JPH0638175A - Signal demodulator - Google Patents

Abstract

PURPOSE:To eliminate the need for the adjustment when a pilot signal component is eliminated from a transmission signal including the pilot signal and the FM signal. CONSTITUTION:A pilot signal extracted from a transmission signal by a band pass filter 16 is converted into 1st and 2nd signals c, s whose phase differs from each other by 90 deg. at a phase shift circuit 69. Balanced modulators 65, 68 apply balanced modulation to the 1st and 2nd signals c, s with 3rd and 4th signals LC, LS fed from low pass filters 64, 67 and the result is outputted to an adder 15. The adder 15 subtracts signals P, Q inputted from the balanced modulators 65, 68 from the transmission signal and outputs the result to a limiter 19. A band pass filter 61 extracts the pilot signal component included in the output of the limiter 19. Synchronization detectors 63, 66 apply synchronization detection to the pilot signal component by using the 1st and 2nd signals c, s outputted from the phase shift circuit 69. A low frequency component of the detected output is extracted by the low pass filter 64, 67 and the 3rd and 4th signals LC, LS are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal demodulation device suitable for use in a video disc player for reproducing a video disc in which a high-definition type video signal is recorded in the MUSE system.

[0002]

2. Description of the Related Art FIG. 10 shows an example of the configuration of a recording device for recording a high-definition video signal as a MUSE signal on a video disk. FM modulator 51
Outputs the frequency-modulated input video signal with a carrier of 12.5 MHz and outputs it as an FM signal f _C to the adder 52. The frequency deviation of this FM signal f _C is ± 1.9 MHz
And the black level is 10.6 (= 12.5-1.9) M
And the white level is 14.4 (= 12.5).
The frequency is +1.9) MHz. In the adder 52,
Further, a pilot signal f _{1 of} 2.3 MHz (= f _H × 135/2 (f _H is a horizontal scanning frequency)) used for TBC (time axis error correction), servo, etc. is supplied.
The adder 52 adds the FM signal f _C and the pilot signal f ₁ and outputs the result to the limiter 53. The limiter 53 limits the level of the input signal to a predetermined level. The signal output from the limiter 53 is supplied to and recorded on a video disk (not shown).

FIG. 11 shows allocation of signals thus recorded on the video disc.

By the way, when the level of the signal obtained by adding the pilot signal f ₁ to the FM signal (main carrier) f _C is limited by the limiter 53, a lower side band f _P and an upper side band f _P ⁺ are generated. . That is, FIG.
As shown in (a), the FM signal f _C is added to the pilot signal f ₁
If the sum of, in response to the phase change of the pilot signal f _1, the vector F ₁ corresponding to the pilot signals f _1, F
It rotates around the tip of the vector F _C corresponding to the M signal f _C. As a result, this mixed signal has not only a phase (frequency) change (FM component) but also an amplitude change (AM component).

On the other hand, if the amplitude of the mixed signal is limited to a predetermined level as shown in FIG.
Vector F ₁ becomes the vector F _P corresponding to the lower sideband f _P, the composite vector of the vector F _P ⁺ corresponding to the upper sideband f _P ^+. Even if the vectors F _P and F _P ⁺ rotate in response to the change in phase, the vector F ₁ does not rotate, and its length becomes longer or shorter in the direction perpendicular to the vector F _C. It will only change. At this time, the amplitudes of the vectors F _P and F _P ⁺ are 1/2 of those of the vector F ₁ .
Becomes To be precise, not only the lower sideband f _P is recorded as a pilot signal, but also the upper sideband f _P ⁺ is simultaneously recorded on the video disc.

By the way, when the frequency of the FM signal f _C is, for example, 10.6 MHz (that is, when it is a blackish image), the frequency allocation of the mixed signal with the pilot signal f _P is as shown in FIG. When passing this to the limiter 53, as shown in FIG. 14, 8.3 (= 10 which is the difference from the frequency f _C (= 10.6 MHz), a frequency f _C and the pilot signal f _P as a main carrier.
6-2.3) MHz higher frequency 18.9 (= 10.
An upper sideband f _P ⁺ is generated at the position of 6 + 8.3) MHz. The upper side band f _P ⁺ is the lower side band f
_The phase is opposite to _P.

