JPH056251B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video tape recorder (VTR), that is, a magnetic tape recording device that can selectively record a composite video signal and a non-video signal.

[Conventional technology]

It is already known that VTRs can be used not only for recording composite video signals, but also for recording non-video signals such as analog or PCM signals.

[Problem that the invention seeks to solve]

However, general-purpose small VTRs have recording circuits configured to be compatible with recording composite video signals of the NTSC system. Therefore, when a non-video analog signal is recorded through a VTR's clamp circuit and clip circuit, the linearity of the waveform may deteriorate.

In order to solve the above problem, Japanese Patent Laid-Open No. 52-29206 discloses separating the clamp circuit and the clip circuit when recording non-video signals. However, it is impossible to achieve good recording of non-video signals by simply separating the clamp circuit and the clip circuit when recording non-video signals.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic tape recording device that can record both composite video signals and non-video signals favorably.

[Means for Solving the Problems] To achieve the above object, the present invention will be described with reference to the reference numerals in the drawings showing the embodiments. A common signal input terminal in a magnetic tape device for selectively recording, by the same magnetic head, a synchronizing signal of the composite video signal and a non-video signal having a synchronizing signal of a different period. 1, an amplifier circuit 3 coupled to the signal input terminal 1, a pre-emphasis circuit 4 coupled to the amplifier circuit 3, and the pre-emphasis circuit 4.
a clamp circuit 5 coupled to the clamp circuit 5 via a first switch circuit 14; a clip circuit 6 coupled to the clamp circuit 5; and a second switch circuit coupled to the clip circuit 6.
an FM modulator 7 coupled via a switch circuit 15, a recording amplifier circuit 8 coupled to the FM modulator 7, magnetic heads 11 and 12 coupled to the recording amplifier circuit 8, and the pre-emphasis circuit. 4 and the FM modulator 7, a non-video signal transmission path is selectively connected via the first and second switch circuits 14 and 15 instead of the clamp circuit 5 and the clip circuit 6; , provided in the non-video signal transmission line so as to apply to the FM modulator 7 a bias voltage that substantially coincides with the center value of the input voltage of the composite video signal to the FM modulator 7 when recording the non-video signal. a synchronization signal separation circuit connected to a line through which both the composite video signal and the non-video signal are selectively transmitted; and a synchronization signal separation circuit for synchronizing the composite video signal from the synchronization signal separation circuit. The composite video signal and the non-video signal are discriminated based on a determination as to whether or not a synchronization signal having the same period as the signal is output, and when a discrimination output indicating the composite video signal is generated, the non-video signal is output. The video signal transmission path is separated and the clamp circuit 5 and the clip circuit 6 are connected.
The first and second switch circuits 14 and 15 are controlled to connect the first and second switch circuits 14 and 15, and when the discrimination output indicating the non-video signal is generated, the clamp circuit 5 and the clip circuit 6 are disconnected to connect the non-video signal. The present invention relates to a magnetic tape recording apparatus characterized in that it includes an input signal discrimination and control circuit that controls the first and second switch circuits 14 and 15 to connect video transmission lines.

[Operations and Effects] In the present invention, when recording a non-video signal, not only the clamp circuit 5 and the clip circuit 6 are separated, but also the DC bias circuit 16 is connected between the pre-emphasis circuit 4 and the FM modulator 7. Therefore, non-video signals can be FM-modulated at the optimum level, and good recording of non-video signals can be achieved.

〔Example〕

Next, a VTR according to an embodiment of the present invention will be described based on FIGS. 1 to 5. This VTR is
A small, general-purpose rotary-head diagonal-scan system configured to record NTSC composite video signals.
It is a VTR with a small amount of circuitry added. 1st
The figure shows a recording circuit for a composite video signal (luminance signal) in the recording system of this VTR. This recording circuit has signal input terminal 1,
AGC (automatic gain control) circuit 2, video amplification circuit 3,
Suitable for recording composite video signals in which a pre-emphasis circuit 4, a clamp circuit 5, a clip circuit 6, an FM modulator 7, a recording amplifier circuit 8, a pair of rotary transformers 9 and 10, and a pair of magnetic heads 11 and 12 are connected in sequence. Has a circuit. Since this circuit is a well-known VTR recording circuit, detailed explanation will be omitted. Incidentally, although a conveyance color signal recording system and a reproduction system are of course provided, illustration thereof is omitted.

