JPS6113883A - Television receiver with automatic input changeover circuit - Google Patents

Abstract

PURPOSE:To improve remarkably the operability by detecting a synchronizing signal among signals inputted from each input terminal, detecting to which terminal a displayed signal is inputted by the synchronizing signal, using a logical circuit, switching selectively a television receiver to the said input terminal and displaying it on a screen. CONSTITUTION:When no signal is given to both input terminals 8, 9, the level of an input of an OR circuit 20 goes to a low level, a switch 5 is controlled and a general television picture inputted from the antenna 1 is displayed on a display tube 7. In applying power of an adaptor (not shown) connected to the input terminal 8, the inputted video signal is subjected to separation and extraction of a synchronizing signal only by a clamp circuit 16 and a synchronizing extraction circuit 17, the result is converted into a continuous level signal (state display signal) at a level signal converting circuit 18, and the video signal inputted to the input terminal 8 is displayed on the display tube 7 via the switches 10, 5.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention provides a plurality of sets of signal terminals (input terminals for video signals and input terminals for three primary color signals of GB, GB, etc.) so that a plurality of additional devices such as video equipment can be connected. A television receiver with an automatic input switching circuit that is equipped with RGB input terminals for direct input (RGB input terminals, etc.) and can display a signal input through a terminal selected from among the plurality of terminals on the screen instead of a television signal. It is related to.

[Background of the invention]

As the types of additional devices added to television receivers have increased, such as video disc players, video tape recorders, teletext receiving adapters, etc., television receivers have come to be equipped with various input terminals. It has become. Recently, television receivers having three video signal input terminals and two input terminals for GB, three primary color signals have become quite common.

However, when using such a television receiver by switching to an additional device, the operation method becomes complicated, and it is actually very difficult to use. For example, if you want to watch a video tape recorder on such a television receiver, first turn on the power to the video tape recorder, check which input terminal of the television receiver it is connected to, and use a switch etc. to connect the input terminal. After selecting and switching to the receiver side,
It is necessary to press a button to start playback, making the device very difficult to use. An object of the invention is to provide a television receiver with an automatic input switching circuit that is easy to operate and extremely user-friendly when used by switching to an arbitrary additional device. [Overview] To achieve the above object, the present invention detects a synchronization signal from among the signals input from each input terminal, and uses this synchronization signal to determine which terminal the signal to be displayed is input to. This feature is characterized in that the television receiver is selectively switched to the corresponding input terminal using a logic circuit to display the screen.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is an antenna of a television receiver, 2 is a tuner, 3 is an IF (intermediate frequency) amplifier circuit, 4 is a detection circuit, 5 is a switch for switching between a television signal and an external input signal,
6 is a video signal amplifier; 7 is a display tube for displaying images; 8
, 9 are input terminals for external video signals, 11.16
12 and 17 are respectively synchronous signal extraction circuits; 13 and 18 are respectively level signal conversion circuits for creating state signals representing signal input states; 14; .19 is a capacitor for extracting the leading edge of the state signal,
10 is a switch for switching and outputting two external video signals (8, 9), 15 is an R8 type flip 70 tube that controls the switch 10, and 20 is an OR circuit.

FIG. 2 is a timing chart showing signal waveforms of important parts in the circuit of FIG. 1.

That is, FIG. 2(a) shows a synchronization signal detected (extracted) by slicing the video signal whose signal level has been clamped output from the clamp circuit 16 by a synchronization extraction circuit (for example, a slicing circuit) 17. 2 (b) shows that as long as the level signal conversion circuit (for example, a retriggerable one-shot multivibrator) 18 receives the synchronization signal from the synchronization extraction circuit 17 at a constant cycle, the signal is not input to the input terminal 8. A state signal indicating that a state signal is being input is outputted as a high level signal.

FIG. 2(c) shows the waveform of the differential output obtained by differentiating the output signal from the level conversion circuit 18 using the capacitor 19.

Next, the circuit operation will be explained with reference to FIGS. 1 and 2.