FIG. 15 shows the frequency band of the base band of the MUSE signal. As shown in the figure, MUSE
The frequency band of the system has a range up to about 8.1 MHz. On the other hand, the main carrier (FM signal) f _C
And the frequency of the beat interference wave generated corresponding to the frequency difference between the pilot signal f _P and the pilot signal f _P is 8.3 (= 10.6-2.3).
It becomes MHz. That is, since this interfering wave is located near the frequency band of the MUSE system, it appears as beat-like noise on the screen. When the frequency of the main carrier f _C is close to 14.4 MHz (that is, when the screen is bright), the frequency at which beat interference occurs is 12.1 (=
14.4-2.3) MHz, which is considerably larger than the MUSE frequency band of 8.1 MHz, so that beat interference becomes less noticeable. That is, beat interference is particularly noticeable on a dark screen.

[0008]

Therefore, in the prior art, 2.3 from the RF signal reproduced from the video disc.
After removing the pilot signal (lower sideband) f _P in the frequency band of MHz, the main carrier f _C is FM-demodulated. However, as described above, since the video disc is recorded with the upper side band f _P ⁺ included, even if the lower side band f _P is removed,
There is a problem that the beat component cannot be suppressed sufficiently.

Even if the upper side band f _P ⁺ is to be removed, this frequency is not constant and difficult to remove because it depends on the frequency of the main carrier f _C. Furthermore, it is difficult to remove the interfering wave itself near 8.3 MHz because its frequency band is close to the original signal frequency band of the MUSE system.

For this reason, conventionally, it has been difficult to sufficiently suppress the interfering wave due to the pilot signal.

The present invention has been made in view of such a situation, and it is possible to effectively suppress beat interference due to a pilot signal.

[0012]

A signal demodulator according to claim 1 separates a pilot signal from a transmission signal in a signal demodulator which demodulates an FM signal from a transmission signal including a pilot signal and an FM signal. The bandpass filter 16 as the first separating means, and the bandpass filter 1
From the pilot signal separated by 6, the phase shift circuit 69 as a generation means for generating a first signal and a second signal whose phases are different from each other by 90 degrees, a first signal and a second signal, Balanced modulators 65 and 68 as modulating means for performing balanced modulation with the third signal and the fourth signal respectively, and an adder 15 as adding means for adding the transmission signal and the outputs of the balanced modulators 65 and 68, A limiter 19 as limiting means for limiting the output level of the adder 15, a bandpass filter 61 as second separating means for separating a pilot signal from the output of the limiter 19, and a pilot separated by the bandpass filter 61. The signal is synchronously detected by the first signal and the second signal generated by the phase shift circuit 69 to generate a third signal and a fourth signal, respectively. And 63,66, characterized in that it comprises a FM demodulator 20 as demodulating means for FM demodulating the output of the limiter 19.

A PLL circuit 32 can be further connected to the bandpass filter 16. Further, when the transmission signal is a reproduction signal from the disc, an inverter as an inverting means for inverting the phase of the output of the PLL circuit 32 supplied to the phase shift circuit 69 in response to the track jump at the reproduction position on the disc. 83 can be further provided. Further, as a signal supplied from the balanced modulators 65 and 68 to the adder 15, a bandpass filter 71 as an extracting means for extracting a pilot signal can be provided.

According to a fifth aspect of the present invention, there is provided a signal demodulating device for demodulating an FM signal from a transmission signal including a pilot signal and an FM signal. The band demodulating device separates the pilot signal from the transmission signal. The filter 16, the synchronous detection circuits 63 and 66 and the balanced modulators 65 and 68 as adjusting means for adjusting the phase and level of the pilot signal separated by the bandpass filter 16.
And an adder 15 as an adding means for adding the outputs of the balanced modulators 65 and 68 to the transmission signal, a limiter 19 as a limiting means for limiting the level of the output of the adder 15, and an FM demodulation of the output of the limiter 19. The FM demodulator 20 as a demodulation means and a comparison circuit 91 as a control means for controlling the addition state of the outputs of the balanced modulators 65 and 68 to the transmission signal according to the frequency of the output of the FM demodulator 20. It is characterized by being provided.

