JPH0421398B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention converts a luminance signal into an FM signal, converts a chroma signal into a low frequency signal, and records both signals on a tape using two heads with different azimuth angles. The present invention relates to a cross-azimuth helical scan video tape recorder, and particularly to a recording/reproducing circuit for NTSC chroma signals.

There is a β method as a chroma signal recording method used in NTSC cross-azimuth helical scan video tape recorders. The problems with this method are (1) it requires a large number of flip-flops (hereinafter referred to as FFs) that require high-speed operation, making it difficult to integrate into ICs, and (2) it is difficult to secure a bandwidth for the chroma signal, especially for tracking control pilot signals. There are problems when performing multiplex recording: (3) the chroma signal IC that can be used for both the NTSC and PAL systems becomes extremely complex, and (4) the chroma signal recording circuit and pilot signal generation circuit cannot be used in combination. The dot was hot.

The conventional problems will be explained in detail below using the drawings. FIG. 1 is a block diagram showing the main parts of a chroma signal recording circuit of a β-system video tape recorder.

First, the method of recording NTSC chroma signals in a β-scheme video tape recorder will be explained. In the β method, the 3.58MHz chroma signal is converted to a frequency of (44-1/4) _H , ( _H is the horizontal synchronization frequency), and
The first track records the frequency-converted chroma signal as it is, and the second track inverts the phase of the frequency-converted chroma signal every horizontal period to change the chroma frequency to (44-1/4). ±1/2) Converted to _H and recorded. As a result of the above, the recording chroma signal frequency has an offset of _H /4, which is a necessary and sufficient condition, and the frequency difference between tracks is
_H /2 is satisfied.

Next, the above operation will be explained using FIG.
1 is a chroma signal input terminal, 2 is a voltage controlled oscillator (hereinafter referred to as VCO) that oscillates at a frequency of 175 _H , 3 is a 1/4 frequency divider, 4 is a first frequency converter,
5 is a filter that extracts the sum frequency signal from the output of 4; 6 is a circuit that does nothing on the first track and inverts the phase every horizontal period on the second track; 40 is an input terminal for a signal indicating the track. , 7 is a second frequency converter, 8 is a low-pass filter that extracts the difference frequency signal from the output of 7, 9 is 1/175
The frequency divider is composed of a 1/5 frequency divider 10, a 1/5 frequency divider 11, and a 1/7 frequency divider 12. A phase comparator 13 detects the phase difference between the output signal of the frequency divider 9 and the horizontal synchronizing signal applied to the terminal 17, and drives the VCO 2. 14 is a 3.58MHz X'tal VCO, and a phase comparator 15 detects the phase difference between the output signal of 14 and the output signal of the burst gate circuit 16. Therefore, a carrier whose frequency matches that of the chroma signal applied to terminal 1 is obtained at the output of VCO 14.
A (175/4 _H +3.58) MHz signal is taken out from the output of the filter 5, and the first signal is taken out from the output of the phase inversion circuit 6.
A signal of (175/4 _H +3.58) MHz is obtained on the first track, and a signal of {(175/4+1/2) _H +3.58} MHz is obtained on the second track. Therefore, the low frequency conversion chroma signal output terminal 19 has a signal of 175/1 for the first track.
The chroma signal converted to _4H frequency is output,
For the second track, a chroma signal converted to a frequency of (175/4±1/2) _H is output.

Next, the above-mentioned problem (1) will be explained. In Figure 1, a 1/175 frequency divider 9 is required, and in order to design this frequency divider 9 to have the minimum chip size and minimum power consumption, a 1/5 frequency divider 10 is required as shown in Figure 1. _.

FIG. 2 is a circuit diagram showing a specific example of the frequency divider 10 of FIG. 1. To divide frequencies over 2MHz, a synchronous counter shown in Figure 2 is required, and FF22, 2
All of 3 and 24 must operate at _175H (=2.75MHz). FF operating at 2MHz or higher is 500KHz
The required chip size and power consumption are approximately 10 times larger than FFs that operate at the following speeds, so the key point is how to reduce the number of high-speed FFs. The frequency divider 9 of the system shown in FIG. 1 requires three high-speed FFs, which causes problems such as chipping and increased power consumption.

Next, the above-mentioned problem (2) will be explained. Figure 3 shows the recorded signal spectrum 2 of the chroma signal band.
6, a pilot signal spectrum 27, and a tape head system frequency characteristic 25 are shown, respectively. As you can see from the figure, the lower side wave of the chroma signal is close to the cutoff frequency of the tape head system, and if you want to secure a sufficient bandwidth of the chroma signal, it is necessary to further increase the low frequency conversion frequency from 688KHz to 700kHz or more. .

