JPH0423322B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording/reproducing apparatus using a video head with a small number of windings. A home video tape recorder (hereinafter referred to as VTR) is an example of a magnetic recording and reproducing device.
The video head used for this requires 15 to 20 turns of winding, and having a large number of windings has been the key to improving video head productivity. FIG. 1 shows an example of the structure of a video head. As you can see from the diagram, the winding of the video head involves passing the copper wire 2 through the window 3 of the head, which looks like the eye of a needle, 20 times, which not only takes time but is also painful for the operator. It was hot at work. Below is the conventional
Using VTR as an example, why is the number of windings in a video head different?
Explain what was chosen for turn 20. FIG. 2 is a block diagram showing the outline of a two-head helical scan type VTR. First, recording will be explained. The video signal applied to the input terminal 12 passes through the recording circuit 10, is converted into a recording signal, is amplified by the write amplifier 7, and flows to the video heads 1, 1' as a recording current. The number of windings in the video head 1 in FIG. 2 is 20 turns, and the inductance value is selected to be approximately 2 μH. The winding ratio of rotary transformers 5a and 5b is set to 1:2, and the number of windings on the primary side (head side) is 4 for 5a.
The number of windings on the secondary side (head amplifier side) is 8 turns for 5a and 6 turns for 5b. The output signal voltage of the write amplifier 7 required to flow the necessary recording current under the above conditions (P-P value)
is 3-4 Vpp for oxide tape. This value of 3 to 4 Vpp is an appropriate value considering that the power supply voltage of the write amplifier 7 is 9 to 12 V. That is, if the head impedance seen from the write amplifier 7 is lowered from the above level by reducing the number of windings in the heads 1 and 1' or by changing the winding ratio of the rotary transformers 5a and 5b, the recording current will increase and the power consumption will increase. Undesirable. On the other hand, if you increase the head impedance,
The output signal voltage of the write amplifier 7 increases, causing distortion in the signal waveform and causing characteristic deterioration. Next, the time of reproduction will be explained. video head 1
The signals read out by the rotary transformers 5a, 5
The head amplifiers 8a and 8b are stepped up at step b.
is input. The capacitors 9a and 9b are intended to resonate with the inductance value seen from the head amplifiers 8a and 8b, respectively, and the resonance frequency is selected near the highest carrier frequency of the reproduced FM signal. The selection of the above resonant frequency is based on the suppression of impedance noise and the head amplifiers 8a and 8b.
It also plays the role of noise matching for the video heads 1 and 1'. In other words, if the signal source impedance is lowered by reducing the number of windings in the head or by changing the winding ratio of the rotary transformer, there will be no problem in securing the above resonance characteristics, but the noise matching between the amplifiers 8a and 8b and the heads 1 and 1' will deteriorate. do. On the other hand, increasing the signal source impedance makes it easier to achieve the noise matching described above, but causes the problem that the resonance characteristics cannot be achieved. Since the above-mentioned resonance frequency is determined by the total capacitance of the head inductance, stray capacitance, amplifier input capacitance, and capacitance of capacitors 9a and 9b, if the head inductance becomes too large, capacitors 9a, 9b,
Even if the capacitance of 9b is minimized, the resonant frequency will not rise to the required frequency. Variable resistors 14a and 14b are used to set the amount of boost at the resonance frequency to a desired value, but they cause S/N deterioration. In FIG. 2, output signals 8a and 8b are input to a reproduced signal processing circuit 11, demodulated into a video signal, and a reproduced video signal is obtained at an output terminal 13. Next, the relationship between the primary inductance of the rotary transformer 5 and the inductance of the video head will be described. If the rotary transformer 5 has a coupling coefficient =
1, it is not necessary to have a specific relationship between the inductance of the rotary transformer and the head inductance. However, the rotary transformer 5 is connected to the air goat 2 as shown in FIG. 3B.