[0015]

In the signal demodulating device according to the first aspect, the pilot signal component contained in the signal output from the limiter 19 is extracted by the bandpass filter 61, which is synchronously detected by the synchronous detectors 63 and 66, That level is detected. Corresponding to this detected level,
The balance modulators 65 and 68 modulate the first signal and the second signal generated by the phase shift circuit 69, and the adder 15 adds (subtracts) the transmission signal. As a result, the adder 15 automatically adjusts the phase and level of the signals to be added, thus eliminating the need for adjustment.

In addition, in the signal demodulating device according to the fifth aspect, the addition state of the outputs of the balanced modulators 65 and 68 to the transmission signal is controlled according to the frequency of the output of the FM demodulator 20. Therefore, for example, in a dark screen, the interference wave can be suppressed.

[0017]

1 is a block diagram showing the configuration of an embodiment of a video disc player to which the signal demodulating device of the present invention is applied. A high-definition video signal is recorded on the video disk 11 as a MUSE video signal. The video disk 11 is rotated by a spindle motor 12. The optical head 13 irradiates the video disc 11 with laser light and reproduces the signal recorded on the video disc 11 from the reflected light.

The RF signal output from the optical head 13 is supplied to bandpass filters (BPF) 14 and 16. The BPF 14 receives 12.5M of the input signal.
Signals in the frequency band centering on Hz (main carrier f
_C ) is extracted and output to the adder 15. Also, BP
F16 separates the 2.3 MHz pilot signal f _P and outputs it to the phase shift circuit 17. The phase shift circuit 17 reverses the phase of the input pilot signal f _P and outputs it to the level adjustment circuit 18. The level adjustment circuit 18 is
The level of the pilot signal input from the phase shift circuit 17 is adjusted to double the level and output to the adder 15.

The adder 15 adds the output of the BPF 14 (mixed signal of the main carrier f _C , the pilot signal (lower side band) f _P and the upper side band f _P ⁺ ) and the output of the level adjusting circuit 18, and the limiter It is output to 19.
The limiter 19 limits the level of the signal input from the adder 15 to a level within a predetermined range, and then the FM demodulator 20.
Is being supplied to. The FM demodulator 20 FM demodulates the signal supplied from the limiter 19 and outputs a low-pass filter (LP
F) 21 to output to the time axis error correction (TBC) circuit 22.

Next, the operation will be described. RF that the optical head 13 reproduces and outputs the video disk 11.
The signal is provided to BPFs 14 and 16. Of these signals, signals in the lower frequency band including the main carrier (FM signal) f _C are extracted by the BPF 14 and supplied to the adder 15. On the other hand, the pilot signal f _P
Is extracted by the BPF 16 and supplied to the phase shift circuit 17. The phase shift circuit 17 receives the input pilot signal f _P
The phase is inverted by 180 degrees (reversed phase) and output to the level adjustment circuit 18. The level adjustment circuit 18 doubles the level of the input anti-phase pilot signal −f _P and outputs it to the adder 15. The adder 15 uses the BPF 14
Signal input from the level adjusting circuit 18 and the pilot signal 2 (-
f _P ) is added and output to the limiter 19. Limiter 1
9 limits the level of the signal input from the adder 15 to a predetermined level.

The above operation will be further described with reference to FIG. As described above, by the optical head 13, the main carrier f _C , the lower side band f _P and the upper side band f _P included in the signal reproduced from the video disk 11 are recorded.
The phase relationship with _P ⁺ is as shown in FIG. The BPF 16 separates the lower side band f _P from the above. Then, the phase shift circuit 17 generates the anti-phase pilot signal -f _P , and the level adjusting circuit 18 doubles the level of the pilot signal -f _P to generate the pilot signal 2 (-f _P ). This is added to the lower side band f _P supplied from the BPF 14 in the adder 15 (FIG. 2 (b)), and the signal output from the adder 15 becomes as shown in FIG. 2 (c).

