JPH0634521B2 - Magnetic recording / reproducing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention separates a luminance signal and a chroma signal from an input color video signal, and then frequency-modulates the luminance signal into an FM luminance signal. Is converted to a low-frequency conversion chroma signal by frequency conversion so that it is located in a lower band than the luminance signal, and the input audio signal is the FM.
An FM audio signal is frequency-modulated in a band lower than the luminance signal and higher than the low frequency conversion chroma signal, and the FM luminance signal, the low frequency conversion chroma signal and the FM audio signal thus obtained are added to each other. A magnetic recording / reproducing circuit, such as a VTR (video tape recorder), for recording on a magnetic recording medium, in particular, when a video signal in which character signals are multiplexed is input and magnetically recorded / reproduced, the chroma signal is recorded. The present invention relates to a magnetic recording / reproducing circuit capable of reducing the interference of the character signals multiplexed in close proximity to each other in frequency with the FM voice signal.

[Background of the Invention]

A conventional magnetic recording / reproducing circuit includes, for example, Japanese Patent Publication No. 53-19.
As described in Japanese Patent No. 717, an LPF (low-pass filter) is provided in a stage subsequent to a required frequency converting means, and thereby an unnecessary frequency component is removed at the time of recording. .

However, when a color image signal in which a so-called character signal is multiplexed is to be input and is to be recorded, the frequency spectrum of the character signal is relatively close to that of the chroma signal, so filtering for the character signal is performed. But this does not work well.

Particularly, in a VTR which records an FM-converted audio signal in a band between a chroma signal frequency-converted to a low frequency band and an FM-converted luminance signal, the character multiplex signal is converted to a low frequency band to generate an FM audio signal. Buzz occurs in the reproduced sound because it overlaps.

This will be described below with reference to FIG. 4, which is a frequency spectrum diagram of a recorded color video signal. In the figure, p is a pilot signal, c is a low frequency conversion chroma signal,
f _a is an FM audio signal, and f _y is an FM luminance signal.

The low-frequency conversion chroma signal c has been low-frequency converted from the original band f _sc (about 3.58 MHz in NTSC) using a carrier of (f _sc +0.74 MHz). At this time, the approximately 2.8 MHz component of the character multiplex signal is converted into f _sc + 0.74−2.8≈1.5 MHz. The 1.5 MHz band is the band of the FM audio signal f _a ,
This causes buzz interference.

In order to prevent this, the chroma signal filter should have a steep characteristic. However, when this is done, the sideband component of the chroma signal itself is also attenuated, and a sufficient reproduced image is obtained. Will not be obtained.

[Object of the Invention] An object of the present invention is to eliminate the drawbacks of the prior art as described above, that is, to prevent an FM voice signal from being disturbed by a character multiplex signal and to ensure a sufficient band for a color signal. , VTR.

[Outline of Invention]

In order to achieve the above object, the present invention provides a gate generation circuit for detecting a character multiplex signal period by utilizing the fact that a character multiplex signal is inserted in a specific period within a vertical blanking period in a video signal. In order to prevent the character multiplex signal from leaking from the chroma signal processing circuit to the recording amplifier, the character generation signal is bypassed to the other and removed.