0, and the coupling coefficient (K) has a value around 0.95. When K≠1, the matching conditions for the inductance (Lh) of the video heads 1, 1' and the primary inductance (L _RP ) of the rotary transformer are as follows. The above equation is a condition where e ₀ /√ ₀ is the maximum, where L ₀ is the inductance seen from the secondary side of the rotary transformer 5 to the head side during reproduction, and e ₀ is the no-load output. That is, in the reproduced FM signal band (3 to 5 MHz in the case of VHS system), e ₀ /√ ₀ is the figure of merit. however

[Equation] means that e ₀ does not change and √ ₀ increases, and the disadvantages of this are a decrease in the resonant frequency and an increase in impedance noise. Therefore, in a system where the resonance frequency can be secured and the noise generated from the tape is greater than the impedance noise,

[Formula] would also be fine. Also, when focusing on reading out the chroma signal multiplexed in the lower frequency band of the FM signal, the signal source impedance in this frequency band is extremely small.
Can be ignored. Therefore, the figure of merit for the chroma signal is e ₀ itself, and it suffices if L _RP ≫Lh. Based on the above, current home VTRs use L _RP and
It is preferable to design Lh as shown in the following equation. γ = 1.0 to 1.5 If γ is too large, inductance L ₀ , stray capacitance, capacitors 9a, 9b, amplifiers 8a, 8b
The resonant frequency generated by the input capacitance of
It becomes difficult to ensure FM equalization characteristics. Therefore,
γ may be selected within a range where the resonance frequency is higher than the reproduced FM carrier frequency. However, in conventional VTRs, no effort has been made to reduce the number of windings in the head, and no consideration has been given to reducing _LRP , increasing K, or selecting a larger value γ. From the above, in a conventional VTR, the number of windings on the video head is 20 turns (Lh = 2μH), and the number of windings on the primary side of the rotary transformer is 3 turns or 4 turns (L _RP =
10μH~12μH, K=0.97) Rotary transformer winding ratio 1:2, signal voltage required for recording 3~4V _PP ,
A head amplifier with a noise matching impedance of 200Ω to 1KΩ was used. Once again, the problems with the conventional technology are summarized as (1)
The number of turns of the rotary transformer is 4 turns on the inside and 3 turns on the outside. (2) In order to match the above rotary transformer, the winding of the video head must be 20 mm.
It is necessary to make a turn. (3) Under the above conditions, the winding ratio of the rotary transformer is selected to be 1:2 so that the recording signal output does not become too large and the NF of the head amplifier does not deteriorate. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a helical scan type VTR that does not deteriorate in performance even when a head with a small number of windings is used. In the present invention, the number of head windings is reduced by setting the winding ratio of the rotary transformer to be greater than 1:2. The reduction in resonance frequency and deterioration in noise matching caused by this can be compensated for by eliminating the conventionally used trimmer capacitor for adjusting the resonance frequency and variable resistor for adjusting the boost amount, and using negative feedback damping instead. There is. Figures 3, 4 and 5 are diagrams showing an embodiment of the rotary transformer used in the present invention, Figures 6 and 7.
The figure shows the number of head windings versus head inductance and the number of head windings versus e ₀ /√
(head performance index), FIGS. 8 and 9 are block diagrams showing essential parts of an embodiment of the recording/reproducing apparatus used in the present invention. As a first embodiment, a case will be described in which the diameter of the rotary transformer 5 shown in FIG. 3 is approximately 45 mm, and the maximum diameter 18 of the winding wire is approximately 40 mm. In this case, L _RP in equation (2) is approximately 10 μH for 2 turns, and K
≒0.97. The primary winding of the rotary transformer is 2
If you choose γ = 1, L _h = 24μH, the number of head windings will be 22 turns, and γ = 1.5.