[0022] That is, at the tip of the vector F _C of the main carrier f _C, and the vector -F _P corresponding to the lower sideband -f _P of opposite phase vector F _P ⁺ is phase corresponding to the upper sideband f _P ⁺ Corresponding to the change, they will rotate in opposite directions. As a result, the composite vector is the vector F
The position of the tip of _C changes in the horizontal direction in the figure. That is, the FM component is removed, leaving only the AM component.
Therefore, by limiting the signal shown in FIG. 2 (c) to a predetermined level by the limiter 19, the main carrier (FM signal) f _C shown in FIG. 2 (d) in which the pilot signal component is completely removed is obtained. You can

When the output f _C of the limiter 19 thus obtained is input to the FM demodulator 20 and FM demodulated, beat interference due to the pilot signal component is almost completely suppressed. The signal demodulated by the FM demodulator 20 is
After removing unnecessary high frequency components by the LPF 21,
It is input to the BC circuit 22 and the time base error is corrected. Then, the signal whose time axis error is corrected is the CRT (not shown).
Will be output to and displayed.

FIG. 3 shows the energy spectrum in each part of FIG. FIG. 3A shows the optical head 1.
3 shows the frequency spectrum of the RF signal output from the device 3. As shown in the figure, this signal includes a lower side band of 2.28 MHz (= about 2.3 MHz) at -22 dB and an upper side band of 18.9 MHz at -33 dB.

FIG. 3B shows the frequency spectrum at the output of the limiter 19, and FIG.
Shows the frequency spectrum of the output of the TBC circuit 22. As shown in FIG. 3B, the level of the lower sideband is -34 dB when the output of the level adjusting circuit 18 is not added by the adder 15, but when this addition is performed, it is -47 dB. . Similarly, the level of the upper sideband is -37 dB when the output of the level adjusting circuit 18 is not added in the adder 15, but when this addition is performed, the level is attenuated to -48 dB. Further, in FIG. 3C, the level of the beat disturbing component of 8.3 MHz is 14 when the output of the level adjusting circuit 18 is added by the adder 15 as compared with the case where the output is not added.
It can be seen that it is attenuated by dB.

FIG. 4 is a block diagram showing a second embodiment of the video disc player of the present invention, in which parts corresponding to those in FIG. 1 are designated by the same reference numerals. In this embodiment, a bandpass filter (BPF) 16
Is output to the PLL circuit 32 via the limiter 31. The PLL circuit 32 compares the phase of the signal input from the limiter 31 with the phase of the output of the frequency dividing circuit 44, and outputs the phase error thereof, and the phase comparing circuit 4
1 low-pass filter (LP
F) 42, a voltage controlled oscillator (VCO) 43 that generates a clock corresponding to the output of the LPF 42, and the output of the VCO 43 is divided into 1/12 and output to the phase comparison circuit 41 and the phase shift circuit 17. And a frequency divider circuit 44. The output of the VCO 43 is also supplied to the TBC circuit 22. Other configurations are similar to those in FIG.

That is, in this embodiment, the BPF 16
The pilot signal extracted by is input to the PLL circuit 32 via the limiter 31, and a pilot signal synchronized with this is newly generated. As a result, even if the pilot signal is dropped due to dropout or its level fluctuates, it is possible to supply the pilot signal having a stable phase and level to the phase shift circuit 17. Therefore, as compared with the embodiment of FIG.
It becomes possible to improve. Since the TBC circuit 22 originally needs to be supplied with a clock synchronized with the reproduction signal, if a PLL for that purpose is shared, there is no need to add a special circuit configuration, which may increase the cost. You're done.

