JP2696623B2 - Control signal writing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control signal writing circuit, and more particularly, to a video tape recorder (camera integrated type, portable type, stationary type, television integrated type, etc .; Use.)
In the control signal writing circuit for rewriting the cue signal.

[0002]

2. Description of the Related Art In recent years, video tape recorders have become remarkably widespread, and their functions have been advanced and diversified. A cueing function is one of such functions. In the cueing function, some mark is attached to a recording start point (that is, a recording start position) on a video tape, and the stop is detected when fast-forwarding or rewinding, and an automatic stop is performed. With this cueing function, when a plurality of programs are recorded, the head position of the program can be searched for even when fast-forwarding or rewinding.

[0003] This cueing function includes VISS (VH
S Index Search System) and VA
SS (VHS Address Search Syss)
tem). In the former case, the cueing position is recorded and auto-stop is sequentially performed at that position. In the latter, the cueing position is stored as a predetermined address, and the specified position is designated by specifying the address. The automatic stop is performed at the cue position.

Here, recording of a cue signal in this cue function is generally performed by changing the duty ratio of a control signal written in a control track of a video tape. This will be described with reference to FIG.
, The tape runs in the direction of arrow Y during reproduction, and control tracks A and A 'are provided on one side thereof. A is a portion where reading and rewriting has not yet been performed, and A 'is a portion where reading and rewriting have already been performed.

The control tracks A and A 'include:
A control signal for synchronizing the video signal 10c and the like stored in the video track is stored. As the control signal, an on / off signal having a fixed duty ratio (that is, a signal magnetized to the N and S poles) is used. The control signal only needs to specify the position of the video track or the like. It is only necessary to be able to identify either the transition point from on to off or the transition point from off to on. If the transition point is not changed, there is no problem even if the duty ratio is changed. Therefore, a cue signal is recorded by changing the duty ratio of the control signal.

In order to write or change such a cue signal, the control signal must be rewritten. In this case, however, the video signal and the like are not rewritten. The portion related to signal synchronization (in the example of the video tape 10, the point at which the magnetization transitions from the south pole to the north pole) is in a state where there is no effect.
The duty ratio of the control signal must be changed. That is, it is necessary to rewrite only the portion related to the duty ratio of the control signal (in the example of the video tape 10, the point at which the magnetization transitions from the N pole to the S pole).

Here, the control head 7 writes and reads control signals to and from the control tracks A and A 'during normal recording. And
Writing is performed in the current direction (from the terminal REC (+) to the terminal REC
(−) Current from terminal REC (−) to terminal REC
(Current to (+)) is performed as DC recording. Therefore, at the time of writing the control signal, the current direction is switched at predetermined time intervals, and the direction of magnetization of the magnetic material in the control tracks A and A '(that is, N pole and S pole) is reversed at predetermined intervals. become.

Next, the rewriting of such a control signal will be described. In a normal state of the video tape 10 recorded normally, the duty ratio is 6 like 10a.
Control signals of about 0% are written in the control tracks A and A '. Further, at the cueing position, a control signal having a duty ratio of about 27.5%, such as 10b, is transmitted to control tracks A and A.
A 'has been written. When the cue signal 10b is erased, a current for writing the N-pole is passed through the control head 7 after the transition from the S-pole to the N-pole has passed the control head 7 (about 8%). From the position where the duty ratio is 60%, a current whose direction is changed so as to write the S pole is supplied to the coil of the control head 7, and the point where the next S pole transitions to the N pole is reached before reaching the control head 7 (about 10 points). %), The current of the coil of the control head 7 is stopped.

On the other hand, when the cue signal 10b is rewritten, the point at which the transition from the S pole to the N pole has passed the control head 7 (about 8%), and then the current for writing the N pole is changed by the control head 7. From the position where the duty ratio is 27.5%, the current whose direction is changed so that the S pole is written is passed through the coil of the control head 7, and the transition point from the next S pole to the N pole is the control head 7 (About 10%), the current of the coil of the control head 7 is stopped. In this way, only the position of the falling portion (the transition point from the N pole to the S pole) is changed without rewriting the rising portion (the transition point from the S pole to the N pole) of the control signal. .

