JPH0419909Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention has two or more rotating heads.
This is a select circuit that is applied to a VTR and can selectively output the respective playback video signals of each rotating head.

[Summary of the idea]

This device has two or more rotating heads.
In the select circuit used to inspect or adjust the playback output of each head of the VTR and the playback video signal of each corresponding channel, the level changes in synchronization with the switching timing of the rotating head, and the low level changes the playback video signal. A circuit that generates a DC voltage that matches the pedestal level of the signal and is set so that the high level is higher than the white level of the reproduced video signal, and a circuit that generates a DC voltage that is set to match the pedestal level of the signal and whose high level is higher than the white level of the reproduced video signal. According to this invention, the clipper clips the side of the reproduced video signal that is higher than the pedestal level and outputs the reproduced video signal without clipping during the period when the DC voltage is at the other level. Playback video can be selectively output, and a synchronization signal can always be output.

[Conventional technology]

When inspecting the circuit of a rotating two-head VTR,
It is required to be able to individually test the reproduction signal of each channel corresponding to each head. For example, when a carrier is missing, it is preferable to be able to determine in which channel the carrier is missing. Further, even when testing frequency characteristics using a multi-burst signal as a test signal or observing a response to a pulse bar waveform, it is desirable to be able to perform these tests or observations for each channel on one side.

[Problem that the invention attempts to solve]

Conventionally, it has been difficult to test only the playback video signal of one channel. In addition to supplying the playback video signal to the oscilloscope, a switching pulse that is synchronized with the head switching timing is also supplied to the oscilloscope as a trigger input, and when expanded in delay mode, only one horizontal period in the playback video signal of one channel can be detected. It is possible to observe the signal waveform. However, what we want to observe with an oscilloscope is the average value of one entire channel, and it is not very meaningful to be able to observe only one horizontal period. Additionally, simply gating only one field using switching pulses causes the monitor receiver or oscilloscope to become unsynchronized with the input video signal because all synchronization signals for the other field are lost.

Therefore, the purpose of this invention is to select a playback video signal that can supply the playback video signal of a VTR to a monitor receiver or oscilloscope, and monitor the playback image and observe the playback video waveform for each channel without any problems. The purpose is to provide circuits.

[Means for solving problems]

This idea changes the level in synchronization with the switching timing of the rotating head, and the low level matches the pedestal level of the reproduced video signal.
a circuit that generates a direct current voltage whose high level is set to be a voltage higher than the white of the reproduced video signal;
A clipper that uses DC voltage as a reference voltage, clips the side of the reproduced video signal greater than the pedestal level during one level of this DC voltage, and outputs the reproduced video signal without clipping during the period of the other level of DC voltage. This is a VTR playback video signal selection circuit equipped with the following.

[Effect]

The level changes in synchronization with the rotation of the rotating head,
The reference voltage is a DC voltage whose low level matches the pedestal level of the reproduced video signal and whose high level is equal to or higher than the white level of the reproduced video signal. With this reference voltage, the reproduced video signal of the selected channel is output without being clipped, and the waveform of the reproduced video signal of the unselected channel that is higher than the pedestal level is clipped. A synchronization signal is output even during periods of unselected channels. Therefore, the synchronization signal is always included in the output signal, and when the video signal selected by this invention is supplied to the monitor receiver or oscilloscope, the monitor receiver or oscilloscope will not respond to this video signal. to ensure synchronization.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, 1A and 1B
indicates a rotating head. Rotating head 1A, 1B
are mounted on a drum at opposite intervals of 180° from each other and rotated at the frame frequency. Rotary heads 1A and 1B alternately contact a tape wound around the circumferential surface of the drum, and one field of video signal is recorded on the tape as one diagonal track. These rotating heads 1A and 1B
The respective output signals are supplied to equalizer circuits 3A and 3B via head amplifiers 2A and 2B, respectively. Output signals of equalizer circuits 3A and 3B are supplied to input terminals a and b of switch circuit 4.

