JP2968279B2 - Video signal format conversion circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a signal format conversion circuit for a video signal.

BACKGROUND ART In a color video signal according to the NTSC system (hereinafter referred to as an NTSC color video signal), the number of scanning lines is 525, the field frequency is 60 Hz, and the frequency of the color subcarrier is 3.58 MHz. In a PAL color video signal (hereinafter referred to as a PAL color video signal), the number of scanning lines is 625, the field frequency is 50 Hz, and the frequency of the color subcarrier is 4.43 MHz.

NTS is performed by a PAL video playback device such as a television receiver that plays back video using this PAL color video signal.
It has been requested to be able to obtain the video recorded on the disc on which the C color video signal is recorded.
It has been conceived to provide a video disk player with a format conversion circuit as shown in FIG. 13 for converting an SC color video signal into a PAL color video signal in a pseudo manner.

In FIG. 13, an NTSC color video signal a read from a disk is directly supplied to a subtracter 2 and an adder 3 via an input terminal IN, and is supplied to a 1H delay circuit 1 for 1H.
After being delayed by (one horizontal scanning period), it is supplied to the subtractor 2 and the adder 3. The subtracter 2 cancels the luminance signal component and outputs only the color signal component, and the adder 3 cancels the color signal component and outputs only the luminance signal component. The color signal component output from the subtracter 2 is supplied to a multiplier 4 and multiplied by the output of an oscillator 5.

The oscillation frequency of the oscillator 5 is the frequency of the color subcarrier in the PAL color video signal (4.43 MHz) and the frequency of the color subcarrier in the NTSC color video signal (3.58 MHz).
The frequency is equal to the difference between z), that is, 854 kHz. Therefore, in the multiplier 4, a signal obtained by converting the frequency of the color signal component from the subtractor 2 from 3.58 MHz to 4.43 MHz is formed. 4.43 MH output from the multiplier 4
the color signal component of z is the center frequency of the pass band is supplied to the fixed contact B ₁ phase shifter 8 and the changeover switch SW ₁ through the band pass filter 6 of 4.43 MHz.

The phase shifter 7 is configured to shift the phase of the supplied signal by + 45 °. The phase shifter 8 is configured to shift the phase of the supplied signal by -45 °. These phase shifters 7,
The output of the 8 is supplied to each of the fixed contact A ₁ and C ₁ of the change-over switch SW _1. Also, fixed contact D of changeover switch SW _1
1 is grounded.

The output of the switching control signal generating circuit 9 is supplied to the control input terminal of the change-over switch SW _1. Changeover switch SW
₁ is configured to contact the one movable contact E ₁ is corresponding to the switching control input of the fixed contact point A ₁ to D _1. The switching control signal generating circuit 9 is, for example, an NTSC color video signal a.
Detecting a period T ₂ in the presence of video information signal by the horizontal synchronizing signal in a color lifetime period T ₁ and other than the period T ₁ to the burst in each horizontal scanning period, in the period T ₁ is movable contact E ₁ contacts alternately with the fixed contact a ₁ and C ₁ in every 1H, the movable contact E ₁ in every 1H is controlled to alternately contact with the fixed contact B ₁ and D ₁ in the period T ₂ It is configured to generate a signal.

Derived signals to the movable contact E ₁ of the changeover switch SW ₁ is
The luminance signal component supplied to the adder 10 and output from the adder 3 is added and synthesized to form a color video signal.
The output of the adder 10 is supplied to an output terminal OUT and sent to a PAL-type video reproducing device (not shown).

In the above configuration, when the FIG. 14 (A) to as shown NTSC color video signal a is supplied to the input terminal IN, the movable contact E ₁ of the changeover switch SW _1, in a period T ₁ 4.43 MHz
A signal obtained by the signal and the color signal component obtained by the frequency converted color signal component phase-shifted by + 45 ° and shifted by -45 ° is output alternately every 1H, in a period T ₂ The color signal component and a signal having an amplitude of zero are alternately output every 1H. Therefore, the color signal component d output from the movable contact point E ₁ of the changeover switch SW ₁ is a such a signal is shown in FIG. 14 (B). Since the color signal component d is supplied to the adder 10 and added and synthesized with the luminance signal component, the color video signal b output from the adder 10 becomes as shown in FIG. 14 (C).

When the color video signal b is sent to a PAL video reproducing device (not shown), the color video signal b is supplied to a demodulation circuit as shown in FIG. 15 in the PAL video reproducing device. . In FIG. 15, the color video signal b is supplied to a Y / C separation circuit 20 and a synchronization separation circuit 21. In the Y / C separation circuit 20, the color video signal b
And a luminance signal component and a chrominance signal component are separated from each other, and the luminance signal component is supplied to a picture tube driving circuit (not shown) for driving the picture tube. The color signal component passes through an ACC (automatic color saturation control) circuit 22, a burst phase discrimination circuit 23, a 1H delay line 24,
It is supplied to the polarity inversion circuit 25 and the adder 26. ACC circuit 22
Is a variable gain amplifier 22a that amplifies the color signal component, a burst gate circuit 22b that separates the color burst signal from the color signal component, and an ACC voltage according to the level of the color burst signal separated by the burst gate circuit 22b. An ACC detection circuit 22c that generates and supplies the gain control signal to the variable gain amplifier 22a is provided, and the gain of the variable gain amplifier 22a is controlled so that the level of the color burst signal becomes constant.

