JPH031740B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a control pulse recording circuit,
In particular, the present invention relates to a circuit that arbitrarily changes the duty cycle of a control pulse recorded at a constant period for servo during reproduction in a helical scanning type magnetic recording/reproducing apparatus during reproduction 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 4-4 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. Note that the arrow pointing to the right in the control track 3 indicates the portion recorded when the control head 2 was excited to the north pole, and the arrow pointing to the left indicates the portion recorded when the control head 2 was excited to the south pole.

Such a recorded magnetic tape 1 is stored, for example, in a cassette and loaded into the VTR main body, but during normal playback (during normal playback or variable speed playback other than still playback), the magnetic tape is pulled out from the cassette. The tape is loaded onto a predetermined tape path (loading state) in which the tape is wound diagonally over a predetermined angular range around a rotating body (for example, a rotating drum) to which a rotating head is attached, and the tape is held and run by a capstan and a pinch roller. The control pulses regenerated by the control head 2 during the drive are used as a reference signal for the phase control system of the head servo circuit to keep the rotational phase of the rotary head constant, or as a reference signal for the phase control system of the head servo circuit to keep the rotational phase of the rotary head constant, or as a reference signal for the phase control system of the head servo circuit to keep the rotational phase of the capstan constant. It is well known that this signal is used as a comparison signal for the phase control system of the Pustan servo circuit.

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 each of the servo circuits, and the negative pulses are not used in the servo circuits. Therefore, as described later, by changing the duty cycle of the control pulse during recording, different information (for example, the title of recorded information,
(recording date and time, other data, etc.)
During playback, this can be played back to perform random access and the like.

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 a signal is re-recorded (rewritten) such 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. 4A, the arrow pointing to the right indicates the north pole and the arrow pointing to the left indicates the south pole). 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 the downward pulse in FIG. 4B corresponds to the reference pulse described above.

The recording voltage shown in FIG. 4C is set from ○A immediately after a certain reference pulse to, for example, the position immediately before the reproduction control pulse after the reference pulse (this position varies depending on the duty cycle to be rewritten).
The section from ○B through the reproduction control pulse position ○C immediately after the reference pulse to the position ○2 immediately before the next reference pulse is a negative DC voltage, and from ○2 to the next The interval immediately after the reference pulse is O(V). The control head to which this recording voltage is supplied is excited to the same magnetic pole (here, N pole) in the section from ○A to ○B, and the magnetic pole is reversed at ○B (here, S pole).
It is excited by the 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.

The magnetic field direction of the control track after this rewriting is completed is as schematically shown in FIG. 4E. Therefore, the reproduction control pulse waveform after this rewriting is completed is as shown in FIG. do is played 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 By the way, the control head 2 finishes rewriting at the ○2 position shown in FIG. While the recording voltage at the input end is several volts, the reproduction output at the head output end is extremely small, several millivolts or less. Therefore, unless the recording voltage converges to approximately 0 volts by the excitation current or counter electromotive force during recording after the end of the rewriting of ○2, it is difficult to reproduce the reference pulse.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a control pulse recording circuit which solves the above-mentioned problems by switching to the reproduction mode after a certain time delay from the end of rewriting.

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 voltage 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 for recording
After a certain period of time has elapsed from the end of rewriting in the above interval and just before the leading edge of the control pulse, transmission of the recording voltage to the control head is stopped and the mode is switched to the reproduction mode.

Function: The control head is supplied with a recording voltage from the start of rewriting to the end of rewriting, and performs recording to change the duty cycle of control pulses according to the rewriting data.
Rather than immediately blocking the recording voltage from entering,
After a certain period of time has elapsed, the supply of recording voltage is cut off and the mode is set to playback. As a result, the control head is switched to the playback mode after the signal at the end of rewriting is stabilized to 0 volts.

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 (reference pulse) and outputs a pulse a shown in FIG. 2A having a relatively narrow pulse width. This pulse a has the same period as the reproduction control pulse (for example, 1 frame)
The signal is then supplied to the MMs 13 and 14 through the AND circuit 12, and these are triggered by the falling edge.

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
and the data binary variable delay (monostable multivibrator) 21, respectively, and the MM 18, which is triggered by its rising edge.

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 transistor _Q1 are commonly connected to one terminal of 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. The pulse d is output to the switch circuit 23,
The pulse e is supplied to the other input terminal of the AND circuit 17, and is output to the output terminal 22.

