JPS60259077A - Signal switching device - Google Patents

Abstract

PURPOSE:To obtain a pattern without any crosstalk even if a personal computer is connected by inserting a switch circuit to a supply path for an RGB signal of the personal computer and opening the switch except that a picture from the personal computer is displayed as a master pattern. CONSTITUTION:An RGB signal switching pulse generating circuit 24 is brought into a high level when the RGB signal (R1, G1, B1) are displayed as the master pattern and into a low level in other cases. As a result, in case of the RGB mode where the RGB signal (R1, G1, B1) of the personal computer is displayed as the master pattern, switch circuits 25, 26, 27 are closed and the R1, G1, B1 signals are one input to inserting circuits 16, 17, 18. In case of the mode other than the RGB mode, since the switch circuits 25, 26, 27 are turned off, the R1, G1, B1 are cut off and even when the personal computer is connected at ON-AIR or with signals of a VTR displayed at a master pattern and a slave pattern, no crosstalk is produced and an excellent pattern is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a signal switching device used in a color television receiver that can simultaneously display two television images on one cathode ray tube screen.

BACKGROUND ART In recent years, a color television receiver called a so-called "Picture in Picture" (hereinafter abbreviated as "PinP"), in which a screen of another program is displayed in a small size on one screen, has been announced. Figure 1 is a conceptual diagram of a PinP television, where 1 is a television receiver, 2 is a main screen section,
3 is a sub-screen section into which another television screen has been reduced and inserted.

On the other hand, recent signal sources for television receivers include not only on-air broadcast signals, but also RGB signals from video tape recorders, video disk players, personal computers, text multiplex signals, etc., and receivers can also handle these signals. It is designed so that you can enjoy various sounds by preparing connection terminals and switching modes.

Below, a conventional switching device will be explained with reference to FIG. 2.0 RGB signal input from a personal computer etc.
R1, G1. B1) is connected to the R insertion circuit 16. through the capacitor 10°11.12. G insertion circuit 17, B insertion circuit 18
is input. On the other hand, the RGB signal (R2+G2 y B
2) is connected to the R insertion circuit 16 through capacitors 13, 14 and 15. The G insertion circuit 17° is input to the B insertion circuit 18. R, G, B are the respective insertion circuits 16, 1, 18
A clamp pulse is supplied from a clamp pulse generation circuit 19 to. A signal switching pulse is also applied from the dimension switching signal generation circuit 20 to the insertion circuit gfi16.17.18.

The respective outputs R' from the insertion circuits 16, 17 and 18,
G' and B' are applied to the signal switching circuit 21. To this signal switching circuit 21, RGB signals (R3, G3, B3) of the image of the main screen section 2 of the television shown in FIG. 21 output R6゜Go, Bo is amplifier 2
2, the light is applied to a color cathode ray tube 23, and projected onto a screen.

Next, the operation of this block will be explained.

(1) When the main screen is the output of the partial computer and the sub screen is the on-air signal output.

The operation of the R insertion circuit 16 will be explained based on FIG.

G insertion circuit 17. The B insertion circuit 18 also operates in a similar manner, so its description will be omitted. In FIG. 3, (a) is the signal waveform of R1, (2) is the signal waveform of R2, and (C) is the signal waveform of R2.

This is a clamp pulse for adjusting the DC level by clamping the noise part (usually a synchronizing signal part) of R1 and R2 in order to match the level of the signal of R2. (4 is a switching signal; when the level is low, the signal of R1 is obtained as the output, and when the level is high, the signal of R2 is obtained as the output.

Therefore, the output R' of the R insertion circuit 16 is t-t3~
During the period t-t4, the signal is R2, and during the other periods, it is the signal R1.

The signal switching circuit 21 has the above-mentioned R' and similarly G/
, B' are added as one input signal, and the switching signal generating circuit 20 outputs, for example, low level signals (R/, G/, and B/ in the case of a low novel level).

At high level, R31, G3. B3 is output) is added to the signal switching circuit 21, the outputs R8 and GO9Bo of the signal switching circuit 21 are R' and G/B3, respectively.
, B/ are obtained, outputs such as RGB personal computer inputs are displayed on the television screen as the main screen section 2, and on-air signals are displayed on the sub-screen section 3.

(11) When the main screen is the on-air signal and the sub-screen is the second video signal, or when the parent screen is the second video signal and the sub-screen is the on-air signal. (At this time, the second video signal is an on-air signal or a VTR.

Refers to video output from cameras, etc. ) At this time, in Fig. 2, the insertion circuit 16°17.1
The switching signal applied to 8 is high level and the insertion circuit 1e5
, 17, 1.8 outputs R', G', R/.

There are small screen signals R2, G2 . B2 is obtained and applied to the signal switching circuit 21. When the switching signal pulse applied to the signal switching circuit 21 is at a low level, the small screen signals R2, G2, . B2 is obtained and the switching signal pulse is at a high level, the main screen signal R3 is output from the signal switching circuit 21.
, G3. B3 can be obtained, and a parent-child screen PinP television can be realized.

As described above, according to the apparatus shown in FIG. 2, it is possible to realize a PinP television in the form of a partial computer, but there are major problems as described below.