Furthermore, the pilot signal 27 for tracking control
When multiplexing chroma signals, it is necessary to further increase the recording frequency of the chroma signal. The most excellent method for pilot signals is the one developed by Phillips, with a pilot frequency of 6.5 _H (102 KHz),
7.5 _H , 9.5 _H , 10.5 _H (165 KHz), and when set to the chroma frequency and 688 wHz, the frequencies are too close to each other, and there is a problem that interference caused by the pilot signal cannot be sufficiently removed.

Next, the problem (3) mentioned above will be explained. β
The frequency of the PAL chroma signal of the video tape recorder is selected to be (44-1/8) _H for the first track and (44+1/8) _H for the second track. Therefore, if NTSC and PAL are shared in the configuration shown in Figure 1, VCO2 will be 175 _H for NTSC, 351 _H for PAL,
It is necessary to switch in three ways: 353 _H. Furthermore, frequency divider 3 is set to 1/4 for NTSC, 1/8 for PAL, and frequency divider 9 is
It is necessary to switch in three ways: 1/175 for NTSC, 1/351 and 1/353 for PAL.

Among the above switching, 1/175, 1/351, 1/35 of frequency divider 9
3 switching is 175=5×5×7, 135=3×3×3×
13,353 = 353 (prime number), and as mentioned above, the frequency divider cannot be divided, and all the FFs that make up the 1/353 frequency divider must operate at high speed, and in the end, frequency divider 9 is converted to NTSC.
It becomes impossible to make it common to PAL.

Next, the aforementioned problem (4) will be explained. FIG. 4 shows a circuit in which a pilot signal generation frequency divider 28 is added to the chroma signal circuit of FIG. 1, and 29 is an output terminal for the pilot signal. At the input of the frequency divider 28,
Since a signal of 175 _H is applied, when the frequency divider 28 is switched to 1/17, 1/19, 1/24, and 1/28 for each track, the pilot signal output terminal 29 receives ₁ = 175/17 _H = 10.29 _H , ₂ = 175/19 _H = 9.21 _H , ₃ = 175/24
Signals of _H = 7.29 _H , ₄ = 175/28 _H = 6.25 _H are obtained, respectively. The ideal pilot frequency is (n+1/3) _H to (n+2/3) _H , n=6, 7, 9, 10. This is determined by the fact that it is less susceptible to harmonic interference from flyback pulses from the television, and the pilot signal is less likely to interfere with chroma and luminance signals.

Furthermore, the condition for stabilizing tracking control is A.
= | ( ₁ − ₂ ) − ( ₃ − ₄ ) | and B = | ( ₁ − ₃
)−( _2
−4 ) | is as close to zero as possible. Fourth
In the figure, the problem is that the frequency deviates considerably from the ideal, and that A=0.05 _H and B=0.04 _H are quite large.

SUMMARY OF THE INVENTION An object of the present invention is to provide a circuit for recording an NTSC chroma signal on a videotape, which solves all of the above-mentioned four problems.

The present invention includes: a reference oscillator that oscillates at a specific oscillation frequency; a low-frequency conversion carrier generator that generates a low-frequency conversion carrier based on an oscillation signal from the reference oscillator; and a low-frequency conversion carrier generator that generates a low-frequency conversion carrier from the low-frequency conversion carrier. A mixer for generating a low-frequency converted carrier color signal by mixing the low-frequency converted carrier and a carrier color signal to be recorded, and a magnetic head for recording the low-frequency converted carrier color signal on a magnetic tape, The carrier frequency of the above low-pass conversion carrier color signal is 47+1/4 times the horizontal frequency, and the phase of this carrier wave is inverted every horizontal period in one field, and inverted every horizontal period in the other field. By determining the frequency and phase transition of the low-frequency conversion carrier, the semiconductor chip size and power consumption required for the frequency divider used in the low-frequency conversion carrier generator can be minimized, and the chroma frequency can be increased to 700kHz or higher. By selecting the appropriate signal, you can secure bandwidth and improve coexistence with pilot signals.

Embodiments of the present invention will be described below with reference to FIGS. 5 to 11.

FIG. 5 is a block diagram showing the main parts of a chroma signal recording circuit according to an embodiment of the present invention. The feature of FIG. 5 is that the oscillation frequency of the VCO 2 is 189 _H = 3 x N _H , and N = 63 = 3 x 3 x 7. Therefore, the difference between FIG. 5 and FIG. 1 is the oscillation frequency of the VCO 2 and the configuration of the frequency divider 9, and as a result, the frequency of the recording chroma signal appearing at the output terminal 19 is (47+1/4). ) becomes _H. The 1/189 frequency divider 9 is composed of 1/3 frequency dividers 30, 31, 32 and 1/7 frequency divider 33. The input frequency of the 1/3 frequency divider 30 is 189 _H = 2.97MHz, which requires high-speed operation. Therefore, as mentioned above, a synchronous counter is desirable, and the configuration of the FF shown in FIG. 6 can be considered. As is clear from FIG. 6, only two FFs are required, and the chip size required for the frequency divider 9 is
Power consumption can be minimized. On the other hand, the frequency of the low frequency converted chroma signal is (47 + 1/4) _H ≒ 743 kHz, and as can be seen from the relationship between the spectrum 39 of this chroma signal and the frequency characteristic 25 of the tape head system shown in Figure 7, the band is 743 ± 500 kHz. It is now the best frequency to ensure that.

