JPS623407A - Erasing circuit of magnetic recording/reproducing device - Google Patents

Abstract

PURPOSE:To obtain a constant deleting ratio regardless of the picture brightness at the time of recording by connecting the capacitor in parallel to the magnetic head, constituting the resonance circuit with high Q, obtaining the large deleting electric current and flatening the deleting electric current to flow at the deleting head by the deleting circuit having the frequency characteristic correcting circuit. CONSTITUTION:A deleting circuit 16 is composed of input terminals 69-71, resistances 55-59, capacitors 60-64, transistors 65 and 66, coils 67 and 68, a rotary transformer 72, and a deleting head 73, and the capacitor 64 is connected in parallel to a magnetic head 73, made into a resonance circuit and the electric power source is impressed to the terminal 71. At the emitter side of the transistor 65, the resonance circuit composed of the coil 67, the capacitor 61 and a damping resistance 58 is provided, and at this time, the resonance characteristic is set so that the deleting electric current supplied to the head 73 can be almost a flat characteristic at a FM carrier band. Namely, when the coil 67, the capacitor 61 and the resistance 58 are respectively L, C and R, a resonance frequency f0 is stipulated to 1/2pi(LC)<0.5> and the Q of resonance is made variable by the value of R.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a recording circuit for a helical scan household magnetic recording/reproducing device (hereinafter referred to as a VTR), and particularly relates to a recording circuit for a helical scan type household magnetic recording/reproducing device (hereinafter referred to as a VTR), and in particular for recording a magnetic tape without using a full-width erase head. The present invention relates to an erasing circuit for a magnetic recording/reproducing device that enables erasing.

[Background of the invention]

In conventional home VTRs, there is a system in which the full-width erase head is removed and a flying erase head is provided separately from the recording/reproducing magnetic head to improve the performance of editing functions such as continuous shooting and insert. For example, JP-A-5
Japanese Patent No. 9-42606 proposes a means for realizing erasing using a single flying erase head having a track width twice or more than the track pitch in a two-head VTR.

This is intended to reduce costs by using one flying erase head, but there is no particular description of the erase circuit, and no problems are raised regarding reductions in power and cost of the erase circuit.

In addition, for example, in Japanese Patent Application Laid-Open No. 58-222402, the recording track is divided into several areas, and each area K, for example, P
A system for recording commercial audio signals (hereinafter referred to as PCM)
(abbreviated as multi-system) has been proposed. However, no specific means has been proposed regarding the erasing method in the above system.

[Purpose of the invention]

It is an object of the present invention to solve the above-mentioned problems and to erase video signals recorded on a magnetic tape and PCM without using a full-width erase head.
An object of the present invention is to provide an erasing circuit for erasing a converted audio signal (hereinafter abbreviated as country P audio signal) using a rotary head.

[Summary of the invention]

That is, the present invention applies to home magnetic recording and reproducing apparatuses (hereinafter referred to as VTRs).
), a capacitor is connected in parallel to the magnetic head to form a high-Q resonant circuit to obtain a large erase current. The feature is that an erasing circuit having a frequency characteristic correction circuit is provided so as to flatten the frequency characteristics, and even in a VTR that divides the recording track into several areas and records and plays a PCM audio signal in each area, the erasing circuit described above can erase the signal. It is possible to realize this.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure is a block diagram of a recording system circuit including an erasing circuit. 1 is a video signal input terminal.

2 to 6 each constitute a luminance signal system circuit, and AG
C circuit 2. Low pass filter (hereinafter abbreviated as ILPF)
3. Pre-emphasis circuit 4°FMf tone circuit 5. Consists of bypass filter (hereinafter abbreviated as HPF) 6, HPF6
The output of is input to the adder 11. In addition, 7 to 10 each constitute a chroma signal system circuit, and the pantono (
Filter (hereinafter abbreviated as BPF)7. Chroma processing circuit 8
, low frequency conversion circuit 9. The output of LPFlo is added to the FM luminance signal (output of HPF6) in adder 11, sufficiently amplified by recording amplifier 12, and then sent to magnetic heads 23 and 24 via rotary transformers 19 and 20.
Supply recording current to. Further, the output of the HPF 6, that is, the FM luminance signal, is input to the erasure circuit 16 and amplified, and then
It is supplied to the erasing head 22 via the rotary transformer 18. In the case of erasing using a normal AC signal, the current required for the erasing head 22 (a current that can sufficiently erase the low-frequency chroma signal) is 100 ~
It is about 150mAp-. At this time, if there is no capacitor 21, the erase voltage supplied from the erase circuit 16 will be 10~
This requires about 12Vp-, which is impossible to achieve with a low power supply voltage of around 5V, which results in an increase in power consumption.