In the burst phase discrimination circuit 23, the color burst signal is separated from the color signal component, and the subcarrier generation circuit 33
The reset signal is generated each time the phase of the color burst signal reaches a predetermined phase. This reset signal is supplied to a T-type flip-flop. The sync separation circuit 22 is connected to the trigger input terminal of the T-type flip-flop 34.
Supplies a horizontal synchronization signal separated from the color video signal, and the T-type flip-flop 34 is inverted every 1H.

On the other hand, in the 1H delay line 24, the color signal component is delayed by 1H and supplied to the adders 26 and 27.

In the adder 26, the color signal component and this color signal component are
And a signal obtained with only a delay. This adder
At 26, the R-Y component in the PAL color video signal whose phase is inverted every 1H is canceled so that only the B-Y component is output. 14 The color signal component is 1H as shown in FIG.
Since only exists in the period T ₂ of the notice, from the adder 26 color signal components present in the period T ₂ of the this every 1H is also output in the period T ₂ in the next 1H, color signal component for each H Will be output.

In addition, the adder 27 adds the inverse phase component of the color signal component and a signal obtained by delaying the color signal component by 1H. In the adder 27, only the RY component whose phase is inverted every 1H is output by canceling the BY component in the PAL color video signal. The color signal component is also output from the adder 27 for each H.

The outputs of the adders 26 and 27 are supplied to synchronous detection circuits 28 and 29. The subcarrier generation circuit 33 is provided in the synchronous detection circuit 28.
The color subcarriers generated by the phase shifter 35 and then shifted by 90 ° are supplied. In the synchronous detection circuit 29, a color subcarrier generated by the subcarrier generation circuit 33 and a signal obtained by shifting the phase of the color subcarrier by 180 ° by the phase shifter 35 are alternately switched every 1H by the changeover switch 36. Is supplied to The BY signal and the RY signal are demodulated by the synchronous detection circuits 28 and 29, and supplied to a picture tube driving circuit (not shown) via low-pass filters 31 and 32 having a cutoff frequency of 1.3 MHz. The image is played.

However, in the conventional signal format conversion circuit as shown in FIG. 13, the phase shifters 7 and 8 are composed of coils, capacitors, resistors, and the like, and are configured to process the input signal in an analog manner and perform phase shift. Therefore, there is a problem that accurate phase shift is difficult due to variations in the values of the respective constituent elements, and the influence of the temperature characteristics of the respective constituent elements is likely to appear, so that a good color image cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made in consideration of the above-described problems, and has been made in consideration of a video signal capable of obtaining a good color image by performing signal format conversion without performing phase shift by analog processing. It is an object to provide a signal format conversion circuit.

The signal format conversion circuit for a video signal according to the present invention is a video signal signal format conversion circuit for converting an NTSC composite video signal into a PAL composite video signal, wherein the NTSC composite video signal is converted into an NTSC color signal and an NTSC composite video signal. A Y / C separation unit that separates and extracts the luminance signal, a PAL conversion unit that converts the NTSC color signal into a PAL color signal corresponding to the PAL system, and adding the PAL color signal and the NTSC luminance signal. Adding means for obtaining the PAL composite video signal, wherein the PAL conversion means generates a reference signal that is an oscillation signal having the same frequency as the chrominance subcarrier in the NTSC method, and a PAL method. A first signal that is an oscillation signal having the same frequency as the color subcarrier, a second signal obtained by delaying the phase of the first signal by 45 degrees, and a phase delayed by 45 degrees of the second signal. An oscillating signal generating means for respectively generating a third signal, and a first and a third signal from among the first to third signals during a color burst period of the NTSC composite video signal every one horizontal period. Phase shift selecting means for alternately selecting and outputting this as a phase shift signal, and multiplying the NTSC color signal by a signal obtained by multiplying the phase shift signal and the reference signal to convert the PAL color signal And a multiplication means for obtaining.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. 1 to FIG.

In FIG. 1, a 1H delay circuit 1, a subtractor 2, an adder 3, a multiplier 4, and a band pass filter 6 are connected in the same manner as in the apparatus of FIG. However, in this example, the output of the band-pass filter 41 is supplied to the multiplier 4. The bandpass filter 41 is configured such that the center frequency is equal to 854 kHz. The output of the multiplier 42 is supplied to the band-pass filter 41. The output of the digital phase shifter 40 and the output of the oscillator 43 are supplied to the multiplier 42. Oscillator 43 is configured to generate a reference signal r ₂ of the same frequency of the color subcarrier of the video signal by the NTSC system.

