JPH039521B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION This invention relates to an erase circuit including a rotary erase head that selectively supplies erase current to a plurality of rotary erase heads using a single channel transmission path.

[Technical background of the invention and its problems]

In magnetic recording and reproducing devices such as VTRs and digital audio tapes that use a rotating head mechanism, a rotary transformer is generally used to electrically connect the rotating head to a stationary electronic circuit. This rotary transformer has a coil winding groove cut into a flat (or coaxial) magnetic core so that the fixed side and rotating side coils face each other, and the coil is attached to the coil. It is used to transmit signals. The same number of rotary transformers as rotary heads are used.

On the other hand, the rotary head installed on the rotary drum is not only a head for recording and reproducing video signals, but also a rotary head for erasing video signals.
Hereinafter referred to as FE head. ) has high utility value by improving the quality of the connecting part during flat recording.
It can also be effectively used when erasing only a portion of a track recorded diagonally on a tape with a rotating head (immediately afterwards recorded with a video head), such as the PCM recording area in .

Conventionally, in the case of a magnetic recording/reproducing device using such an FE head, when a plurality of these FE heads are installed on a rotating drum and used selectively, it is necessary to prepare a rotary transformer channel for each FE head. It was hot.

Here, multiple FE heads are required in the following cases.

When the track pitches are different, such as in standard and long-time modes, or when recording with the tape running direction reversed from normal, the above cases correspond to each track pitch.
A head with the width of the FE head is used, and in the above case, another FE head with the head installation height set for running in the opposite direction is provided.

In addition, in both of the above cases, the mounting position on the rotating drum (angle with respect to the video head) can be arbitrarily determined in terms of design, and the multiple FE heads may be placed in different locations (for example, 180 degrees opposite each other).
The so-called double gap structure may be provided at one predetermined location.

FIG. 3 shows a typical conventional example of an erasing circuit equipped with two rotary erasing heads, where 1 is an oscillation circuit, 3,
3' is a rotary transformer, 4 and 6 are a pair of FE heads, 5 and 7 are capacitors of approximately the same capacity connected in parallel to each of the FE heads 4 and 6, and 8 is the erase current of the oscillation circuit 1 that is connected to the FE heads 4 and 6. This is a changeover switch that selectively switches to 6.

Since a conventional magnetic recording/reproducing device equipped with an FE head is constructed as described above, for example, three to four rotating heads are used as video heads,
If two FE heads are used, 5 to 6 channels of transmission lines are required, so the same number of rotary transformers are also required, which has the disadvantage that it is difficult to secure the number of channels for a small rotating drum such as an 8mm VTR. had.

[Purpose of the invention]

This invention was made in order to eliminate the drawbacks of the conventional method using multiple FE heads as described above.
Enables selective supply of erase current to the FE head,
The purpose is to provide an eraser circuit for the FE head with a simple configuration.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention connects a plurality of FE heads each having a capacitor connected in parallel to an oscillator whose oscillation frequency can be switched through a single channel transmission line connected in series, and which switches the oscillation frequency according to the oscillation frequency of the oscillator. It is configured to selectively supply erase current to the FE head.

〔Example〕

Hereinafter, an embodiment of the present invention will be described based on FIGS. 1 and 2, in which parts corresponding to the conventional one shown in FIG. 3 are given the same reference numerals.

A rotating drum (not shown) has an FE head 4 and an FE head connected to parallel resonant capacitors 5 and 7, respectively.
A head 6 is attached, and the inductance of the FE heads 4 and 6 and the capacitance of the capacitors 5 and 7 are set so that their resonance frequencies are different.

These parallel resonant circuits are connected in series and connected to the rotating side coil of the rotary transformer 3. An oscillator 1 as an erase current source is connected to the fixed coil of the rotary transformer, and the erase current is supplied through a single channel transmission path. A changeover switch 2 is connected to the oscillator 1 to change its frequency.

The different resonance frequencies f and f caused by the respective FE heads 4 and 6 and the parallel capacitors 5 and 7 are not equal, and the oscillation circuit 1 is configured to switch and output the resonance frequencies f and f of the resonance circuit. ing.

To explain the operation of the eraser circuit configured in this way, the FE head 4 and the parallel capacitor 5
Similarly, let f be the resonance frequency of the FE head 6. If the inductance L of FE heads 4 and 6, the equivalent series resistance R of the heads (a component caused by core loss and winding resistance), and the required amount of parallel resonant capacitor are c, then the resonant frequency f is given by the following formula. .

Here, if the resistance R is sufficiently small, approximately f=1/2π√Lc.