Therefore, if the capacitor 21 is connected in parallel to the magnetic head 21 to form a resonant circuit, the erasing head 2
2, the frequency characteristic of the current flowing through the rotary transformer 18 becomes a curve 25, and the current supplied to the stator side of the rotary transformer 18 is
27), a specific frequency (here approximately 5 MFIz)
can be made large enough. In other words, the power supply voltage of the erase circuit can be lowered, resulting in power saving.

However, as in the embodiment shown in FIG.
When using an FM luminance signal 1 For example, 8 mm video song V
In TR, the carrier frequency is 4.2 MHz to 5.4
MHz and 1.2 MHz, and in order to obtain a sufficient cancellation rate, if a frequency characteristic such as curve 25 with a high resonance Q is provided, it will be flat in the 4.2 Mflz to 5.4 MHz band. The characteristics cannot be obtained (4 dB difference here), and the current flowing through the erasing head 22 changes depending on the brightness and darkness of the recorded picture, resulting in different erasing rates.

That is, in the case of 25 in FIG. 2, in the case of a dark pattern or a bright pattern, unerased chroma signals become a problem. For example, if a resistor is connected in series with the erasing head 22 (not shown) to lower the resonance Q and create a characteristic like the curve 26 shown by the broken line in FIG. 2, then 4.2 MHz to 5.4 MHz
Although it becomes close to flat in the MHz band.

As a result of the overall decrease in erase current, unerased disturbances of the chroma signal occur.

Therefore, in the embodiment shown in FIG.
This makes it possible to obtain an erase current with almost flat characteristics in the M carrier frequency band.

FIG. 3 shows the characteristics after f-characteristic correction. 28 is.

This is a resonance characteristic caused by the erasing head 22 and the capacitor 21, and the resonance point is set near the 100% white carrier frequency (5.4 MHz for 8 mm video). At this time, near the carrier frequency (42 MHz) of the sync chip, the level decreases by about 13 dB compared to near 5.4 MHz. Therefore, the characteristics of the f-characteristic correction circuit 13 are
Set as follows (resonance point approximately 4.2MHz, Q approximately 8d)
Set the total f% of the erase current ih to the carrier frequency band (4.2 MIl [z ~ 5.4
MHz), the characteristics are almost flat. It is also clear that the head resonance may be set at 4.2 Mflz and the resonance point of the f-characteristic correction circuit may be set at 5.4 MHz. In FIG. 1, a switch 15 is a switch for controlling an erase signal, and the control signal is inputted from a terminal 17.

A specific example of control will be described later.

Next, a second embodiment of the present invention will be described with reference to FIG. Figure 4 shows a VTR recording system that has both a mode for recording video signals such as 8mm video (hereinafter referred to as video mode) and a mode for recording the aforementioned PCM multi (hereinafter referred to as PCM multi mode). It is a block diagram of a circuit.

As I know, 8mm video is as shown in Figure 5.
It is used to multiplex record FM audio signals of VC15Mh±100KIIz between the fFT signal (750KfTz) and the 4-frequency pilot signal (approximately 100KFIzS-) necessary for playback tracking. 16
0 KHz) is also multiplex recorded. These signals are recorded in a 180 degree section on the recording pattern shown in Figure 1M7. In addition, as shown in Fig. 6, a signal obtained by frequency multiplexing the PCM signal (the highest frequency is about 5.8 MHz) and the pilot signal is overlapped with the video signal on the extension of the video signal track in the KBFi degree section as shown in Fig. IK7. Record (see IE12rI4).

Furthermore, in the PCM-f multi-system, PCM signals are recorded in track divisions as shown in FIG. 1118. For 8 mm video, magnetic tape 75 is wound around the rotating cylinder by approximately 216 degrees as shown in FIG. 76, 77
78 and 79 are magnetic heads, and 80 is an erase head. therefore.

36 degree area with 6 channels (hereinafter abbreviated as ah)
It is possible to provide Here, as shown in FIG. 8, from the bottom edge of the magnetic tape 53, VC, ch1. c-n2. It is defined as cn3, -, ch6. The PCM audio signal recorded on each chJi is the 7th [! ! Recording and playback can be performed using exactly the same signal processing as that used for overlapping recording with video signals such as 2+, and there is no increase in cost except for system switching.