[0010]

The rewriting of the control signal is performed as described above. This rewriting is performed by rewriting a part of the already written signal. For this reason, there may be a difference in the degree of magnetization on the video tape 10 between the already written control signal and the rewritten signal. In particular, when rewriting is performed on a control signal written by another video tape recorder, a slight difference in the degree of magnetization and the position of magnetization cannot be avoided.

Therefore, a step occurs in the degree of magnetization of the control signal at the start and end of rewriting. That is, on the control tracks A and A ', N
At the place where the current for writing the pole is passed through the coil of the control head 7 to start the rewriting, and where the current of the coil of the control head 7 is stopped and the rewriting is finished, the signal which was originally written and the rewritten Is connected to the signal, but at this point, the intensity of magnetization tends to be discontinuous. For this reason, when a control signal is read through the control head 7 during reproduction, a signal according to the rate of change of the magnetic flux density is read, so that the place where the magnetic susceptibility changes, that is, the place where the rewriting is started There is a possibility that a place where rewriting is completed is erroneously recognized as a rise or fall of a control signal, and problems such as loss of synchronization may occur.

In order to solve such a problem, it is conceivable to gradually increase or decrease the current flowing through the coil of the control head 7 at the start and end of rewriting. By doing so, the rate of change of the magnetic flux density at the time of reproduction is reduced, so that a change in the current of the read signal by the control head 7 is suppressed, and
Factors that become noise in the control signal during reproduction are suppressed, and the risk of erroneous recognition is greatly reduced.

In order to gradually change the current, the output of the trapezoidal wave generating circuit 11 mainly composed of the capacitor C1 is usually sent to the control drive circuit 12 for controlling the current of the coil of the control head 7. It is conceivable that the rise and fall are blunted by utilizing the function of the charge / discharge circuit formed by the connection and the resistors R1, R2 and the capacitor C1 (see (L waveform in FIG. 3)).
In this conventional example, the capacitor of the trapezoidal wave generation circuit 11 is C1
And charge and discharge are switched using the switch circuits SW1 and SW2.

However, in a circuit configuration for generating a trapezoidal wave L using a capacitor, since a capacitor is externally provided, it is difficult to integrate a control signal writing circuit. In addition, since the slope of the trapezoidal wave L is not constant, the maximum value of the slope cannot be made too small in order to complete the change within the predetermined allowable time, so that the noise of the recorded signal is large. There is. The present invention solves such a problem of the conventional technology. By generating a more ideal trapezoidal wave without using a capacitor, the present invention is suitable for integration, and the factor of a noise component is reduced. It is an object of the present invention to realize a control signal writing circuit capable of rewriting a suppressed signal.

[0015]

In order to achieve this object, a control signal writing circuit of the video tape recorder according to the present invention comprises a detection circuit, a clip circuit, a counter, a timing signal generation circuit, a control drive circuit, a trapezoidal wave. It has a generator circuit and a control head, and can rewrite the cue signal by rewriting the duty ratio of the control signal stored in the control track of the video tape. It has the following features. The control head, by magnetic-electric conversion,
A control signal stored as a magnetization direction in a control track of a video tape is written and read.

The trapezoidal wave generating circuit receives a part of bits of the value of the counter for generating a timing signal, and selects one of the bit and a complemented one according to the timing signal. The selected digital value is D / A converted to generate a trapezoidal wave having a constant slope with the waveform thereof as a slope portion, and outputs this to the control drive circuit. The control drive circuit receives the timing signal for writing and the trapezoidal wave, controls the magnitude and direction of the current to the control head coil according to these signals, and controls the rise of the rewriting current of the control head coil. The control signal is written to the control track while the current change at the time and at the time of falling is gradually performed at a constant gradient.

