JPH07105968B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus for a color image signal used in 8 mm video, and more particularly to a low-pass filter for recording a chroma signal and a reproducing low-frequency wave signal. The present invention relates to a magnetic recording / reproducing apparatus which can be used also as a bandpass filter to reduce the size of the apparatus and improve the transient characteristics of color signals.

[Background of the Invention]

In a magnetic recording / reproducing apparatus for a domestic color video signal, a luminance signal of a color video signal is frequency-modulated (hereinafter referred to as FM modulation), and a chroma signal has a band lower than that of the FM-modulated luminance signal. The mainstream method is to perform frequency conversion into and to multiplex and record these frequencies. In a device of this type, when a chroma signal is frequency-converted, an unnecessary frequency component is generally generated. That is, if the frequency of the chroma signal to be written on the recording medium is f _LSC and the original chroma signal frequency is f _SC , f _SC +
By signal and multiplication of f _LSC comprising frequency, in order to record obtains f _LSC of the difference frequency. At this time,
At the same time, a signal of the sum frequency of 2f _SC + f _LSC is also generated. Therefore, a low-pass filter (hereinafter abbreviated as LPF) is provided in the subsequent stage of the frequency conversion means to remove unnecessary components, and at the same time, remove noise outside the band.

At the time of reproduction, of the frequency-multiplexed signals reproduced by the magnetic head, the chroma signal on the low frequency side is taken out, and thereafter the processing for returning the chroma signal to the original high frequency region is performed.
After all, LPF is necessary at the beginning of the chroma signal processing system. Examples of this type of device include Japanese Utility Model Publication No. 54-15550 and Japanese Patent Publication No. 53.
-19717 is available.

By the way, since the recording LPF and the reproducing LPF have the same pass band, it is conceivable to use them in common to reduce the size of the circuit and improve the reliability. However, in that case, the recording LPF and the reproduction LPF
And, it is necessary to make the optimum out-of-band attenuation characteristics different, and accordingly, the cutoff frequency also becomes slightly different. This is because if the LPF has a cutoff characteristic to the extent that it is possible to prevent FM audio signals having a lower level than the chroma signal and FM luminance signals separated from the chroma signal band from mixing in the chroma signal during playback. On the other hand, it is sufficient, but at the time of recording, it is necessary to determine the cutoff characteristic of the LPF so as to sufficiently prevent the chroma signal from being mixed in the FM luminance signal and the FM voice signal of a relatively low level. For this reason, simply using the LPF for both recording and reproduction would cause the band of the cross signal to be too narrow to deteriorate the color transient characteristics, or conversely, the band of the cross signal to be too wide to allow other recording signals to be recorded. There is a problem that interferes with.

[Object of the Invention]

An object of the present invention is to provide a magnetic recording / reproducing apparatus which solves the above problems, has good color transient characteristics, does not cause interference of a chroma signal to other signals, and is compact and highly reliable. Is.

[Outline of Invention]

In order to achieve this object, the present invention uses an LPF as a first LPF.
And a second LPF that can be cascade-connected to the
The attenuation characteristic of the PF is made relatively gentle, and the combined attenuation characteristic of the first and second LPFs is made relatively steep so that the first LPF is used for both recording and reproduction. In addition, during recording, the second LPF is added to the first LPF.
It is characterized by using in cascade connection.

