JPH0213384B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control signal reproducing device for a video tape recorder or the like.

Conventionally, in a video signal magnetic recording/reproducing apparatus using a magnetic tape, such as a video tape recorder, a control signal indicating a reference phase at the time of recording recorded on the magnetic tape is reproduced by a wound ring head. Such a wound ring head has the advantage that control signals can be recorded and reproduced using a single head. However, the output signal level during playback is proportional to the relative speed between the magnetic tape on which the control signal is recorded and the wound ring head, so if the relative speed is slow, the signal-to-noise ratio of the playback control signal will be poor and the playback will be extremely slow. In some cases, there was a problem that the control signal was not reproduced.

In order to solve this problem, the present inventors first input the output signal of a magnetic flux response type head and the output of a reference magnetic head as a control signal reproducing device into a differential amplifier, and reproduced the signal from its output terminal. A method to obtain the control signal was presented. However, in these methods, difficulties were found in the method of adjusting the slight difference in resistance value between the reproduction head and the reference head, or the change in temperature resistance.

The present invention uses a magnetic flux responsive head to solve the above problems.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of the main parts of the video tape recorder of the present invention in playback mode. In FIG. 1, 1 and 2 are video heads, 3 is a rotational phase detection magnet, and these are attached to a rotating disk 4. A rotational phase detector 5 is installed on the fixed part corresponding to the magnet 3.

The rotating disk 4 is rotationally driven by a DC motor 6. The output signal of a frequency generator 7 attached to the DC motor 6, the output signal of the rotational phase detector 5, and the output signal of the reference oscillator 10 are supplied to a rotating head servo circuit 8. The output signal of the head servo circuit 8 is supplied to the DC motor 6 via a drive circuit 9. Thereby, phase control of the rotating disk 4 during reproduction is performed. The magnetic tape 20 is connected to a capstan 11 and a pinch roller (not shown).
is driven at a constant speed in the direction of arrow 21. The capstan 11 is driven by a DC motor 15 via a pulley 12, a belt 13, and a pulley 14. The capstan servo circuit 18 is supplied with an output signal of a frequency generator 16 for detecting the rotation speed of the DC motor 15 and an output signal of the reference oscillator 10. Furthermore, the reproduced output of the control signal head 19 is supplied to the capstan servo 18 via an input signal coupling stage (AC coupling) 23, an amplifier 24, an output signal coupling stage (AC coupling) 25, and a waveform shaping circuit 26. . With these, capstan 1
1 speed control and phase control are performed.

The recording pattern of the magnetic tape 20 is shown in FIG. In FIG. 2, magnetic tracks 31, 32,
33, 36 are recorded video signal tracks, and 41, 42, 43 are recorded control signals. Reference numeral 19 denotes a magnetoresistive head (hereinafter referred to as MR head), which is a type of magnetic response head, and is designed to reproduce control signals 41, 42, and 43 recorded on a magnetic tape by contacting them. It is located.

FIG. 3 shows the input signal combining stage 23 in FIG.
2 shows a specific circuit configuration of the amplifying section 24, the output signal combining stage 25, and the waveform shaping circuit 26.

One end of the MR head 19 is grounded and the other end is connected to a resistor 1.
01 to the power supply +V _cc 100.
As the tape 20 runs, a control signal reproduction voltage is generated at the output terminal 102 of the MR head 19, and the resistance value is highly temperature dependent by the capacitor 104.
DC fluctuations due to temperature changes in the MR head output are removed, and only stable signal (alternating current) components without DC fluctuations are transmitted to the resistor 105 (signal input coupling stage).

Note that the switch 106 will be described later.

The resulting signal is then applied to the non-inverting input terminal of operational amplifier 110 and amplified by a gain determined by the ratio of resistors 107 and 109. The variable resistor 108 performs zero point adjustment (offset adjustment) of the operational amplifier (hereinafter referred to as amplifier).

A capacitor 11 is connected to the output terminal of the operational amplifier 110.
2. A resistor 113 is connected to remove the DC component at the output terminal 114 due to the temperature characteristics of the elements constituting the amplifier 24 and obtain a stable signal component at the terminal 115 (the above is an output signal coupling stage).

In the waveform shaping circuit 26, the signal obtained at the terminal 115, 142, 143, 144 in FIG.
A, 116B and a signal below a threshold level 14 determined by the power supply voltage _-Vcc 118 is detected by an operational amplifier 121 to obtain a target control pulse signal at an output terminal 120 (the above is a waveform shaping circuit).