Reference numerals 13, 14, and 15 are switch circuits for changing part of the recording circuit. Of these, the switch circuit 13 returns the output of the video amplifier circuit 3 to the AGC circuit 2 via contact a when recording a composite video signal to operate the AGC, and when recording a non-video signal, returns the output of the video amplifier circuit 3 to the AGC circuit 2 via contact b. 2 is grounded.

The switch circuits 14 and 15 are connected to the clamp circuit 5 by their respective contacts a when recording a composite video signal.
and the clip circuit 6 are connected to the recording circuit, and when recording a non-video signal, the clamp circuit 5 and the clip circuit 6 are separated from the recording circuit, and instead of this, the DC bias circuit 16 is connected to the pre-emphasis circuit 4 and the FM modulator by contact b. 7.

The DC bias circuit 16 includes a coupling capacitor C ₁
, bias setting resistors R ₁ and R ₂ , and voltage source +
V and biases the waveform of the non-video signal so that it falls within the input voltage range of V ₁ to _{V 2} of the FM modulator 7 shown in FIG. That is, the FM modulator 7 responds to the input voltage of V ₁ to _{V 2} at 3.8MHz.
Configured to generate a frequency output of ~5.4MHz, the center level of non-video signals can be reduced to V ₁
The DC bias circuit 16 is configured to shift preferably to the center within ~ _V2 .

Based on the distinction between the composite video signal and the non-video signal supplied to the input terminal 1, the switch 13,1
Although it is conceivable to manually operate the switches 4 and 15, the switching operation is troublesome, and there is a possibility that the switch may be forgotten. Therefore, in order to automatically discriminate between a composite video signal and a non-video signal, a horizontal synchronizing signal separation circuit 17 is connected to the output line of the video amplification circuit 3.
and the vertical synchronization signal separation circuit 18 are connected to each other,
A discrimination circuit 19 is connected to these output stages. The discrimination circuit 19 consists of two discrimination circuits: a discrimination circuit based on the horizontal synchronization signal and a discrimination circuit based on the vertical synchronization signal. Now, the second discriminator circuit based on the horizontal synchronization signal is
To explain in detail with the waveforms shown in Figures 4 to 4,
A capacitor 21 is connected to the output line of the horizontal synchronizing signal separation circuit 17 via a backflow blocking diode 20, and an MMV
A monostable multivibrator 22 indicated by is connected. The charging time constant of capacitor 21 is small;
Since the discharge time constant is set large, if a normal horizontal synchronization signal is generated as shown in FIG. 2A, the capacitor 21 is immediately charged in response to this horizontal synchronization pulse, and the horizontal synchronization pulse Discharge begins in response to the fall of the capacitor 21, and the voltage of the capacitor 21 changes as shown in FIG. 2B. Monostable multivibrator 22 is triggered in response to the rise of the waveform of FIG. 2B from a high level to a low level, and generates a low level output pulse of pulse width T as shown in FIG. 2C. This pulse width T is set so that the rising point from the low level to the high level is near the trailing edge of the horizontal synchronizing pulse. 23
is a D flip-flop for discrimination, its data input terminal is connected to the upper end of the capacitor 21, and its clock input terminal is connected to the monostable multivibrator 22.
is connected to the output terminal of the Therefore, when the horizontal synchronizing pulse of the composite video signal is detected as shown in _FIG . The output terminal becomes high level. A high level on the Q output terminal of D flip-flop 23 means that a composite video signal is being transmitted.

When a non-video signal including a synchronization signal with a longer period than the horizontal synchronization signal is input, the waveforms of each part become as shown in FIGS. 3A, B, and C. Since the pulse width of the monostable multivibrator 22 is kept constant, the trailing edge time t ₁ of the low level output pulse is earlier than the synchronization pulse occurrence time of FIG. 3A. As a result, the clock input signal of the D flip-flop 23 is applied while the terminal voltage of the capacitor 21 is at a low level, and the Q output terminal becomes a low level. On the other hand, even when the period of the synchronization signal of the non-video signal is shorter than the period of the horizontal synchronization signal as shown in FIG. 4, the D flip-flop 23 Since the data input terminal of is at a low level, the Q output terminal is at a low level. The low level of the Q output terminal of the D flip-flop 23 is
Refers to the transmission of non-video signals.

The discrimination circuit based on the vertical synchronization signal, which is composed of a diode 24, a capacitor 25, a monostable multivibrator 26, and a D flip-flop 27, is modified so that the output pulse width of the monostable multivibrator 26 corresponds to the period of the vertical synchronization signal. Except for this point, it is the same as the discrimination circuit based on the horizontal synchronization signal, and discriminates between a composite video signal and a non-video signal with the same operation.