[0017]

In the control signal writing circuit according to the present invention having such a configuration, some bits (usually lower bits) of the count value are D / A converted, so that a step due to slight quantization is ignored. With a sufficient number of bits as much as possible, a sawtooth wave having a substantially ideal rising slope is generated. Then, by taking the complement of some bits of the count value and performing D / A conversion, a sawtooth wave having a substantially ideal falling slope is generated. Further, when one of the rising slope sawtooth waves is taken at the rewriting start point and one of the falling slope sawtooth waves is taken at the rewriting end point, a trapezoidal wave having an almost ideal slope is generated. You.

According to the almost ideal trapezoidal wave as described above,
Since the control drive circuit controls the magnitude and direction of the current to the coil of the control head, the slope of the current change at the time of rising and falling of the rewriting current of the coil of the control head is constant. Therefore, under the constraint that the change is completed within a predetermined allowable time, the value of the slope is smaller than the maximum value of the slope of the curved signal change portion in the conventional circuit. It is possible to suppress the rate of change of the connection part, which causes the noise of the signal read as the rate of change of the connection part, to be small. In addition, since no capacitor is used to generate the trapezoidal wave, no external components are required. Therefore, the control signal writing circuit of the present invention is suitable for integration.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a control signal writing circuit according to the present invention.
FIG. 7 is a signal waveform diagram for explaining the operation. 1 is a transmission circuit for generating a clock P, and 2 is a counter which is initialized at the rising edge of a control signal (finally, a signal E), counts the clock P, and outputs a timing signal generation count value M.

Reference numeral 103 denotes a timing signal generation circuit for generating timing signals C, D, F, Qa, and Qb from the count value M. Reference numeral 112 controls the magnitude and direction of current to the coil of the control head via signals H and K. And a control drive circuit 111 for generating a trapezoidal wave L. Reference numeral 7 denotes a control head for writing and reading a control signal stored as a magnetization direction in a control track of a video tape, 8 a detection circuit for detecting a transition point from the read control signal and outputting a signal B, and 9 a reference circuit. A clip circuit 10 for extracting only a rising component from the signal B and outputting a signal E is a video tape and runs in the Y direction during reproduction.

Further, the trapezoidal wave generating circuit 111 includes, for example, specifically, a waveform shaping circuit 111a, a D / A converter 11
1b and a complement circuit 111c. Complement circuit 111c
Generates the complement of the lower bits of the count value M, receives the signal Qc, and selects and outputs either the value of the lower bits of the count value M as it is or the complement thereof. The D / A converter 111b receives the digital value from the complement circuit 111c, performs D / A conversion, and outputs a sawtooth wave. The waveform shaping circuit 111a includes a D / A converter 111
A trapezoidal wave L having a slope at the timing indicated by the signal Qc is generated from the sawtooth wave output by b (FIG. 1 (L waveform)).
reference). Note that the trapezoidal wave generating circuit 111 generates a digital value trapezoidal wave by the waveform shaping circuit 111a receiving the output of the complement circuit 111c and shaping it, and converts the digital value trapezoidal wave into a D / A converter 111b. May be subjected to D / A conversion to generate a trapezoidal wave L having an analog value.

When the video tape 10 is loaded, the control head 7 is arranged at a position facing the control tracks A and A 'of the video tape 10. By passing a current through the coil of the control head 7, a control signal can be written to the control tracks A and A '. At the time of reproduction, control signals are read out by the control head 7. The control of the write current to the coil of the control head 7 is performed by the control drive circuit 112. In other words, the control driver 112 controls the timing signal generation circuit 1
03, the gate signal F and the write signal C are received, and when the gate signal F is on, a current corresponding to the write signal C is
It is supplied to the coil of the control head 7.