The output of the oscillator 44 is supplied to the digital phase shifter 40. Oscillator 44 is configured to generate a reference signal r ₁ of 4 times the frequency of the color subcarrier of the video signal by the PAL system. In the digital phase shifter 40,
The reference signal r ₁ is divided by a frequency divider 45 to 1/4 while D
D-type flip-flop which is directly supplied to the clock input terminal of the type-type flip-flop 47 and is connected via an inverter 48
It is supplied to 46 clock input terminals. The output of the frequency divider 45 is supplied to the fixed contact C ₁ of the change-over switch SW ₁ is supplied to the D input terminal of D-type flip-flop 46. The output of the D-type flip-flop 46 is supplied to the fixed contact B ₁ of the changeover switch SW ₁ is supplied to the D input terminal of D-type flip-flop 47. Also, D
The output form the flip-flop 47 is supplied to the fixed contact point A ₁ of the switch SW _1. Also, changeover switch SW ₁
Fixed contact D ₁ of the is grounded. The switching control input terminals of the changeover switch SW _1, the output of the case as well as the switch control signal generating circuit 9 in the apparatus of FIG. 13 is supplied.

The color signal component output from the band pass filter 6 is supplied to one input terminal of the adder 10 via the gain control circuit 50. Gain control circuit 10 includes means for generating a detection to gain reduction instruction signal period T ₁ in which the presence of the color burst signal, for example by switching the output of the control signal generating circuit 9, decreases the gain in response to the gain reduction instruction signal Variable gain amplifier. Luminance signal component is supplied as the output of the adder 3 which is delayed by the time T _D by the delay circuit 51 to the other input terminal of the adder 10. The color signal component and the luminance signal component are added and synthesized by the adder 10 to form a color video signal. still,
The delay time T _D in the delay circuit 51 is 1H in the NTSC system.
(= 250n) of the time corresponding to a half of the difference between 1H in the PAL system and the delay time ΔD in the bandpass filter 6
s + ΔD).

The output of the adder 10 is supplied to an amplitude suppression circuit 52 and a vertical synchronization separation circuit 53. In the vertical sync separation circuit 53, a vertical sync signal is separated from the color video signal output from the adder 10, and the monostable multivibrator (hereinafter, MMV) is output.
). MMV54 is a vertical sync separation circuit 5.
It is configured to generate a pulse triggered by the rising edge of the output of No. ₃ and existing over a period T3 from the disappearance of the vertical synchronization signal to the end of the vertical blanking period. The output pulse of this MMV 54 is supplied to an amplitude suppression circuit 52
Supplied to The amplitude suppression circuit 52 is configured to limit the instantaneous level of the input signal to a level slightly lower than the level _VA slightly higher than the pedestal level according to the output pulse of the MMV 54, for example. The output of the amplitude suppression circuit 52 is supplied to an output terminal OUT.

In the above configuration, the reference signal r ₁ of 4 times the frequency of the color subcarrier of the video signal by the PAL system as shown from the oscillator 44 in FIG. 2 (A) is output. Then, the output of the frequency divider 45 for dividing the reference signal r ₁ 1/4 half becomes as shown in FIG. 2 (D). The output of the frequency divider 45, a fixed contact of the changeover switch SW ₁ is supplied as a phase shifted signal f sc ₃ color subcarrier having the same frequency to the D input terminal of D-type flip-flop 46 in the PAL system C
Supplied to ₁ .

Since the reference signal r ₁ is supplied through an inverter 48 to the clock input terminal of D-type flip-flop 46, D
The shape flip flop 46 falling phase signal by the edge f sc ₃ of the reference signal r ₁ is stored and held, the output of D-type flip-flop 46, the phase shift signal f sc ₃ as shown in FIG. 2 (C) Is advanced by 45 °. The output of this D-type flip-flop 46 is a transfer signal
As f sc ₂ is supplied to the D input terminal of D-type flip-flop 47 is supplied to the fixed contact B ₁ of the switch SW _1.

Since the reference signal r ₁ to the clock input terminal of D-type flip-flop 47 is supplied directly, the transfer signal by the rising edge of the reference signal r ₁ is the D-type flip-flop 47
f sc ₂ is stored and held, the output of D-type flip-flop 47, a phase shift signal f sc ₂ phases as shown in FIG. 2 (B) 4
It is a signal obtained by advancing by 5 mm. The output of the D-type flip-flop 47 is supplied as the phase shift signal f sc ₁ with the fixed contact A ₁ of the changeover switch SW _1.

Here, FIG. 3 as shown in (A) NTSC color video signal a is supplied to the input terminal IN, the movable contact E ₁ of the changeover switch SW ₁ by the switch control signal generating circuit 9 is solid-contact A
₁ , C ₁ , D ₁ , and B ₁ , respectively, as shown in FIGS. 3 (B) to 3 (E). That is, the movable contact E ₁ in every 1H in the period T ₂ in the presence of the color burst is alternately contacted to the solid contacts A ₁ and C _1, the video information signal exists movable contacts every 1H during a period T ₁ to E of ₁ is in contact alternately with the fixed contact B ₁ and D _1. Then, the phase signal f in a period T ₁
sc ₁ and f sc ₃ are alternately led out to the movable contact E ₁ every 1H,
Phase signal f sc ₂ and the ground level signal in the period T ₂ is 1
Alternately derived to the movable contact E ₁ to H intervals. This movable contact E
_The signal derived to ₁ is supplied to the multiplier 42 and multiplied by the 3.58 MHz reference signal r ₂ , so that the frequency of the phase shift signals f sc _{1 to} f sc ₃ and the reference signal r _{2 in} the multiplier 42 A signal having a frequency equal to the difference between the signals, that is, a signal of 854 kHz, in which the phase alternately changes by + 45 ° and −45 ° every ₁ H in the period T ₁ , and the amplitude becomes zero every 1 H in the period T ₂ . The third
A conversion signal c is formed as shown in FIG.

