JPH03127592A - Color signal system conversion circuit - Google Patents

Abstract

PURPOSE:To attain the conversion of a color signal without phase rotation by switching the phase of an input subcarrier signal to a B-Y axis color difference demodulator and an R-Y axis color difference modulator in in-phase and in opposite phase for each horizontal scanning line synchronously with a horizontal synchronizing signal repetitively. CONSTITUTION:A burst phase shift circuit 1 shifting only a color burst signal by -45 deg. among color signals at a pre-stage of a B-Y axis color difference modulator 5 and an R-Y axis color difference modulator 8 is provided. Then a phase of 90 deg. of a subcarrier and a phase of 270 deg. (in opposite phase to 90 deg.) of a subcarrier inputted to an B-Y axis color difference demodulator 3 are alternately switched for each 1H and the phase of a subcarrier inputted to the R-Y axis color difference modulator 8 is 90 deg., which is the same as a conventional phase. Thus, the device is simplified, and even when a color signal is subjected to phase rotation, the phase rotation is corrected and the color change is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to, for example, magnetic recording and reproducing devices, etc.
The present invention relates to a color signal method conversion circuit that converts a PAL color signal into a PAL color signal.

[Conventional technology]

Figure 3 shows the reproduction system signal processing of a conventional PAL magnetic recording/reproducing device, and it is also possible to convert the color signal obtained by reproducing an NTSC magnetic tape to PAL format and play it back by changing a switch or the like. A configuration diagram of a reproducing system of a possible magnetic recording/reproducing device is shown. In the figure, 15 is a magnetic tape;
6 is a video head, 17 is a preamplifier, 18 is a bypass filter, 19 is an FM equalizer, 20 is an FM demodulator
.

21 is a low-pass filter, and 21 is a mixer, which are connected in this order. 23 is a low-pass filter after the preamplifier 17, 24 is a main frequency converter after the low-pass filter 23, 25 is a band-pass filter after the main frequency converter 25, and 26 is a filter for 2H (H is horizontal scanning time). A comb filter 27 using a delay line is a comb filter using an IH delay line, and the input terminals of both comb filters 26 and 27 are connected to the output terminal of the bandpass filter 25.

28 is a switch that selects one of the comb-shaped filters 26 and 27 according to the input state of the NTSC signal, and 29 is a signal conversion switching section after the switch 28, which is a pseudo-PAL that converts the NTSC color signal into a pseudo-PAL color signal. Color signal conversion circuit 30
and a switch 31 that switches the output of the pseudo PA, L color signal conversion circuit 30 or the bypass line of the circuit 30 according to the input state of the NTSC signal.

32 is a band-pass filter that outputs a signal to the main frequency converter 24; 33 is a band-pass filter that receives output signals from the crystal oscillator 34 and a phase-shifting PS circuit 35 and outputs a side frequency-converted signal to the band-pass filter 32; The side frequency converter 36 is a voltage controlled oscillator that outputs a voltage controlled oscillation signal to the PS circuit 35.
Connected to input the SC signal.

54 is a color difference demodulator connected to the switch 31, 55 is a color difference processing circuit, and 56 is a color difference modulator, which are connected in this order to constitute the color difference signal processing unit 58. The output side of the 0 color difference signal processing unit 58 is connected to the input side of the mixer 22.

Next, the operation of the conventional example will be explained.

First, the operation in PAL mode will be explained.

The video head 16 reads the signal recorded in PAL mode from the magnetic tape 15, and the reproduced signal is sent to the preamplifier 1.
7 and is separated into a luminance signal which is FM modulated by a bypass filter 18 and a color signal which is low-pass converted by a low-pass filter 23. The FM luminance signal passes through an FM equalizer 9, is demodulated by an FM demodulator 20 and a low-pass filter 21, becomes a luminance signal, and is input to a mixer 22.

On the other hand, the low-frequency color signal is converted into a high-frequency color signal by the main frequency converter 24 and bandpass filter 25. The signal is passed through a comb filter 26 using a delay line, and then converted to a pseudo PAL color signal conversion circuit 30.
The signal is bypassed and sent to the color difference signal processing section 58. The color difference demodulator 54 converts the color difference signal into a color difference signal, the color difference processing circuit 55 performs processing such as color edge enhancement and S/N ratio improvement, and the color difference modulator 56 returns the color signal to a mixer. 22, and is combined with the luminance signal and output as a composite video signal.

