JPH0438043B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a digital signal recording device suitable for application to digital VTRs and the like.

BACKGROUND ART AND PROBLEMS Saturated recording is generally used for digital data recording where the linear packing density of recording is relatively low. In this case, the recording circuit is configured to simply turn on and off the current flowing to the recording head by switching, and erasing is often done by simply applying a direct current magnetic field to the tape.

In such a case, if a channel code with less direct current or low frequency components is used during recording, overwriting can be performed without impairing the error rate. AC erasure is mainly used in data recorders that require higher linear density to improve the S/N ratio, but compared to the previous example, it not only requires a special erasure circuit but also has the disadvantage of increased power consumption. There is also.

To increase the data rate itself with longitudinal recording,
A method of performing several parallel reproductions is used in the case of data recorders, but a method using a rotating head is a method that can dramatically increase the data rate.

This method uses multiple heads serially (and in parallel) to record and reproduce data in bursts, so it is necessary to consider temporal discontinuities that occur at the joints between bursts. Furthermore, since a rotating body (rotating drum) is used, there are restrictions on signal transmission methods and power transmission when an electronic circuit is provided inside the rotating body. Due to these circumstances, magnetic recording systems using rotating heads are limited to some special data recorders or VTRs that mainly use FM modulation.

In recent years, various studies have been conducted on so-called digital VTRs, which record and reproduce digitized video signals as digital signals through appropriate channel coding. Digital VTRs have a high recording rate (200 Mb/sec), and in order to avoid unnecessarily increasing tape consumption, an extremely high-density magnetic recording method is required.
Research is currently being conducted primarily using rotating head methods.

Due to the above-mentioned limitations in channel coding for digital VTRs, coding without DC components is desirable, and codes with no DC components and few low-frequency components may also be overlapping. Since then, a lot of research has been going on.
However, at present, ideal channel coding has not yet been developed, and the ^M2 code (Miller Squared Code), which has no DC component and can be overwritten, is not necessarily suitable for all purposes. It is not suitable for In order to perform electronic editing using other codes that have problems with overwriting, it is necessary to perform partial erasure before re-recording the part of the tape that needs to be rewritten, and the erase head and recording If the gap positions of the heads are far apart, it is necessary to accurately control the on/off timing of energization to the coils of each head. On the other hand, in the rotary head method, the recording and erasing signals have conventionally been transmitted by power via a rotary transformer, so even if digital recording is performed, erasing is performed using the AC erasing method, and recording is performed using a recording method that does not have a DC component. It was limited.

Now, if you use a rotary transformer to transmit power, send power into the rotating drum using a power generation circuit and rectify it, or directly send direct current using a slip ring, it is possible to send power into the rotating drum. It is possible to send power. In such a case, it becomes possible to provide an electronic circuit for recording or reproducing within the rotating drum. When an electronic circuit is installed in a rotating drum, there are two methods: using relays or electronic switches for recording and playback to switch heads, rotary transformers, etc. for common use, and using dedicated heads and rotary transformers for each. Conceivable. When using the former type of relay, there are problems mainly due to the acceleration (G) that occurs when the rotating drum rotates and reliability, while when using an electronic switch, there are mainly problems such as loss and crosstalk in the circuit. However, none of them have reached a practical state with current technology.

In the latter case, the electrical characteristics are good, but the number of heads and rotary transformers is doubled. In addition, when performing the partial erasure mentioned above, the head,
Not only does the number of rotary transformers increase, but when performing AC erasure, a large high-frequency current is required for the erasing current, which may cause crosstalk to other circuits (such as a head amplifier for simultaneous reproduction).
It is difficult to make a practical product due to problems such as increased power consumption within the rotating drum.

OBJECTS OF THE INVENTION The present invention aims to provide a digital signal recording apparatus that can commonly control the operation timing of a recording head and an erasing head, and can perform overwriting regardless of channel coding.

Summary of the Invention A digital signal recording device according to the present invention includes a first coil wound around an erasing head and having one end connected to one pole side of a drive power supply, and a recording head disposed near the erasing head. A second coil is wound around the coil and the other end of the first coil is connected to the midpoint, one and the other winding ends are separated by the midpoint of the second coil, and the other end of the drive power source is connected to the second coil. The coil drive means selectively drives the pole side with the same current value at a constant current depending on the logic level of the digital recording signal.

Embodiment An embodiment of the present invention will be described below with reference to FIG. TP is a magnetic tape that runs to the left in the diagram. H _R and H _E are a recording head and an erasing head, respectively, which are arranged close to each other, and both can be fixed heads or rotating heads. W _R and W _E are the coils of the recording head H _R and erasing head H _E , respectively.

Power supply +B (12V) connects the coil through coil W _E
Connected to the midpoint of W _R. A smoothing capacitor C is connected between the power supply +B and the midpoint of the coil W _R.
The coil W _R consists of two parts (the respective windings are not necessarily equal) W _A and W _B , and one end of each of the parts W _A and W _B is connected to a differential transistor (npn type) Q _A of a differential amplifier DA, Q Connected to each collector of _B.