Also, when multiplexing the pilot signal 27, the pilot signal frequency is 102 to 165 KHz.
Approximately 80k between 243kHz and the lower end frequency of the chroma signal
Hz, and the frequency arrangement is appropriate to prevent mutual interference.

FIG. 8 is a block diagram showing the main parts of a chroma signal recording circuit according to another embodiment of the present invention. The difference between FIG. 8 and FIG. 5 is that in FIG. 8, the frequency divider 3 in FIG. 5 is divided into 1/2 frequency dividers 41 and 42.
The reason is that a waveform shaper 43 is added and the type of the phase inversion circuit 6 is changed.

The reason why the frequency divider 3 is divided into the 1/2 frequency dividers 41 and 42 is to supply the 189/2 _H signal to the waveform shaper 43, and to supply the 1899/4 _H signal, which has a phase difference of about 180° from each other. This is to obtain a signal. (The Q and output of the FF can be used as is.) The phase inversion circuit 6 in FIG _.
The first track outputs the input signal on one side as it is, and the second track is switched so that the two input signals are alternately output every horizontal period.

The waveform shaping circuit 43 has the function of adjusting the rising timing of the output signal of the phase inversion circuit 6. An embodiment of the waveform shaping circuit 43 is shown in FIG.
By applying the output signal of the 1/2 frequency divider 41 to the T input terminal 45 of the FF and the output signal of the phase inversion circuit 6 to the D input terminal 46, a signal with a well-timed rise can be obtained at the output terminal 47.

FIG. 10 is a block diagram showing the main parts of an embodiment in which the NTSC chroma signal recording circuit of the present invention is used in a PAL chroma signal recording circuit.

In Figure 10, NTSC chooses the chroma signal frequency to be (47 + 1/4) _H in the first track, and (47 + 1/4 ± 1/2) _H in the second track.
The recording method performs phase inversion so that PAL
is (47-1/8) _H in the first track, and (47-18+1/4) _H in the second track, so that the phase is advanced by 90° every horizontal period, or Or in the second track (47
-1/8-1/4) A recording method is used in which a phase shift is performed in which the phase is delayed by 90 degrees every horizontal period so that the signal becomes _H.

The difference between Fig. 10 and Fig. 8 is that the output of the 1/4 frequency divider 3 has different phases of 0°, 90°, 180°, and 270°.
It outputs four signals that differ by 90 degrees, and instead of the phase inversion circuit 6, there is no phase inversion or phase shift for the first track in NTSC and PAL, and a phase inversion in NTSC for the second track. In PAL
In NTSC, the same frequency as the input chroma signal ( _SC = 3.579545MHz) is input to the first converter 4, and in PAL, the frequency of the input chroma signal ( _SC = 3.579545MHz) is provided. = 4.433618MHz), a switch 50 for inputting a carrier with a frequency 3/8 _H lower than 4.433618MHz) to the first converter 4, an X'tal oscillator 51, and a control signal input terminal for switching between NTSC and PAL. 49, a pilot signal generation circuit 52, and a pilot signal output terminal 53.

The pilot signal generation circuit 52 has the following formulas: ₁ = 189/18 _H = 10.50 _H , ₂ = 189/20 _H = 9.45 _H , ₃ = 189/25
It can output four signals: _H = 7.56 _H , ₄ = 189/29 _H = 6.52 _H , which is the ideal value for the pilot frequency.
(n+1/3) _H < ₁ , ₂ , ₃ , ₄ < (n+2/
3) _H is satisfied. Also, A=|( ₁ − ₂ )−( ₃ − ₄ )
｜
=0.01 _H , B=｜( ₁ − ₃ )−( ₂ − ₄ )｜=0.0
_1H , ensuring sufficient characteristics as a pilot signal.