Next, the operation of the mode in which color signals obtained by NTSC reproduction are converted into PAL format will be explained.

A video head 16 reads signals recorded in the NTSC mode from the magnetic tape 15. At this time, the magnetic tape 15 and video tape 16 are each switched to the NTSC speed. The operation of the luminance signal system is the same as in the PAL mode, but the characteristics of the FM equalizer 19 and the like can be switched to be optimal for the NTSC signal.

-4, NTSC separated by low-pass filter 23
The low frequency converted color signal is converted to a high frequency signal by the main frequency converter 24. At that time, the crystal oscillator 34 is 4.43361875
The oscillation continues at the MHz PAL subcarrier frequency, but the voltage controlled oscillator 36 and PS circuit 35 are switched to NTSC mode operation. That is, the oscillation frequency is 40 f
ll (fm is the horizontal scanning frequency), and the phase of the channel R field of the video head increases by +90 every 1H.
, the phase of channel L is shifted by 90 degrees for each IH. (For PAL mode operation, the oscillation frequency will be 40.125 f,l, and its phase will be shifted by 190" for each IH, with no phase rotation for channel R and 190" for each IH.) 4.43361 with the same frequency and phase rotation signal as the NTSC low-pass conversion color signal
The 875 MHz signal is input to the side frequency converter 33, the sum component of the frequency is extracted by the band pass filter 32, the sum component and the NTSC low-pass converted color signal are input to the main frequency converter 24, and the band pass filter 32 extracts the sum component of the frequency. The frequency difference component is extracted by the pass filter 25, and an NTSC color signal is finally output. However, the subcarrier frequency is PAL's 4.
43361875 MHz. When this reproduced color signal is passed through a comb filter to remove crosstalk from adjacent tracks, the reproduced color signal becomes 4.4336
Since it has a spectrum centered at 1875 MHz and spaced by If, it is switched to a comb filter 27 consisting of an IH delay line using a switch 28. (PAL signal is 0.
It has a spectrum of 5 f , intervals. ) Next, this reproduced color signal is sent to the pseudo PAL color signal conversion circuit 30.
In this step, color signal system conversion from NTSC to pseudo-PAL is performed. This is explained in detail in the two signal conversion switching sections in Figure 3.
This will be explained with reference to FIGS. 4 and 7 showing 1rfi.

The reproduced color signal has the signal waveform and vector shown in Figure 7(a) (the figure shows the case of maze and tan monochrome), that is, the color burst signal has a phase of 1806 with respect to the B-Y axis. , and the magnitude and phase (angle) of each 14 are unchanged. This signal is switched by a switch 37 between a color burst part and a color signal part other than the color burst part (however, the switch 37 is used for burst gate pulses (BG
P)), the color burst part is -45
@phase shifter 1 or +45″ -45″ by phase shifter 41
Or, the color burst signal whose phase is rotated by +45" is alternately switched and outputted by the switch 2 for each IH, and the color signal portion other than the color burst portion is amplified twice by the 6 dB amplifier 3B, and the color signal is output from the switch 3.
9, it is output every 2H (+, every other H). These two signals are combined by an adder 40, resulting in a color signal having the signal waveform and vector shown in FIG. 7(b). That is, in the color burst part, those with a phase of 135" and 225' with respect to the B-Y axis appear alternately every 1), and the phase of the magenta color signal remains unchanged, and the phase of the magenta color signal remains unchanged, and the phase of 135" and 225' (no signal) appears alternately. ) appears alternately for each IH.The T flip-flop 14 creates a rectangular wave with a frequency of 0.5 f whose logic value alternates between H and L for each horizontal pulse, and switches 2,
39 control signals.

When the switch 31 is in PAL mode, the above NTSC
→This is to bypass the pseudo PAL color signal conversion circuit 30 that converts the pseudo PAL color signal system.