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention, in which 1 is an input terminal of a video signal, 2 is a band pass wave filter (hereinafter abbreviated as BPF), 3 is an ACC circuit, Four
Is a recording processing circuit having a burst emphasis function or a non-linear emphasis function, 5 is a frequency conversion circuit (hereinafter referred to as a converter), 6 is a recording / reproduction changeover switch circuit, 7 is an LPF, 8 is a 1.5 MHz trap circuit, and 9 is addition. A circuit, 10 is a luminance signal recording processing circuit (hereinafter referred to as Y recording processing circuit) including an AGC circuit, LPF, pre-emphasis circuit, FM modulation circuit, etc., 11 is an audio signal input terminal, 12 is an FM modulation circuit, etc. An audio signal recording processing circuit (hereinafter referred to as A recording processing circuit) 13 including a pilot signal generating circuit, 14 a recording amplifying circuit, 15 a magnetic recording head, 16 a magnetic tape recording medium, 17 a magnetic reproducing head, and 18 a Preamplifier circuit, 19 AC
C circuit, 20 is a converter, 21 is BPF, 22 is a reproduction processing circuit having a burst de-emphasis function, a comb filter, a non-linear de-emphasis function, etc., 23 is an addition circuit,
24 is an output terminal for the reproduced video signal, 25 is a luminance signal reproduction processing circuit (hereinafter referred to as Y reproduction processing circuit) including HPF, FM demodulation circuit, de-emphasis circuit, etc., 26 is audio having an FM demodulation circuit, etc. A signal reproduction processing circuit (hereinafter, referred to as A reproduction processing circuit) 27 is an output terminal for the reproduced audio signal, and 28
Is a BPF, and 29 is an output terminal of a pilot signal.

In this embodiment, the LPF having a relatively gentle specification of the out-of-band attenuation characteristic is the reproducing LPF 7, and the recording LPF is
This LPF 7 and 1.5 MHz trap circuit 8 are connected in cascade. This is because in a VTR in which an FM-converted audio signal is frequency-multiplexed and recorded between a low frequency conversion chroma signal and an FM luminance signal, the FM luminance signal is separated from the low frequency conversion chroma signal in frequency, For near audio signal band,
This is because what kind of damping characteristics to give is a problem.

First, the operation during recording will be described. The video signal input from the input terminal 1 is guided to the BPF 2 and the recording processing circuit 10.
Only chroma signal is overselected by BPF2, and ACC circuit 3
Be led to. The ACC circuit 3 keeps the chroma signal level constant, and guides its output to the recording processing circuit 4 and, after desired processing, to the converter 5. The converter 5 converts the low-frequency chroma signal into a switch circuit 6. The switch circuit 6 is closed at the position shown in the drawing at the time of recording, and its output is led to the LPF 7 and further to the 1.5 MHz trap circuit 8,
LPF7 and trap circuit 8 remove all unnecessary frequency components. The output is supplied to an adder circuit 9 where it is added to an FM-modulated luminance signal, an FM-modulated audio signal and a pilot signal and supplied to a recording magnetic head 15 via a recording amplifier circuit 14 for a magnetic tape recording medium. Record on 16th.
The luminance signal in the video signal is converted into an FM modulation signal by the Y recording processing circuit 10 and supplied to the adding circuit 9. Also, the audio signal is input from the terminal 11 and the A recording processing circuit
An FM modulated signal is supplied by 12 to the adder circuit 9. Further, the pilot signal generated by the pilot signal generating circuit 13 is supplied to the adding circuit 9.

Next, the operation during reproduction will be described. Magnetic tape recording medium 16
The signal reproduced by the reproducing magnetic head 17 is supplied to the switch circuit 6, the Y reproduction processing circuit 25, the A reproduction processing circuit 26 and the BPF 28 via the preamplification circuit 18. Switch circuit 6
Is closed at the contact opposite to that shown in the figure during reproduction, and guides the reproduction signal to LPF7. In LPF7, only the low frequency chroma signal is taken out, and the ACC circuit 19 absorbs the output variation between the channels of the reproducing head and processes it to a certain level, and then is converted into the original high frequency chroma signal by the converter 20. . After the unnecessary frequency component is removed by the BPF 21, the chroma signal is subjected to desired processing by the reproduction processing circuit 22 and supplied to the adding circuit 23. On the other hand, the FM-modulated luminance signal in the output of the preamplifier circuit 18 is demodulated by the Y reproduction processing circuit 25 to be the original luminance signal, and is added to the chroma signal by the addition circuit 23. Therefore, the original color video signal can be obtained from the adder circuit 23 at the output terminal 24. The reproduced signal is supplied to the A reproduction processing circuit 26, the FM modulated audio signal is FM demodulated, and the original audio signal is obtained at the output terminal 27. In addition, output terminal 2 through BPF28
A pilot signal is obtained at 9, and this pilot signal is used for automatic adjustment of reproduction tracking (not shown).

