JPS6211416B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic playback speed switching device for automatically switching the playback speed in accordance with the recording speed in a magnetic recording and playback device, particularly in a so-called video tape recorder.

Some magnetic recording and reproducing devices are capable of performing recording and reproducing by switching the tape feed speed in two stages. For example, in a video tape recorder
You can switch between 2H mode and 6H mode,
A 2-hour tape can record and play back 2 hours in 2H mode and 6 hours in 6H mode.

For this type of tape, it is necessary to match the mode during playback and recording, and during playback, the control signal (hereinafter referred to as
It is called CTL signal. ) has been proposed to determine the tape feeding speed (playback speed), or in other words, the mode, by detecting the playback CTL signal obtained by playing back the tape. You can play a tape recorded in 2H mode in 2H mode, or play a tape recorded in 6H mode.
When playing in 6H mode, a CTL signal is obtained every 33.3mS.

If a tape recorded in 2H mode is played back in 6H mode, the CTL signal will be three times as large as normal.
Obtained every 99.9mS.

Also, when playing back a tape recorded in 6H mode in 2H mode, a CTL signal is obtained every 11.1mS, which is 1/3 of the normal time.

Therefore, during playback, the cycle of the CTL signal is determined, and if it is about 99.9mS, which is greater than 33.3mS, the playback speed is set to the high speed side, that is, 2H mode.
If the playback speed is about 11.1mS, which is smaller than 33.3mS, the playback speed may be set to the low speed side, that is, 6H mode.

In view of this point, the following example can be proposed as an automatic playback speed switching device.

In FIG. 1, a CTL signal obtained during reproduction is introduced via an inverter 1 to a high-speed detection multivibrator 2 (hereinafter referred to as MV ₁ ) and a low-speed detection multivibrator 3 (hereinafter referred to as MV ₂ ).

MV ₁ is triggered in response to CTL signal S
An output is obtained that is at a low level for 20mS, but when the CTL signal S is inputted next time with a cycle smaller than 20mS, it is retriggered and maintains a low level.

MV ₂ is also triggered in response to the CTL signal S.
An output is obtained that is at a low level for 70mS, but when the CTL signal S is inputted at a cycle shorter than 70mS, the low level is maintained.

The flip-flop 6 (hereinafter simply referred to as FF) receives the output of MV ₁ as one input through a low-pass filter 4 (hereinafter simply referred to as LPF 1), and the output of MV ₂ as the other input through a low-pass filter 5 (hereinafter simply referred to as LPF 1). (referred to as LPF2).

FF controls the playback speed, in other words, the mode, and can switch between 2H mode and 6H mode by input from LPF1 and LPF2.
In 6H mode, the output is at a high level (hereinafter simply H).
That's what it means. ), low level (hereinafter simply L) in 2H mode.
That's what it means. ).

Note that this FF is set or reset so that the output becomes H or L when the 6H mode or 2H mode is selected by the user's operation.

Now, if this speed matches the recording speed during playback, LPF 1 will cause the output to settle to a constant voltage level corresponding to the time constant, while the LPF
The output of No. 2 is maintained at L, and the playback speed of FF is maintained without any switching operation.

Now, if the playback speed is slower than the recording speed,
In other words, if a tape recorded in 2H mode is played back in 6H mode, there is a period in which the output of MV ₂ is H, so the output level of LPF 2 increases in correlation with the time constant, and in response to this, the FF is reversed and the output becomes L, switching to 2H mode. Conversely, when the playback speed is faster than the recording speed, that is, when a tape recorded in 6H mode is played back in 2H mode, the output of MV ₁ maintains L and the output of LPF 1 rises to H. is reversed and the output becomes H, switching to 6H mode.
Note that the LPF 1 can be realized as a configuration in which, for example, a transistor that is turned on when the output of MV ₁ is H is included in a capacitor discharge circuit, and the capacitor is discharged when the transistor is turned on, and is otherwise charged as appropriate.

However, with this, for example, when playing back a tape recorded in 6H mode in 6H mode, if the CTL signal is missing three times in a row due to dropout, the MV ₂ output Because of this lack, it becomes H, so there is a risk that the FF will be inverted and switched to 2H mode.

To prevent such erroneous switching,
It is possible to increase the time constant of LPF2 so that the switching operation is not executed even if about three CTL signals are missing, but this would prevent a tape recorded in 2H mode from being played back in 6H mode by mistake. In such cases, it takes a long time to switch to 2H mode, and the response characteristics of automatic switching are sacrificed.

In view of this, it is an object of the present invention to provide an automatic playback speed switching device for a magnetic recording and playback device that is improved so as to prevent malfunctions due to lack of CTL signals. This will be explained in detail with reference to the drawings.