Two sets of resonant circuits are formed in the FE heads 4 and 6, and L or c or both L and c are set to different values so that the respective resonant frequencies f and f are different. For example f=8MHz, f=4MHz
Assuming that L is equal, capacitor 7 should have a capacity four times that of capacitor 5.

These two sets are connected in series, and the frequency of the erase current supplied from the rotary transformer 3 is set to f or f.
Switch to either one and apply.

For example, when a resonance frequency f of 8 MHz is applied, the impedance on the FE head 4 side at the resonance frequency f is large because it is the resonance point, and due to the drive from the rotary transformer 3, the parallel resonance circuit of the FE head 4 and the capacitor 5 is The oscillating current increases, and the magnetic flux generated by the current causes the FE head 4 to perform an erasing operation.
At this time, since the FE head 6 side differs from the resonance frequency f, the oscillating current is small, and the FE head 4 does not generate enough magnetic flux to perform an erasing operation.

When the parallel resonant circuit is excited at the resonant frequency in this manner, the current supplied from the outside for excitation is small compared to the current flowing through the resonance L and c. The value can be reduced as the resistance R is smaller (the loss of the resonant circuit is smaller).

Moreover, in this example, since the resonant frequency f is lower than the resonant frequency f, the resonant circuit of the FE head 6 and the capacitor 7 becomes capacitive with respect to the excitation current of the resonant frequency f. Therefore, the excitation current mainly flows through the capacitor 7.

Conversely, when applying the resonant frequency f of 4MHz, the FE head 6 performs an erasing operation due to the resonant current between the FE head 6 and the capacitor 7.
The current flowing through the FE head 4 is only the excitation current to the resonant circuit on the FE head 6 side, and therefore has a value that does not lead to the erase operation.

Next, an advanced embodiment of the present invention will be explained based on FIG.

The above embodiment simply has a parallel resonant circuit.
Although the FE heads were configured in series, the excitation current for other low-resonance circuits that flows to the side with a higher resonant frequency flows to the L side of the circuit set to a higher resonant frequency, that is, to the head side, so from the perspective of separation. It may be disadvantageous.

If a series resonant circuit corresponding to a low resonant frequency is further connected in parallel to such a parallel resonant circuit having a high resonant frequency f, the higher excitation current can be bypassed, thereby improving the degree of separation. Such a circuit configuration is shown in FIG. 2(a). In Fig. 2(a), a series resonant circuit consisting of an inductance 9 and a capacitor 10 is connected in parallel to the FE head 4, and the resonant frequency of this series resonant circuit is set to the parallel resonant frequency of the FE head 6 and capacitor 7. They are configured so that they are equal (however, f>f).

Furthermore, if the losses of the FE heads 4, 6 themselves are large and the equivalent series resistance R is large, the sharpness of the resonance will be lost and the separation will be poor. to improve this
Good quality for FE heads (small R, generally Q
By connecting inductors in series (with a large
The resonance can be sharpened and thus the isolation can be improved. Such a circuit configuration is shown in FIG. 2(b).
In FIG. 2(b), inductances 11 and 12 are connected in series to FE heads 4 and 6, respectively.

Further, although a rotary transformer is used for the channel transmission path, the connection between the rotating side and the stationary side of the rotating drum may be a slip ring type that makes mechanical contact.

〔Effect of the invention〕

As explained above, according to the present invention, parallel resonant circuits each having a capacitor in parallel are connected in series to each of a plurality of FE heads, and each parallel resonant frequency is set to be unequal. By selecting the frequency of the erase excitation current supplied to the series circuit of connected FE heads, it is possible to control the erase current to flow only to a specific head among multiple FE heads, simplifying the channel transmission path. can be measured.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIGS. 2a and 2b are main circuit diagrams showing another embodiment of the invention, and FIG. 3 is a block diagram showing a conventional example. 1... Oscillator, 2... Selector switch, 3... Rotary transformer, 4, 6... FE head, 5,
7... Capacitor.

Claims (1)

[Scope of Claims] 1. A magnetic recording/reproducing device comprising a plurality of rotating erasing heads provided on a rotating drum and an oscillator supplying an erasing current to the rotating erasing heads, each of which has a capacitor connected in parallel. forming resonant circuits with different resonant frequencies and connected in series with each other and connected to the oscillator by a single channel transmission line, and the oscillator has a plurality of oscillation frequencies equal to the resonant frequencies of the resonant circuit; An erasing circuit equipped with a rotating erasing head, characterized in that it is configured to selectively supply erasing current to the rotating erasing head according to the plurality of oscillation frequencies.