A signal recorded by the recording magnetic head 15 and a signal reproduced by the reproducing magnetic head 17 will be described with reference to FIG. As shown in the figure, the pilot signal P is about 0.1 to 0.15 MHz,
Downconverted chrominance signal C is approximately 0.74 ± 0.5 MHz, FM audio signals f _a
About 1.5 ± 0.1 MHz, FM luminance signal f _Y has each band of the carrier frequency and 1.8MHz~4.2MHz and 5.4MHz or more sidebands 4.2～5.4MHz.

LPF7 specifications during playback, FM audio signals f _a and FM luminance signal
It is decided that f _Y is sufficiently attenuated. FM voice signal f
_{Since the} recording level of a is much lower than that of the low-frequency chroma signal C, there is little interference with the reproduced chroma signal, and in particular, there is little need to provide a trap circuit. Even if a trap characteristic is added, it may be relatively shallow. FM luminance signal
f _Y has a higher recording level than the low frequency chroma signal, and if it leaks into the reproduction chroma signal processing circuit, it interferes with the chroma signal. Therefore, as an example, the LPF7 specification is -10d at 1.5MHz.
It can be set to -40 dB or lower at B and 4 MHz or higher. An example of the LPF 7 that realizes this will be described with reference to FIG. In FIG. 1A, 40 is input terminals 41 and 42 are resistors, 43 to 45 are capacitors, 46 is an inductance, and 47 is an output terminal. In this example, the resistors 41 and 42 are 1 kΩ, the capacitance 43 is 278 pF, the capacitance 44 is 10.5 pF, the capacitance 45 is 168 pF, and the inductance 46 is 151
If it is μH, the frequency characteristic is as shown in FIG. The features of this specific example are that it has only one inductance, it can be realized in one block when it is made into blocks, good cost performance, and the maximum frequency of the low-frequency conversion chroma signal. 1.24MHz is hardly attenuated, and the color transient characteristics are good.

The specifications of the LPF 7 and the 1.5 MHz trap circuit 8 at the time of recording must be determined in consideration of not disturbing other signals from the chroma signal, unlike at the time of reproduction. In particular, with respect to the FM audio signal, since the band is very close to the low frequency chroma signal and the recording level is considerably smaller than that of the low frequency chroma signal, buzz interference to the audio signal is likely to occur.
Therefore, at the time of recording, the 1.5 MHz trap circuit 8 is cascade-connected in addition to the LPF 7. The specifications when connected in cascade are
It can be -20 dB or less at 1.4 MHz, -30 dB or less at 1.5 MHz, and -40 dB or less at 4 MHz or more. To meet this,
1.5MHz trap circuit 8 added to LPF7 specified from playback specifications
A specific example will be described with reference to FIG. The same figure (a)
, 48 is an input terminal, 49 and 50 are resistors, 51 and 52 are capacitors,
53 is an inductance and 54 is an output terminal. In this example, the resistance 49 is 200Ω, the resistance 50 is 920Ω, and the capacity 51 is 34Ω.
When the capacitance is 0 pF, the capacitance 52 is 125 pF, and the inductance 53 is 33.1 μH, the frequency characteristic is as shown in FIG. Therefore, the integrated frequency characteristics of the LPF 7 and the 1.5 MHz trap circuit 8 satisfy the specifications. The feature of this concrete example is that the 1.5MHz trap circuit 8 has only one inductance, and when it is made into a block, it can be realized in one block and the cost performance is good, and the trap frequency of the 1.5MHz trap circuit 8 is It is possible to have peak characteristics on the lower side,
Therefore, the attenuation of 1.4MHz to 1.5MHz is increased, and the attenuation of the maximum frequency of the low frequency chroma signal of 1.24MHz is small. As a result, the color transient characteristic does not deteriorate. In practice, a buffer amplifier is provided at the output of LPF7 and the output is guided to the 1.5 MHz trap circuit 8.

FIG. 5 is a block diagram showing another embodiment of the magnetic recording / reproducing apparatus according to the present invention, and the parts corresponding to those in FIG. This embodiment differs from the embodiment of FIG. 1 in that a recording / reproducing changeover switch 30 is newly provided.
F2 is configured to be used for both recording and playback, and the BP in Fig. 1 is used.
That is the deletion of F21. In this case, the cost performance is further improved because one BPF is less required. The switch circuit 30 takes the switching position shown in the drawing during recording and the switching position opposite to that shown in the drawing during reproduction.