Example of Invention

 An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a video signal input terminal, 2 is a color subcarrier frequency BPF (band pass filter), and 3 is an ACC.
(Automatic chroma level control) circuit, 4 a recording processing circuit having a burst emphasis function, a non-linear emphasis function, etc., 5 a frequency conversion circuit (hereinafter referred to as a converter), 6 LPF (low pass filter), 7 Is an adder circuit, 8 is a recording amplifier circuit, 9 is a luminance signal processing circuit including AGC, LPF, pre-emphasis circuit, FM modulation circuit, etc. (hereinafter referred to as Y recording processing circuit), 10 is an audio signal Input terminal, 11
Is an audio signal recording processing circuit including an FM modulation circuit, 12 is a pilot signal generating circuit, 13 is a recording magnetic head, and 14 is a recording magnetic head.
Is a recording medium, 15 is a BPF of (color subcarrier frequency + low range color subcarrier frequency), 16 is a pulse delay circuit for generating a burst gate pulse from a horizontal synchronizing signal, and 17 is a phase for so-called APC (automatic phase control). Detecting circuit, 18 VCO (voltage controlled oscillator) of color subcarrier frequency, 19 converter, 20 phase rotation circuit, 21 (1/8) frequency dividing circuit, 22 VCO (NTS
378F _H in C mode, the oscillation frequency of 375F _H in the PAL system, f _H is a horizontal sync frequency), 23 NTSC / P
A frequency dividing circuit for switching to (1/378) / (1/375) by AL, 24 is a phase detection circuit for so-called AFC, 25 is a terminal for supplying a head switching pulse, 26 is a horizontal synchronizing signal input terminal, 27 Is a NOT gate, 28 is an AND gate, 29,
Reference numeral 32 is a resistor, 30 is a capacitor, 31 is a transistor, 33 is a counter, and 34 is a character multiplex signal elimination circuit.

The recording operation is as described below.

The chroma signal in the video signal input from the input terminal 11 is selectively filtered by the BPF 2. At this time, the character multiplex signal also leaks a little because the band is close to the chroma signal. ACC
A constant level is set by 3 and the recording processing is performed by the recording processing circuit 4. The converter 5 converts the low frequency band and leads to the LPF 6. L
A low-frequency conversion chroma signal is obtained at the output of PF6 and is added to the FM luminance signal, the FM audio signal, and the pilot signal by the adder circuit 7, and recorded on the medium 14 via the recording / amplifying circuit 8 and the head 13.

The phase detection circuit 17 and the VCO 18 form an APC loop, and thereby a signal synchronized with the chroma signal in the input video signal is obtained at the output of the VCO 18. Since this synchronizing operation is performed on the burst signal, the burst gate pulse is supplied from the output of the pulse delay circuit 16 to the phase detection circuit 17.

AFC with the VCO 22, frequency divider 23, and phase detector 24
It forms a loop, which allows N times the horizontal synchronizing signal in the input video signal (N is 378 (at NTSC), 37
5 (at the time of PAL)) is obtained at the VCO 22 output. This is led to the (1/8) frequency dividing circuit 22, and phase rotation processing is further performed in the phase rotation circuit 20 to remove adjacent crosstalk during reproduction, and the output is multiplied by the VCO 18 output in the converter 19.

The output of the converter 19 has a frequency of f _SC + f _LSC (f _SC is a color subcarrier frequency, and f _LSC is a low-frequency conversion color subcarrier frequency). The BPF 15 removes unnecessary components and the converter 5
Lead to. Thereby, as described above, the output of the converter 5 is f
It becomes the chroma signal of _LSC .

Here, the character multiplex signal removing circuit 34 will be described. The burst gate pulse is led to the NOT gate 27 and the logic is inverted to be one input of the AND gate 28. Counter 33
Is a circuit for counting the horizontal synchronizing signal, and the counting start timing is the rising edge and the falling edge of the head switching pulse. The output of the counter 33 has a count value of "H" only in a specific period when the character multiplex signal exists.
"High". For example, "High"
The count value of "h" is set to 15 to 25. As a result, the output of the counter 33 always accurately represents the character multiplex signal period because the head switching pulse is synchronized with the vertical synchronizing signal of the input video signal and has a constant phase. Become a signal.

When this signal is used as the other input of the AND gate 28 described above, the output of the gate 28 is a signal which becomes "High" only during the vertical blanking period in which the character multiplex signal exists and in the absence of the burst signal. Becomes This signal is led to the base of the transistor 31 via the resistors 29 and 32. As a result, when the transistor 31 is turned on, 30 acts as a bypass capacitor, and the character multiplex signal in the output of the converter 5 can be bypassed to GND and removed.

By the above operation, there is no interfering character multiplex signal in the FM audio signal band, and good audio and video are obtained.

Note that one end of the capacitor 30 is not limited to the output of the converter 5,
It may be connected to the output of the BPF 2, the output of the ACC 3, the inside or the output of the recording processing circuit 4, the output of the LPF 6, or the like. In essence, it is essential to remove the signal during the character multiplex signal period before the adding circuit 7.