Each emitter of transistors Q _A and Q _B is a constant current source.
Grounded through a series circuit of IK and recording control switch SW. The switch SW is controlled by the recording control signal b (see FIG. 2), and the switch SW is turned on when the signal b is at the H (high) level and turned off when the signal b is at the L (low) level.

A digital recording signal a (see FIG. 2) from an input terminal t is supplied to a recording amplifier RA, and its positive-phase and negative-phase outputs are supplied to the bases of transistors Q _A and Q _B , respectively.

In FIG. 1, hr and he are the respective magnetic fields of the recording head _HR and erasing head _HE . The direction of the magnetic field he is constant, but the direction of the magnetic field hr depends on the digital recording signal a.
Flips in both directions depending on. Also, _IE is the erase head
The erase current flowing through the coil W _E of HE, I _A and I _B represent _the respective collector currents of transistors Q _A and Q _B , and their waveforms are shown in Fig. 2. Further, I _O is a constant current of a constant current source IK, and substantially I _O = I _A = I _B.

M in Figure 2 indicates the residual magnetic charge of the magnetic tape TP,
The upper side of the horizontal axis (zero line) is due to the erase current I _E , and the lower side is due to the current I _A , which are in opposite directions.

Let us explain the operation shown in Fig. 1 below. In the recording operation state, the switch SW is turned on, and depending on the state of the recording signal a, current flows through one of the transistors Q _A or Q _B , and does not flow through the other.

Now, when the recording signal a is at the logic level (H level in this case) indicating the truth value "1", the transistor Q _A
It is assumed that a current I _A flows through the transistor Q B and a current I _B flows through the transistor Q _B when the logic level indicates the truth value "0" (L level in this case). The currents I _A and I _B are supplied to the midpoint of the winding W _R of the recording head H _R , but since they are also supplied through the winding W _E of the erasing head H _E , their value is Equal to erase current _IE .

The capacitor C connected in parallel with the erase head H _E absorbs the slight fluctuations that occur when switching the currents I _A and I _B so that the fluctuations do not flow into the erase current I _E.

If recording is performed after performing such DC erasing, nonlinear distortion will generally occur because the tape TP is experiencing unidirectional DC magnetization. As a way to improve this, it may be possible to perform magnetization in the opposite direction again for neutralization, but in the present invention, the winding W _R of the recording head H _R is divided into two. By using this method, the center point is shifted from the electrical center point, and the wire is wound unbalanced, thereby making a connection that cancels out the distortion, thereby improving non-linear distortion. Further, since fine adjustment cannot be performed by this alone, if necessary, fine adjustment can also be performed by changing the occupation ratio (duty ratio) of the recording signal. In addition, by taking different values for the currents I _A and I _B ,
There is also a method of keeping the turns ratio of parts W _A and W _B of the winding W _R as 1:1, but in this case, the capacitor C
If the value of is not made sufficiently large, if the recording signal a contains many low-frequency components, there is a possibility that ripples will occur in the erase current _IE and remain as erase noise.

As is clear from the above explanation, the recording current and the erasing current always maintain a constant relationship. For example, when the amplitude of the recording current is constant with respect to the frequency, as in digital recording, it depends on the physical characteristics of the tape. When the optimum recording conditions are determined, the recording/erasing conditions become constant, and the non-linear distortion remaining on the tape due to erasing also becomes constant. Therefore, the degree of unbalance in the windings of the recording head to counteract this problem remains constant.

Also, due to the difference in position (distance, relative height, etc.) between the erasing head H _E and the recording head H _R , the exact same part of the tape TP that was erased by the erasing H _E may not necessarily be erased by the recording head H _R. There is a possibility that distortion may remain on either side of the track because recording is not possible, but since the present invention uses DC erasing, the erasing head
It is possible to bring the _HE and recording head _HR very close to each other with little mutual interference. Therefore, for example, by fixing the erasing head H _E and the recording head H _R on the same substrate or manufacturing them so that they are structurally integrated, errors that tend to occur in track width and relative height can be avoided. can be minimized.

At the beginning of partial erasure/recording on the same track, distortion occurs because it is recorded without experiencing the erasure magnetic field (because distortion is applied in the opposite direction to cancel non-linear distortion). In addition, at the end of erasing/recording, only demagnetization is performed and nothing is recorded, so there is a part that appears as if a long section of "1" or "0" continues. These parts are unusable and are not used for actual data. Therefore, erasing head H _E and recording head H _R
When the distance difference becomes large, a method is generally adopted in which erasing and recording are controlled at different timings to reduce this waste.

However, in the present invention, the erasing head is
Since the distance between _HE and recording head _HR can be reduced,
Depending on the structure of the head, the distance difference can be kept within about 1 mm, for example _.
Even if the timing of the operation period of the recording head _HR is not controlled, waste can be kept to a sufficiently low level, and the system can also be simplified.