The output line of the signal H from the driver 105 of the control drive circuit 112 is connected to one end of the coil of the control head 7 via the REC (+) terminal, and the output line of the signal K from the driver 106 is
It is connected to the other end of the coil of the control head 7 via a (-) terminal. The control drive circuit 112 switches the output levels of the signals H and K according to the high level and the low level of the write signal C.
EC (+) terminal, coil of control head 7, RE
The direction of the DC current at the C (-) terminal is switched. As described above, since the direction of the current flowing through the coil of the control head 7 is reversed according to the level of the write signal C, the direction of the magnetization is sequentially reversed in the control tracks A and A 'facing the control head 7. The stored control signal is stored.

In the control drive circuit 112, the switch circuit SW2 is connected to the signal H line, and the switch circuit SW1 is connected to the signal K line. The other ends of the switch circuits SW1 and SW2 are connected to an output line of the trapezoidal wave generation circuit 111 and receive the trapezoidal wave L. Therefore, when the switch circuit SW1 is receiving the signal I, the trapezoidal wave L
Output to EC (-) terminal. At this time, the driver 106
Has an output state of high impedance according to the signal J so as not to disturb the signal K. Then, the driver 105 sets the signal H to a low level according to the signal G '. As a result, a DC current flows in the direction of the REC (-) terminal, the coil of the control head 7, and the REC (+) terminal.

Conversely, when the switch circuit SW2 is receiving the signal G, the trapezoidal wave L is set to the signal H, and REC
Output to the (+) terminal. At this time, the driver 105
The output state is high impedance according to the signal G 'so as not to disturb the signal H. Then, the driver 106 sets the signal K to a low level according to the signal J.
As a result, a DC current flows in the direction of the REC (+) terminal, the coil of the control head 7, and the REC (-) terminal. In order to clearly show a comparison with the conventional example, the switch circuits SW1 and SW2 are illustrated by switch symbols, and the drivers 105 and 106 are illustrated by amplifier symbols.
The switch circuit SW1 and the driver 106 form a pair,
A push-pull transistor circuit in which the switch circuit SW2 and the driver 105 form a pair may be used.

Next, a case where the control signal is rewritten in such a control signal writing circuit will be described in detail with reference to the waveform diagram of FIG. 2. Figure 1
And the corresponding waveforms in FIG. The waveform A (magnetization state A) illustrates the state of the control signal currently written in the control track A. The place where the rectangular wave rises (the transition point from the S pole to the N pole) is necessary for synchronizing a video signal or the like. Then, the duty ratio of the control signal is known from the falling point (the transition point from the N pole to the S pole), and it is distinguished whether or not the signal is a cue signal.

In the example of FIG. 2, the first and fourth control signals are normal signals, and the second, third and fifth control signals are cue signals. In the figure, for the sake of explanation, a cue signal and several normal signals are shown, but usually, dozens of continuous cue signals are used.
One cue is formed. A waveform B is an example of the signal B output by the detection circuit 8 when the control signal of the control track A (corresponding to the waveform A) is read by the control head 7 as it is.
The change point of the magnetization of the control signal is detected from the signal B.

A waveform C is an example of the write signal C at the time of rewriting the cue signal. According to the write signal C, the control drive circuit 112 rewrites the control signal to the control track A. That is, the rewriting signal C corresponds to the control signal (corresponding to the waveform A ') of the control track A' after rewriting. The waveform D is output from the detection circuit 8 and the clipping circuit 9 responsible for reproduction.
This is an example of a signal D for controlling on / off of the input of a read signal to the control head 7. When this signal D is on, the coil of the control head 7 operates as a read coil, and the signal B is output from the detection circuit 8, From the signal B, a signal E used for synchronization of a video signal and the like and initialization of the counter 2
Is generated by the clip circuit 9. Since the signal D only needs to detect the rise of the control signal, in this example, it is turned on between -10% and + 10% of one cycle.