Now, let us consider a case where no signal is input to both the input terminals 8 and 90, that is, a case where the power of an external additional device (not shown) is turned off. At this time, the OR circuit 200 Å power becomes low level, and the output also becomes low level. This signal controls a switching device 5, which is connected to a detection circuit 4, and a general television image inputted from an antenna 1 is displayed on a display tube 7.

At this point, the power of an additional device (not shown) connected to the input terminal 8 is turned on. From the video signal input from this device, only the synchronization signal is separated and extracted by the clamp circuit 16 and the synchronization extraction circuit 17 (see the beginning of FIG. 2). This signal is then converted into a continuous level signal (status display signal) by the level signal conversion circuit 18 (see Figure 2).
9, only the rising edge is extracted (see Figure 2),
It is input to the reset terminal R of the RS flip 70 knob 15. The reset output of this R87 lip 70 tube 15 connects the switch 10 to the input terminal 8 side.

Therefore, the video signal from input terminal 8 is input to switch 5.

On the other hand, the output of the level signal conversion circuit 18 passes through an OR circuit 20 and connects the switch 5 to the switch 10 side.

That is, the video signal input to the input terminal 8 is displayed on the display tube 7 via the switching devices 10 and 5.

After all, when the power of the additional device connected to the input terminal 8 is turned on, the input signal is automatically switched to the additional device side.

If you then input the video signal to input terminal 9 in this state,
This time, the edge Kendagawa force from the capacitor 14 (see FIG. 2C) is input to the set terminal S of the Rs flip-flop 150, and the set output connects the switch 10 to the input terminal 9 side.

In addition, when video signals are input to both input terminals 8 and 9, the S flip 70 tab 15 is connected to the capacitor 14.
Set with the edge signal that passed through 9.

Since it is reset, the video signal input later is automatically selected and the switch 10 is switched. When both signals disappear, the output of the OR circuit 20 becomes low level, and the switch 5 automatically switches to the television side.

As can be easily inferred from the above, this embodiment can be expanded using the same concept even if the number of external input terminals is increased. In addition to video signals, KGB signals and the like can also be considered in exactly the same way.

〔Effect of the invention〕

According to the present invention, simply by turning on the power of the additional device without requiring any complicated operation, the signal is immediately switched to the side of the additional device, so that operability can be greatly improved. Furthermore, the user does not need to be aware of which additional device is connected to which terminal, and anyone can easily operate the system.

Furthermore, since the present invention is based on detecting a synchronization signal that is necessarily included in a video signal, etc., it cannot be applied to a combination of devices made by different manufacturers, for example. Problems caused by this are also less likely to occur.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
The figure is a timing chart showing the signal waveforms of the main parts in the circuit of FIG.
...IF' amplifier circuit, 4...Detection circuit, 5...Switcher, 6...Video signal amplification circuit, 7... Display tube, 8, 9...Video signal input terminal, 10...Switcher, 11゜1
6... Clamp circuit, 12, 17...
Synchronization extraction circuit, 13, 18...Level signal conversion circuit, 14°19...Capacitor, 15...
...R87 lip 70 knobs, 20...OR circuit agent patent attorney Akio Namiki Figure 1 (('n (ha)

Claims (1)

[Claims] 1) A plurality of sets of signal terminals are provided so that a plurality of additional devices can be connected, and a signal input through a terminal selected from the plurality of sets is replaced with a television signal. A television receiver with an automatic input switching circuit capable of displaying a screen on a screen, comprising means for extracting a synchronization signal from a signal input through the signal terminal, and a status signal representing a signal input state using the synchronization signal. means for creating a signal terminal, a means for detecting a start point of the state signal, and a means for preferentially selecting a signal terminal to which a signal has been input last from among the plurality of signal terminal sets using the start point detection output. and means for switching the television receiver from a side that receives television signals to a side that receives signals inputted via the signal terminal selection means using the status signal created by the status signal generation unit. A television receiver with an automatic input switching circuit.