JPH0311155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for switching between two different types of signals in a television receiver.

As an example of two types of signals, demodulated signals of normal television broadcasting and teletext broadcasting will be explained.

One type of television multiplex broadcasting is teletext, and the demodulated signal of teletext is often treated as a digital signal because of its ease of control, ease of information storage, and resistance to distortion.

When displaying a teletext signal using a color television receiver, the demodulated teletext signal is a digital signal with three primary colors, R and GB, and this signal is subjected to controls such as brightness and contrast.
A common method is to input the image to a CRT drive circuit and display it.

On the other hand, as a normal method for displaying television signals, after performing color demodulation, (a) a color difference signal (R-
(b) When four signals, Y, G-Y, B-Y) and luminance signal Y are input to the CRT drive circuit, and (b) three of the three primary color signals (R, G, B) after passing through the matrix circuit.
There are cases where two signals are input to the CRT drive circuit.

When displaying normal television broadcasts and teletext by automatically or manually switching between them on one color television receiver, in the case of (b) above, the demodulated output of normal television broadcasts can also be displayed as teletext. The demodulated output of is also a three primary color signal, so if the pedestal level, signal amplitude, etc. are aligned, each can be easily displayed using a switching circuit, but in the case of (a) above, the four signals input to the CRT drive circuit, it is necessary to convert the three primary color demodulated output of the teletext broadcast into another format.

In addition, if one circuit or IC is used to configure a circuit or IC that can be used in both cases (a) and (b), the circuit becomes complicated, especially when integrated into an IC. As the number of pins increases, the price increases.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks, simplify the circuit configuration, and provide a signal switching device that can reduce the number of pins and reduce the cost especially when integrated into an IC.

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a main part of an example of a teletext receiver in case (a) mentioned above. In Figure 1, 1
2a is a video detection circuit, 2a is a color demodulation circuit, 3a is a signal switching device, 4a is a CRT drive circuit, 5 is a teletext demodulation circuit, 6 is a control circuit for contrast, brightness, etc., and 7 is a CRT (cathode ray tube). Each color difference signal output R-Y, G-Y, B- of the color demodulation circuit 2a
Y, and the luminance signal Y and the output R of the control circuit 6,
G and B are automatically or manually switched by the signal switching device 3a, and sent to the CRT drive circuit 4a as R-Y, G-Y, B-Y, and Y signals.

The output of the teletext demodulation circuit 5 is R, G,
Since it is often treated as a digital signal of the three primary colors of B, after controlling the contrast, brightness, etc. in the control circuit 6, the signal switching device 3a
In this case, the three primary colors R, G, and B output from the control circuit 6 and a certain brightness level Y' are given, and R, G, and B are
The respective relationships of Y' are the outputs R-Y, G-Y, B-Y of the color demodulation circuit 2a in the CRT drive circuit 4a.
If the relationship is made to be equal to that, images can be displayed on the CRT 7 with the circuit of the CRT drive circuit 4a unchanged.

FIG. 2 is a block diagram of a main part of an example of a teletext receiver in the case (b) mentioned above. In Figure 2, 1
2b is a video detection circuit, 2b is a color demodulation circuit, 3b is a signal switching device, 4b is a CRT drive circuit, 5 is a teletext demodulation circuit, 6 is a control circuit for contrast, brightness, etc., and 7 is a CRT.

Since the output of the color demodulation circuit 2b is the primary colors R, G, and B, if the outputs R, G, and B of the control circuit 6 are given the same pedestal level and the same amplitude as the output of the color demodulation circuit 2b, characters will be displayed on the CRT 7. Broadcast signals can be displayed.

Next, considering the cases of FIG. 1 and FIG. 2, in the above example, for example, the color demodulation circuit 2a,
If the output of 2b is 3 primary colors, the pedestal level is
In the case of 2V and color difference output, the color difference signal is 7.8V and the luminance signal is 6.5V, which are different values, so a pedestal level must be given to the output of the teletext control circuit 6 according to each case. .

Now, if we compare the cases in Figure 1 and Figure 2,
When the outputs of the color demodulation circuits 2a and 2b are three primary colors, the number of inputs is one less than the color difference output. Therefore, it is possible to switch the pedestal level corresponding to the cases of FIG. 1 and FIG. 2 using the components of the luminance signal. In other words, it is possible to determine that when a luminance signal component is present, it is a color difference signal input, and when no luminance signal component is present, it is a primary color signal input.

FIG. 3 is a block diagram showing an embodiment of the present invention which is effective for use in 3a of FIG. 1 and 3b of FIG. 2. In FIG. 3, 8, 9, 10, and 11 are input terminals connected to the output terminal of the color demodulation circuit 2a or 2b, and 8', 9', 10', and 11' are connected to the teletext control circuit 6. input terminal, 12,1
3, 14, 15 are switching circuits; 16 is a discrimination circuit whose input terminal is connected to the input terminal 11; 17 is a control circuit subsequent to the discrimination circuit 16; 18, 19,
20 and 21 are output terminals of the switching circuits 12, 13, 14, and 15, and 22 is an input terminal for a switching signal.

Input terminals 8, 9, 10 have R, G,
B3 primary color output or 3 of R-Y, G-Y, B-Y
Color difference output is input. When the color demodulated output is three primary colors, nothing is supplied to the input terminal 11, and when the color demodulated output is a color difference output, a luminance signal is supplied. Input terminal 8',
9' and 10' are the three primary color signals R, G, and B for teletext broadcasting.
are given respectively. A certain constant voltage is applied to the input terminal 11'. Switching circuit 12, 13, 1
4 and 15, the signals obtained at the output terminals 18, 19, 20, and 21 by the switching signal applied to the terminal 22 are changed to 8, 9, 10, 11, or 8', respectively.
9', 10', or 11', and the output of the control circuit 17 changes the teletext signal level. Discrimination circuit 16 has input terminal 1
The presence or absence of the signal 1 is determined and the output is sent to the control circuit 1.
Give to 7. The control circuit 17 functions to change the signal level of teletext for the switching circuits 12, 13, 14, and 15 based on the output of the discrimination circuit 16.

With the above configuration, even if the output of the color demodulation circuit of the television receiver is three primary colors or a color difference signal and a luminance signal, the television broadcast signal and teletext signal can be switched and displayed. A circuit or IC can be constructed.

Next, a specific example of the configuration of the discrimination circuit 16 shown in FIG. 3 will be explained with reference to FIG. 4. In FIG. 4, 30 is a power supply terminal, 32 and 35 are NPN transistors, and 33, 34, 36, and 37 are resistors. Transistor 32 and transistor 35 constitute a differential amplifier circuit. A bias voltage is applied to the base of the transistor 35 by a resistor 36 and a resistor 37.
_VR is given. When the color demodulation circuit 2a outputs the color difference signals R-Y, G-Y, B-Y and the luminance signal Y, the luminance signal is input to the terminal 31, and the color demodulation circuit 2b outputs the three primary color signals R, G, When B is output, no signal is input. Therefore, depending on the signal level applied to the terminal 31,
If the bias voltage V _R is set so that the transistor 35 is turned ON and OFF, a binary signal corresponding to the presence or absence of a luminance signal can be obtained from the terminal 38. The same effect can be obtained even if an NPN transistor is used as the current source instead of the resistor 33.

FIG. 5 shows another specific circuit example of the discrimination circuit 16. In FIG. 5, 40 is a power supply terminal, 42, 4
3, 44, 46, 48, 50, 51, 53, 5
9, 60, 62, 64, 67, 68 are resistances, 4
5, 55, 56, 57, 61, 63 are NPN transistors, 47, 49, 66 are PNP transistors, 52, 54, 65 are diodes, 58 is a DC power supply, 69 is an input terminal, and 41 is an output terminal.

In FIG. 5, when a luminance signal of a certain level is input to terminal 69, the emitter potential of transistor 66 rises, and therefore the base potential of transistor 56 also rises. When the base potential of this transistor 56 is higher than the base potential of the transistor 55, the transistor 56 is turned on and the transistor 55 is turned off. Therefore, no current flows through the resistor 53 and the diode 54, and the transistor 4
9 is also turned off, no current flows through the resistor 50, the resistor 51, and the diode 52, and the output potential obtained at the terminal 41 becomes zero. When the three primary color signals R, G, and B are output from the color demodulation circuit 2b, the terminal 6
9 becomes the ground voltage, and the base voltage of the transistor 56 becomes lower than the base voltage of the transistor 55, so that the transistor 56 is turned off and the transistor 55 is turned on. At this time, a potential drop occurs across the resistor 53 and the diode 54, current flows through the transistor 49, and an output voltage determined by the current flowing through the resistor 51 and the diode 52 is obtained at the output terminal 41. Also, since the voltage obtained by the resistor 50, resistor 51, and diode 52 is applied to the base of the transistor 61, the transistor 61
ON, and as a result, the base voltage of the transistor 56 changes the emitter voltage of the transistor 63 to the resistor 6.
4, the voltage is divided by the resistor 60 and the resistor 62, and this voltage is set to a value low enough to turn off the transistor 56, so the ON-OFF characteristic of the transistor 56 is extremely sharp. This circuit is a type of Schmitt trigger circuit with hysteresis characteristics.

Next, a specific circuit example of the control circuit 17 shown in FIG. 3 will be described with reference to FIG. 6.

In FIG. 6, 70 is a power supply terminal, 71, 7
3, 74, 75, 77, 81, 85, 87, 91
is resistance, 72, 78, 80, 82, 84 are PNP
Transistor, 76, 86, 89, 90, 92,
94 and 96 are NPN transistors, and 79 and 83 are diodes. Terminal 88 is an input terminal that provides the output of the luminance signal discrimination circuit 16, terminal 93 is a control input terminal that determines the pedestal level, and terminal 95 is an output terminal.

