JPH01241002A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the picture quality of the title device by providing a means which reduces or cancels the DC component contained in the erase current supplied to an erase head. CONSTITUTION:DC power sources 26 and 27 are selected by means of a switch 28 and supply direct currents to an erase head 20 through a variable resistor 29. Because of these direct currents, a DC bias component 24 can be canceled. Therefore, the residual magnetism remaining on an erased magnetic tape can be reduced or completely eliminated and appearance of beat components in pictures at the time of recording and reproduction can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current drive circuit for an erase head of an RA magnetic recording/reproducing device.

[Prior Art] FIG. 3 is a diagram showing a conventional erase head current drive circuit. In FIG. 0, (1) is an oscillation circuit, (2) is a buffer circuit, (3) is a capacitor, and 4) and the output of the buffer circuit (2). Transisladder (4) is resistor (5), (8)
, (7) and (8) together with the phase splitting amplifier (4
0). Transistor (15), (1G)
are the resistances (11), (12), (13),
(14), (17), and (18) constitute a push-pull power amplifier (50). Capacitor (9)
and (10) are connected between the collector of transistor (4) and the base of transistor (15), and between the emitter of transistor (4) and the base of transistor (16), respectively. Erase spatula F (20)! *, connected to the collector of the transistor (1B) via the capacitor (18). (21) is a power source.

Next, the sine wave oscillation output of the 0 oscillation circuit (1), whose operation will be explained, is supplied to the buffer circuit (2), and the transistor (4) constituting the phase splitting amplifier (4o) is supplied to the buffer circuit (2) via the capacitor (3). supplied to the base. Transistor (
The sine wave outputs taken from the collector and emitter of 4) and having approximately the same amplitude with a phase of 180% are connected to a push-pull power amplifier (50) via capacitors (9) and (10). transistor (15),
, (113), the power is amplified, and then the erase head (113) is supplied to the erasing head (
20) and erase the signal recorded on the magnetic tape.

Next, the erasing operation on one magnetic tape will be explained. FIG. 4 is a diagram for explaining the erasing operation on a magnetic tape. FIG. When a sinusoidal current with a wavelength sufficiently short compared to the gap distance provided in the erase head (20) is supplied, the erase magnetic field distribution at a certain point on the magnetic tape becomes approximately symmetrical between positive and negative as shown in FIG. Become. The magnetic tape is magnetized by this erasing magnetic field so as to draw a hysteresis curve (22) shown in the figure (A), and as the erasing magnetic field decreases, it draws a minor loop similar to the hysteresis curve (22). The ideal sine wave erasing current waveform at this time, which converges to the origin O of the curve and leaves no residual magnetism, is shown in the same figure (
Shown in D).

However, the actual erase current does not become an ideal sine wave current as shown in FIG. 1D due to the nonlinearity of the circuit configuration and elements, and always includes a distortion component. Assuming that this erase current has a distorted waveform as shown by the solid line in FIG. 4(E), this erase current is.

This corresponds to the ideal sine wave shown by the broken line in the figure plus the shaded area, and includes a direct current component proportional to the area of the shaded area. That is, it can be considered that a waveform in which an ideal sine wave is superimposed on a DC component is the distorted current waveform shown in FIG. In this way, the erasing head (20) generates a current with a waveform in which an ideal sine wave is superimposed on direct current.
It is thought that when the erase magnetic field is supplied to the magnetic field, the distribution of the erase magnetic field is distorted as shown in FIG. 4(C). The magnetic field distribution in Figure (C) was drawn assuming that a DC magnetic field component (24) was generated, and the hysteresis curve due to this erase magnetic field distribution is
As shown by the dashed line (23) in the same figure (A), even if the hysteresis curve (23) converges while drawing a minor loop, the original The problem is that the magnetic tape does not converge to ImO but converges to the point of residual magnetism (25), that is, the distortion component of the erase current leaves magnetism in the magnetic tape that was supposed to be erased, that is, it is recorded. arise. In this way, with the magnetism remaining,
Next, when the signal that should originally be recorded is recorded and played back by the recording/playback head, harmonic distortion occurs in the original signal, and beat disturbance corresponding to the sum or difference between the signals occurs, and +IrIr
The beat component of the front screen appears, and the image quality is extremely degraded.