FIG. 6 is a block diagram showing still another embodiment of the magnetic recording / reproducing apparatus according to the present invention, in which 60 is an f _SC trap circuit (f _SC is a color sub-transmission frequency = 3.58 MHz), and 61 and 63 are. The subtraction circuit, 62 is a 1H delay line, 64 and 65 are addition circuits, and the same reference numerals are given to the portions corresponding to FIG. The difference from this embodiment is that the video signal from the input terminal 1 is trapped by the trap circuit 60, the subtraction circuits 61, 63, the addition circuits 64, 65 and the 1H delay line 62.
The luminance signal is added to the Y / C separation circuit composed of
This is the point that the output of 5 is obtained and supplied to the Y recording processing circuit 10, and the chroma signal is obtained at the output of the subtraction circuit 63 and supplied to the switch circuit 30.

The operation of the Y / C separation circuit will be described. f _SC trap circuit
The frequency component near the color subcarrier is removed from the output signal of 60. Therefore, the output signal of the subtraction circuit 61 is a signal having a frequency near the color subcarrier. The output signal of the subtraction circuit 61
The 1H delay line 62, the subtraction circuit 63, and the addition circuit 64 are supplied.
The 1H delay line 62 and the subtraction circuit 63 constitute a so-called chroma comb filter, and a so-called chroma signal having no cross color component is obtained at the output of the subtraction circuit 63. 1H delay line 62
A so-called Y-comb filter is constituted by the addition circuit 64 and the addition circuit 64, and a high-frequency luminance signal having no dot interference component can be obtained at the output of the addition circuit 64. By adding this luminance signal to the signal from which the frequency component in the vicinity of the color subcarrier has been removed by the adder circuit 65, a luminance signal in the entire band without dot interference components can be obtained.

The feature of this embodiment is that the specifications of the trap circuit 8 can be loosened and the color transient characteristics can be improved more than those of the embodiments of FIGS. 1 and 5.
The reason is that the component that interferes with the FM audio signal f _a during recording is the upper band of the low-frequency subcarrier frequency, which is the lower band of f _SC in the chroma signal before being converted to the lower band. Equivalent to. This is because in this band, especially in the case of a white character multiplex signal, the high frequency energy of the luminance signal becomes high, and the high frequency component of this luminance signal interferes with the FM audio signal f _a . In this embodiment, when separating the chroma signal,
And removing the high-frequency component of the luminance signal, thus, it is possible to loosely trap attenuation characteristic of the trap circuit 8 disruptive to FM audio signals f _a is decreased, the maximum frequency of the low frequency chroma frequency 1.24 Less MHz attenuation and better color transients.

FIG. 7 is a block diagram of still another embodiment of the magnetic recording / reproducing apparatus according to the present invention, in which 70 is a sync separation circuit and 71 is an H / H circuit.
2 removal circuit, 72 pulse delay circuit, 73 inverter, 74
Is a head switching pulse input terminal, 75 is a counter, 76 is an AND gate, 77 and 78 are resistors, 79 is a transistor, and 80 is a capacitor, and the same reference numerals are given to the portions corresponding to the above drawings.

In this embodiment, a signal for character multiplexing existing immediately after a vertical synchronizing signal of a video signal is removed. As mentioned above, the signal for character multiplexing has a high energy especially in the high frequency range, and when the chroma signal is converted into the low frequency range, the FM voice signal is generated.
It becomes a frequency near f _a and becomes a source of interference, so it is necessary to remove it.