In FIG. 4, the audio signal input from terminal 33 is F
The M audio processing circuit 34 converts the FM signal (AFM 1) into
It is input to the adder 32. Further, the pilot signal ('P) generated by the servo circuit 35 is first added to the previous chroma signal (C) and the FM audio signal (Any) in the adder 32, and then added to the FM luminance signal (T) in the adder 31. ) to form a frequency multiplexed signal (Y+C+AFM+P), while the adder 4o adds the PCM audio signal (PCM)
, i.e., (PCM+P) is formed.

The above (Y+C+AFM+P) and (PCM+P) are switched by switch circuits 41 and 43, respectively, and the recording amplifier 4
After being sufficiently amplified, recording current is supplied to magnetic heads 47 and 48 via rotary transformers 45 and 46. Here, the switching of the switch circuits 41 and 43 is not directly related to the present invention and the details are omitted, but by this switching, recording is performed on the magnetic tape 1 as shown in Figures 7 and 8. It is.

The switch circuit 5o switches between the video mode and the PCM multi-mode. For example, in the video mode, the control signal from the terminal 51 becomes low, turning the switch 5o off (not shown), A signal (y+c+Ary+P) is supplied to circuits 41 and 43. In the PCM multi mode, the control signal M goes high, the switch circuit 50 turns on, and the signal (Y+
C+AFM+P) is turned off and only the signal (PCM+P) is supplied to the switch circuits 41 and 43.

The erase circuit 16 is similar to the previous embodiment (FIG. 1). However, the signal supplied to the erasure circuit 16 (output of the HPF 6) differs from that in FIG. 1 and changes between the video mode and the PCM multimode. FIG. 9 shows an input signal to the FM modulation circuit 50. In video mode, a video signal is input, but in PCM multi mode.

There are cases in which a video signal is input to the VTR and cases in which it is not input. In the former, the input to the FM modulation circuit 5 is of course a video signal, but in the latter, as shown in Figure 9, only the DCe, which is clamped to the sync chip level, is the FM signal.
input to the modulation circuit 5, and the output of the FM modulation circuit 5 is 4.2
It becomes a single wave of MHz. This single wave component causes the PC
This is for erasing the M multi signal. Figure 10 shows FM
The spectrum of the output of the modulation circuit 5 (or the output of the HPF 6) is shown. Figure (a) shows the spectrum when a video signal is input to the VTR, and Figure (b) shows the spectrum when no video signal is input.

Next, a specific example of the erasing circuit 16 will be explained using FIG. 69, 70, and 71 are input terminals, 55 to 59 are resistors, 60 to 64 are capacitors, 65 and 66 are transistors, 67 and 68 are coils, and 72 is a rotary transformer.

73 indicates an erase head. As explained in FIG. 1, the capacitor 64 is connected in parallel to the magnetic head 73 to form a resonant circuit. Terminal 71 is a power supply terminal. A control signal input from the terminal 70 is transmitted to the base of the transistor 65, and a resonant circuit (coil 67°, capacitor 61, damping resistor 5) provided on the emitter side.
8) and is input to an amplifier consisting of a transistor 66 and a resistor 59. As shown in FIG. 3, the resonance characteristics of the resonance circuit described above are such that the erase current ih supplied to the erase head 73I/C is within the FM carrier band (4,2M) Iz ~5.
4 MHz) so that the characteristics are almost flat. Coil 67, capacitor 61. The resistors 58 are L and C, respectively.
, R Next, the timing of flowing the erase current to the erase head will be explained. No. 12 is a top view of the one-rotation cylinder, with reference numeral 75 a magnetic tape, 76° and 77 a guide post, 74 a rotating cylinder, 78 and 79 recording magnetic heads, and 80 an erasing head.

The magnetic tape 75 is wound about 216 degrees around the cylinder for one rotation, and the PCM signal is transmitted in the 36 degree section.

A video signal is recorded in a 180 degree section.

One erasing head 80 is installed at a position 901i ahead of the magnetic head 78, and its track width is selected to be approximately twice (40 μm) more than the track pitch PT (20 μm), so that it can write two fields of recording tracks. The data is erased in one field period.

FIG. 13 shows a timing chart for video mode. Signal M is a signal that is 1...A in PCM multi mode, RFC is a signal that is high during recording, and signal is high in insert mode.

S is the head-off 1tlL pulse, PG is the signal that remains high during the recording period of the PCM audio signal, and E is the period during which the erasing current flows.
The signal that becomes low, ih is the erase current waveform, iI, i
2 indicates the recording current of the magnetic heads 47 and 48 in FIG. 4 (corresponding to the magnetic heads 78 and 79 in FIG. 12, respectively).