For example, when a VHSHt Fi audio signal is recorded and played back on a magnetic tape with residual magnetism, the frequency between the carrier frequencies (1.3 MHz and 1.7 MHl) of the HiFi audio signal will be distorted due to harmonic distortion. These components are generated and cause significant interference to the low-frequency converted chroma signal, appearing as striped beats of color on the screen, resulting in an unsightly screen.

[Problems to be Solved by the Invention] The current drive circuit for the erasing head of the conventional magnetic recording/reproducing device is configured as follows. Distortion occurs in the current waveform and remains on the erased magnetic tape. 4. Magnetism is generated and the image quality is severely degraded.

The present invention was made to eliminate the above-mentioned interpolation, and an object of the present invention is to provide a magnetic recording and reproducing apparatus that can cancel the residual magnetism of a magnetic tape.

[Means for Solving the Problems 1] The magnetic recording/reproducing apparatus according to the present invention is characterized in that it is provided with a means for canceling a low frequency or direct current component contained in an erasing current applied to an erasing head.

[Function] The means for reducing or canceling the DC component included in the erase current in the present invention reduces or cancels the DC component of the erase current input to the erase head 2, thereby reducing the residual magnetism of the erased magnetic tape. Reduce or eliminate. Therefore, when recording and reproducing are performed using this magnetic tape, defects such as beat stripes do not occur on the playback screen.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1st
In the figure, the same symbols as in Figure 3 indicate the same components, (2B) and (27) are DC power supplies with different polarities, one of which is selected by a switch (28), and the output voltage is controlled by a variable resistor. capacitor (1
9) and the erasing head (20), and (22) to (25) constitute a DC bias component canceling means (60).

Next, the operation of the above configuration will be explained.

DC power supply (2B), (2?) is switch (28)
The direction of the current selected by the controller and which causes the direct current to flow through the erase head (20) through the variable resistor (2B) can be changed by switching the switch (28).

This DC current makes it possible to cancel the DC bias component (24) shown in FIG. 4(C). The variable resistor (29) is used to finely adjust the magnitude of the canceling direct current.

Note that since the DC bias component (24) has a substantially constant value depending on the device, the DC bias component canceling means (60)
may be composed of a DC power source with one polarity that cancels out this DC bias component (24), and a series body of a fixed resistor that determines the current value.

Moreover, FIG. 2 is a diagram showing another embodiment, in which an inductor (3
0) is inserted between the capacitor (13) and the erasing head (20), and a capacitor (31) is connected between the connection point between the inductor (30) and the erasing head (20) and the ground. The inductor (30) and capacitor (31) in this example constitute a low-pass filter (70),
Only the fundamental wave component of the erasing current supplied to the erasing head (20) passes through and acts to attenuate second and higher harmonics.Therefore, the erasing current supplied to the erasing head (20) has no harmonic distortion. becomes a sufficiently suppressed waveform and the DC bias component (24) is removed, so the residual magnetism can be reduced to a negligible level.

[Effects of the Invention] As described above, according to the present invention, since a means for reducing or canceling the DC bias component included in the erase current is provided, the residual magnetism of the erased magnetic tape is reduced or eliminated. Thus, a magnetic recording and reproducing device is obtained in which no beat component appears on the screen during recording session reproduction.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment according to the present invention, FIG. 2 is a circuit diagram showing main parts of another embodiment according to the present invention, FIG. 3 is a diagram showing a conventional current drive circuit for an erase head, and FIG. FIG. 4 is a diagram for explaining how residual magnetism is generated on the magnetic tape during erasing due to the DC bias component included in the erasing current. (1)...Oscillation circuit, (20)...Erasing head,
(40)...Phase division amplifier, (50)...Push-pull power amplifier, (80)...DC bias component canceling means, (70)...Low pass filter. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) A magnetic recording/reproducing device characterized by comprising means for reducing or canceling the DC component of the AC erase current supplied to the erase head.