The pulse f shown in FIG. 2F taken out from the AND circuit 17 is supplied to the switch circuit 24. One terminal of each of the switch circuits 23 and 24 is commonly connected to the connection point between the non-inverting input terminal of the operational amplifier 25 and the resistor _R8 , and is also connected in series with the resistor _R6 and the capacitors _{C2 and C3} . Connected to the negative DC voltage -Vcc input terminal. Further, the other terminal of the switch circuit 23 is connected to the input terminal of the positive DC voltage +Vcc via a resistor _R5 . Furthermore, the other terminal of the switch circuit 24 is connected to the connection point of capacitors C ₂ and C ₃ , and is also connected to the negative DC voltage -Vcc input terminal via a resistor R ₇ . The switch circuit 23 is controlled to be on during the high level period of the pulse d and off during the low level period, and the switch circuit 24 is controlled to be on during the high level period of the pulse f and off during the low level period. Switching controlled.

As a result, the output terminal of the operational amplifier 25 has
When the switch circuit 23 is on and the switch circuit 24 is off, a constant positive voltage is extracted from the start of rewriting for a period corresponding to the rewritten data, and when the next switch circuit 23 is off and the switch circuit 24 is off, a constant positive voltage is extracted. During the period until the end of rewriting when the circuit 24 is on, a constant negative voltage is taken out, and during the period when the next pulses d and f are both low level and the switch circuits 23 and 24 are both off, a voltage of 0 volts is taken out. taken out. This output voltage is determined by the variable resistor 26
After level adjustment, the signal is supplied to the switch circuit 28 through the drive amplifier 27 as a recording voltage h as shown in FIG. 2H.

Here, the switch circuit 28 rises in phase synchronization with the rising edge of pulse c taken out from MM 18, delays the falling edges of pulses c and f, and immediately before the falling edge of pulse b. Switching is controlled by falling pulse g. That is, the pulse g is selected to have a width narrower than the pulse width of the pulse b and longer than the pulse width of the pulse c, and rises a certain time T (for example, 2 ms) after the falling edge of the pulse c. Go down. The switch circuit 28 is turned on only during the high level period of the pulse g and supplies the recording voltage h to the control head 2 to be recorded on the control track, and is turned off during the low level period of the pulse g to supply the recording voltage h to the control head 2. The transmission to the control head 2 is blocked and the control head 2 is switched to the reproduction mode. Therefore, control head 2
is the point at which rewriting is completed (indicated by a circle under G in Figure 2)
After a certain period of time T has elapsed, and immediately before the next reference pulse, the mode is switched to the playback mode, and after the signal is stabilized at the time of rewriting (until it converges to 0 volts). Since the reference pulse can be regenerated stably, the reference pulse can be regenerated stably.

According to this embodiment, the drive impedance of the drive amplifier 27 is made sufficiently smaller than the head impedance of the control head 2 (for example, about 1/50), and the drive amplifier 27 and the control head 2 are always connected. It is also effective against disturbances such as excitation current. However, in that case, DC drift during reproduction and a decrease in reproduction output occur, making the adjustment complicated, and the amplification degree of the drive amplifier 27 also needs to be increased by about 30 dB. Note that connecting a high-pass filter to the input side of the head amplifier 7 in order to prevent DC saturation of the head amplifier 7 is also effective against disturbances in the excitation current.

Effects of the Invention As described above, according to the present invention, since the control head is placed in the regeneration mode after a certain period of time has elapsed from the end of rewriting, the input signal of the control head at the end of rewriting does not converge to almost 0 volts. After that, it is possible to switch to the reproduction mode, and thus the reference pulse (leading edge of the control pulse) can be easily and reliably reproduced.

[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 a signal waveform diagram 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. 2...Control head, 11, 13, 14,
16, 18...monostable multivibrator (MM),
19... Rewriting data input terminal, 21... Data 2
Value variable delay, 23, 24, 28... switch 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. The recording circuit supplies a recording voltage whose polarity changes at a time point according to the duty cycle of a control pulse to record data to a control head, and starts rewriting between adjacent leading edges of the previously recorded control pulses. After a certain period of time has elapsed from the rewriting end point and immediately before the leading edge of the control pulse, the transmission of the recording voltage to the control head is blocked and the rewriting mode is set. A control pulse recording circuit characterized in that it is configured to switch to.