FIG. 2 shows an embodiment of the present invention different from that shown in FIG.

In FIG. 2, parts corresponding to those in FIG. 1 are given the same numbers. Reference numeral 41 denotes a color killer circuit, which operates when the input video signal is black and white and prevents noise from being mixed into the adding circuit 7. In order to operate the color killer circuit 41, a killer detection circuit 42 is provided to detect the monochrome mode. This is because the output of the VCO 18, which is 90 ° out of phase with the signal to the converter 19, and the signal in the burst signal period of the input video signal are phase-detected to obtain the multiplication factor of the in-phase signal. This is based on obtaining an output according to the burst amplitude of the input video signal.

That is, when the burst amplitude is small, the killer detection circuit 42
Enters the killer operation mode and turns on the color killer circuit 41. The output of the AND gate 28 obtained by the same processing as that of the embodiment of FIG. 1 is input to the killer detection circuit 42, and the color killer circuit 41 is turned on when this output is "High". ing.

FIG. 3 is a circuit diagram showing a specific example of such a color killer circuit 41 and its peripheral circuits. In FIG. 3, the same components as those in the previous figures are given the same numbers. 5
1 to 57 are voltage sources, 61 to 65 are capacitors, 71 to 92 are resistors, 101 to 122 are transistors, 131 and 132 are diodes, and 141 is a switch circuit.

The operation during color killer will be described. When the burst signal level is very small, there is no signal supplied to the differential pair transistors 116 and 117 through the capacitor 64, and the collector currents of the transistors 116 and 117 are almost the same.

On the other hand, the signals supplied from the VCO 18 via the capacitor 63 are differential pair transistors 112, 113 and 114, 11
Switch 5 on. As a result, the transistor 11
The collector currents of 0 and 111 are almost the same. Resistance 80
Is set larger than the resistor 81, and the transistor 1
The emitter currents of 10 and 111 are larger in the transistor 111, so that a part of this current flows into the voltage source 57 through the diode 132.

Therefore, 120 of the differential pair transistors 119 and 120 are turned on, and current flows into the resistor 92 through the current mirror circuits 121 and 122. As a result, the transistors 108 and 109 are turned on, and the differential pair transistors 105 and 106 are turned off. As described above, the output of the color killer circuit 41 becomes the output of only DC without the AC signal component.

In the color mode, the burst signal of the output of the VCO 18 and the output of the recording processing circuit 4 are in phase and the transistor 11
The state in which 6,113 is on and the state in which 117 and 115 are on alternate. Therefore, the collector current of the transistor 111 is zero, and the collector currents of the transistors 113 and 115 are supplied from the voltage source 57 via the diode 131. As a result, the states of the differential pair transistors 119 and 120 are reversed from those in the color killer, and the transistors 108 and
109 is turned off. Therefore, color killer circuit 41
The output of the converter 5 is generated at the output of.

In the killer detection circuit 42 as described above, the above-mentioned AN
The output signal of the D gate 28 is led to the base of the transistor 123 via the resistors 89 and 90.

As described with reference to FIG. 1, the output signal of the AND gate 28 is a signal representing the character multiplex signal period generated from the horizontal synchronizing signal and the burst gate pulse, that is, the vertical blanking period in which the character multiplex signal exists. ,
Further, it is a signal that becomes "High" only during the period when the burst signal does not exist. Therefore, in FIG.
When the output signal of the transistor becomes "High", the transistor 12
3 is turned on, a current flows through the resistor 92, and as a result, the transistors 108 and 109 are turned on, and the color killer circuit 41 operates so as to cut off the low frequency conversion chroma signal.
Therefore, the low-frequency conversion chroma signal can be prevented from being recorded only during the character multiplex signal period excluding the period in which the burst signal exists.

The advantage of this method is that the number of pins does not increase when integrated into an IC. That is, in the embodiment shown in FIG. 1, the bypass capacitor 30 has a value too large to be integrated, and a new pin for connecting the capacitor 30 is required. However, in the embodiment shown in FIG. This is because it is unnecessary.