If you choose L _h = 1.6μH, the number of head windings will be 18 turns, whereas conventionally it was chosen to be 20 turns and 2.0μH. Therefore, if you want to reduce the number of head windings compared to the conventional one, you must either choose a large value of γ, or make the primary winding of the rotary transformer one turn to reduce _LRP . First, a case where the primary winding of the rotary transformer has one turn will be explained. In this case, L _RP is
If K=0.97, the head inductance L _h should be selected between 0.4 and 0.6 μH. (γ=1.0 to 1.5) From the graph of the number of head windings versus head inductance shown in FIG. 6, the number of head windings n _H is 8 to 10 turns. Therefore, there are three possible numbers of head windings: 8, 9, and 10 turns. A case will be described in which these three types of heads are implemented with the configurations shown in FIGS. 8 and 9. If n _H = 10 turns and n ₁ = 1 turn, the possible n ₂ is 4. The reason is that the above-mentioned resonant frequency cannot be set to the desired value unless the inductance seen from the preamplifier to the secondary side of the rotary transformer is equal to or slightly larger than the conventional value (2 μH x 4 = 8 μH). When n _H = 10 turns, n ₁ = 1, n ₂ = 4, the inductance seen from the preamplifier to the rotary transformer is 0.58 μH × (4/1) ² ≒ 9.3 μH, which is slightly larger than the conventional one, and the resonant frequency becomes difficult to secure. The present invention solves this problem by eliminating the trimmer capacitor for adjusting the resonance frequency.
That is, the capacitance of conventionally used trimmer capacitors varies within a range of about 20 _PF to 70 _PF due to the necessity of adjustment range. Therefore, by removing the trimmer capacitor, the above increase in inductance can be almost absorbed, and the resonant frequency and noise matching can be maintained as before. In the above case, the resonant capacitance is the sealed wire _20P F, capacitor _18P F, other and preamplifier input capacitance.
It consists of 70 _PF , ensuring a resonant frequency of approximately 5MHz. Therefore, capacitors 28a, 28b
By removing , the resonant frequency can be further increased by 10%. If n _H = 10 turns, n ₁ = 1, and n ₂ = 5, the inductance seen from the preamplifier to the rotary transformer is 0.58 x (5/1) ² = 14.5 μH, and to make the resonant frequency 5MHz, the resonant capacitance must be increased. It needs to be around 80 _PF . In order to achieve the resonant capacitance of 80 _P F as shown in FIG. 8, the capacitors 28a and 28b may be removed and the input capacitance (including stray capacitance) of the preamplifier may be lowered to 60 _P F or less. Current preamplifiers use about 9V as _Vcc , so the input capacitance is large, but if you lower _Vcc to about 6V or less, you can use an isoplanar transistor, etc. In this case, lower the input capacitance to 60 _P F or less. be able to. The configuration shown in FIG. 9 is suitable for achieving a resonant capacitance of 80 _PF . The feature of Fig. 9 is that the rotary transformer 5 and preamplifiers 8a and 8b are directly connected.
There is no shield wire. As a result, the shield line capacitance is removed, so even if a conventional preamplifier is used, a resonance point of 5MHz can be secured. In FIG. 9, reference numeral 32 indicates a substrate provided on the cylinder to which the video head 1 is attached;
indicates a different substrate from 32. 30 in Figure 9
Reference numeral 31 indicates an amplifier that switches the outputs of preamplifiers 8a and 8b, and 31 indicates a reproduction signal processing circuit. Next, the case where γ=1.2 and n _H =9 turns will be explained. In this case, L _h =0.49μH,
When n ₁ = 1, n ₂ = 5, the inductance looking from the preamplifier to the rotary transformer side is 12.3 μH + α, n ₁
= 1, n ₂ = 6 becomes 17.6μH + α (α is the inductance caused by increasing γ) and becomes 5MHz
To ensure the resonant frequency of the resonant capacitance _74P respectively
F, 52 _P F, and can be realized using the configurations shown in FIGS. 8 and 9, similar to when n _H =10 turns. When γ = 1.4 and n _H = 8 turns, L _h = 0.4μH
So, when n ₁ = 1, n ₂ = 5, the inductance looking from the preamplifier to the rotary transformer side is (10 +
β) μH, n ₁ = 1, n ₂ = 6 (14.4 + β) μH,
When n ₁ = 1 and n ₂ = 7, it becomes (19.6 + β) μH (β is the inductance caused by the further increase of γ, which is even larger than α and is about 1.5 μH when γ = 1.5). To ensure the resonant frequency, the resonant capacitances may be set to 84 _P F, 61 _P F, and 47 _P F, respectively. Next, compensation for the deterioration of the figure of merit shown in FIG. 7, which is a problem other than the resonance frequency, will be described. As can be seen from FIG. 7, the performance index of the head deteriorates as the number of head windings is reduced. e ₀ /√ _h indicates the ratio of head output (e ₀ ) to impedance noise (√ _h ), and in system design, consideration should be given to ensuring that equipment noise (impedance noise + amplifier noise) is sufficiently small compared to tape noise. must be done. Normally, the design is such that equipment noise is -6 dB or less compared to tape noise. In the conventional design, the number of head windings was set to 20 in the configuration shown in Figure 2.