FIG. 2 shows a block diagram of an embodiment of an automatic reproduction speed switching device for a magnetic recording and reproducing apparatus according to the present invention.
In FIG. 2, parts equivalent to those in FIG. 1 are designated by the same reference numerals.

The structure is similar to that in FIG. 1 in that the output of MV ₁ is introduced into LPF 1, but the Q output of MV ₁ is input into MV ₂ .

Therefore, when the output rises from L to H, the Q output falls from H to L and the output of MV ₂ falls, and then the output of MV ₂ remains L for 70 mS.

The output of this MV ₂ is input to gate 7,
The output of the inverter 1 is applied to this gate 7 as a gate signal. This gate 7 turns on when the output of the inverter 1 is L, that is, in synchronization with the CTL signal, and introduces the output of MV ₂ into the FF in synchronization with the CTL signal.

Therefore, if the CTL signal arrives when the output of MV ₂ is H, the FF is inverted as soon as the H signal is input. However, even if the output of MV ₂ is H, if the CTL signal does not arrive, the FF will be H.
Since the signal is not input, it is not inverted.

In addition, in response to the output of MV ₁ , the signal is transmitted through LPF 1.
The system for operating the FF is the same as that shown in FIG.

FIGS. 3a, 3b, and 3c show waveform diagrams of various parts for explaining the operation of the above embodiment. In this diagram,
S ₁ , S ₂ , S ₃ , S ₄ and S ₅ are MV ₂ , gate 7, MV ₁ ,
It corresponds to the output of LPF and FF.

Now, the playback mode is set by the user's operation, and if this playback mode matches the recording mode, the operation is executed as shown in FIG. 3a.

For example, if a tape recorded in 6H mode (2H mode) is operated to play back in 6H mode (2H mode), the command signal in response to the operation
The FF is set (reset) to a state where the output _S5 becomes H (L).

At this time, the CTL signal comes at a period of 33.3 mS, and the output of MV ₂ is triggered to become L in response to the CTL signal S, so it is maintained at L, and therefore the output S ₂ of gate 7 also becomes L. will be maintained,
FF is not given an input that inverts it.

On the other hand, the output _S3 of MV ₁ goes low for 20 mS every time the CTL signal S arrives, then goes high, and the output of LPF1
_S4 settles to a constant level corresponding to the time constant of LPF1, and no input is given to FF to reverse it.

In this way, the reproduction mode is maintained without being switched.

Also, if you accidentally record a tape recorded in 2H mode, it will become 6H.
mode, the third
The operations shown in Figure b are performed.

Since the FF output S ₅ becomes H and is reproduced in 6H mode, the period of the CTL signal S approaches 99.9 mS, and the MV ₂ output S ₁ becomes H after 90 mS of the CTL signal S. After this becomes H, the next CTL signal arrives and gate 7 turns on.
At the same time, the output _S2 of gate 7 becomes H and becomes FF.
and invert it.

Therefore, the output _S5 of the FF becomes L, the 2H mode is set, and the correct reproduction mode is automatically switched.

Also, you may accidentally record a tape recorded in 6H mode in 2H mode.
When set to play in mode, the operations shown in Figure 3c are performed.

Since the FF output _S5 becomes L and is reproduced in 2H mode, the period of the CTL signal S approaches 11.1mS, so the output of MV ₁ is maintained at L by the CTL signal S, and the output of LPF2 S ₄ continues to rise. Eventually, the output _S4 of LPF1 reaches a level sufficient to invert the FF. In this way, FF is inverted and the output _S5 is switched to H, thereby switching to the correct reproduction mode, that is, the 6H mode.

However, for example, if you play a tape recorded in 6H mode,
When playing in 6H mode, if for some reason the CTL signal S is missing due to dropout, gate 7 will not turn on due to the lack of CTL signal even if MV ₂ 's output S ₁ is H. Therefore, the inverted input is not transmitted to FF6.

In this way, erroneous switching operations due to lack of CTL signal are prevented.

FIG. 4 shows an electrical circuit diagram of one embodiment of the present invention. In FIG. 4, parts equivalent to those in FIG. 2 are represented by the same symbols.

In this example, when the 6H mode is operated, an H pulse is applied to the terminal 6H in response, and the 2H
It is assumed that when the mode is operated, an H pulse is applied to terminal 2H.

Now, if the 2H mode is operated, the terminal 2H will be set to H.
A pulse of is temporarily applied to transistor _Q5
is turned on, the output _S5 becomes L and the transistor _Q3 is turned off.