The 854 kHz conversion signal c is supplied to the multiplier 4 via the band pass filter 41. Then, the multiplier 4 is a 4.43 MHz signal whose frequency differs from that of the NTSC color signal component by 854 kHz, and the phase of the color burst signal alternates by + 45 ° and −45 ° every 1H, and the video information A color signal component d is formed as shown in FIG. 3 (G) in which the amplitude of the portion becomes zero every 1H. This color signal component d
Is supplied to the gain control circuit 50 via the band pass filter 6, and the level of the color burst is reduced by a predetermined value. FIG. 3 (H) output from the gain control circuit 50.
The color signal e as shown in FIG.
The signal 51 is added and synthesized with the luminance signal component delayed by T _D by 51 to form a color video signal b as shown in FIG. 3 (I).

The color video signal b is supplied to an amplitude suppression circuit 52 and a vertical synchronization separation circuit 53. Then, FIG. 4 (A) to indicate such a color video signal b of the vertical blanking interval T FIG (B) are shown, such as a vertical synchronizing signal v which is present over the vertical synchronization period T _V in _E vertical sync Output from the separation circuit 53.
When the vertical synchronizing signal v is supplied to the MMV54, pulse p which MMV54 by the rising edge of the vertical synchronizing signal v is present over a period T _Q as shown in FIG. 4 is triggered (C) is outputted from the MMV54 You. When the pulse p is supplied to the amplitude suppression circuit 52, the amplitude is limited so that the instantaneous level of the color video signal b is equal to or lower than the level _VA slightly higher than the pedestal level over the period in which the pulse p exists. so inserted code signal to a predetermined line of FIG. 4 vertical blanking period T _E of the color video signal as shown in (D) is substantially eliminated. Since the color video signal b output from the amplitude limiting circuit 51 is transmitted to the PAL video reproducing device (not shown) supplied to the output terminal OUT, the color video signal b is unobtrusive formed by a change in luminance due to the code signal. No image is produced.

Also, the color video signal b derived to the output terminal OUT
Since the frequency of the horizontal synchronizing signal is equal to the horizontal synchronizing frequency of the NTSC system, when this color video signal b is supplied to a PAL system video reproducing device (not shown), FIG. Since the delay time of the 1H delay line 24 in the demodulation circuit as shown is set to 1H of the PAL color video signal, ie, 64 μs, a color shift occurs. That is, during the period in which the amplitude of the color signal component of the color video signal b is zero, only the color signal component before 1H supplied to the adders 26 and 27 via the 1H delay line 24 is supplied to the synchronous detection circuits 28 and 29. During the period when the amplitude of the color signal component does not become zero, only the color signal component directly supplied to the adders 26 and 27 is supplied to the synchronous detection circuits 28 and 29 to reproduce a color image. As shown in the figure, the scanning lines L _n to
The difference between the colors on L _{n + 3} corresponds to 500 ns which is the difference between 1H of the PAL color video signal and 1H of the NTSC color video signal.
It has. However, the color video signal b
As shown in FIG. 6 (A), T _D is applied to the color signal component as shown in FIG.
(≒ 250 ns) and a luminance signal component as shown in FIG. Therefore, the contour becomes to be positioned in the middle of deviation between colors as indicated by a chain line y in FIG. 5, which is formed by a luminance signal component on the scanning line L _n ~L _{n + 3} close to each other, The color shift becomes inconspicuous.

Further, the color signal component of the color video signal b, the amplitude is zero for a period T ₂ in every 1H and the color video signal b is supplied to a video reproducing apparatus of the PAL system (not shown) One of the two inputs of the adders 26 and 27 in the demodulation circuit as shown in FIG. 15 in the video reproducing apparatus, that is, the amplitude of one of the color signal component and one of the signals obtained by delaying the color signal component by 1H. Becomes zero. Accordingly, the adder as compared with the case where normal PAL color video signal amplitude of the color signal component is not zero is supplied in the period T ₂ 26, 27
, The level of the color signal component output from the device decreases.

The color signal component of the normal PAL color video signal can be represented by a vector diagram as shown in FIG. 7 (A). In FIG. 7 (A), the color signal component at continuous 2H
f ₁ and the color burst signal accompanying this color signal component f ₁
g ₁ is shown. R-Y component of the color signal component f ₁ is phase-inverted with respect to B-Y axis for each 1H, color burst signal g
₁ is ± 1 from the BY axis corresponding to the phase inversion of the RY component.
Output at 35 ゜. In the case of normal PAL color video signal, Figure 7 in which the color signal component f _1, obtained by adding the signal obtained by inverting only R-Y component of the color signal component f ₁ of the previous 1H ( color signal component f ₂ as shown in B) is synchronously detected.