Next, the operation of the color difference signal processing section 58 will be explained with reference to FIG. 5 showing the detailed configuration of the color difference signal processing section 58 in FIG. The reproduced color signal is processed by B-Y in order to perform color image quality improvement processing such as color edge enhancement and S/N ratio improvement in the color difference signal.
The axial position difference demodulator 3 and the RY axis position difference demodulator 6 each provide B-Y
, R-Y, which is converted into a B-Y-axis position difference processing circuit 4 and a R-Y-axis position difference processing circuit 7, and then outputted to a B-Y-axis position difference modulator 5 and a R-Y axis position signal. With difference modulator 8, 4.4336
The signals are each returned to a signal having a frequency of 1875' MHz, and the adder 9 combines the two orthogonal axes components to output as a color signal. In addition, at this time, the B-Y axis position difference demodulator 3 and the B-Y axis
The axial position difference modulator 5 is used by inputting a subcarrier of phase O'' from the reference oscillator 10.
The R-Y axis phase difference modulator 8 is +90° from the reference oscillator 10.
A subcarrier wave whose phase is shifted by 90'' is input through a phase shifter 11 and used.

Finally, the fact that colors can be reproduced on a PAL television receiver using the pseudo PAL color signal shown in FIG. 7 will be explained. 6th
The figure shows the color difference demodulation circuit of a PAL television receiver.
The color difference demodulation section shown in the figure is shown in detail. In FIG. 6, an IH delay line 43 is used, whereby the IH-delayed color signal and the undelayed color signal are added and subtracted to extract the BY component and the RY component, respectively. An adder 45 extracts the BY component, and a subtracter composed of an 1800 phase shifter 44 and an adder 46 extracts the RY component.

Therefore, the color signal is averaged before and after IH, and even if a line with no signal appears every 2H as shown in Figure 7 (b), the color signal amplitude of the line with signal is ), a color difference signal similar to that of the original PAL can be obtained.

[Problem to be solved by the invention]

Since the conventional color signal system conversion circuit is configured as described above, when the color signal undergoes phase rotation, the IH delay line 43, adder, etc. 45.44.46
P that the hue rotation is corrected and the hue does not change.
The fact that the characteristics of the AL system will be lost is clear from 1) (i!!) Figure 8 (C), which shows a vector diagram of the NTSC→PAL conversion signal as a result of addition with the post-post signal (however, U is B -Y axis, V corresponds to R-Y axis respectively), 8th
Figure (a) is a signal vector diagram of the nth line, and Figure 8) is a signal vector diagram of the (n+1)th line. Figure 8 (
a) - (As shown in C1, the broken line indicates the position when there is no distortion, and as shown in Fig. 8(a) and Fig. 8(b), θ
.

When the phase distortion is applied to the H side by θ°, the color burst signal is corrected, but the color signal is not corrected and is distorted by θ° to the (C) side, as shown in Figure 8 (C). There is. Furthermore, if the phase shift precision of the 145° phase shifter 1 and the +45'' phase shifter 41 in FIG. , because the color signal is doubled, the BYfitFl unit 47 and R-Yl adjuster 48 of the PAL television receiver
17)F[[The teno amplifier, etc., required twice the normal dynamic range, which could not be achieved with a normal PAL television receiver, and this also had problems such as the possibility of causing phase distortion.

This invention was made to solve the above-mentioned problems, and is an ideal NTSC-+ system without phase rotation of color signals.
The object of the present invention is to obtain a color signal system conversion circuit capable of converting PAL color signals.

(Means for Solving the Problems) A color signal system conversion circuit according to the present invention converts only a color burst signal among color signals into a 45-bit signal at a stage before a B-Y axis color difference modulator and a R-Y axis color difference modulator. ``Equipped with a burst phase shift circuit that shifts the phase, the phase of the subcarrier input to the R-Y axis color difference demodulator (or R-Y axis color difference modulator) is
90'' (with respect to the axis) and 270'', which is the opposite phase thereof, are alternately switched for each IH, and are input to the R-Y axis color difference modulator (or R-Y axis color difference demodulator). The phase of the subcarrier is 90'', which is the same as before.

[For production]

The color signal system conversion circuit according to the present invention shifts the phase of only the color burst signal of the color signal by -45 degrees by a burst phase shift circuit constituted by a -45 degree phase shifter and a switch, and shifts the phase of only the color burst signal by +90 degrees by using another switch. The output subcarrier of the ° phase shifter and the output subcarrier of the 190" phase shifter are switched alternately for each IH and input to the R-Y axis demodulator (or R-Y axis modulation H), and the +90" The output subcarrier of the phase shifter is input to an RY-axis modulator (or RY-axis demodulator).