28 is an AND gate, which obtains the AND output of the two D flip-flops 23 and 27. That is, a high level composite video signal detection output is generated when both the horizontal synchronization signal and the vertical synchronization signal are detected, and when only either the horizontal synchronization signal or the vertical synchronization signal is detected, or When neither is detected, a low level non-video signal detection output is generated. Therefore, this discrimination circuit 19 cannot detect a non-video signal if the non-video signal contains exactly the same synchronization signal as both the horizontal synchronization signal and the vertical synchronization signal. However, it is rare to set the synchronization signals of the composite video signal and the non-video signal to be exactly the same. When the synchronization signal of the non-video signal is made to match either the horizontal synchronization signal or the vertical synchronization signal, the output of the AND gate 28 becomes low level, so that the non-video signal can be detected.

When a high level composite video signal detection output is generated from the AND gate 28, the switch circuit 1
Contacts a of 3, 14, and 15 are turned on, and the general
A recording circuit identical to that of a VTR is formed, and a composite video signal is recorded on a magnetic tape by rotating magnetic heads 11 and 12. On the other hand, when a low level non-video signal detection output is generated from the AND gate 28, the contact b of the switch circuits 13, 14, 15
is turned on and some of the recording circuitry is switched to circuitry compatible with non-video signals.

The invention is not limited to the embodiments described above, but can be modified. For example, if it is acceptable to perform AGC operation when a non-video signal is input, the switch circuit 13 may be omitted. In addition, in addition to the bias circuit 16, if a circuit suitable for recording non-video signals is required,
You may add this. If the non-video signal does not include a synchronization signal that is the same as either the horizontal synchronization signal or the vertical synchronization signal, the discrimination circuit 19 may be used only as a discrimination circuit for either horizontal synchronization or vertical synchronization.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a VTR according to an embodiment of the present invention, FIGS. 2, 3, and 4 are waveform diagrams showing the states of points A, B, and C in FIG. 1, and FIG. 1st
FIG. 3 is a characteristic diagram showing the relationship between the input voltage and oscillation frequency of the FM modulator shown in the figure. 5...Clamp circuit, 6...Clip circuit, 7...
FM modulator, 11, 12...magnetic head, 13, 1
4, 15... Switch circuit, 16... DC bias circuit, 17... Horizontal sync signal separation circuit, 18... Vertical sync signal separation circuit, 19... Discrimination circuit.

Claims (1)

[Claims] 1. A composite video signal consisting of a video signal and a synchronization signal and a non-video signal having no synchronization signal or having a synchronization signal with a different period from the synchronization signal of the composite video signal are connected to the same magnetic field. In a magnetic tape device for selectively recording by a head, a common signal input terminal 1 and an amplifier circuit 3 coupled to the signal input terminal 1 are provided.
a pre-emphasis circuit 4 coupled to the amplifier circuit 3; a clamp circuit 5 coupled to the pre-emphasis circuit 4 via a first switch circuit 14; and a clip circuit 6 coupled to the clamp circuit 5. A second switch circuit 15 is connected to the clip circuit 6.
an FM modulator 7 coupled via the FM modulator 7; and a recording amplifier circuit 8 coupled to the FM modulator 7.
and a magnetic head 1 coupled to the recording amplifier circuit 8.
1, 12, and between the pre-emphasis circuit 4 and the FM modulator 7, the first and second switch circuits 1 are provided instead of the clamp circuit 5 and the clip circuit 6.
4 and 15, and a bias voltage that substantially matches the center value of the input voltage of the composite video signal to the FM modulator 7 when recording the non-video signal. a DC bias circuit 16 provided on the non-video signal transmission line so as to provide the signal to the FM modulator 7; and a DC bias circuit 16 connected to a line through which both the composite video signal and the non-video signal are selectively transmitted. a synchronization signal separation circuit; and determining whether or not a synchronization signal having the same cycle as a synchronization signal of the composite video signal is output from the synchronization signal separation circuit, and distinguishing between the composite video signal and the non-video signal. However, when a discrimination output indicating the composite video signal is generated, the non-video signal transmission path is disconnected and the clamp circuit 5
and the first clip circuit 6 are connected to each other.
and second switch circuits 14 and 15 to disconnect the clamp circuit 5 and the clip circuit 6 and connect the non-video transmission line when the discrimination output indicating the non-video signal is generated. A magnetic tape recording apparatus comprising an input signal discrimination and control circuit for controlling the first and second switch circuits 14 and 15.