Further, the waveform F is an example of the gate signal F for controlling the operation of the control drive circuit 112. The waveform F is turned on after a lapse of a predetermined time from the rise of the signal E.
It stays on for a certain period of time. This gate signal F
Is ON, the control head 7 is in the write mode. The gate signal F indicating writing and the signal D indicating reading are set so that the ON states do not overlap.
Also, the point in time when the gate signal F is turned on must be before the rise of the control signal indicating cueing, and the point in time when the gate signal F is turned off is after the fall of the normal control signal. There is a need. By complying with this condition, any control signal originally stored can be rewritten as a rewrite signal (see waveforms C and A ').
In this example, the gate signal F is turned on for 15% to 85% of one cycle based on the rise of the control signal.

Here, if the gate signal F is turned on and the write signal C at this time is turned on, a direct current flows in the direction of the REC (+) terminal, the coil of the control head 7, and the REC (-) terminal. Flows. At this time, the trapezoidal wave L is supplied via the switch circuit SW2 by the signal G changing like the waveform G, so that the voltage change at the REC (+) terminal gradually rises with a constant slope like the waveform H. I do.
When the write signal C is turned off, a direct current flows in the direction of the REC (-) terminal, the coil of the control head 7, and the REC (+) terminal. At this time, since the trapezoidal wave L is supplied via the switch circuit SW1 by the signal I changing like the waveform I, the voltage change at the REC (-) terminal gradually decreases at a constant slope as the waveform K. I do.

The broken lines of the waveforms H and K indicate the timing of the read mode. At this time, in order not to disturb the read signal, the switch circuits SW1, SW2 and driver 10 are used.
Numerals 5 and 106 are in a high impedance state, and the storage of the control tracks A and A 'is not rewritten.
As a result, the control track A 'is rewritten only in the portion corresponding to the hatching in the waveform example A'.

As described above, according to the control signal writing circuit of this embodiment, the rise and fall of the current flowing through the coil of the control head 7 at the time of rewriting can be performed gradually with a constant slope. Therefore, even if there is a slight difference in magnetization between the originally written control signal and the rewritten signal, the change is performed gradually, so that a large peak does not occur in the reproduced signal. Therefore, noise in the rewritten control signal can be significantly reduced.

[0033]

As can be understood from the above description, since the trapezoidal wave L is generated by the D / A conversion in the control signal writing circuit of the present invention, no external capacitor is required, so that the control signal writing circuit can be integrated. Since a suitable slope is constant, there is an effect that the maximum value of the slope can be reduced and a signal in which the cause of noise is suppressed can be rewritten.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a control signal writing circuit according to the present invention.

FIG. 2 is a signal waveform diagram in the control signal writing circuit of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional control signal writing circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transmission circuit, 2 ... Counter, 3 ... Timing signal generation circuit, 4 ... Switching control circuit, 5 ... Driver, 6 ... Driver, 7 ... Control head, 8 ... Detection circuit, 9 ... Clip circuit, 10 ... Video tape, 11: trapezoidal wave generation circuit, 12: control drive circuit, 105: driver, 106: driver, 103: timing signal generation circuit, 112: control drive circuit, 111: trapezoidal wave generation circuit, SW1: switch circuit, SW2: switch circuit .

Claims (1)

(57) [Claims] 1. A control signal writing circuit of a video tape recorder for rewriting a duty ratio of a control signal stored in a control track of a video tape and rewriting a cue signal, wherein the control signal is written and read. A control head; a counter for counting clocks in accordance with a control signal read by the control head; and a D / A conversion of the count value of the counter in order to generate a trapezoidal waveform having a constant slope having the waveform as a slope portion. A trapezoidal wave generating circuit for receiving and outputting, a timing signal for writing and the trapezoidal wave,
A control drive circuit for controlling the magnitude and direction of the current to the coil of the control head according to these signals and writing a control signal to the control track.