On the other hand, the color signal component of the color video signal b can be represented by a vector diagram as shown in FIG. In FIG. 8 (A), it is continuous similarly to FIG.
Shows a color burst signal g ₁ 'accompanying the color signal component f _1' and the color signal component f ₁ 'in 2H. Color burst signal g ₁ 'is printed, as well as a color burst signal g ₁ of the normal PAL color video signal, the color signal components f _1'
The amplitude becomes zero every 1H. Accordingly, in the case of the color video signal b, as shown in FIG.
f ₁ ′ becomes a color signal component f ₂ ′ that is synchronously detected as it is,
The level of the color signal component supplied to the synchronous detection circuits 28 and 29 is lower than that of a normal PAL color video signal.

However, the level of the color burst signal g ₁ 'of the color video signal b is reduced by the amplitude suppression circuit 52 as shown in FIG. 9 (A). Thus, Figure 9 by ACC circuit 22 in the video reproducing apparatus' level color burst signal g ₁ until a predetermined level of 'color burst signal g ₁ as shown in (B) and the color signal component f _1' Since the gain of the amplifier to be amplified increases and the level of the color signal component f ₂ ′ that is synchronously detected increases as shown in FIG. 10C, it is possible to prevent a decrease in saturation.

FIG. 10 is a block diagram showing another embodiment of the present invention, in which 1H delay circuit 1, subtracter 2, adder 3, multiplier 4, band-pass filter 6, delay circuit 51, amplitude suppression circuit 52, The vertical sync separation circuit 53 and the MMV 54 are connected in the same manner as in the apparatus shown in FIG. However, the output of the band-pass filter 6 in this example is being supplied directly to the adder 10, addition signal derived to the movable contact C ₂ of the change-over switch SW ₂ to the multiplier 4 feed. The output of the changeover switch SW ₂ of the switching to the control input terminal control signal generating circuit 61 is supplied. Changeover switch SW ₂ is configured to contact one of the movable contacts C ₂ corresponding to the switching control input of the fixed contact point A _2, B _2. Switching control signal generating circuit 61, for example, it detects the period T ₂ in the presence of period T ₁ and the video information signal in the presence of the color burst in each horizontal scanning period by the horizontal synchronizing signal in the NTSC color video signal, the period T the movable contact C ₂ is in contact with the fixed contact B ₂ in _1, configured for generating a signal for controlling such that the movable contact C ₂ contacts alternately with the fixed contact a ₂ and B ₂ in every 1H in the period T ₂ It has become.

The fixed contact A ₂ of the changeover switch SW ₂ output of the band-pass filter 62 is supplied. This bandpass filter
The center frequency of the 62 pass bands is 8.01 MHz.
The output of the bandpass filter 41 is supplied to the fixed contact B ₂ of the switch SW _2. The outputs of the multiplier 42 are supplied to the bandpass filters 62 and 41. The output of the digital phase shifter 40 and the output of the oscillator 43 are supplied to the multiplier 42 in the same manner as in the apparatus of FIG.

Digital phase shifter 40 is constructed similarly to the apparatus of FIG. 1, switch control signal generating circuit 9 in the digital phase shifter 40 in this example, the changeover switch SW in every 1H in the period T _{1 1} movable contact E ₁ contacts alternately with the fixed contact a ₁ and C _1, the fixed contact the movable contact E ₁ in the period T ₂
And it has a configuration for generating a switching control signal so as to contact the B _1.

In the above configuration, Fig. 11 when as shown in (A) NTSC color video signal a is supplied to the input terminal IN, the switching control signal generating circuit 9 by the movable contact E of the change-over switch SW _1
1 denotes fixed contacts A ₁ , C ₁ , and B ₁ in each of FIGS.
Contact each other as shown in FIG. That is, the movable contact E ₁ is in contact alternately with the fixed contact A ₁ and C ₁ in every 1H in the period T ₁ in the presence of the color burst, the movable contact E ₁ in the period T ₂ in the presence of video information signals a fixed contacting the contact B _1.
Then, the phase signal f sc ₁ and f sc ₃ during the period T ₁
There is derived to the movable contact E ₁ alternately every 1H, phase signal f sc2 is derived to the movable contact E ₁ during the period T _2. Derived signals to the movable contact E ₁ is supplied to the multiplier 42 3.58
Since the multiplied reference signal r ₂ of MHz, the multiplier 42 phase signal f sc ₁ ~f sc ₃ and a reference signal between the frequencies of the r ₂ difference and two respective frequency equal to the sum of the two frequencies in phase alternately every 1H during a period T ₁ a two signals of the signal i.e. 854kHz and 8.01MHz is +45 ° and -45
° only changed, the two signals do not change in the period T ₂ are formed. Signal 854kHz of these two signals is supplied through a band-pass filter 41 to the fixed contact B ₂ of the changeover switch SW _2, the signal of 8.01MHz is the changeover switch SW ₂ through a bandpass filter 62 It is supplied to the fixed contact a _2.

Movable contacts C ₂ of the change-over switch SW ₂ is in contact as shown in FIG. 11 to each of the fixed contact B _2, A ₂ by the switch control signal generating circuit 61 (D) and FIG. (E). That is, the movable contact C ₂ in period T ₁ is in contact with the fixed contact B _2, the movable contact C ₂ in period T ₂ are in contact alternately every 1H with the fixed contact A ₂ and B _2. Then, in a period T ₁ signal 854KHz is derived to the movable contact C _2, 854kHz in the period T ₂
And the movable contact C ₂ 2 two signals 8.01MHz is alternately every 1H
And a conversion signal c 'as shown in FIG. 11 (G) is formed. The conversion signal c ′ is supplied to the multiplier 4. Then, the multiplier 4 multiplies the color signal component by the NTSC method and the conversion signal c ′.