In this state, when the input of the transistor Q ₄ , that is, the signal S ₄ reaches a level that turns on the transistor Q ₄ , it is inverted. That is, the period of the CTL signal S is
If it is about 33.3mS, use multivibrator 2.
Since transistor Q ₁ discharges in response to the period when the output of (MV ₁ ) is high, capacitor C settles to a certain level in response to the charging/discharging time constant, but transistor Q ₄ does not turn on at this level. .

However, if a tape recorded in 6H mode is accidentally played back in 2H mode, the period of the CTL signal will be shorter than 33.3mS, so the output of MV ₁ will be
The period in which _S3 is at H level disappears and it starts to maintain L level, and at the same time, transistor _Q1 comes to be turned off all the time, so that the voltage of capacitor C (output of LPF1
S ₄ ) increases. When the output S ₄ reaches a level sufficient to turn on the transistor Q ₄ , the transistor Q ₅ is turned off to turn on the transistor Q ₄ and the output S ₅ becomes H. In this way, the playback mode automatically switches to the correct 6H mode.

Also, when operated in 6H mode, an H pulse is temporarily applied to terminal 6H, transistor Q ₃ is turned on, transistor Q ₅ is turned off, output S ₅ becomes H, and playback occurs in 6H mode. be done.

In this state, when the output _S2 , which is the input of the transistor _Q6 , becomes H, it is inverted. That is, when the output _S2 becomes H, the transistor _Q6 turns on and the output _S5 becomes L.

This is the output of multivibrator 3, i.e. MV ₂ .
If the CTL signal S arrives during the period when S ₁ is H and transistor Q ₂ is turned on, in other words, the CTL signal S
This is the case when the period of is around 99.9mS. More specifically, if a tape recorded in 2H mode is accidentally played back in 6H mode, the period of the CTL signal S will change.
It becomes 99.9mS. Therefore, in response to the CTL signal S, the output _S3 of the multivibrator 2 (MV ₁ ) obtained at the terminal rises after being low for 20 mS, and the output of the Q terminal becomes high for 20 mS and then falls. , in response to this falling, multivibrator 3
(MV ₂ ) output S ₁ remains low for 70mS and then rises. That is, the output _S1 becomes H after 90 mS from the CTL signal S.

When the next CTL signal S arrives during the period when the output S ₁ is H, the transistor Q ₂ (gate 7) is turned on, so that the output S ₂ of the transistor Q ₂ becomes H and turns on the transistor Q ₆ . This results in the output
_S5 becomes L and switches to 2H mode.

However, if the output _S1 becomes H due to the lack of CTL signal due to dropout, it is clear that transistor _Q2 will not turn on due to the lack of CTL signal, and the 2H mode will not be activated. It never switches to .

In the embodiment described above, a multivibrator is employed to monitor the period of the CTL signal S, but it is obvious that other means for determining the period can be used, and the present invention is not limited to this. Furthermore, it is clear that the flip-flop 6, gate 7, and low-pass filter 8 are not limited to the embodiments, but can be modified in various ways within the scope of the idea of the present invention.

According to the automatic playback speed switching device of the magnetic recording and playback device of the present invention, the playback speed does not switch from the low speed side to the high speed side while the playback control signal is absent as described above, so that dropout occurs. This makes it difficult for erroneous switching of the playback speed due to the lack of a playback control signal caused by the like, which helps improve reliability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a proposed automatic reproduction speed switching device for a magnetic recording and reproducing device, FIG. 2 is a block diagram of an embodiment of an automatic reproduction speed switching device according to the present invention, and FIGS. 4c shows a waveform diagram of each part explaining the operation of the same as above, and FIG. 4 shows a specific example of the same circuit. 2 and 3...Multivibrator, 4 and 5...Low pass filter, 6...Flip-flop, 7...Gate, Qn (n=1,...6)...Transistor, C
...capacitor.

Claims (1)

[Claims] 1. The feeding speed of the recording medium is switched between high speed and low speed, and a control signal of a constant period is recorded on the recording medium during recording, and during playback, the control signal on the recording medium is reproduced and reproduced. In a magnetic recording and reproducing device that obtains a control signal, inputting the reproduction control signal to a first monostable multivibrator having a relatively narrow pulse width;
The output signal of the first monostable multivibrator is inputted to a first input terminal of a flip-flop via an integrating circuit, and the output signal of the first monostable multivibrator is inputted to a second monostable multivibrator having a relatively wide pulse width. input into a stable multivibrator, gate the playback control signal by the output pulse of the second monostable multivibrator, input the gated signal into a second input terminal of the flip-flop, and input the output signal of the flip-flop. An automatic playback speed switching device for a magnetic recording and playback device, characterized in that the feeding speed of the recording medium is switched based on the following.