JPH0332147B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a control pulse recording circuit,
In particular, in helical scanning type magnetic recording and reproducing devices, the duty ratio of control pulses recorded at a constant cycle for servo during reproduction is
The present invention relates to a circuit for arbitrarily changing and recording cycles during playback mode.

Prior Art FIG. 3 shows an example of a recording track pattern of a recorded magnetic tape recorded by a helical scanning type magnetic recording/reproducing apparatus (VTR). In the figure, a control track 3 is formed on a recorded magnetic tape 1 along the longitudinal direction of the tape by a control head 2, on which a control pulse of one frame period, for example, is recorded, and an information signal such as a video signal is also recorded. Inclined video tracks 4-1 to 4-2 recorded by the rotating head are formed. Furthermore, in FIG. 3, an audio track 5 is formed at the upper end of the tape along the longitudinal direction of the tape. The rightward arrow in the control track 3 indicates the portion recorded when the control head 2 was excited to the north pole, and the leftward arrow indicates the portion recorded while the control head 2 was excited to the south pole.

The recorded magnetic tape 1 is stored, for example, in a cassette and loaded into the VTR main body, but during playback, the magnetic tape is pulled out from the cassette and rotated over a predetermined angular range onto a rotating body (for example, a rotating drum) to which a rotating head is attached. The tape is loaded onto a predetermined tape path (loading state), which is wound diagonally over the entire length of the tape, and is run while being held between a capstan and a pinch roller.During this run, the control pulses regenerated by the control head 2 are transmitted to the rotating head. As is well known, it is used as a reference signal for the phase control system of the head servo circuit to keep the rotational phase constant, or as a comparison signal for the phase control system of the capstan servo circuit to keep the rotational phase of the capstan constant. It is.

Here, while the control pulse during recording is a square wave, the reproduction control pulse is differentiated due to the differential characteristics of the head, and becomes a positive polarity pulse at the rising edge of the recording square wave, and a negative polarity pulse at the falling edge. Of the reproduced control pulses, only the positive pulses are used as control pulses in the servo circuit, and the negative pulses are not used in the servo circuit. Therefore, as described later, by changing the duty cycle of the control pulse during recording, other information (for example, the title of recorded information, recording date and time, and other data) is recorded, and this is reproduced during playback to create a random・Can access etc.

In this case, the recorded magnetic tape 1 is reproduced, a positive polarity control pulse (hereinafter referred to as a reference pulse) used for the servo circuit is supplied to perform normal servo operation, and the duty of the control pulse is Since it is necessary to perform recording to change the cycle, the section between adjacent reference pulses is erased, and the signal is re-recorded (rewritten) so that the reproduction control pulse becomes negative polarity.
Action is required. This rewriting begins with the control track 3 of the recorded magnetic tape 1 (the polarity of the recording magnetic field is schematically shown in FIG. After reproducing and obtaining a reproduction control pulse as shown in FIG. 4B, a recording voltage as shown in FIG. 4C is obtained. Note that in FIG. 4B, the downward pulse corresponds to the reference pulse described above.

The recording voltage shown in Figure 4C ranges from a certain negative polarity ○a to, for example, the immediately preceding position ○ro of the reproduction control pulse immediately after the reference pulse (this position varies depending on the duty cycle to be rewritten). The section is a positive DC voltage, and the section from ○B through the negative polarity regeneration control pulse position ○C to the position ○D immediately before the next reference pulse is a negative DC voltage, and from ○D to the next reference pulse. The interval immediately after is 0 (V). The control head, to which this recording voltage is converted into a current and supplied, is excited to the same magnetic pole (in this case, N pole) in the section from ○A to ○B, and the magnetic pole is reversed (here in this case) at position ○B. S pole) and is excited, and continues to be excited with that magnetic pole until ○D.
As a result, the control track in the section ○I to ○D is erased, and the magnetic poles from ○RO to ○D are rewritten, and the rewriting ends at the position ○D.

After this rewriting is completed, the polarity of the magnetic field of the control track becomes as schematically shown in FIG. 4E, and the strength of the magnetic field of the control track becomes as shown in FIG. 4F. Therefore, the control pulse waveform after this rewriting is as shown in FIG. The control pulse d ₀ is reproduced at the new timing after rewriting. That is, the control pulse is regenerated with a changed duty cycle.