By using a turn, the above-mentioned -6 dB or less is achieved. In the present invention, equipment noise is improved by about 2 to 3 dB by using feed pack damping. Therefore, if the head is combined with a preamplifier using feedback damping, there will be no problem even if its figure of merit e ₀ /√ _h decreases by 2 to 3 dB. If we allow 2 dB of deterioration in e ₀ /√ _h , the number of head windings can be reduced to 4 turns. e ₀ /
√ If we allow 3dB of deterioration in _h , we can reduce the head winding to 3 turns. The main reason why e ₀ /√ _h shown in FIG. 7 decreases as the number of head turns decreases is that the head inductance shown in FIG. 6 is not proportional to the square of the number of turns. 25 in FIG. 6 is a calculated value obtained assuming that the inductance is proportional to the square of the number of turns, and 24 in FIG. 6 is a measured value. The reason why the calculated value and the measured value do not match is due to the presence of stray inductance that occurs in the lead wire connecting the rotary transformer and the head. Therefore, the deterioration of e ₀ /√ _h due to head winding reduction is essential, and it is important to combine this with the reduction of amplifier noise by the above-mentioned feedback damping. Next, we will discuss solutions to the problems that arise when the number of windings in a rotary transformer is set to one turn. If the rotary transformer, which used to have 2 turns, is changed to 1 turn, the coupling coefficient will be K = 0.97→
0.95, the inductance becomes L _RP = 10μH → 2μH. Furthermore, it is extremely inefficient to make a one-turn loop using a thin wire and embed it in a rotary transformer, as in the conventional method. This is because even if a one-turn ring is formed into the groove shape of a rotary transformer, it will deform during the work and cannot be embedded in the groove. In the present invention, as shown in FIG. 4, 16 and 17, a method of making a one-turn coil is devised. 17 in Figure 4 is a one-turn coil,
It is characterized by a large cross-sectional area and a rectangular wire shape. The one-turn coil 17 can be easily produced by, for example, placing a thick round wire in a mold and pressing it. By adopting a one-turn coil with this shape, it is possible to improve the coupling coefficient K = 0.95 → 0.97 and the inductance L _RP = 2.0 → 2.5μH, and by pressing and forming a thick wire, the above-mentioned workability problem can be solved. Deformation during implantation can also be prevented. Next, a case will be explained in which the primary winding of the rotary transformer has two turns. In this case, if the number of head windings is to be reduced, γ should be made as large as possible within an allowable range. The maximum value of γ is γ≒1.5
If K=0.97, L _h =1.6 μH, n _H =18 turns, and n ₁ =2, n ₂ =5 are considered. In this case, the inductance seen from the preamplifier to the rotary transformer side is 1.6 x (5/2) ² + β = 11.5 μH, and to secure 5 MHz, the resonant capacitance should be 87 _P F, as shown in Figures 8 and 9. This can be achieved with a diagram. If the coupling coefficient of the rotary transformer is improved to K=0.98 and γ≈1.5, then L _h ≈1.3 μH and n _H =16 turns. In this case n ₁ = 2, n ₂ = 5
Or, if n ₁ = 2, n ₂ = 6, the inductance looking from the preamplifier to the rotary transformer side is 1.3×
(5/2) ² +β=9.6μH, 1.3×(6/2) ² +β=13.
