JPS5954005A - Information recording circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an information recording circuit, and is applied to, for example, a magnetic recording device such as a video tape recorder (VTR).

[Background technology and its problems]

In this type of magnetic recording apparatus, such as a VTR, an information recording circuit as shown in FIG. 1 has conventionally been used to record information on a magnetic tape as a recording medium using a magnetic head. In FIG. 1, (1) is a luminance (rT number amplification circuit), (2) is a color signal amplification circuit, and the amplified luminance signal S1
and chroma signal S2 are mixed in a mixing circuit (3) and given to a recording amplifier circuit (4). Recording amplification circuit (4
) is the output signal current of the load resistor (5
) and (6) to the magnetic head circuit (7), and the secondary winding (
Video head (9B) consisting of a magnetic head connected to
) is given to Note that (10) is a DC drive power source.

In the information recording circuit shown in FIG. 1, an optimum recording current is applied to the video head (9) in order to record the video signal from the video head (9) onto the magnetic tape under the best conditions, and thus the information is reproduced from the magnetic tape. This is to prevent overmodulation or deterioration of image quality in the video signal. Therefore, conventionally, gain setting resistors (1
1) and (12) are provided, and the gain setting resistors (11) and (12) are adjusted so that the current or voltage on the primary side of the rotary transformer (8) becomes a predetermined set value. .

The setting value for the primary side current or voltage of this rotary transformer (8) is determined according to the various constants of the rotary transformer (8) 7':C video head (9) adopted in the model of the magnetic recording device. Therefore, when manufacturing magnetic recording devices of the same model, the gain setting resistors (11) and (12) are adjusted so that they all meet the same reference setting value.

However, doing so has the following disadvantages.

First, since the impedance of each video head varies, it is difficult in practice to adjust the current that actually flows through the video head so that it exactly matches the optimum recording current value. Incidentally, even if a rotary transformer (
Even if it is possible to accurately set the gain setting resistors (11) and (12) so that the primary current or voltage in step 8) matches the reference setting value, the impedance of the video head (9) currently being used may If there is a variation from the standard design value, the current actually flowing through the video head (9) will not match the optimum recording current, and the configuration shown in FIG. 1 cannot correct this mismatch.

Secondly, even if the adjustment at the time of manufacture matches the optimum recording current value, the gap depth may increase due to wear of the video head (9) while the magnetic recording device is in use. If the impedance of the video head (9) changes due to changes in the
There is a disadvantage that this change cannot be corrected by the configuration shown in FIG. If the impedance of the video head (9) changes during use in this way, the optimal recording current will no longer flow through the video head (9), and as a result, the recorded video signal will drop to a recording level that causes deterioration in image quality. It deteriorates to.

[Purpose of the invention]

The present invention has been made in consideration of the above points, and even if the impedance of the employed magnetic head varies from the standard design value or the impedance of the magnetic head changes during use of the magnetic recording device, This paper attempts to propose an information recording circuit that can always maintain the recording current that actually flows through the magnetic head at an optimum recording current value.

[Summary of the invention]

In order to achieve this object, the present invention obtains a detection signal corresponding to the value of the current and voltage supplied to the magnetic head circuit, and based on this detection signal, determines whether the current and voltage are adjusted to flow the optimum recording current to the magnetic head. The current and voltage gains are then adjusted to the required values.

〔Example〕

Below, one embodiment of the present invention will be described in detail with reference to the drawings.
In FIG. 2, in which parts corresponding to those shown in the figure are given the same reference numerals, the output signal current 1 of the recording amplifier circuit (4) is passed through the signal detection resistor (15) with a sufficiently small resistance value to the load g 6
), and this signal detection resistor (15)
Voltages (1) and (2) at connection points P1 and P2 at both ends of the impedance change detection circuit (16) are applied to the impedance change detection circuit (16).

The impedance change detection circuit (16) receives the voltages ■□ and ■2 at the connection points P1 and P2 through the neutral bus filters (17) and (18), respectively, to the inverting input terminal and non-inverting input terminal of the comparison circuit (19). The voltage output (3) of the difference between these voltages is converted into DC in a diode-configured DC conversion circuit (1), and is applied to the addition input terminal of the subtraction circuit (21).

Here, the difference output ■3 of the comparator circuit (21) is the voltage difference between the connection points P1 and 22, so it is passed through the resistor (]5) to the primary circuit of the rotary transformer (8) (primary winding # (8A)) and the load. This value corresponds to the current value flowing through the resistor (6) in parallel circuit.