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a configuration diagram of a reproduction system signal processing circuit of a magnetic recording and reproduction apparatus including an NTSC color signal conversion circuit according to an embodiment of the present invention.
．． 32 to 36, and 54 to 56, and the explanation thereof will be omitted.

53 is a burst phase shift circuit provided between the output side of the switch 28 and the input side of the color difference demodulator 54-, which phase-shifts only the color burst part of the NTSC color signal by 145'' in the NTSC mode. Outputs color signal.57 is NTSC
A color signal method conversion circuit (burst phase shift circuit 53, color difference demodulator 54,
This is a color signal system conversion section that includes a color difference modulator 56 and a lateral and color difference processing circuit 55.

FIG. 2 is a block diagram showing the detailed structure of the color signal system conversion section 57 in FIG. 1. In FIG. 2, the same parts as the conventional one are given the same reference numerals 3 to 11 as in FIG.
Switched by SC signal and burst gate pulse (BGP) synchronized with color burst part, NTSC
In the mode, the selected output side is switched to the output side of the -451 phase shifter 1 during the period when the burst gate pulse is input, and to the input terminal side of the -45'' phase shifter l during the other periods. - Connected to each input terminal of the Y-axis position difference demodulation f183 and the R-Y axis color difference demodulator 6.The BY-axis position difference demodulation!i3 is followed by the BY-axis position difference processing circuit 4,
-Y-axis color difference modulator 5 and adder 9 are connected in this order.

Further, a RY-axis position difference processing circuit 7, a RY-axis color difference modulator 8, and an adder 9 are connected in this order to the rear stage of the RY-axis position difference detector 1i.

The output terminals of the reference oscillator 10 which inputs the NTSC color signal are a BY-axis color difference demodulator 3, a BY-axis color difference modulator 5, a +900 phase shifter 11, and a -90" 4% phase shifter. The output terminal of the +90' phase shifter 11 is connected to the R-Y axis color difference modulator 8, and the switch 13 connects the +90' phase shifter 11 and the -90° phase shifter 12. It is connected to the output terminal of the R-Y axis position difference detector tJRfi 6, and inputs the output signal of the T flip-flop 14 which inputs the horizontal synchronizing pulse, and the NTSC signal so that it can be switched for each IH. It is connected to the. -45″ phase shifter 1 above
The burst phase shift circuit 53 shown in FIG.
It consists of

Next, the operation of this embodiment will be explained. In FIG. 1, the circuit operations of the parts other than the color signal system conversion section 57 are completely the same as in the conventional case, so the description of FIG. 2 will be centered on the section 57.

In the NTSC playback mode, the color signal input to the NTSC-+PAL color signal method converter 57 has the signal waveform and vector shown in FIG. 7(a), as in the case of the conventional method. -45@e phase shifter 1 and switch 2 phase shift only the color burst signal of this color signal by 145 degrees. That is, the phase of each IH color burst signal changes from 180'' to 135'' with respect to the BY axis. This switch 2
The chrominance signals from the chrominance signal are input to the BYY axis difference demodulator 3 and the RY axis difference demodulator 6. Here, the phase of the subcarrier (demodulation axis) used in the B-Y axis differential demodulator 3 is 0°, which is the same as in the conventional method, but the phase of the subcarrier used in the R-Y axis differential demodulator 6 is +90°. The output of the phase shifter 11 and the output of the 190° phase shifter 12 are alternately switched for each IH and input to the RY-axis phase difference converter y4 6. That is, the demodulation axis has two phases of 90'' and 270m (with respect to the BY axis).

On the other hand, the phases of the subcarriers used in the B-Y axis phase difference modulator 5 and the R-Y axis phase difference modulator 8 in the subsequent stage are 0° and 900°, respectively.
(fixed), so this 4.43361875 old]2
When the two-axis precepts modulated by the adder 9 are synthesized, the result shown in Fig. 7 (
The signal waveform and vector are shown in C). The color signal output from this adder 9 is divided into 1 RY and 1 H (B
- This is the original PAL signal itself, which is inverted (around the Y axis).