7, and to secure 5MHz, the resonant capacitance must be 105 _P F,
73 _P F. When the primary winding of a rotary transformer has 2 turns, the head winding has 18 to 16 turns, which is a lower reduction rate than the conventional 20 turns. However, 20 turns is 18 turns.
By reducing the number of turns to ~16 turns, the workability of the head winding will be greatly improved. Further, in this case, there is no deterioration in the performance index shown in FIG. 7, and due to the effect of feedback damping, both performance and workability can be improved at the same time compared to the conventional method. As a second embodiment, a case will be described in which the diameter of the rotary transformer 5 shown in FIG. 3 is about 30 mm and the minimum diameter of the winding is about 15 mm. In this case, L _RP in equation (2) is approximately 12μH for 4 turns, and K≒
It becomes 0.97. If the primary winding of the rotary transformer has 4 turns, if γ=1 is selected, L _h =2.9μH, γ=
If you choose 1.5, L _h = 1.9 μH and the number of head windings is 25.
turn to 20 turns, and conventionally it is set to 20 turns. Conventionally, n _H = 20 turns, L _h = 2.0 μH, n ₁ =
4, n ₂ = 8, so the inductance when looking from the preamplifier to the rotary transformer side is
2.0×(8/4) ² +β=9.5μH (β≒1.5), and the resonant capacitance to secure 5MHz is 106 _PF . As a first embodiment of the present invention, a case will be described in which the primary winding of the rotary transformer has three turns and the secondary winding has eight turns. If γ≒1 is chosen, L _h = 1.6 μH, n _H = 18 turns, and the inductance looking from the preamplifier to the rotary transformer side is 1.6 × (8/3) ² = 11.4 μH, and the resonance to ensure 5 MHz. The capacity will be 88 _PF . If γ≒1.5 is selected, L _h = 1.1 μH, n _H = 15 turns, and the inductance looking from the preamplifier to the rotary transformer side is 1.1 μH × (8/3) ² + β = 9.3 μH (β
= 1.5μH), and the resonant capacitance to secure 5MHz is 108 _PF . Next, a case will be described in which the rotary transformer has a primary winding of 2 turns and a secondary winding of 8 turns. In this case, L _RP = 3 μH, so if you choose γ≒1, L _h = 0.8, n _H = 12 turns, and the inductance when looking from the preamplifier to the rotary transformer side is
0.8×(8/2) ² ×12.8μH, and the resonant capacitance to secure 5MHz is _78PF . If γ≒1.5 is chosen, L _h = 0.48 μH, n _H = 9 turns, and the inductance when looking from the preamplifier to the rotary transformer side is 0.48 × (8/2) ² + β = 9.2 μH, and the resonance to ensure 5 MHz. The capacity will be 110 _PF . Next, a case will be described in which the primary winding of the rotary transformer has one turn and the secondary winding has eight turns. In this case, L _RP =0.78μH, so if you choose γ≒1, L _h =0.175μH, n _H =5, and the inductance when looking from the preamplifier to the rotary transformer side is
0.175×8 ² =11.2 μH, and the resonant capacitance to secure 5 MHz is 90 _P F. If we choose γ≒1.5, L _h =0.12μH, n _H =4,
The inductance seen from the preamplifier to the rotary transformer side is 0.12 x 8 ² + β = 9.2 μH, and the resonant capacitance to ensure 5 MHz is 110 _P F. Next, a case where the rotary transformer has a primary winding of 3 turns and a secondary winding of 9 turns will be described. If γ≒1 is selected, L _h = 1.6 μH, n _H = 18 turns, and the inductance (hereinafter referred to as resonant inductance) looking from the preamplifier to the rotary transformer side is 1.6 × × (9/3) ² = 14.4 μH, 5 MHz. The resonant capacitance to ensure this is 70 _PF . If you choose γ≒1.5, L _h = 1.1μH, n _H = 15, and the inductance looking from the preamplifier to the rotary transformer side is 1.1
×(9/3) ² + β = 11.4μH, and the resonant capacitance to secure 5MHz is _88PF . Next, we will explain the case where the primary winding of the rotary transformer is 3 turns and the secondary winding is 10 turns.If γ≒1, L _h = 1.6 μH, n _H = 18, and the resonant inductance is 1.6 × (10/3) ² = 17.8μH, and the resonant capacitance to secure 5MHz is 56 _PF . If γ≒1.5 is selected, L _h =1.1 μH, n _H =15, and the resonant inductance is 1.1 × (10/3) ² + β = 13.7 μH, and the resonant capacitance is 73 _P F.