During recording, signal E is input to terminal 17 (Fig. 4),
During the low period, an erase current ih consisting of an FM carrier signal is supplied to the erase head 22K (FIG. 4). E is low
The interval is approximately 216 degrees from the time point tIK when the magnetic head 78 comes into contact with the magnetic tape 75 in FIG.
7), the PCM area and video area in FIG. 7 are all erased.

When inserting, the PCM area is left and the video area is erased, so the period when E is low is about 90 degrees with respect to the 180 degree section (section from t3 to t2) corresponding to the video area.
15, i2 in FIG. 13, only the video signal is supplied as the recording current.

During playback, E goes high and switch 15 (FIG. 4) is turned off.

Figure 14 shows a timing chart in PC'M multi mode during recording. Any one of cht to ch6 in FIG. 8 is specified. According to CA1, ah2, . . . , ah6, the signal PG is shifted by <36 degrees as shown in FIG. For example l? A11c P When recording a CM audio signal, the magnetic head 78 (FIG. 12)
36 degree interval (until t4) IC from time t1 facing 5
On the other hand, in a period approximately 90 degrees earlier, E becomes low and an erase current flows as shown in ih. At this time, ih consists of an FM carrier signal or a single frequency of 4.2 MHz, as described above.

When recording a PCM audio signal on CA2, E is detected approximately 90 degrees before the 36 degree interval (ts) from time t4, which is a 36 degree period after the magnetic head 78 comes into contact with the magnetic tape 75. It becomes low and an erase current flows as shown in ih. Similarly, when recording a ch6IlcP CM audio signal, E goes low and L people flow during a period approximately 90 degrees before the interval t6 to t7. 13 and 15 (FIG. 4) are in the off state.

As explained above, in this embodiment, when the FM carrier signal is used as the erase current of the flying erase head, a capacitor is connected in parallel to the magnetic head, and a sufficiently large Q.
At the same time, in order to obtain a flat frequency characteristic in the FM carrier band (4.2 MHz to 5.4 MHz for 8 mm video), a frequency characteristic correction circuit was installed before the eraser. It has characteristics.

Also, in VTRs that have video mode and PCM multi mode, such as 8 mm video.

Both modes use the FM modulation circuit output for the luminance signal as the cancellation signal.

〔Effect of the invention〕

According to the present invention, since the output signal of the FM modulation circuit for the luminance signal is used as the erasing signal supplied to the flying erase head, the erasing circuit can be configured at low cost.

Since the frequency characteristics of the erase current can be almost flattened in the FM luminance signal band, a constant erase rate can be obtained regardless of the brightness or darkness of the image during recording, and it is also possible to lower the power supply voltage, resulting in lower power consumption. This has the effect of making it possible.

[Brief explanation of drawings]

Fig. 1 is a recording system circuit diagram showing one embodiment of the present invention, Figs. 2 and 3 are characteristic diagrams showing the frequency characteristics of the erase current, and Fig. 4 is a recording system circuit diagram showing another embodiment. , FIGS. 5 and 6 are spectrum diagrams showing examples of recording signals, FIGS. 7 and 8 are explanatory diagrams showing recording butter, and FIG. 9 is a waveform diagram of a video signal. FIG. 10 is a spectrum diagram of the signal in FIG. 9, FIG. 11 is a specific circuit diagram of the erasing circuit, FIG. 12 is an explanatory diagram showing an example of cylinder tape loading, and FIGS. 13 and 14 are explanations of the operation. FIG. 13... f special correction circuit, 14... erasure amplifier. 15... Switch circuit, 16... Erasing circuit. 22, 80...Flying erase head. 30... Erasing current f characteristic. Heba person yP burial officer Ogawa! ! Man No. 5 l Chi/L liver old h

Claims (1)

[Claims] A helical scan type magnetic recording and reproducing device having at least two magnetic heads mounted on a rotating cylinder, comprising at least one erasing head on the rotating cylinder,
When a capacitor is connected in parallel to the erasing head, the inductance of the erasing head is L_H, and the capacitance of the capacitor is C, the first resonance frequency f_1 is 1/[2π√
(L_HC) is one of the upper and lower carrier frequencies of the FM luminance signal (first frequency)
and an erase amplifier is provided on the stator side of the rotary transformer connected to the erase head to amplify the erase signal, and the frequency characteristics of the erase current flowing through the erase head are set to the carrier in the preceding (or subsequent) stage. A frequency characteristic correction circuit having a second resonant frequency f_2 is provided at the other of the upper and lower limit frequencies of the carrier frequency so as to be even across the frequency band, and an FM luminance signal is used as the cancellation signal. An erasing circuit for a magnetic recording/reproducing device characterized by: