorded on a disc-shaped recording medium, and in that case, equation (2) can be expressed approximately as follows. FIG. 2(a) shows the nubectrum distribution.

fF M(t)” A(J-41cas (ω0-ω,
)t+J. (yn)cosω. t+J,&n)C
QS (ω. 10ω, ) t ) −−=(3)=A(
-夛瀉(ω.-ω1)t-ωot+ aas(ω.+ω1
)t] ・ ・ (4) Figure 2 (b) shows the frequency characteristics of the disc at the inner circumference of the disc, and Figure 2 (C) shows the spectral distribution of the FM carrier reproduction signal reproduced from this disc. It shows.

The FM carrier wave reproduction signal f and M reproduction (t) at this time are shown as follows.

11M playback (t) -A[-t(ω.-ω,)t+Bfishω
. t+Ct(ω0+ω, ) t :l] −(5)=
Bow [-Fish (ω0-ω1)t] + A C(B-”')CQS ω.t + Ccts
(ω-,)t) (6) However, B and C are ω, respectively, as shown in Figure 2 (b).
. , ω. It shows the signal decrease during disk playback at an angular frequency of +ω1. The first term in equation (6) is the carrier wave angular frequency ω. −3, which is the same as the signal obtained by the AM modulation method in which the carrier 2 2 transmission wave having a modulation wave frequency of 2 is suppressed.

FIG. 3 (&) is a waveform diagram of the FM carrier reproduction signal fFM reproduction (t) where (i-)<-(or 2 is B<m) and C<1 in equation (6). At this time, the alternating current center of the FM carrier reproduction signal fFM reproduction (t) is shifted from the center of the signal amplitude due to the -L downward asymmetry of the signal waveform, as shown in FIG. 3 (&). FIG. 3('b) shows the output signal obtained by inputting this signal to the duty correction circuit 11 in the form of a limit-tsuta circuit. Figure 3(b) is Figure 3(IL)
is corrected so that a zero crossing point occurs at the center of the limiter. For this reason, the FM carrier wave reproduction signal f7M shown in FIG.
In the vicinity where the amplitude of the reproduction (t) envelope becomes small,
The zero crossing point of the duty-corrected FM carrier reproduction signal shown in FIG. 3Q)) has disappeared.

It is difficult for the frequency correction circuit 12 in the next stage to restore the zero crossing point of the FM carrier wave reproduction signal in which the zero crossing point is missing, and the FM carrier wave reproduction signal with the missing zero crossing point is demodulated and displayed on the screen. When outputting to , there was a problem in that incorrect image information in the form of black spots or streaks appeared periodically due to missing zero crossing points. Furthermore, when duty correction is performed by subtracting -E from the correction sensitivity of the duty correction circuit 11, the duty correction circuit 11 operates in the direction in which the limiter center moves away from the AC center as shown in FIG. In order to correct the deviation, the degree to which zero crossing points of the FM carrier reproduction signal outputted from the duty correction circuit 11 are missing increases, and the degree of erroneous image information such as black spots and streaks on the screen increases. do. Therefore, the duty correction circuit 11
There is also the problem that the correction sensitivity must be lowered and the duty correction effect is also small.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems.
By increasing the level of the high frequency part within the FM signal band of the carrier wave reproduction signal to recover the zero crossing point of the FM carrier wave reproduction signal and then correcting the duty, the modulation index can be adjusted at the inner circumference of the disk. The purpose of this invention is to eliminate erroneous image information such as black spots and streaks that appear periodically when a small FM carrier reproduction signal is demodulated, and to greatly improve the duty correction effect.

Structure of the Invention In order to achieve the above object, the FM carrier reproduction signal correction device of the present invention includes a high frequency correction circuit that increases the level of the high frequency part in the FM signal band, and an output from the above high frequency correction circuit. and a duty correction circuit for correcting the shift in duty at the zero crossing point of the FM carrier reproduction signal.

With this configuration, the levels of the carrier wave component and the upper side wave component of the FM carrier wave reproduction signal in which the zero crossing point is missing are increased, and as a result, the missing zero crossing point is recovered, so that the inner peripheral part of the disk-shaped recording medium It is possible to eliminate erroneous image information such as black spots and streaks that occur periodically when demodulating the FM carrier reproduction signal of By doing so, the correction sensitivity of the duty correction circuit can be further increased, and the duty correction effect can also be greatly improved.

Description of examples A block diagram of an embodiment of the present invention is shown in FIG.

In FIG. 4, the FM carrier wave reproduction signal reproduced from the disk-shaped recording medium by the video disc pink amplifier circuit 1 is increased in level of the high frequency part within the FM signal band by the high frequency correction circuit 51, and the duty correction is performed. circuit 1
1. The FM carrier reproduction signal subjected to i duty correction by the duty correction circuit 11 is transferred to the demodulation circuit 2o in FIG. In addition, the high frequency correction circuit 51
The radial direction correction circuit 13 is configured to change the increase in the level of the high frequency part in the FM signal band at the inner circumference of the disk to be larger than that at the outer circumference. The high frequency correction circuit 61 and the duty correction circuit 11 constitute an FM carrier reproduction signal correction circuit 5o.

The operation of the FM carrier reproduced signal correction circuit 60 configured as described above will be described below with reference to FIG.