【table】

[Table] Table 1 summarizes the various cases mentioned above. To summarize the points of the present invention again, (1) the winding ratio of the rotary transformer is 2
Make it bigger. Specifically, as shown in Table 1
It can be selected from 2.5 to 10.0. (2) By (1), the number of windings in the video head is reduced to 4 to 18 turns, improving the productivity of the head. (3) The increase in equipment noise, which is a side effect of (2), can be reduced by feedback damping.
The increase in resonant inductance is compensated for by reducing the resonant capacitance by using a trimmer capacitor or a fixed capacitor, or by removing the shield wire, respectively. (4) Furthermore, if noise matching between the video head and the rotary transformer is required, select the number of windings in the head within a range where γ is 1.5 or less and the desired resonance frequency can be secured. As described above, by using the present invention, the number of windings in a video head can be reduced from the conventional 15 to 20 turns to 3 to 16 turns.
Turns can be reduced and head productivity can be greatly improved.

[Brief explanation of drawings]

Figure 1 is a plan view showing an example of the structure of a video head, and Figure 2 is a conventional two-head helical scan type head.
3A and 3B are plan views and sectional views showing an example of the configuration of a rotary transformer, and FIG. 4 is a block diagram showing the main parts of the recording and reproducing system of a VTR. FIG. 5 is a cross-sectional view showing the main part of an example of a rotary transformer with a two-turn primary winding used in the present invention, and FIG. 6 shows the number of head windings and A characteristic diagram showing the relationship between inductance, Figure 7 is a characteristic diagram showing the relationship between the number of head windings and the performance index of the head, and Figure 8 is an example of the main part of the recording and reproducing system of the two-head helical scan VTR of the present invention. FIG. 9 is a block diagram showing another example of the essential parts of the recording and reproducing system of a two-head helical scan VTR according to the present invention. 1...Video head, 5...Rotary transformer, 1
6, 17... Primary winding of rotary transformer, 21,
22... Secondary winding of rotary transformer, 18... Maximum diameter of rotary transformer winding, 19... Minimum diameter of rotary transformer winding, 27... Shield wire, 29
...Feedback resistor for feedback damping.

Claims (1)

[Claims] 1. A magnetic head for reproducing information signals recorded on a magnetic tape, a primary winding connected to the magnetic head, and a secondary winding disposed opposite the primary winding. It consists of a rotary transformer, a preamplifier connected to the secondary winding of the rotary transformer, and a negative feedback means provided between the input and output of the preamplifier for feedback damping the resonance occurring at the input section of the preamplifier, A playback device for a helical scan type video tape recorder, characterized in that the primary winding of the rotary transformer is formed of a one-turn rectangular wire, and the number of windings of the rotary transformer is selected to be larger than two. 2. A playback device for a helical scan video tape recorder according to claim 1, wherein the secondary winding is formed by a winding having a plurality of turns and having a round cross section.