Problems to be Solved by the Invention However, in the reproduction control pulse waveform after the above rewriting, as shown by n ₁ and n ₂ in FIG. Noise often occurs at the position and end position. The cause of this noise (pseudo pulses to be described later) is as follows.

For example, if the height position of the control head is not completely the same for each magnetic recording/playback device (the height position of the control head differs within the installation tolerance), the recorded magnetic tape may be rewritten with another magnetic recording/playback device. When recording, the control head of the magnetic recording/reproducing device that rewrites and records cannot completely overlap the control track of the recorded magnetic tape, and if rewriting and recording is started in this state, the recording will start as shown in FIG. The control track of the completed magnetic tape is not completely rewritten and a track shift occurs (a part of the original control track remains), and at the rewriting start position, most of the original control track is the same as the width of the control head. Although it is newly magnetized to the north pole, the portion of the track deviation is not newly magnetized to the north pole. Although not shown here, a similar change in magnetization occurs at the rewriting end position in this state as well.

In this way, when the rewritten magnetic tape is played back using the same magnetic recording and reproducing device, the rewriting start position and end point are determined separately from the original reference pulse (pulse generated at the position where the magnetic field changes from the S pole to the N pole). Since some parts are magnetized and some parts are not magnetized at each position, the amount of magnetization changes here as well, and a differential pulse called a pseudo pulse is generated accordingly. This pseudo pulse has the same polarity as the reference pulse, and its magnitude is proportional to the change in magnetic quantity.

If a pseudo pulse is mistakenly detected as a reference pulse, there is a risk that the head servo circuit, capstan servo circuit, etc. will malfunction.If these servo circuits malfunction, tracking deviation, synchronization failure, mode (standard mode and long-time mode) ) error detection,
There was a problem in that absolute address miscounting occurred.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a control pulse recording circuit that solves the above problems by supplying a recording current having a slope at the start and end points of rewriting (erasing) to the control head. do.

Means for Solving the Problems The control pulse recording circuit according to the present invention has the following features:
In the playback mode, a recording current whose polarity changes within the interval between adjacent leading edges of previously recorded control pulses and at a time point corresponding to the duty cycle of the control pulse to be rewritten is supplied to the control head. A circuit recorded with
Recording currents having sloped portions are generated and recorded in the vicinity of the rewriting start time and the rewriting end time in the above-mentioned section, respectively.

Operation At each of the above-mentioned vicinity of the rewriting start time and the vicinity of the rewriting end time, the control head is supplied with a recording voltage whose value gradually changes with the passage of time. In other words, since the above-mentioned pseudo pulse is generated that is proportional to the change in the amount of magnetization, if the degree of change in the amount of magnetization is made gradual (the recording current supplied to the control head at the rewrite (erase) start position is gradually increased from a small level). If the recording current supplied to the rewrite (erase) end position is gradually decreased from a large value), this pseudo pulse can be made small and will not be erroneously detected as a reference pulse. In this way, when the control track of the magnetic tape whose duty cycle of the control pulse has been rewritten is played back, almost no noise is generated in the control head playback signal at the time when the rewriting starts and the time when the rewriting ends. , it is possible to prevent noise from being superimposed due to a steep excitation current or the like.

Embodiment FIG. 1 shows a circuit system diagram of an embodiment of the circuit of the present invention. In the figure, control pulses reproduced from a control track of a recorded magnetic tape by a control head 2 are supplied through a head amplifier 7 to a positive control pulse detector 8 and a determination circuit 9, respectively. The determination circuit 9 samples the level of the reproduction control pulse from the head amplifier 7 at the time when the signal from the positive control pulse detector 8 is received, and outputs the resulting signal (detection signal) to the output terminal 10. In addition, the positive control pulse is output to a servo circuit (not shown), and is also output to a monostable multivibrator (hereinafter referred to as MM) 11 and an AND
are supplied to the circuits 12, respectively. The MM 11 is triggered by a positive reproduction control pulse and outputs a pulse a shown in FIG. 2A having a relatively narrow pulse width. This pulse a is supplied to the MMs 13 and 14 through the AND circuit 12 at the same period (for example, one frame) as the reproduction control pulse, and
Trigger these on their falling edges.