FIG. 5 is a circuit diagram showing a concrete example of the counter 33 used in the embodiments of FIGS. 1 and 2.

In FIG. 5, 151 to 164 are NOT gates, 171
179 is a NAND gate, 180 is an AND gate, 1
Reference numerals 91 to 195 are D flip-flops.

FIG. 6 is a timing chart of this circuit. Each of (a) to (g) and (s) in FIG. 6 is the signal shown in FIG. Further, the input of the gate 151 is the R input of the counter 33, the input of the gate 161 is the CK input,
The output of the counter 33 corresponds to the output of the AND gate 180, respectively.

The output indicated by VGP1 in FIG. 5 is a pulse output corresponding to the burst blanking period. By using this, for example, a recording APC operation, a reproduction APC operation, a recording AFC operation, a reproduction AFC operation (frequency disk operation) The mine operation), the ACC operation, etc. can be stopped in the burst blanking period. According to these, the transient in the vertical blanking period can be improved. Thus, the counter 33 used in the embodiment of the present invention can be obtained by adding a few elements to the counter circuit used for other purposes.

It is also possible to blank and record the character signal mixed as the luminance signal by using the output VGP2 of the counter 33. For example, a trap circuit for the character multiple signal band is provided in the Y recording processing circuit 9 and this trap is turned on only during the VGP2 period, or the signal is forcibly clamped to the pedestal level during the VGP2 period and not during the horizontal synchronizing signal period. The means of.

〔The invention's effect〕

According to the present invention, since the character multiplex signal can be removed in the magnetic recording / reproducing circuit, the character multiplex signal does not interfere with the FM voice signal from the chroma processing circuit, and the filter for the chroma signal can have a wide band. , It is possible to improve the performance of voice and image.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, and FIG. 3 is a concrete example of a color killer circuit used in the embodiment of the present invention. FIG. 4 is an explanatory diagram showing an example of a frequency spectrum of a color video signal recorded by the magnetic recording / reproducing circuit according to the present invention, and FIG. 5 is a concrete example of a counter used in the embodiment of the present invention. FIG. 6 is a circuit diagram showing an example, and FIG. 6 is a timing chart of the counter in FIG. Reference numeral 28 ... AND gate, 33 ... Counter, 41 ... Color killer circuit, 42 ... Killer detection circuit

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Claims (1)

[Claims] 1. A luminance signal and a chroma signal are separated from an input color video signal, and then the luminance signal is frequency-modulated to be an FM luminance signal, and the chroma signal is located in a lower band than the luminance signal. Frequency conversion is performed to obtain a low-frequency conversion chroma signal, and the input audio signal is the F
An FM audio signal is frequency-modulated in a band lower than the M luminance signal and higher than the low frequency conversion chroma signal.
In the magnetic recording / reproducing circuit, wherein the FM luminance signal, the low-frequency conversion chroma signal and the FM audio signal thus obtained are mutually added by an adding means and recorded on a magnetic recording medium. When a character signal or the like is input to the color video signal in frequency proximity to the chroma signal and multiplexed with the chroma signal, the character signal in the color video signal is based on the input synchronization signal. First detecting means for detecting at least an existing horizontal scanning period and outputting a signal indicating the horizontal scanning period; a burst gate pulse for indicating an existing period of a burst signal corresponding to the color video signal; 1 and the signals output from the detecting means, and based on these signals, the burst in the horizontal scanning period in which the character signal or the like exists. Second detection means for detecting a period excluding a period in which a signal is present to determine the period in which the character signal or the like is present, and outputting a signal indicating a period in which the character signal or the like is present, and the second detection means. Input the signal output from the means,
Based on the signal, at least during the period when the character signal or the like is present, a shutoff unit that shuts off the supply of the low frequency conversion chroma signal to the adding unit is provided, and the low frequency conversion in which the character signal or the like leaks A magnetic recording / reproducing circuit characterized in that a chroma signal is not recorded on the magnetic recording medium.