Although a pulse generator that generates detection pulses synchronized with the rotational phase of the rotary heads 1A and 1B is not shown,
A switching pulse whose level is inverted for each field is formed from this detection pulse,
This switching pulse is supplied to terminal 7.
The switching circuit 4 is controlled by the switching pulse, and in the field where the switching pulse is at a high level, the input terminal a and the output terminal c of the switching circuit 4 are controlled.
In the field where the switching pulse is at a low level, the input terminal b and the output terminal c of the switch circuit 4 are connected. The reproduced signal converted into one channel by the switch circuit 4 is supplied to the FM demodulator 5. A reproduced video signal is taken out from this FM demodulator 5 to an output terminal 6.

In the case of a color video signal, the carrier color signal is FM modulated along with the luminance signal, or the carrier color signal is converted to a lower carrier frequency. In this invention, the color signal processing is not particularly important, so its explanation is omitted.

The reproduced video signal is supplied from the FM demodulator 5 to the clamp circuit 11, and in the clamp circuit 11,
The pedestal level is clamped to a predetermined level. The output signal of this clamp circuit 11 is supplied to a clipper consisting of transistors 12, 16, 17, 20, etc.

The output terminal of the clamp circuit 11 is connected to the base of the PNP transistor 12.
The emitter is connected to the positive power supply terminal 14 through the resistor 13.
, and the collector of the transistor 12 is grounded via a resistor 15. The emitter of the transistor 12 is led out as an output terminal 23 via a capacitor 21 and a resistor 22. The output signal obtained at this output terminal 23 is supplied to a monitor receiver or an oscilloscope.

The emitter of transistor 12 and the emitter of PNP transistor 17 are connected, and transistor 1
7 is grounded via a resistor 19.
The base of transistor 17 is connected to the movable element of variable resistor 18 . A stator of variable resistor 18 is inserted between power supply terminal 14 and ground. The voltage supplied from the mover of the petal resistor 18 to the base of the transistor 17 is matched with the vedestal level of the video signal supplied from the clamp circuit 11 to the base of the transistor 12. Unlike this embodiment, when the clamp circuit 11 is not provided, the variable resistor 18 is adjusted according to the APL (average brightness level) of the reproduced video signal, and the voltage supplied to the base of the transistor 17 and the pedestal are adjusted. The level is matched.

The collector of transistor 12 is connected to the base of NPN transistor 16, and transistor 16
The emitter of the transistor 16 is grounded, the collector of the transistor 13 is grounded, and the emitter of the transistor 13 is grounded.
A transistor 20 is provided relative to transistor 17.

A variable resistor 18 is connected to the base of the transistor 17.
The DC voltage selected by the mode switch 24 and passed through the diode 27 is superimposed on the DC voltage determined by . The switching pulse from terminal 7
The signal is supplied to the base of the NPN transistor 25 via a resistor, and is also supplied to the input terminal a of the mode switch 24. The emitter of transistor 25 is grounded, and the collector of transistor 25 is connected to power supply terminal 14 via resistor 26. The power supply terminal 14 and the input terminal b of the mode switch 24 are connected, and the collector of the transistor 25 and the input terminal c of the mode switch 24 are connected.

Resistors 15, 19 and transistors 16, 20
This element is not necessarily necessary for the clipper because it is provided to perform a sharp clipping operation.

In one embodiment of the invention described above, when the reproduced video signal shown in FIG. 2A is supplied from the clamp circuit 11 to the base of the transistor 12, and the switching pulse shown in FIG. 2B is supplied from the terminal 7, Explain the operation.