The output pulse of MM13 is passed through output terminal 15.
The signal is output to a microcomputer (not shown) for controlling the operation of the VTR. Also, from MM14, the second
As shown in FIG. B, a high level pulse b of a constant width is outputted until just before the rising edge of the next incoming pulse a. The low level period of this pulse b is a short period before and after the reproduction time point of the positive reproduction control pulse (reference pulse). This pulse b is fed to the MM 16, which is triggered on its rising edge and converted into a pulse C, shown in FIG. 2C, which is narrower than pulse b.
Output pulse c of MM16 is output from 2-input AND circuit 17
is supplied to one input terminal of the data binary variable delay (monostable multivibrator) 21, and is applied as a switching pulse to the switch circuit 18, which is turned on during the high level period and turned on during the low level period. Turn off.

On the other hand, the input terminal 19 receives rewritten data (information such as numbers, comments, etc.) output from the microcomputer according to the user's intention. This rewrite data is low level when it is “1”,
When it is “0”, it is high level and the inverter 20
After the _polarity is reversed _by
Supplied to the base and emitter of PNP transistor _Q1 , respectively. The collector and emitter of the transistor _Q1 are commonly connected to one terminal of the capacitor _C1 via resistors _R3 and _R4 . Delay 21 is triggered by the rising edge of pulse c,
The transistor _Q1 , which is switched and controlled according to the rewritten data from the terminal 19, is variably controlled so that its time constant is determined by _C1 and _R4 , or C1 _{, R3} , and _R4 . As a result, day 2
From 1 onwards, as shown in Fig. 2 D and E, pulses d and e whose pulse width (duty cycle) changes according to the rewritten data and have the same period as the reproduction control pulse and have opposite phases to each other are generated. Generate output. Pulse d is output to the output terminal 22, pulse e is supplied to the other input terminal of the AND circuit 17, while the pulse e is supplied to the other input terminal of the AND circuit 17.
It is supplied to the base of NPN transistor _Q2 via resistor _R5 . A pulse f as shown in FIG. 2F is extracted from the AND circuit 17 and supplied to the base of the NPN transistor _Q3 in the second bootstrap circuit 29 via the resistor _R8 .

The bootstrap circuit 28 includes resistors R ₅ to _{R 7} , capacitors C ₂ and C ₃ , transistor Q ₂ , and a diode.
D ₁ and an operational amplifier 23. During the period when the pulse e is at a high level, the transistor Q ₂ is on, the output voltage of the operational amplifier 23 is 0 (V), and the diode D ₁ is on and the capacitor
Current is supplied to _C3 to charge the feedback capacitor _C3 . In this state, when the pulse e becomes low level, the transistor Q ₂ turns off, and the capacitor C ₂ begins to be charged through the resistors R ₇ and R ₆ , and the potential of the cathode of the diode D ₁ rises, causing the diode D ₁ to reverse The biased terminal voltage of the capacitor C ₂ is outputted through an operational amplifier 23 constituting a voltage follower and is also supplied to the capacitor C ₃ . In this way, the capacitor C ₂ is charged with a constant current, and the output voltage of the operational amplifier 23 gradually rises to the power supply voltage +V _cc with good linearity according to the charging time constant of the capacitor C ₂ After reaching _cc , the value is retained. In this state, when the pulse e becomes high level, the transistor Q ₂ and the diode D ₁
are turned on, the charge in the capacitor C ₂ is instantly discharged via the resistor R ₆ and the transistor Q ₂ , and the output voltage of the operational amplifier 23 instantly becomes 0 (V).
becomes.

The other bootstrap circuit 29 has a resistor R ₈ ~
R ₁₃ , capacitor C ₄ , C ₅ , NPN transistor Q ₃ ,
Q ₅ , PNP transistor Q ₄ , linearity improving diode D ₂ and operational amplifier 24, and pulse f
During the period when is at a high level, transistors Q ₃ to _{Q 5} are turned on, and the output voltage of the operational amplifier 24 is -
It becomes V _cc . In this state, when the pulse f becomes low level, each of the transistors Q ₃ to Q ₅ is turned off and the capacitor C ₄ starts to be charged by the power supply voltage +V _cc , so that the output voltage of the operational amplifier 24 is changed to the voltage of the capacitor C ₄ . Gradually + according to charging time constant
It increases towards V _cc and after reaching +V _cc it is held at that value. Furthermore, when the pulse f becomes high level in this state, the output voltage of the operational amplifier 24 immediately becomes _-Vcc .