In the embodiments shown in FIGS. 1 and 4, the phase amount and the level adjustment amount in the phase shift circuit 17 and the level adjustment circuit 18 are fixed. Therefore, at the time of manufacturing, it is necessary to adjust the phase amount and the level adjustment amount so as to have predetermined values. Therefore, for example, by configuring as shown in FIG. 5, it is possible to eliminate this adjustment work.

In the embodiment shown in FIG. 5, the output of the bandpass filter (BPF) 16 is supplied to the phase shift circuit 69. The phase shift circuit 69 receives the input pilot signal f _P
Of the first signal c and the second signal c whose phases differ from each other by 90 degrees.
Signal s. The first signal c is supplied to the balanced modulator 65 and the synchronous detector 63, and the second signal s is supplied to the balanced modulator 68 and the synchronous detector 66. The synchronous detectors 63 and 66 synchronously detect the output of the amplifier 62 with the first signal c and the second signal s, and output the detected outputs to the low-pass filters (LPF) 64 and 67.
The outputs of the LPFs 64 and 67 are supplied to the balanced modulators 65 and 68, respectively, as the third signal and the fourth signal.

The balanced modulator 65 supplies the first signal c supplied from the phase shift circuit 69 to the third signal supplied from the LPF 64.
The signal L _C is balanced-modulated and output to the adder 15. The balanced modulator 68 balance-modulates the second signal s output by the phase shift circuit 69 with the fourth signal L _S supplied by the LPF 67, and outputs the second signal s to the adder 15. The adder 15 adds (subtracts) the outputs P and Q of the balanced modulators 65 and 68 to the RF signal supplied from the optical head 13 with opposite polarities, and outputs it to the limiter 19. The output of the limiter 19 is supplied to the FM demodulator 20, and a part of its signal is BP.
The signal is supplied to F61 and the pilot signal component is extracted. The output of the BPF 61 is amplified by the amplifier 62 and supplied to the synchronous detectors 63 and 66.

Next, the operation will be described. BPF
Reference numeral 61 extracts the pilot signal component that is not removed and is included in the signal output from the limiter 19. This pilot signal component is amplified by the amplifier 62 and supplied to the synchronous detectors 63 and 66. Synchronous detector 63 and 66
Uses the first signal c and the second signal s output from the phase shift circuit 69 to synchronously detect the pilot signal component supplied from the amplifier 62. Then, the low-frequency components of the outputs of the synchronous detectors 63 and 66 are extracted by the LPFs 64 and 67, respectively, and the third signal L _C and the fourth signal L _S are generated. That is, for the third signal L _C and the fourth signal L _S , the output of the amplifier 62 is F, and the demodulation sensitivities of the synchronous detectors 63 and 66 are k.
_{When C} and k _S are the low frequency components of the product of F, c and k _C or the low frequency components of the product of F, s and k _S , they can be expressed by the following equation. L _C = LPF (k _C · c · F) L _S = LPF (k _S · s · F)

The balanced modulator 65 outputs the first signal c output from the phase shift circuit 69 to the third signal L _C output from the LPF 64.
The output P can be expressed by the following equation when the modulation sensitivity of the balanced modulator 65 is G _C. P = L _C・ G _C・ c

The balanced modulator 68 also includes a phase shift circuit 69.
Since the second signal s output by the signal is balanced-modulated by the fourth signal L _S output by the LPF 67, its output Q can be expressed by the following equation. Q = L _S・ G _S・ s

As described above, the signal Y input to the adder 15 includes the main carrier (FM signal) f _C and the pilot signal lower side band f _P and upper side band f _P ^+. (Fig. 2 (a)). The signals P and Q output from the balanced modulators 65 and 68 are subtracted from the two signals (upper and lower sidebands), and the difference signal is output from the adder 15. The output of the adder 15 is input to the limiter 19 and the level thereof is limited to generate the sideband component as described above. However, the pilot signal component included in the output Z of the limiter 19 is extracted by the BPF 61. Since the signals are detected by the synchronous detectors 63 and 66, after all, the servo is applied so that the pilot signal included in the output Z of the limiter 19 becomes zero.