The operation of this embodiment will be described. The video signal from the input terminal 1 is supplied to the sync separation circuit 70 to extract only the sync signal, and the H / 2 removal circuit removes the H / 2 pulse existing in the vicinity of the vertical sync signal to obtain the H pulse. . This H pulse is supplied to the pulse delay circuit 72 and the counter 75. The pulse delay circuit 72 forms a pulse BG (for example, a width of about 4.5 μsec) that becomes “high” from the H pulse only during the period when the burst signal exists, and inverts this by the inverter 3 to form the pulse BG, and the AND gate Supply to 76. While the counter
The head switching pulse input from the input terminal 74 is supplied to 75, and the counter 75 is reset each time the pulse rises or falls. The counter 75 counts the H pulse as a clock and outputs a signal that becomes “high” only for a predetermined count value, and this output signal is used as the other input of the AND gate 76. This predetermined count value may be set to, for example, 10 to 20 so that the output signal of the counter 75 represents the period in which the signal for character multiplexing exists. Due to these signals, the output of the AND gate 76 becomes "high" only during the period when the signal for character multiplexing exists and is not the burst signal period. This output is supplied to transistor 79 through resistors 77 and 78, which turns it on during the "high" period. As a result, among the output signals of the converter 5, the signals for character multiplexing, etc. are transmitted through the capacity 80 to the GRD
It can be removed by bypass.

In this embodiment, again because the signal which becomes interference to FM audio signals f _a can pre Ji because removal, trap circuit 8 can loosely trap attenuation, the color transition characteristic is further improved.

The position to bypass the signal for character multiplexing is LP
It may be anywhere before F7, for example, next to the ACC circuit 3 or next to the recording processing circuit 4.

In addition, since the chroma signal recording processing circuit usually has a killer circuit that detects the black and white mode and makes the chroma signal output non-output, the killer circuit using the output signal of the AND gate 76 for this killer circuit. You may make it operate | move.

Further, if the Y / C separation circuit as in the embodiment of FIG. 6 is provided for the embodiment of FIG. 7, the specifications of the trap circuit 8 can be further relaxed and the color transient characteristics can be improved. Also, BP
The F2 and the BPF 21 may be shared as in the embodiment of FIG.

Further, if the LPF 7 and the trap circuit 8 are integrated into an IC, the increase in the number of internal elements can be suppressed to the minimum, and further the device can be downsized and the reliability can be improved.

Needless to say, each of the above embodiments is effective even when the pilot signal P is not frequency-multiplexed.

〔The invention's effect〕

As described above, according to the present invention, the color transient characteristic is excellent, the chroma signal does not interfere with other signals, and further, the size and reliability can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention, FIG. 2 is a spectrum diagram of recording and reproducing signals in FIG. 1, and FIG. 3 (a) is a low-pass signal of FIG. FIG. 4B is a circuit diagram showing a specific example of the filter, FIG. 4B is a characteristic diagram thereof, FIG. 4A is a circuit diagram showing a specific example of the 1.5 MHz trap circuit of FIG. 1, and FIG. Its characteristic diagram, FIG. 5,
6 and 7 are block diagrams showing another embodiment of the magnetic recording / reproducing apparatus according to the present invention. 1 ... Input terminal, 6 ... Switch circuit, 7 ... Low pass filter, 8 ... 1.5 MHz trap circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Kubo, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Pref., Within Hiritsu Video Engineering Co., Ltd. (56) References JP-A-56-140792 (JP, A) JP-A-SHO 60-109990 (JP, A) JP 59-77784 (JP, A)

Claims (1)

[Claims] 1. A luminance signal of a color video signal is converted into a frequency modulation luminance signal, an audio signal is converted into a frequency modulation audio signal, and a chroma signal of the color video signal is converted into 1H (H).
Is a low-frequency conversion chroma signal that is frequency-converted into a band lower than the frequency-modulated luminance signal and the frequency-modulated audio signal by the frequency conversion means after separating with a chroma comb filter including a delay line. The low-pass conversion chroma signal is a signal obtained by removing the character signal transmitted in the vertical retrace period of the color video signal by the removing means, and the low-pass conversion chroma signal is an LPF circuit having a frequency characteristic necessary for reproduction. After passing through a filter circuit that is connected in series with a band attenuating trap circuit for the frequency-modulated audio signal, frequency-multiplexes with the frequency-modulated audio signal at a relatively lower level than the frequency-modulated luminance signal and the low-frequency conversion chroma signal. When recording and reproducing, by passing only the LPF circuit and not the trap circuit, the low frequency conversion chroma signal from other signals Apart removed magnetic recording and reproducing apparatus, characterized in that the frequency conversion to the original chroma signal.