In addition, each demodulator 3.6 and modulator 5.8 for B-Y and R-Y
The B-Y axis position difference processing circuit 4 and the R-Y axis position difference processing circuit 7, which are provided between the It is.

In the PAL mode, switch 2 is set so that the signal from the -45° phase shifter l is not selected even when a burst gate pulse is generated, and switch 13 is set to always select the signal from the +90° phase shifter, thereby eliminating the color difference of the conventional method. It can perform the function of the processing section 58.

9(a) to 9(C) show the phase of the color signal in the PAL color receiver according to this embodiment when the color signal is subjected to phase distortion, and FIG. 9(a) shows the phase of the color signal in the n-th horizontal scanning line. FIG. 9(B) is a vector diagram of the color signal of the (n+1)th horizontal scanning line, and FIG. 9(C) is a vector diagram of the color signal output from the adder 9.

In FIG. 9, the broken line shows the case where there is no phase distortion.

As shown in FIG. 9(C), after addition with the IH-delayed color signal, the phase distortion is corrected and disappears.

This is because the vector at the time of addition becomes symmetrical with respect to the line (broken line) with no phase difference.

In this embodiment, in the NTSC reproduction mode, the subcarrier phase of the RY modulation axis was fixed at 90'', and the subcarrier phase of the RY demodulation axis was switched between 9v and 270'' for each IH. -The subcarrier phase of the Y demodulation axis is fixed at 90°, and the R-
The subcarrier phase of the Y-axis modulation axis is set to 90″ and 270°.
Even if the switching is performed every 4, the same effect as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, only the color burst portion is demodulated and modulated by shifting the phase by 1453, and the phase of the input subcarrier signal to the demodulator and modulator of one color difference axis is synchronized with the horizontal synchronization signal. Since the structure is configured so that the in-phase and anti-phase are repeated for each IH, the equipment can be simplified, and even if the color signal undergoes phase rotation, the hue rotation is corrected and the hue does not change, and the amplifier etc. can be used as usual. Since the dynamic range is good, it does not cause phase distortion, and even if the accuracy of the phase shift angle of the -45° phase shifter is poor, the effect is that the color tone does not change.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a reproducing system of a magnetic recording and reproducing apparatus including a color signal system conversion circuit according to an embodiment of the present invention, and FIG.
FIG. 3 is a configuration diagram showing the detailed configuration of the color signal system conversion section in the figure. FIG. 3 is a configuration diagram of a reproduction system of a conventional magnetic recording and reproduction device.
The figure shows a detailed configuration diagram of the pseudo PAL color signal conversion circuit etc. in Figure 3, Figure 5 shows a detailed configuration diagram of the color difference signal processing section in Figure 3, and Figure 6 shows color difference demodulation of a PAL television receiver. Fig. 7 is a diagram showing the converted color signals and vectors of the present invention and the conventional method, and Fig. 8 is an explanatory diagram showing the vector of the converted color signal when the color signal of the conventional method is subjected to phase distortion. , FIG. 9 is an explanatory diagram showing a vector of a converted color signal when the color signal is subjected to phase distortion according to an embodiment of the present invention. In the figure, 1...-45° phase shifter, 2... switch, 3
...B-Y axis color difference demodulator, 5...B-Y axis color difference modulator, 6...R-Y axis color difference demodulator, 8...R-Y axis color difference modulator, IO...・Reference oscillator, 11...+90°
Phase shifter, 12... -90'' phase shifter, 13... switch, 14... T flip-flop. Note that the same reference numerals in the drawings indicate the same or equivalent parts.

Claims (1)

[Claims] A burst phase shift circuit that shifts only the color burst portion of an NTSC color signal with a phase of 180 degrees by -45 degrees, and a color signal output from the burst phase shift circuit that shifts the color signal on the B-Y axis and R
- a demodulator and a modulator that perform demodulation and modulation on two orthogonal color difference axes of the Y axis, the phase of the input subcarrier signal to the R-Y color difference axis demodulator and the phase of the input subcarrier signal to the R-Y color difference axis modulator; A color signal method conversion circuit characterized in that the phase of an input subcarrier signal can be repeatedly switched between in-phase and anti-phase for each horizontal scanning line in synchronization with a horizontal synchronization signal.