Therefore, the BPF 61, the amplifier 62, the synchronous detectors 63 and 66, the LPFs 64 and 67, the balanced modulator 65,
The pilot signal component is automatically removed by the feedback loop including the adder 68 and the adder 15.

In the embodiment shown in FIG. 5, the output of the BPF 16 is directly supplied to the phase shift circuit 69. In this way, if the pilot signal f _P has a dropout or a level change, the pilot signal input to the adder 15 for offsetting will change and the S / N of the output signal will deteriorate. Therefore, as in the case of the embodiment shown in FIG. 4, as shown in FIG. 6, the BPF 16 and the phase shift circuit 69 are provided.
It is possible to insert the PLL circuit 32 between the two and supply the pilot signal f _P generated by the PLL circuit 32 to the phase shift circuit 69.

In the embodiment of FIG. 5, the outputs of the balanced modulators 65 and 68 are directly supplied to the adder 15. On the other hand, in the embodiment of FIG. 6, the outputs of the balanced modulators 65 and 68 are input to the adder 70 and added, and the added output is supplied to the adder 15 via the BPF 71. When the pilot signal component is extracted by the BPF 71 in this way, the balanced modulators 65, 6
If the signals P and Q generated by 8 have distortion, the pilot signal cannot be canceled accurately.
Since the component having this distortion is removed by the PF 71, it is possible to cancel the pilot signals more accurately.

By the way, on the video disk 11, one frame of video signal is recorded for one rotation. A high-definition video signal has one frame including 1125 horizontal scanning lines. The frequency of the pilot signal is set to 135/2 times the frequency of the horizontal scanning line. In other words, the pilot signal is 1H
Only 135/2 waves are included in the period of (horizontal scanning period). Therefore, one frame (video disc 11
The number of waves of the pilot signal during one rotation period of
It becomes 75937 + 1/2 (= 1125 × 135/2). Therefore, when the optical head 13 jumps one track on the video disk 11, the phase of the pilot signal is shifted by 180 degrees.

Therefore, in the embodiment of FIG. 7, the PLL
The pilot signal f _P output from the circuit 32 is the inverter 8
3, the phase is inverted and supplied to the phase shift circuit 69. That is, in this case, when the command for the optical head 13 to jump one track is input from the input terminal 81, the flip-flop 82
Inverts the logic of its output. When the logic of the flip-flop 82 is 1, the switch 84 is switched to the left side in the figure, for example, and when the logic is 0, it is switched to the right side in the figure. As a result, the phase of the pilot signal f _P generated by the PLL circuit 32 is inverted by 180 degrees every time it is jumped to the adjacent track and supplied to the phase shift circuit 69. As a result, the phase of the pilot signal input to the adder 15 immediately after the track jump is performed,
It is prevented that the signals P and Q generated by the balanced modulators 65 and 68 are out of phase with each other and the pilot signal component cannot be canceled.

In the embodiment of FIG. 7, the inverter 83 is provided to invert the phase of the pilot signal, but this inversion processing should be performed in the PLL circuit 32 or the phase shift circuit 69. Is also possible.

When the frequency of the FM signal f _C as the main carrier is low, the interference frequency (f _C -f _P ) due to the pilot signal f _P is also low and the beat interference becomes conspicuous, but the main carrier f _C is As the frequency becomes higher, the interference frequency f _C -f _P also becomes higher and is outside the band of the MUSE signal, so that the beat interference becomes inconspicuous.