Here, one output of the multiplier 4 is set to cos α, and the other input of the multiplier 4 is set to cos β. Then, the multiplier 4
Is expressed by the following equation.

cos α · cos β = (1/2) ｛cos (α + β) + cos (α−β)｝ (1) Now, one input of the multiplier 4 is the conversion signal c ′, so that cos α is, in a period _{T 1 cos (ω P -ω N} )
, And the alternately every 1H in the period T ₂ cos (ω _P -
ω _N ) and cos (ω _P + ω _N ). Also, the multiplier 4
The other input has a color signal component according to the NTSC system, so that cos β becomes cos (ω _N + φ). Note that ω _P is PA
The angular frequency of the sub-carrier of the L system, ω _N is the angular frequency of the sub-carrier of the NTSC system.

Thus, the output of the multiplier 4 is a signal represented by the following equation in the period T _1.

_{cos (ω P -ω N) ·} cos (ω N + φ) = (1/2) {cos (ω P + φ) + cos (ω P -2ω N -φ)} ...... (2) Also, the multiplier 4 the output is a signal represented by signal and the following equation represented by alternately (2) in every 1H during the period T _2.

The output of the _{cos (ω P -ω N) ·} cos (ω N + φ) = (1/2) {cos (ω P + 2ω N + φ) + cos (ω P + φ)} ...... (3) the multiplier 4, since passing through the band-pass filter 6 of 4.43MHz (ω _P), Fig. 11 the color signal component of 4.43MHz as shown in (H) d 'is obtained whose phase is inverted every 1H with respect to B-Y axis It will be. This color signal component d '
Is supplied to an adder 10 and added and synthesized with a luminance signal component delayed by T _D by a delay circuit 51 to form a color video signal b ′ as shown in FIG. 11 (I).

The color signal component of the color video signal b 'has an amplitude of 1H
Since it does not become zero every other time, the saturation does not decrease even if the color video signal b 'is supplied to the PAL video reproducing apparatus.

FIG. 12 is a block diagram showing a video disc player provided with a signal format conversion circuit according to the present invention. In the figure, a disk 71 is driven to rotate by a spindle motor 72. A signal recorded on the disk 71 is read by the pickup 73 as the disk 71 rotates. A so-called RF (high frequency) signal, which is a read signal output from the pickup 73, is supplied to a demodulation circuit 74 including an FM demodulator and the like, and a color video signal is demodulated. The color video signal is transmitted by a CCD (Charge Coupled Device)
e) supplied to 75. A clock pulse output from a VCO (voltage controlled oscillator) 76 is supplied to the CCD 75. In the CCD 75, the color video signal is delayed by a time corresponding to the frequency of the clock pulse. The color video signal having passed through the CCD 75 is supplied to a variable phase shifter 77, a burst gate circuit 78, and a sync separation circuit 79.

In the synchronization separation circuit 79, a horizontal synchronization signal is separated from the color video signal, and supplied to the phase comparison circuit 80 as a reproduced horizontal synchronization signal. In the phase comparison circuit 80, the phase of the reference horizontal synchronization signal output from the reference signal generation circuit 81 is compared with the phase of the reproduced horizontal synchronization signal, and a time axis error signal corresponding to the phase difference between the two signals is generated. This time axis error signal is supplied to the equalizer 82. equalizer
At 82, the time axis error signal is amplified and phase compensated to generate a control voltage for the VCO 76 and to form a drive signal for the spindle motor 72. The drive signal generated by the equalizer 82 is supplied to the spindle motor 72 via the drive circuit 83, and the rotation speed of the disk 71 is controlled so that the phase difference between the reference and the reproduced horizontal synchronization signal becomes a predetermined value. . Further, the control voltage formed by the equalizer 82 is supplied to the VCO 76 so that the signal delay time in the CCD 75 is controlled so that the phase difference between the reference and the reproduced horizontal synchronization signal becomes a predetermined value, and the time axis error is compensated. Done.

On the other hand, in the burst gate circuit 78, a color burst signal or a pilot burst signal is separated from the color video signal and supplied to the phase comparison circuit 85. The phase comparison circuit 85 compares the phase of this burst signal with the reference subcarrier signal output from the reference signal generation circuit 81, and generates a phase error signal corresponding to the phase difference between the two signals. This phase error signal is supplied to the variable phase shifter 77, and the color video signal is shifted so that the phase of the color burst signal matches the phase of the reference subcarrier signal. The color video signal output from the variable phase shifter 77 is supplied to a character insertion circuit 86. The character insertion circuit 86
Made by the reference signal r ₃ output from the reference signal generating circuit 81 configured to be inserted into the color video signal to generate a video signal in response to the character indicated by the data output from the system controller (not shown) or the like ing.