In addition to this, the impedance change detection circuit (16) filters the voltage (2) at the connection point P2 through a bypass filter (23).

It is supplied to a diode-configured DC converting circuit (25) through an amplifier circuit (24) in series, and this DC converting circuit (25
) is converted into direct current and applied to the subtraction input terminal of the subtraction circuit (21). Here, the output voltage ■4 of the DC conversion circuit (25) becomes a value corresponding to the value obtained by multiplying the average voltage level value of the voltage ■2 at the connection point P2 by the amplification degree of the amplifier circuit (24), and therefore, the output voltage ■4 at the connection point P2 When the voltage changes in the direction of rising or falling from the reference setting value, the output of the direct current converting circuit (25) changes at the ratio of the amplification degree of the amplifier circuit (24).

The subtraction output voltage ■5 of the subtraction circuit (21) is the comparison circuit (26
) as a comparison input, and the error voltage ■6 with respect to the output voltage ■8 of the reference voltage source (27) at the reference input terminal is applied as the detection output signal of the impedance change detection circuit (16) to the luminance signal gain adjustment circuit (28). ) and the color signal gain adjustment circuit (29). This gain adjustment circuit (28)
and (2) gives the gain adjustment signals S3 and S4 of the magnitude corresponding to the error voltage v6 to the luminance signal amplification circuit (1) and the chrominance signal amplification circuit (2), and adjusts the gain so that the error voltage v6 becomes O. Adjust to.

In this embodiment, the adjustment circuits (28) and (29) are configured to be able to adjust the gains of the luminance signal S1 and color signal S2 at predetermined relative ratios.

In this embodiment, bypass filters (17), (1
8) and (23) are configured to pass the vertical synchronization signal among the output signals of the recording amplifier circuit (4), and thus utilize the vertical synchronization signal appearing at both ends of the detection resistor (15) as a pilot signal. It is possible to obtain a detection signal that accurately responds to changes in the current and voltage supplied to the magnetic head circuit (7).

In the configuration shown in FIG. 2, the impedance Z of the video head (9) is the design standard value Z as shown in FIG.

And this design standard value Z. the smaller value ZL and the design standard value Z. When the recording current is varied to a larger value ZH, the recording current at the connection point P3 between the secondary winding (8B) of the rotary transformer (8) and the video head (9). When set to the optimum recording current value, the DC conversion circuits (20) and (25
) are on the straight lines 3 and 4, respectively, as shown in FIG.
The relationship is directly proportional to .

This means that the impedance Z of the video head (9) is the design standard value Z. When the voltage varies from ZL or ZH, the primary current of the rotary transformer (8) (the value of detection signal ■3 corresponds to this) and the primary voltage (the value of detection signal ■4 corresponds to this) This means that the secondary current of the rotary transformer (8), and hence the recording current of the video head (9), can always be maintained at the optimum recording current value if it can be changed along the straight lines (3) and (4). In other words, under the condition that the recording current is always maintained at the optimum recording current value, the change in the impedance Z of the video head (9) from the standard design value Zo is controlled by the current supplied to the primary side of the rotary transformer (8). It turns out that compensation can be achieved by changing the voltage and voltage.

To compensate for this, the impedance change detection circuit (16
) has a positive slope with respect to the change in impedance Z, as shown by straight line ■3 in Figure 4, by applying the current detection signal ■3 of the DC conversion circuit (20) to the addition input terminal of the subtraction circuit (21). By applying the voltage detection signal V4 of the DC conversion circuit (25) to the subtraction input terminal of the subtraction circuit (21), the slope is reversed as shown by straight line 4 in Fig. 4. The impedance Z is applied so as to vary with a negative slope with respect to the change in impedance Z, thereby obtaining a subtracted output 5 which can be expressed as 5-3+4 at the output terminal of the subtraction circuit (21). Here, the amplifier circuit (24
), the value of the subtracted output signal ■5 will be determined by the impedance Z as shown by the straight line V5 in Figure 4.
is the standard design value Z. It is possible to set the constant value ■o approximately equal to the value of the subtracted output signal ■5 in the case of .

In practice, the reference voltage of the comparator circuit (26) is a constant value.
. As a result, when the value of the subtracted output signal ■5 is smaller than the constant value VR (= Vc), the error signal ■6
is generated and the gain adjustment circuits (28) and (29) are operated to change the gains of the luminance signal amplification circuit (1) and the color signal amplification circuit (2) so that the value of the error signal V6 becomes 0.