The horizontal and vertical synchronization frequencies of personal computers and the horizontal and vertical synchronization signals of on-air signals and V'TR signals often deviate considerably. When a personal computer (main screen) and on-air or VTR signals (child screen) are being output on the TV screen, there is no problem because the clamp is applied in synchronization with the main screen of the computer.
(ii) Main screen.

If the child screen is an on-air signal or a VTR signal, the synchronization of the clamp pulses is the synchronization of the main screen, which is different from the synchronization of a personal computer. Insertion circuit 16, 17.18
It is common to switch the signals at the same time as clamping, but the signals of R1, G, , B1 and R2, G2 . B2
If the phases of the signals of R1, G1 . The clamp level changes depending on the signal component of B1, and the outputs R', G/
, B/ changes and switches. This appears as crosstalk in which the personal computer influences the contents of the child screen on the television screen.

OBJECTS OF THE INVENTION It is an object of the present invention to make it possible to process on-air signals, VTR signals, and personal computer signals without adversely affecting sub-screens in a PinP television state.

Structure of the Invention The present invention +d includes a first insertion circuit for synthesizing a first RGB signal (for example, a personal computer signal) and a second RGB signal (for example, an on-air signal), and a clamp on the first insertion circuit. A second insertion circuit is provided which adds a pulse and a signal switching pulse and combines the output of the first insertion circuit with a third RGB signal. The present invention is characterized in that a switch circuit that closes only when a specific signal is received is provided between the signal and the first insertion circuit.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention is shown in FIG. Components in the figure that are the same as those in FIG. 2 are given the same numbers. RGB output signals R, , G1 . of a personal computer, etc. B1 is added to switch circuits 25, 26, and 27, respectively, and this switch circuit 2
5, 26, 27 outputs to capacitors 10, 11, 12
We are trying to supply it to These switch circuits 25
, 26. '27 is configured to apply a switching signal from the RGB signal switching pulse generation circuit 24 so that it is turned on when the main screen is a personal computer, and turned off at other times.

Therefore, the main screen and sub-screen are on-air signals and VTRs.
In the case of the signal, the RGB signals (R1, G1. B1) from the partial computer will never pass through the switch circuit.

FIG. 5 shows a specific embodiment of the switch circuits 25, 26, and 27.

The RGB signal switching pulse from the RGB signal switching pulse generation circuit 24 is at a high level when the RGB signals (R1, G1, B) are the main screen, and is at a low level at other times. The transistor 20 and the resistor 31 form a shemisota follower circuit, and the output ends of the emitter follower circuit are connected to the diodes 32, 34, and 3 through the resistors 33 and 36.37, respectively.
Connect to the anode of 6, and the cathode side is R, G, and B1.
Connect to the side. Here, 38.39.40 is the load resistance.

In the above configuration, the RGB signal (R4, G1.B1) of the partial computer is displayed as the main screen.
When in mode, the base potential of transistor 30 is high and its emitter potential is also high. Therefore, diode 32
．． 34.36 (d both on, R1, G1.B
The signal 1 becomes one input of each insertion circuit 16, 17, and 18.

Except for the RGB seventh bead, the base potential and emitter potential of the transistor 3o are low, and the diodes 32, 34,
36 becomes a cutoff, and the signal of R1t"1 yBl is cut off. Therefore, when on-air or VTR signals are displayed as the parent screen and child screen, there is no crosstalk even if a personal computer is connected. Good images can be obtained.

Effects of the Invention As described above, according to the present invention, the RGB of the personal computer supplied as one input of the first insertion circuit
A switch circuit is inserted in the signal supply path, and when the RGB signals of the personal computer are displayed as the main screen, the switch circuit is closed to supply the RGB signals, and at other times, the supply of the RGB signals is stopped. Depending on the parent screen,
When on-air or VTR signals are displayed as a sub screen, a clear image without crosstalk can be obtained even if a personal computer is connected.

[Brief explanation of drawings]

FIG. 1 is a front view of the screen of a television receiver, and FIG. 2 is a block diagram of a conventional switching device for a television receiver.
FIG. 3 is a waveform diagram for explaining the operation of the first insertion circuit, FIG. 4 is a block diagram of a signal switching device according to an embodiment of the present invention, and FIG. 5 is a diagram showing main parts of the signal switching device. FIG. 3 is a circuit diagram showing a specific example. 1 Television receiver, 2... Main screen, 3...
Child screen, 16, 17, 18...first insertion circuit, 21
Second insertion circuit, 24... B, G, B signal switching pulse generation circuit, 25, 26.27... Switch circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person
Figure 2 Figure 3

Claims (1)

[Claims] A first RGB signal that combines a first RGB signal and a second RGB signal.
and a second insertion circuit that combines the output signal of the first insertion circuit and the third RCiB signal, which adds a clamp pulse and a signal switching signal to the first insertion circuit, and adds a clamp pulse and a signal switching signal to the first insertion circuit. A signal switching signal is applied to the second insertion circuit, and the gap between the first RGB signal and the first insertion circuit is closed only when the first RGB signal is a specific signal, and the signal is transferred to the first insertion circuit. A signal switching device equipped with a switch circuit that supplies power to the insertion circuit.