High level period of switching pulse To
is one field from which a reproduced video signal is obtained from, for example, the rotary head 1A, and the low level period Te of the switching pulse is, for example, one field from which a reproduced video signal is obtained from the rotary head 1A.
This is one field from which a reproduced video signal from B is obtained. The low level of this switching pulse is equal to or smaller than the pedestal level of the video signal supplied from the clamp circuit 11 to the base of the transistor 12,
The high level of the switching pulse is set by variable resistor 1.
When added to the voltage of 8, the voltage is higher than the white level of the video signal supplied to the base of the transistor 12. Furthermore, the reproduced video signal includes a vertical synchronizing signal VS and a horizontal synchronizing signal HS.

As an example, input terminal a of the mode switch 24
When and output terminal d are connected, Fig. 2B
The switching pulse shown in is the mode switch 24.
and a diode 27 to the base of the transistor 17. During the period To when the switching pulse is at a high level, the diode 27 is turned on,
The base of transistor 17 is above the white level, and transistors 17 and 20 are always cut off. Therefore, in the field of period To,
A reproduced video signal is taken out to an output terminal 23 between the base and emitter of the transistor 12, via a capacitor 21, and a resistor 22.

During the period Te in which the switching pulse is at a low level, the diode 27 is cut off and the base potential of the transistor 17 becomes the petestal level.
Therefore, when the emitter of transistor 17 reaches a voltage equal to or higher than the pedestal level plus the voltage between the base and emitter of the transistor, transistor 1
7 and 20 are turned on and the video signal is clipped. Therefore, only the synchronization signal passes during the period Te. FIG. 2C shows the waveform of the output signal when the input terminal a and the output terminal d of the mode switch 24 are connected as described above.

Next, when the input terminal b and the output terminal d of the mode switch 24 are connected, the anode of the diode 27 is always at the power supply voltage, and therefore,
Transistors 17 and 20 are always cut off. In this case, there is no clipping action;
The input video signal is output as is.

Furthermore, when the input terminal c and the output terminal d of the mode switch 24 are connected, the switching pulse whose phase is inverted by the transistor 25 is supplied to the anode of the diode 27 via the mode switch 24. The video signal of field To is clipped, and the video signal of field Te is obtained as an output signal.

When the output signal of the embodiment of this invention described above, for example a video signal in which one field To is not clipped and the other field Te is clipped, is supplied to a monitor receiver, flicker will occur, but synchronization will not occur. First, as shown in Figure 3,
In a microscopic sense, the image of field To is visible through the black scanning line of the other field Te.

Also, if one similar field supplies the selected output signal to the oscilloscope and observes it with a horizontal trigger, the video signal of the channel you want to see (field To) and the video signal of the channel you don't want to see (field Te) The pedestal levels overlap. However, as shown in Figure 4, you can see the waveform of one horizontal period Th with a horizontal line drawn well below the effective image part that requires observation, so you can observe only the waveform of the channel of interest. be able to.

[Effect of idea]

According to this invention, a playback video signal of a desired channel is selected from a plurality of channels corresponding to a plurality of rotating heads of a VTR, and a synchronization signal is set for playback video signals of other channels that are not selected. Since the signal is output, various inspections, measurements, etc. can be performed for each channel without synchronization of the monitor receiver or oscilloscope.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram of an embodiment of this invention, Fig. 2 is a waveform diagram of each part to explain the operation of an embodiment of this invention, and Figs. 3 and 4 are explanations of an embodiment of this invention. FIG. Explanation of main symbols in the drawings, 1A, 1B...
...Rotating head, 4...Switch circuit, 7...Switching pulse supply terminal, 12, 17...Transistor constituting the cutter, 18...Variable resistor, 23...Output terminal, 24...Mode switch.

Claims (1)

[Claims for Utility Model Registration] The level changes in synchronization with the switching timing of the rotating head, and the lower level corresponds to the pedestal level of the reproduced video signal, and the higher level has a voltage higher than the white of the reproduced video signal. means for generating a direct current voltage set as such; using the direct current voltage as a reference voltage; clipping the side of the reproduced video signal greater than the pedestal level during one level period of the direct current voltage; A clipper for outputting the reproduced video signal without clipping it during the period of the other level.