The output terminal of operational amplifier 23 is connected to the cathode of diode _D3 , and the output terminal of operational amplifier 24 is connected to the anode of diode _D3 via resistor _R14 . As a result, the smaller output voltage of the output voltages of the operational amplifiers 23 and 24 (a voltage having the same waveform as that of FIG. 2G described later) is taken out at the anode of the diode _D3 . This output voltage is non-invertingly amplified by an operational amplifier 25, level-adjusted by a variable resistor 26, and further current-converted by a drive amplifier 27 to obtain a recording voltage g as shown in FIG. is supplied to Note that the reference voltage obtained from the resistors R ₁₅ , R ₁₆ , the diodes D ₄ , D ₅ , the capacitor C ₆ and the DC voltage +V _cc is input to the inverting input terminal of the operational amplifier 25 . A parallel circuit of a capacitor C ₇ and a resistor R ₁₇ is connected between the output terminal and the inverting input terminal.

As described above, the switch circuit 18 is turned on only during the high level period of the pulse c, so during the high level period of the pulse c, the recording current g is passed through and supplied to the control head 2 to perform recording. Therefore, for example, when the pulse c becomes high level at time _t1 shown in FIG. 2, the recording current g becomes 0.
(V) gradually rises toward +V _A until time t ₂ , the control head 2 is excited to, for example, the N pole, and from time t ₂ the pulse c becomes low level (switch circuit 18 _{S _}
Excited to the pole. During the low level period of the pulse c from time _t3 to time _t4 , the switch circuit 18 is off, the transmission of the recording current g to the control head 2 is blocked, and the control head 2 reproduces the previously recorded control pulse.

As a result, according to this embodiment, the direction of the magnetic field of the control track after the rewriting is completed is as schematically shown in FIG. 2H. Therefore, the reproduction control pulse waveform after _this rewriting is completed is as shown by the solid line in _FIG . As shown by ₁ to _i4 , the data is reproduced at new timing according to the rewritten data. Furthermore, in the _past , noise sometimes occurred at the position indicated by the broken line in _FIG . Since the recording voltage g at the end of rewriting, such as time _t3, etc., also begins to rise with a slope, the generation of the above-mentioned noise is reduced to a level that poses no problem in practice.

In the above embodiment, the saturation level of the magnetic tape, the impedance of the head, the amount of back electromotive force,
Since the nozzle changes depending on the gap width, etc., a trapezoidal waveform recording voltage having a sloped portion with good linearity is desirable, so the bootstrap circuits 28, 2
9 was used, but it is not necessarily limited to this.

Effects of the Invention As described above, according to the present invention, when a magnetic tape in which the duty cycle of the control pulse has been rewritten according to information is played back, the rewriting start position, rewriting end position, etc. that should originally be rewritten are This can significantly reduce the noise generated at different positions compared to conventional methods, thereby preventing tracking errors, synchronization failures, mode (standard mode and long-time mode) error detection, and absolute address miscounts due to this noise. It has the advantage of being able to prevent such malfunctions.

[Brief explanation of the drawing]

FIG. 1 is a circuit system diagram showing an embodiment of the circuit of the present invention, FIG. 2 is a diagram showing signal waveform diagrams for explaining the operation of the circuit system shown in FIG. 1, and FIG. 3 is a recording track pattern on a magnetic tape. FIG. 4 is a diagram showing an example of the magnetic field direction and signal waveform on the tape according to a conventional circuit, and FIG. 5 is a diagram illustrating the generation of pseudo pulses caused by track deviation. 2...Control head, 11, 13, 1
4,16...monostable multivibrator (MM),
18... Switch circuit, 19... Rewriting data input terminal, 21... Data binary variable delay, 28, 29... Bootstrap circuit.

Claims (1)

[Claims] 1. In the playback mode of a recorded magnetic tape in which square wave control pulses are recorded on the control track at a constant cycle, within the section between the leading edges of adjacent recorded control pulses, and when an attempt is made to rewrite. A recording circuit for recording by supplying a recording current whose polarity changes at a time point according to the duty cycle of a control pulse to be recorded to a control head, and for starting rewriting between adjacent leading edges of the already recorded control pulse. 1. A control pulse recording circuit characterized in that the control pulse recording circuit is configured to generate a recording current having a slope portion near a time point and near a rewriting end time point and supply the generated recording current to the control head.