When the main carrier f _C is low and when it is high, the levels of the upper and lower side bands become unbalanced due to the influence of the MTF including the optical head 13. That is, since the MTF has the same characteristics as the low-pass filter, the higher the frequency component, the smaller its output level.
As a result, for example, as shown in FIG. 8A, when the frequency of the main carrier f _C is low, the frequency of the upper side band f _P ⁺ also has a relatively low value, so that the level of the upper side band f _P ⁺ is It becomes relatively large. However, FIG. 8 (b)
As shown in FIG. 8, when the frequency of the main carrier f _C increases, the frequency of the upper side band f _P ⁺ also increases, so the level of the upper side band f _P ⁺ becomes smaller than that in the case shown in FIG. 8A. As a result, the level of the pilot signal required for cancellation will have different values depending on whether the main carrier f _C is low or high. According to the embodiment shown in FIGS. 5 to 7, even if the levels of the upper and lower sidebands are unbalanced as described above, the level of the pilot signal necessary for cancellation is automatically set to an appropriate value. Is set.

However, the outputs of the LPFs 64 and 67 are low-frequency components of the change component of the pilot signal in the signal output from the limiter 19, and it is difficult to respond rapidly. As a result, for example, when a relatively bright screen suddenly changes to a dark screen, beat interference is expected to be conspicuous immediately after the switching. In order to solve this, it can be configured as in the embodiment of FIG.

That is, in the embodiment of FIG. 9, LPF6
The outputs of 4 and 67 are supplied to the balanced modulators 65 and 68 via the switches 93 and 95, respectively. Then, the switches 93 and 95 and the balanced modulators 65 and 68
Hold capacitors 94 and 96 are connected between the two. The switches 93 and 95 are controlled by a comparison circuit 91 that compares the levels of the reference voltage output by the reference voltage generation circuit 92 and the signal output by the LPF 21.

That is, the comparison circuit 91 compares the level of the video signal output by the LPF 21 with the reference voltage output by the reference voltage generation circuit 92. The reference voltage output by the reference voltage generation circuit 92 is set to a threshold voltage corresponding to the brightness of the screen where beat interference is conspicuous (for example, 20% when the voltage corresponding to the brightest screen is 100%). ing. The comparator circuit 91 turns on the switches 93 and 95 when the level of the video signal demodulated by the FM demodulator 22 is lower than the reference voltage and the screen is dark (when the frequency of the main carrier f _C is low). When the screen is brighter than the reference voltage and bright (when the frequency of the main carrier f _C is high), it is turned off. As a result, when the level of the video signal is lower than the preset reference value and the screen is dark, the servo loop for canceling the pilot signal included in the signal input to the adder 15 is turned on and cancels. So the servo will work.

When the screen becomes bright, the switches 93, 95
Is turned off. However, the output voltages of the LPFs 64 and 67 immediately before the switches 93 and 95 are turned off are held in the capacitors 94 and 96. As a result, after that, the screen changes from the bright screen to the dark screen again, and the switches 93 and 95
When is turned on, the voltage held in the capacitors 94 and 96 is acting, so that it is possible to quickly start the operation of canceling the pilot signal. Therefore, the noticeable beat interference is suppressed immediately after the bright screen is switched to the dark screen.

In the embodiment shown in FIG. 9, the pilot signal component is canceled in correspondence with the voltage held in the capacitors 94 and 96 even when the screen is bright, but beat interference occurs in the bright screen. Since it is not conspicuous, it is possible to completely cancel the pilot signal canceling operation when a bright screen is detected. In this case, for example, the adder 70 and the BPF 7
A switch may be provided between the switch 1 and the switch 1, and when a bright screen is detected corresponding to the output of the comparison circuit 91, the switch is turned off, and when a dark screen is detected, the switch is turned on. .

In the above, the case where the present invention is applied to a video disc player has been described as an example, but the present invention is applied when demodulating an FM signal from a transmission signal including other FM signals and pilot signals. It is possible.

[0049]

As described above, according to the signal demodulating device of the first aspect, a signal obtained by balance-modulating the first signal and the second signal with the third signal and the fourth signal, respectively. Is added to the transmission signal, no adjustment is required, and the pilot signal can be reliably suppressed.

According to the signal demodulating device of the fifth aspect, the addition state of the output of the adjusting means to the transmission signal is
Since the control is performed in accordance with the frequency of the output of the demodulation means, it is possible to suppress the beat interference from being conspicuous particularly on a dark screen without adversely affecting the original signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a video disc player to which a signal demodulating device of the present invention is applied.