When the magnetic recording device was manufactured, the impedance Z of the video head (9) was the standard design value Z. If the value of the output signal v5 (-v3+■4) of the subtraction circuit (21) is equal to the reference voltage V8 (=Vo), the error output v6 of the comparison circuit (26) becomes O, and the gain adjustment The circuits (28) and (29) operate the luminance signal amplification circuit (1) and the color signal amplification circuit (2) with their current gains,
In this way, the current and voltage that cause the optimum recording current to flow through the video head (9) are supplied to the primary side of the rotary transformer (8).

In this state, if the impedance of the video head (9) increases due to the use of a magnetic recording device, the current flowing into the rotary transformer (8) will decrease, so the current detection signal 3 of the DC conversion circuit (20) will decrease. Become,
In response to this, an error signal ■6 is generated and the gain adjustment circuit (2
8) and (29) are adjusted to increase the gains of the amplifier circuits (1) and (2). In this way, the current and voltage supplied to the rotary transformer (8) rise, and the output signal V5 of the subtractor circuit (21) reaches the constant value (2) in FIG. It stabilizes when it becomes.

Similarly, when the impedance 2 of the video head (9) is set low, the output signal ■5 of the subtraction circuit (21) is
Constant value V in the figure. It stabilizes when it becomes.

In this stable state, changes in the recording current caused by changes in the impedance of the video head (9) can be returned to the optimum recording current value by correcting the supply current and voltage on the primary side of the rotary transformer (8).

Also, the video head (9) used in the manufacture of magnetic recording devices.
Due to variations in the impedance Z of
), the current and voltage supplied to the primary side of the rotary transformer (8) will be constant values (■) in Fig. 4. If they match, the error output ■6 of the comparator circuit (26) becomes O, and a stable state is achieved; however, if they do not match, the error output ■6 is generated in the same way as in the above case, and the gain adjustment circuit ( 28
) and (29) correct the current and voltage of the rotary transformer (8) so that the error output v6 becomes O, thereby achieving the constant value ■ in FIG. return to a stable state consistent with

Therefore, in this case as well, the recording current of the video head (9) can always be maintained at the optimum recording current value.

In the above description, the impedance change detection circuit (16
), the current detection signal (3) and the voltage detection signal (V4) are subtracted by the subtraction circuit (21), and the gain adjustment signals S3 and S4 are obtained based on the subtraction result, but instead of this,
The impedance may be calculated by a calculation circuit based on the current detection signal (3) and the voltage detection signal (4), and the gain adjustment signals S3 and S4 may be obtained in accordance with changes in the calculation results.

〔Effect of the invention〕

As described above, according to the present invention, by supplying current and voltage to the magnetic head circuit so that the recording current always becomes the optimum recording current value, even if the gap depth changes due to variations or wear, It is possible to easily obtain an information recording circuit that can always record at the optimum recording current value even if the impedance of the magnetic head changes due to, for example, changes in the impedance of the magnetic head. In this way, since the current and voltage gains can be adjusted automatically, the adjustment of the magnetic recording device can be further simplified.

[Brief explanation of drawings]

Figure 1 is a route connection diagram showing a conventional information recording circuit;
The figure is a line connection diagram showing one embodiment of the information recording circuit according to the present invention, and FIGS. 3 and 4 are characteristic curve diagrams for explaining its operation. (1), (2)... Luminance signal two-color signal amplification circuit,
(3)... Mixing circuit, (4)... Recording amplifier circuit, (
7)...Magnetic head circuit, (8)...Rotary transformer, (9)...Video head, (16)...Impedance change detection circuit, (17), (18)
. (23)...Bypass filter, (19)...Comparator, (20). (25)...DC conversion circuit, (21)...Subtraction circuit,
(26)...Comparison circuit, (28), (29)...
・Gain adjustment circuit. Applicant's agent: Takahashi 5 Hikaru No. 2 Figure L J
J Haya 3 Figure 4 Figure zL ′Z0 ZH2 25-

Claims (1)

[Claims] A detection signal that adjusts the current and voltage values supplied to the magnetic head circuit is obtained. Based on this detection signal, a correction signal necessary to flow an optimum recording current to the magnetic head in accordance with a change in the impedance of the magnetic head is generated. An information recording circuit comprising: a circuit for detecting a change in impedance that occurs; and a gain adjustment circuit for adjusting the gain of the current and voltage supplied to the magnetic head based on the correction signal.