FIG. 11 is a block diagram showing another embodiment of the NTSC and PAL chroma signal recording circuit described in FIG. 10. The difference between Figure 11 and Figure 10 is that the oscillation frequency of VCO2 is (47 +
1/4) x 8 _H = 378 _H , (47-1/8) x 8 for PAL
_H = 375 _H , frequency divider 9 is 1/378 = 1/3 x 1/3 x 1/3 x 1/2 x 1/7 for NTSC, 1 for PAL.
/375 = 1/3 × 1/5 × 1/5 × 1/5, and in particular, to minimize the chip size and power consumption when converting the frequency divider 9 into an IC, 1/3 Frequency divider 31 is NTSC
and PAL, and the frequency divider 55 is 1/6 for NTSC,
Switch to 1/5 in PAL, and set frequency divider 56.
The frequency divider 57 is switched to 1/3 for NTSC and 1/5 for PAL, and the frequency divider 57 is switched to 1/7 for NTSC and 1/5 for PAL.

In addition, by newly installing the 1/2 frequency divider 54, the output of the frequency divider 54 is _189H for NTSC and (187+H for PAL).
1/2) becomes _H. Therefore, the switch 50 and the X'tal onrator 51 provided in FIG. 10 are no longer necessary.

According to the present invention, the number of flip-flops that require high-speed operation can be minimized, and when integrated into an IC, the chip size and power consumption can be minimized. Furthermore, the chroma signal recording circuits for the NTSC and PAL systems can be made similar, making it extremely easy to design an IC for both NTSC and PAL. Further, the chroma signal recording circuit of the present invention can be used in combination with a pilot signal generation circuit very easily, and the resulting pilot signal frequency can be set to an optimum value.

[Brief explanation of drawings]

Figure 1 shows the NTSC β format video tape recorder.
A block diagram showing the main parts of the chroma signal recording circuit, Figure 2 is a circuit diagram showing an example of a 1/5 frequency divider, and Figure 3 shows the chroma signal spectrum of a β-format video tape recorder and the frequency characteristics of the tape head system. 4 is a block diagram showing an example of generating a pilot signal from the chroma circuit shown in FIG. 1.
FIG. 5 is a block diagram showing the main part of an embodiment of the present invention, FIG. 6 is a circuit diagram showing an example of a 1/3 frequency divider, and FIG. 7 is an embodiment of the chroma signal spectrum of the present invention. A characteristic diagram showing the frequency characteristics of a tape head system, FIG. 8 is a block diagram showing the main part of another embodiment of the present invention, FIG. 9 is a circuit diagram showing an example of a waveform shaping circuit, and FIG. 10 is a diagram showing the main part of another embodiment of the present invention. chroma signal recording circuit
FIG. 11 is a block diagram showing the essential parts of an embodiment for use in PAL, and shows a chroma signal that can be used both in the NTSC chroma signal recording circuit of the present invention and in the PAL chroma signal recording circuit that is compatible with the NTSC chroma signal recording circuit. FIG. 2 is a block diagram showing the main parts of an embodiment of a recording circuit. <Explanation of symbols>, 1... Chroma signal input terminal,
4...First frequency converter, 6...Phase inversion circuit, 7
...Second frequency converter, 2...Voltage controlled oscillator, 9
... Frequency divider, 2... Pilot signal, 30... 1/3 frequency divider, 43... Waveform shaping circuit.

Claims (1)

[Claims] 1. A reference oscillator that oscillates at a specific oscillation frequency, a low-frequency conversion carrier generator that generates a low-frequency conversion carrier based on an oscillation signal from the reference oscillator, and the low-frequency conversion carrier generation. a mixer for generating a low-frequency converted carrier color signal by mixing the low-frequency converted carrier from the receiver with a carrier color signal to be recorded; and a magnetic head for recording the low-frequency converted carrier color signal on a magnetic tape. The carrier frequency of the above low-pass converted carrier color signal is 47 + 1/4 times the horizontal frequency, and the phase of this carrier wave is inverted every horizontal period in one field, and inverted every horizontal period in the other field. A recording device for an NTSC chroma signal, characterized in that the frequency and phase shift of the low-frequency conversion carrier are determined so as not to occur. 2. A reference oscillator that oscillates at a specific oscillation frequency, a low-frequency conversion carrier generator that generates a low-frequency conversion carrier based on the oscillation signal from the reference oscillator, and a low-frequency conversion carrier that generates a low-frequency conversion carrier from the low-frequency conversion carrier generator. A mixer that mixes the carrier and a carrier color signal to be recorded to generate a low-frequency converted carrier color signal, and a pilot signal having a frequency divided by eight times the frequency of the low-frequency converted carrier color signal. It consists of a pilot generation circuit that generates a pilot signal, a synthesis circuit that synthesizes the low-frequency conversion carrier color signal and the pilot signal, and a magnetic head that records the output signal from this synthesis circuit on a magnetic tape. The carrier frequency of the color signal is 47 + 1/4 times the horizontal frequency, and the phase of this carrier wave is inverted every horizontal period in one field, and the above is set so that inversion does not occur in the other field every horizontal period. A recording device for an NTSC chroma signal, characterized in that the frequency and phase transition of a low frequency conversion carrier are determined.