The time constant determined by the capacitor 104 and the resistor 105 is set large enough to reproduce the control signal up to slow speed (near still images) (the control signal is 30Hz at 1x speed reproduction,
For example, cutoff frequency 1/2πCR=
Select 0.07 (Hz) and CR=2.2sec. ) As a result of this, when the power is turned on, the power supply voltage V _cc is applied to the terminal 102.
A DC voltage divided by the resistance values of the resistor 101 and the MR head 19 is generated, and in a transient state where the capacitor 104 is not sufficiently charged, DC components unnecessary for amplifying and reproducing the signal are also transmitted to the terminal 103. switch 106 for a short time after the power is turned on.
This has the effect of quickly charging the capacitor 104 and bringing it into a steady state.

FIGS. 5 and 6 respectively show timing charts for the case without the switch 106 and for the case with the switch 106 added and with the switch 106 turned on during t ₀ →t _0FF (signal components not included).

A in FIGS. 5 and 6 shows the voltage change at the power supply terminal 100, and the power is turned on at _t0 . b is the voltage change at the signal terminal 102 of the MR head, which is the power supply voltage due to the resistance value _r19 of the MR head 19 and the resistance value r101 of the resistor ₁₀₁ .
A voltage value r ₁₉ /r ₁₉ +r ₁₀₁ V _cc is generated by dividing V _cc .

d is the voltage change after the input signal coupling stage 23, and immediately after the power is turned on, the voltage b at the terminal 102 is output as is, but in FIG. 5, T (time constant) = capacitor 10
4. It is decreased by the resistor 105, and in FIG. e is the output terminal 114 of the amplifier section 24
d (voltage change at terminal 103)
A voltage change occurs that is multiplied by the gain of the amplifier section. however
Terminal 11 called r ₁₉・V _cc・G/(r ₁₉ + r ₁₀₁ )V _cc
4 cannot be generated, so e in Figures 5 and 6
It shows a waveform like .

As is clear from the comparison of Figures 5 and 6 above, the resistance value of switch 106 is sufficiently smaller than resistor 105, so T≫T', and by turning on switch 106 for a certain period of time after power-on, control regeneration is achieved. It becomes possible to shorten the unusable period of the device. (t ₁ ≫ t ₂ ·t ₁ , t ₂ : No switch, unusable period of the control reproducing device when added) The switch 106 is constituted by, for example, a semiconductor switching element.

In addition, as shown in FIG. 7, the semi-fixed variable resistor 108 in FIG. 3 is a fixed resistor, and the resistor 113 is
It is also possible to create a circuit configuration in which a switch 130 is added in parallel with the above-described switch effect.
In this way, the MR head 19 is independent of temperature changes by using AC coupling in the coupling part, and
The control signal can be stably reproduced at any magnetic tape running speed up to the vicinity of a still image, and the control signal can be reproduced immediately after the device is powered on.

Furthermore, the same effect can be obtained by using a magnetic head that utilizes the Hall effect in place of the MR head 19.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the main part of an example of a video tape recorder using the present invention in playback mode, FIG. 2 is a diagram showing an example of a recording pattern, and FIG. 3 is a diagram of the main part circuit of an embodiment of the present invention. , Fig. 4 is a simple explanation diagram of the operating principle of waveform shaping, Figs. 5 and 6 are timing charts showing the switch effect, Fig. 7
The figure is a diagram showing the main circuit configuration of another embodiment of the present invention. 19... Magnetic flux responsive head, 23... Input signal coupling stage, 24... Amplifying section, 25... Output signal coupling stage, 26... Waveform shaping circuit.

Claims (1)

[Claims] 1. When reproducing control signals recorded on a magnetic tape using a magnetic flux responsive head, the output signal of the magnetic flux responsive head is detected by an input signal combining stage, amplified by an amplifier, and the output is supplied to a waveform shaping circuit. The control signal reproducing device obtains a reproduction control pulse by using an AC coupling in the input signal coupling stage, and sets a large time constant due to a capacitor and a resistor constituting the AC coupling to increase the magnetic tape running speed up to the vicinity of a still image. A control signal reproducing device characterized in that the control signal reproducing device is provided with a switch means for shortening the time constant of the AC coupling in order to be able to regenerate the control signal and to immediately regenerate the control signal for a certain period of time after the device is powered on. .