Next, another embodiment of the present invention will be described with reference to FIG. In this embodiment, the present invention is applied to a digital VTR, and the recording head H _R and the erasing head _HE are both rotary heads that are attached to the rotating drum of the tape guide drum and rotate together with it. In FIG. 3, parts corresponding to those in FIG. 1 are given the same reference numerals, and some redundant explanations will be omitted.

A digital recording signal a (see FIG. 4) from an input terminal t is supplied to a recording amplifier RA. input terminal
A recording control signal b (see FIG. 4) from t' is supplied to the recording amplifier RA, and its amplification function is turned on and off. That is, only when signal b is at H level,
Amplified output is obtained from amplifier RA. amplifier ra
The positive phase and negative phase outputs are supplied to the primary coil of the rotary transformer.

Further, one end of the secondary coil of the rotary transformer RT is connected to the base of a pnp type transistor Q _D , and the other end is connected to the base of a pnp type transistor Q _C. The emitters of the transistors Q _D and Q _C are grounded through resistors R ₃ and R ₄ , respectively, and the collectors of each transistor are connected to the power supply -B (-12V). Power supply -B is grounded through capacitor _C2 . The emitters of transistors Q _D and Q _C are differential transistors (npn type) Q _A and Q _B of differential amplifier DA.
are respectively connected to each base.

The collectors of the differential transistors Q _A and Q _B are respectively connected to both ends of the coil _WR of the recording head _HR .
A damping resistor _R6 is connected between the collectors of transistors Q _A and Q _B. Transistor Q _A ,
Each emitter of Q _B is connected to the anode of a diode D via a resistor R ₅ as a constant current source, and its cathode is connected to the power supply -B. This diode D is provided to widen the dynamic range of the transistors Q _C and Q _D. A decoupling capacitor _C1 is connected in parallel to both ends of the diode D. The anode of diode D is connected to the bases of transistors Q _D and Q _C via resistors R ₁ and R ₂ , respectively, to provide base bias to these. Thus, the recording head H _R is driven by a B-clasp push-pull amplifier.

Connect one end of the coil W _E of the erasing head H _E to the recording head.
Connect the coil W _R of H _R to the middle point of the coil W R, and ground the other end.
Connect a smoothing capacitor to both ends.

Figure 4 shows the waveforms of the signal c supplied to the base of the transistor Q _D , the collector currents I _A and I _B of the transistors Q _A and Q _B , and the erase current I _E flowing through the coil W _E of the erase head H _E. show. The operation of the circuit shown in FIG. 3 is substantially the same as that shown in FIG. 1, so a description thereof will be omitted.

In addition, in Figures 1 and 3, the erase head
When the gap length of H _E is large, capacitor C ₃
can be omitted. In addition, the collectors of transistors Q _A and Q _B are connected through resistors of equal value, respectively.
The connection point may be connected to switch SW or diode D. This increases the variable range of the recording signal level and improves the degree of freedom in design. By connecting an inductor in series with each resistor, low frequency compensation is possible. In addition, the erase head
The erasing effect can be improved by comprising a head equipped with a double gap that generates magnetic fields in opposite directions as H _E , and by selecting the strength of each magnetic field.

Effects of the Invention According to the present invention described above, it is possible to obtain a digital signal recording device that can commonly control the operation timing of the recording head and the erasing head and can perform overwriting regardless of channel coding. can.

Furthermore, the circuit configuration is simple and the power efficiency is high. Since the distance between the recording head and the erasing head can be made extremely small, machining accuracy is improved and the relative height of each head can be eliminated without adjustment.

In the case of a rotating head type magnetic recording/reproducing device, there is no need to provide separate rotary transformers for recording signals and erasing signals. The recording/erasing circuit itself does not need to be adjusted, so by changing the conditions of the external signal while it is inside the rotating drum and making adjustments while watching the playback output, the optimal conditions for recording can be achieved almost in real time. You can ask for it.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a waveform diagram for explaining its operation, FIG. 3 is a circuit diagram showing another embodiment of the present invention, and FIG. 4 is a waveform diagram for explaining its operation. H _R and H _E are the recording head and erasing head, _respectively .
W _E is each coil, +B and -B are power supplies, SW is a switch, RA is a recording amplifier, and DA is a differential amplifier that drives the recording head H _R and inverts and controls the generated magnetic field.

Claims (1)

[Scope of Claims] 1. A first coil wound around the erasing head and having one end connected to one pole side of a drive power source, and a first coil wound around the recording head disposed near the erasing head, A second coil with the other end of the first coil connected to the midpoint, and one and the other winding ends of the second coil separated by the midpoint are connected to the other pole of the drive power source. 1. A digital signal recording apparatus comprising coil drive means for selectively driving a coil at a constant current value at the same current value for each side depending on the logic level of the digital recording signal.