In the reference signal generation circuit 81, the reference horizontal synchronization signal is
Output from the movable contact C ₃ of the switch SW _3. The fixed contact A ₃ of the switch SW ₃ the output of the frequency divider 81b is supplied. Divider 81b is configured to peripheral 1/910 half the derived signal to the movable contact C ₈ of the changeover switch SW _8.
Each of the fixed contacts A ₈ and B ₈ of the changeover switch SW ₈ has an oscillator 81a,
Each output of 81g is provided. The oscillator 81a is NTSC
It is configured to generate a signal having a frequency 4f sc (N) which is four times the frequency of the color subcarrier in the system. The oscillator 81g has a frequency of 4f sc (N) · f
It is configured to generate a signal _{H (N) / f H (} P). Note that f _H (N) represents a horizontal synchronization frequency in the NTSC system, and f _H (P) represents a horizontal synchronization frequency in the PAL system.

Changeover switch SW ₈ outputs the output of the oscillator 81a in contact with the movable contact C ₈ fixed contact A ₈ when the switching control input is high selectively, the movable contact when the switch control input is low C ₈ is a selectively output constitutes the output of the oscillator 81g in contact with the fixed contact B _8. This changeover switch SW
Switching control input terminal ₈ is connected to one end of the switch SW ₆ of the locking. At one end of the switch SW _6, the power supply voltage via the resistor R is applied. Also switch
The other end of SW ₆ is grounded. Low-level signals derived at one end by the switch SW ₆ is turned on is output as a signal format conversion instruction signal.

The the fixed contact B ₃ of the switch SW ₃ the output of the oscillator 81d
The output of the frequency divider 81e that divides the frequency by 1/240 is supplied. The oscillator 81d is configured to generate a frequency of 3.75 MHz, which is a frequency of a pilot burst signal inserted into a predetermined section of the PAL color video signal when the PAL color video signal is recorded on a disc.

Changeover switch SW ₃ is the switching control input the movable contact C ₃ is at high level selectively outputs the output of the divider 81b in contact with the fixed contact A _3, when the switching control input is low become selectively outputs constituting the frequency of the signal is equal to the horizontal synchronizing frequency of output or the PAL system of the movable contact C ₃ contacts the fixed contact point B ₃ divider 81e. The output of the signal format discrimination circuit 87 is supplied to the switching control input terminal of the change-over switch SW _3. The signal format discriminating circuit 87 detects whether or not a pilot signal has been inserted into, for example, a color video signal read from the disk 71, and according to a result of the detection, it is either a PAL or NTSC color video signal. It is configured to generate a signal format discrimination signal indicating whether or not the signal is valid.
The signal format discrimination circuit 87 is described in Japanese Patent Application
63-12240.

The reference sub-carrier signal is output from the movable contact C ₄ of the changeover switch SW _4. The fixed contact A ₄ of the changeover switch SW ₄ output of the frequency divider 81c for outputting a reference signal r ₂ and 1/4 frequency-divided output of the changeover switch SW ₈ is supplied. The output of the oscillator 81d is supplied to the fixed contact point B ₄ of the changeover switch SW _4. Changeover switch SW ₄ is switching the movable contacts C ₄ when control input is high level is output selectively outputting the contact with the fixed contact A ₄ divider 81c, when the switching control input is low the movable Contact C ₄ contacts fixed contact B ₄ and oscillator
An output of 81d, that is, a signal having a frequency equal to the frequency of the pilot burst is selectively output.
The output of the signal format discrimination circuit 87 is supplied to the switching control input terminal of the changeover switch SW _4.

The reference signal r _3, the movable contact C ₅ of the changeover switch SW ₅
Output from The fixed contact A ₅ of the changeover switch SW ₅ output of the changeover switch SW ₈ is supplied. The output of the oscillator 81f is supplied to a fixed contact B ₅ of the changeover switch SW _5. Oscillator 81f is configured to generate a reference signal r ₁ of 4 times the frequency of the color subcarrier in the PAL system. The changeover switch SW ₅ is switching control input is movable contacts C ₅ when the high-level output outputs selectively fixed contacts A ₅ to contact with the changeover switch SW _8, when the switching control input of the low level and it has a configuration in which the movable contact C ₅ selectively outputs the reference signal r ₁ of 4 times the frequency of the color sub-carrier at the output or the PAL system oscillator 81f in contact with the fixed contact B _5. This changeover switch SW ₅
The output of the signal format discriminating circuit 87 is supplied to the switching control input terminal of.

The color video signal output from the character insertion circuit 86 is
Is supplied to the signal format converting circuit 97 is supplied to a fixed contact A ₇ of the changeover switch SW _7. Changeover switch SW
The fixed contact B ₇ of ₇ output signal format conversion circuit 91 is supplied. The components of the signal format conversion circuit 97 are the same as those of the circuit of FIG. 1 except that the oscillators 43 and 44 are removed. The multiplier 42 in the signal format conversion circuit 97 includes a frequency divider 81c.
The reference signal r ₂ output from being supplied. The reference signal r ₁ output from the oscillator 81f is supplied to the frequency divider 45, D-type flip-flop 47 and the inverter 48 in the signal format converting circuit 97.

Changeover switch SW ₇ is a switch control input is movable contact C ₇ when the high level is outputted color video signal outputted from the character insertion circuit 86 in contact with the fixed contact A _7, switching control input is low when has a structure which outputs a color video signal the movable contact C ₇ is converted format is performed by a signal format converter 97 into contact with the fixed contact B _7. Color video signal derived to the movable contact C ₇ of the changeover switch SW ₇ is supplied to the output terminal OUT.