In FIG. 6, when the color demodulation circuit 2a outputs the color difference signals R-Y, G-Y, B-Y and the luminance signal Y, the input terminal 88 of the control circuit 17 becomes the ground voltage as described above. , transistor 8
6 is turned off, and current flows through the transistor 84. A resistor 7 is connected to the base of the transistor 84.
1, 73, 74, 75, voltage determined by diode-connected transistors 72, 76
A voltage V ₁ is applied to the base of the transistor 80, and a voltage V ₂ similarly determined by the resistors 71, 73, 74, and 75 and the transistors 72 and 76 is applied to the base of the transistor 80. Therefore, when transistor 86 is off, the base potential of transistor 89 is
V ₁ +2V _BE , the base potential of transistor 90 is V ₂ +2V _BE , and since V ₁ >V ₂ , transistor 89 is turned on and transistor 90 is turned off.

Further, three primary color signals R, G,
When B is output, the input terminal 88 of the control circuit 17 is given a certain constant voltage as described above,
Transistor 86 is turned on and current flows through resistor 85. If the voltage across resistor 85 is kept lower than V ₁ , the voltage across the base of transistor 89 is determined by resistor 85 and diode 83 . If the value of the resistor 85 is set so that the base voltage at this time is lower than V ₂ +2V _BE , when a certain voltage is applied to the terminal 88, the transistor 90
is turned on, and the transistor 89 is turned off.

Next, set the resistance value of the resistor 91 to R, and set the resistance value of the transistor 91 to R.
If the collector current of 2 is I, when the terminal 88 is grounded, the transistor 89 is ON.
Therefore, the emitter potential of transistor 89 is V ₁ +V _BE . Therefore, the collector potential of the transistor 92 becomes V ₁ +V _BE −RI, and the output terminal 9
5, a potential of V ₁ −RI is obtained. When a certain potential is applied to terminal 88, transistor 90
To turn on, the emitter potential of transistor 90 is V ₂ +V _BE and the collector potential of transistor 92 is
V ₂ +VBE-RI, and output terminal 95 has V ₂ -
A potential called RI is obtained. Since the collector current I of the transistor 92 can be changed by the bias applied to the terminal 93, the pedestal level can be switched in two stages and a range of variation can be provided at the same time with the configuration shown in FIG.

Furthermore, a differential amplifier circuit can be used as an example of a part of the specific circuits of the television signal and teletext signal switching circuits 12, 13, 14, and 15.

By adopting the above configuration, signal switching is possible that allows teletext signals to be displayed even when the color demodulation circuit output of the television receiver is the three primary colors of R, G, and B, or when the color difference signal and luminance signal are used. It has the excellent advantage of being able to implement a device, and especially when integrated into an IC, costs can be reduced.

In the above explanation, the circuit that switches between the output of the color demodulation circuit of the television receiver and the output of the demodulation circuit of the teletext receiver has been described. For example, when using computer calculation results,
It can also be used when displaying on a CRT, or when displaying the R, G, B output of a video camera on a CRT, and can also be used when switching between two types of signals other than television signals. Needless to say, the present invention can also be applied to the case where the output is controlled by the method.

[Brief explanation of the drawing]

1 and 2 are main part block diagrams showing an example of a teletext receiver, FIG. 3 is a circuit configuration diagram showing an embodiment of the present invention, and FIGS. 4 and 5 are used in the present invention, respectively. FIG. 6 is a wiring diagram showing a specific example of a control circuit that can be used in the present invention. 8, 8', 9, 9', 10, 10', 11, 1
1'...Input terminal, 12, 13, 14, 15...
Switching circuit, 16... Discrimination circuit, 17... Control circuit, 18, 19, 20, 21... Output terminal, 22
...Input terminal.

Claims (1)

[Claims] 1 In a television receiver, a first signal input terminal having a plurality of terminals, a second signal input terminal having the same number of terminals as the number of the first signal input terminals, and the first signal input terminal The first input terminal includes a switching circuit, a discrimination circuit, a control circuit, and an output terminal having the same number of terminals as the number of the first signal input terminals. The output of the color demodulation circuit of the television receiver is applied to the second input terminal, and the output of the control circuit of the teletext receiver is applied to the second input terminal.
RGB signal output is given, the input terminal of the discrimination circuit is connected to the luminance signal input terminal of the first signal input terminals, the output of the discrimination circuit is connected to the control circuit, and the output of the control circuit is connected to the luminance signal input terminal of the first signal input terminals. is connected to the plurality of switching circuits, the first input terminal and the second input terminal are connected to the switching circuit, and the switching circuit is connected to the discrimination circuit and the first signal input terminal. A constant voltage is applied to the connected second signal input terminal from the control circuit of the teletext receiver, the outputs of the plurality of switching circuits are respectively connected to the output terminal, and the discrimination circuit The control circuit determines whether the color demodulation circuit output of the television receiver is a color difference signal and luminance signal or a three primary color signal, and according to the output of the determination circuit, the control circuit sets the pedestal level of the character signal to two levels. By switching and controlling the brightness of the character signal, whether the color demodulation circuit output of the television receiver is a color difference signal and a luminance signal or three primary color signals, the character signal, etc.
A signal switching circuit characterized by being able to switch between RGB and RGB.