FIG. 2 is a vector diagram for explaining the operation of the embodiment of FIG.

FIG. 3 is a frequency spectrum diagram illustrating the operation of the embodiment of FIG.

FIG. 4 is a block diagram showing the configuration of another embodiment of a video disc player to which the signal demodulating device of the present invention is applied.

FIG. 5 is a block diagram showing a configuration of a third embodiment of the signal demodulation device of the present invention.

FIG. 6 is a block diagram showing the configuration of a fourth embodiment of the signal demodulating device of the present invention.

FIG. 7 is a block diagram showing the configuration of a fifth embodiment of the signal demodulation device of the present invention.

FIG. 8 is a diagram for explaining the effect of MTF characteristics on the upper sideband.

FIG. 9 is a block diagram showing the configuration of a sixth embodiment of the signal demodulation device of the present invention.

FIG. 10 is a block diagram showing a configuration of an example of an apparatus for recording a signal on a video disc.

FIG. 11 is a diagram showing frequency allocation in a MUSE type video disc.

12 is a diagram for explaining the principle that upper and lower sidebands of a pilot signal are generated by the processing of the limiter 53 of FIG.

13 is a diagram showing a frequency spectrum at the input of the limiter 53 of FIG.

14 is a diagram showing a frequency spectrum at the output of the limiter 53 of FIG.

FIG. 15 is a diagram illustrating beat interference caused by a pilot signal when a conventional MUSE video disc is played back.

[Explanation of symbols]

 11 Video Disc 13 Optical Head 14 Band Pass Filter 15 Adder 16 Band Pass Filter 17 Phase Shift Circuit 18 Level Adjusting Circuit 19 Limiter 20 FM Demodulator 31 Limiter 32 PLL Circuit 52 Adder 53 Limiter 63 Synchronous Detector 64 Low Pass Filter 65 Balanced Modulator 66 Synchronous detector 67 Low pass filter 68 Balanced modulator 69 Phase shift circuit 71 Band pass filter 83 Inverter 91 Comparison circuit 92 Reference voltage generation circuit

Claims (5)

[Claims] 1. A signal demodulating device for demodulating the FM signal from a transmission signal including a pilot signal and an FM signal, comprising: first separating means for separating the pilot signal from the transmission signal; and the first separation. Generating means for generating a first signal and a second signal having phases different from each other by 90 degrees from the pilot signal separated by the means; the first signal and the second signal, and the third signal. And a fourth signal for performing balanced modulation, an adding means for adding the transmission signal and the output of the modulating means, a limiting means for limiting the level of the output of the adding means, and an output of the limiting means. Second separating means for separating the pilot signal from the first signal, and the pilot signal separated by the second separating means, the first signal and the second signal generated by the generating means. And more synchronous detection, the signal demodulating device for a detection means for generating Zorezo Re said third signal and the fourth signal, comprising: a demodulating means for FM demodulating the output of said limiting means. 2. The signal demodulating device according to claim 1, wherein the first separating unit includes a PLL circuit. 3. The transmission signal is a reproduction signal from a disc, and further includes inverting means for inverting a phase of an output of the PLL circuit supplied to the generating means in response to a track jump at a reproduction position on the disc. The signal demodulating device according to claim 2, further comprising: 4. The extracting means for extracting the pilot signal as a signal supplied from the modulating means to the adding means, further comprising:
The signal demodulating device according to. 5. A signal demodulating device for demodulating the FM signal from a transmission signal including a pilot signal and an FM signal, a separating means for separating the pilot signal from the transmission signal, and the separation means separated by the separating means. Adjusting means for adjusting the phase and level of the pilot signal, adding means for adding the output of the adjusting means to the transmission signal, limiting means for limiting the level of the output of the adding means, and FM for the output of the limiting means. A signal demodulating device comprising: demodulation means for demodulating; and control means for controlling the addition state of the output of the adjusting means with respect to the transmission signal in accordance with the frequency of the output of the demodulating means.