In the above configuration, when the switch SW ₆ is off,
Low level signal format conversion command signal is not output, the reference signal generating circuit output from the changeover switch SW ₈ of the oscillator 81a in 81 i.e. 4f sc signal format together with the signal of (N) is selectively output determination circuit 87 The switches SW _{3 to} SW ₅ are controlled by the output, and NTSC
And PAL color video signals can be read satisfactorily on any of the two types of discs on which each is recorded. Also, this time from the change-over switch SW ₇ is supplied to the output terminal the color video signal output from the character insertion circuit 86 is output as a color video signal read from the disk is output as it is.

Then, when the switch SW ₆ is turned on by a manual operation, a low level signal format conversion instruction signal is output. Then, the output of the oscillator 81g from the changeover switch SW ₈ in the reference signal generating circuit 81 i.e. 4f sc (N) · f
Signal _{H (N) / f H (} P) is selectively output. As a result, a reference horizontal synchronization signal having the same frequency as the horizontal synchronization frequency in the PAL system is output. The burst phase comparison is performed based on a signal obtained by dividing the output of the oscillator 81g by / 4, and the color signal conversion is also performed by the oscillator 81g.
Is output by dividing the output by 1/4. At the same output signal format conversion circuit 91 is derived from the change-over switch SW ₇ simultaneously.

Therefore, by mounting a disk on which an NTSC color video signal is recorded, a pseudo PAL color video signal converted by the signal format conversion circuit 91 can be obtained. The horizontal synchronization frequency of the pseudo PAL color video signal is equal to the horizontal synchronization frequency of the regular PAL color video signal. Therefore, when this pseudo PAL color video signal is supplied to a PAL demodulation circuit as shown in FIG. 15, the color signal component is exactly delayed by 1H by the 1H delay 24, and the color shift on the screen is reduced. Will not occur. Therefore, in the signal format conversion circuit 91, the delay amount of the delay circuit 51 for delaying the luminance signal component may be the same as the delay amount of the band-pass filter 6.

As described in detail above, in the signal format conversion circuit for a video signal according to the present invention, first, the first signal which is an oscillation signal having the same frequency as the color subcarrier in the PAL system, and the phase of this first signal is set to 45 A second signal delayed by a degree,
And a third signal in which the phase of the second signal is delayed by 45 degrees. At this time, when the input NTSC composite video signal is in the color burst period, the first and third signals are alternately added to the reference signal having the same frequency as the NTSC color subcarrier every horizontal period. Multiply, and
A PAL color signal is obtained by multiplying the NTSC color signal separated and extracted from the NTSC composite video signal. Here, a signal obtained by adding the PAL color signal and a luminance signal separated and extracted from the NTSC composite video signal is output as a PAL composite video signal. Therefore, in the signal format conversion circuit for a video signal according to the present invention, a phase shifter for performing a phase shift by analog processing is not required, so that there is no influence by the variation in the values of the components of the phase shifter or the temperature characteristic. And a good color image can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 to 4 are waveform diagrams showing the operation of each part of the apparatus shown in FIG. 1, and FIG. 6 is a waveform diagram showing the operation of the delay circuit 51, FIGS. 7 to 9 are vector diagrams showing color signal components, and FIG. 10 is a block diagram showing another embodiment of the present invention. FIG. 11, FIG. 11 is a waveform diagram showing the operation of each part in FIG. 10, FIG. 12 is a block diagram showing still another embodiment of the present invention, and FIG. 13 is a block diagram showing a conventional format conversion circuit. FIG. 14 is a waveform diagram showing the operation of each part of the circuit of FIG. 13, and FIG. 15 is a block diagram showing a demodulation circuit in the PAL system. Explanation of Signs of Main Parts 40 ... Digital Phase Shifter 42 ... Multiplier 43,44 ... Oscillator 50 ... Gain Control Circuit 51 ... Delay Circuit 52 ... Amplitude Suppression Circuit

Claims (1)

(57) [Claims] 1. A video signal format conversion circuit for converting an NTSC composite video signal into a PAL composite video signal, wherein the signal format converter separates and extracts an NTSC color signal and an NTSC luminance signal from the NTSC composite video signal. / C separation means, PAL conversion means for converting the NTSC color signal into a PAL color signal corresponding to the PAL method, and obtaining the PAL method composite video signal by adding the PAL color signal and the NTSC luminance signal. An adder, wherein the PAL generator has a reference signal generator for generating a reference signal which is an oscillation signal having the same frequency as the color subcarrier in the NTSC system, and has the same frequency as the color subcarrier in the PAL system. Oscillation signal generating means for generating a first signal as an oscillation signal, a second signal in which the phase of the first signal is delayed by 45 degrees, and a third signal in which the phase of the second signal is delayed by 45 degrees; During the color burst period of the NTSC composite video signal, the first and third signals are alternately selected from the first to third signals every one horizontal period and output as a phase shift signal. Means for obtaining a PAL color signal by multiplying a signal obtained by multiplying the phase-shifted signal and the reference signal by the NTSC color signal. Signal format conversion circuit.