As mentioned above, the disk-shaped recording medium has F expressed by equation (4).
M carrier signal F,,(t)(=A(4CO3(ω.-ω
, ) t+〉ω. The base cm(ω0+ω,)B) is recorded, and the video disk pink amplifier circuit 1 reversely reproduces the recorded data on the inner circumference of the disc-shaped recording medium using equation (6).
FM carrier wave reproduction signal f, M reproduction (t) (=
Question A (-min (ω0-ω,)t+ccsω.t) +
A ((” 2) CIIISω.
)1)) has a carrier angular frequency ω compared to the FM carrier signal fFM(t). signal amplitude and upper sidewave angular frequency ω. +ω
, the signal amplitude is decreasing. FIG. 5 (2L) shows the spectrum distribution of the FM carrier signal f, M(t), and the sixth
Figure (b) shows the frequency characteristics at the inner circumference of the disk-shaped recording medium, and Figure 5 (C) shows the frequency characteristics of the FM reproduced from the disk-shaped recording medium.
The spectrum distribution of the carrier wave reproduction signal f, M reproduction (t) is shown.

The FM carrier reproduction signal 4M reproduction (t) having the spectrum distribution shown in FIG. 5(C) is corrected by the high frequency correction circuit 61 for the level drop in the high frequency part within the FM carrier band during reproduction. be done. As shown in FIG. 5(d), the characteristic of the high frequency correction circuit 51 is that the FM carrier angular frequency ω decreases when reproducing the FM carrier signal from the disk. Recover the signal level of the upper sidewave angular frequency ω. It is configured to increase the level of the high frequency part within the FM carrier signal band so that the signal level of 10ω can be recovered appropriately.

FIG. 5(d) shows the percentage characteristics of the high frequency correction circuit 51. Although FIG. 5(d) shows that frequency components lower than the FM carrier signal band are also passed, there is no problem with a circuit configuration that does not pass them. The FM carrier wave reproduction signal f and M correction (t) outputted from this high frequency correction circuit 61 can be expressed as follows.

'FM reproduction (t) = A(-CtB(ω.-ω1) to ovary ω.t+CDHcos(ω.+ω,)t)] ・-,
, , (7) where D is the upper side wave angular frequency ω. 10ω1
This is the signal increase amount of the high frequency correction circuit 51 in .

FIG. 5(a) shows the spectrum 7M corrected distribution of the FM carrier wave reproduction signal f(t).

FIG. 6(a) shows the signal waveform of the FM carrier wave reproduction signal f, M reproduction (t) reproduced from the inner peripheral part of the disc-shaped recording medium having the spectrum distribution shown in FIG. 6(c). . At this time, the modulation index is small and the FM carrier angular frequency ω. and the upper wave angular frequency ω. The amount of decrease of the +ω1 signal is large yb, the FM carrier angular frequency ω0 and the lower side wave angular frequency ω. −ω, the signal level varies by the same amount, and the upper side wave angular frequency ω. It is assumed that the signal level of +ω1 is small and can be ignored. This FM carrier wave reproduction signal f1M reproduction (t) is shown in Fig. 5 (
When applied to the high frequency correction circuit 61 having the frequency characteristics shown in d), an output waveform shown in FIG. 6) is obtained. In this way, the signal shown in FIG.
Compared to the signal shown in Figure (a), the degree of change in the envelope of the signal is smaller, and zero crossing points are not missing at the center of AC. The FM carrier wave reproduction signal outputted from the high frequency correction circuit 61 shown in FIG. 6(Cb) is applied to the duty correction circuit 11 in the form of a limiter circuit, and the zero crossing point is at the center of the O-mitter shown in FIG. 6(b). Corrected to occur. 6th
Figure (C) shows the output waveform of the duty correction circuit 11.

As described above, according to this embodiment, the FM carrier reproduction signal reproduced from the disc-shaped recording medium is
High frequency correction circuit 51 that increases the level of the frequency section
This eliminates the loss of the zero crossing point of the FM carrier signal at the AC center, and the zero crossing point is not lost even if the correction sensitivity of the duty correction circuit 11 is increased.
The correction effect is also greatly improved.

Effects of the Invention As described above, the present invention includes a high frequency correction circuit that increases the level of a high frequency portion within the signal band of an FM carrier signal, and a duty correction circuit connected to the next stage. , so-called image information such as black spots and streaks on the screen due to the lack of zero crossing points of the FM carrier wave reproduction signal that conventionally occurred on the inner circumference of the disk is now restored by the recovery of the zero crossing points of the FM carrier wave reproduction signal. In addition to significantly reducing the duty
Since the correction sensitivity can be increased, the correction effect can be greatly improved, and its practical effects are significant.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the main parts of an example of a video disc playback device using a conventional FM carrier wave playback signal correction device; Fig. 2 is a frequency distribution diagram for explaining the operation of Fig. 1; FIG. 4 is a waveform diagram for explaining the operation of FIG. 1, and FIG. 4 is a block diagram of essential parts showing an embodiment of a video disc playback device using the FM carrier wave reproduction signal correction device according to the present invention.
FIG. 6 is a frequency distribution diagram that does not provide a detailed explanation of the present invention;
FIG. 6 is a waveform diagram for detailed explanation of the present invention. 60...FM carrier wave reproduction signal correction circuit, 51.High frequency correction surface 1 path, 11...Tenity correction circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 3 We -1"r Wo 'Ja f l" HM M
i 4 ships Zumaru - Daisakikenkabi 5

Claims (1)

[Claims] Fi of FM carrier wave reproduction signal reproduced from disk-type recording medium
An FM carrier characterized by having a high frequency correction means for increasing the level of a high frequency part within the t signal band, and a duty correction means for correcting a duty shift of a zero crossing point of an FM carrier reproduction signal. Reproduction signal correction device.