JPS6355832B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-system color television receiver, and more particularly to an improvement in an automatic discrimination switching circuit.

Examples of this type of receiver include PAL and
Figure 1 shows a block diagram of a multi-system color television receiver compatible with the SECAM system. In the figure, 1 is a color signal input terminal, 2 is a first decoder, 3 is a second decoder, 4 is a changeover switch, and 5 is an output terminal. 6 is a method discrimination output for switching the changeover switch 4. FIG. 2 shows the circuit shown in FIG. 1 in which the automatic switching malfunction is corrected when an abnormal signal is received. 8 is a manual discrimination output changeover switch, 7 is a discrimination output obtained from the second decoder 3, 10 is an inverter, 7 is an inverted output of the discrimination output 7, and 9 is an output switched by a discrimination output changeover switch 8.

Next, the operation will be explained. In FIGS. 1 and 2, decoders 2 and 3 have a so-called color killer function that demodulates signals of each system and simultaneously stops the demodulation function for signals of other systems. The system discrimination outputs 6, 7 represent outputs related to the color killer operation of the respective decoders. The state of this output is shown in FIG.
Here, if the color signal applied to the color signal input terminal 1 is a poor quality signal from a VTR, or if the signal is degraded due to ghosting or other interference during ON-AIR reception, Each decoder function does not necessarily work satisfactorily. This is especially true when it is necessary to expand the color killer margin in the case of a weak electric field. The abnormal signal shown in FIG. 3 means a signal under adverse conditions as described above. In addition, the first and second
In the figure, the changeover switch 4 is set to the first decoder 2 side when the system discrimination output 6 is "H" in FIG. 1, and when the discrimination output 9 is "H" in FIG. It is assumed that the operation is performed on the second decoder 3 side when . Moreover, the first decoder 2
It is assumed that the PAL decoder and second decoder 3 are SECAM decoders.

When an abnormal PAL signal arrives at the color signal input terminal 1, there is no problem in the states shown in FIGS. 1 and 2, but when an abnormal SECAM signal arrives, the discrimination output 6 in FIG. H”,
Further, in FIG. 2, since the discrimination output 9 is set to "H", the changeover switch 4 is operated to the first decoder 2 side, and a normal demodulated output cannot be obtained at the output 5. In such a case, if the discrimination output changeover switch 8 in FIG. 2 is turned to the side opposite to that shown in the figure, that is, to the second decoder 3 side, the discrimination output 9 becomes "L", and the changeover switch 4 is operated to the second decoder 3 side. Normal reception is possible. That is, in Figure 2,
The discrimination output changeover switch 8 has no effect on normal signals, but the discrimination output changeover switch 8 can correct malfunctions caused by automatic switching of the changeover switch 4 in response to abnormal signals.

Since the conventional multi-system color television receiver is configured as described above, when an abnormal signal is received, both the first decoder 2 and the second decoder 3 are operating, so switching is not possible. An undesired signal is always applied to one of the switched terminals of the switch 4. Changeover switch 4
The switch 4 is usually constructed from an electronic switch, but this switch 4 requires a circuit configuration with very little crosstalk, and its realization requires high cost and high design precision.

This invention was made in order to eliminate the drawbacks of the conventional decoders as described above, and uses a discrimination changeover switch to correct malfunctions caused by automatic switching when an abnormal signal is received. By controlling the other decoder so that it does not operate at the same time, the signal is configured so that it appears only on one of the switched terminals of the switch, thereby eliminating the need for special consideration of crosstalk between the switch. The purpose of the present invention is to provide a multi-system color television receiver.

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 4, 1 to 7 are the same as shown in FIG. 11 and 12 are transistors, 13
20 are resistors, 21 and 22 are diodes, and 23 is a discrimination switch. c and d are the first
This is a convenient terminal for stopping the decoding function of the decoder 2 and the second decoder 3. For example, if the cathodes of the diodes 21 and 22 are grounded, the system determination outputs 7 and 6 of the respective decoders will go to "L" level. It is configured so that FIG. 5 is an explanatory diagram of the operation of FIG. 4.

Now, considering the case where a normal PAL signal arrives at the color input terminal 1, the discrimination output 6 is at the "H" level, so the changeover switch 4 operates on the first decoder 2 side, and the demodulated output on the PAL side changes. Appears on output terminal 5. On the other hand, the discrimination output 6 is connected to the base of the transistor 11 through a resistor 19, but the emitter of the transistor 11 is reverse biased with respect to the base potential by resistors 15 and 16.
When the discrimination changeover switch 23 is operated to the b side, the transistor 11 is cut off. Therefore, diode 21 is also cut off,
The decoder 3 is not affected in any way, and furthermore, due to its own color killer operation, no demodulated signal is output. Further, since the determination output 7 is "L", the transistor 12 is cut off, the diode 22 is also cut off, and the operation of the decoder 2 does not stop. Further, when the switch 23 is operated to the a side, the potential of the emitter of the transistor 11 decreases and the transistor 11 is turned on, so that the diode 21 is turned on and the decoding function of the decoder 3 is stopped. Since the discrimination output 7 becomes "L", the transistor 12 and the diode 22 are cut off, and the operation of the decoder 2 does not stop. In the end, the switching of the discrimination changeover switch 23 has no effect on the output 5.

Next, considering the case where a normal SECAM signal arrives, the discrimination output 6 of the decoder 2 is at the "L" level, and the switch 4 operates on the decoder 3 side to take out the output of the decoder 3. Switch. In this case, as in the case of normal PAL signal reception, transistor 11 switches to switch 23.
The decoder 3 is turned off regardless of the
The determination output 7 of the transistor 12 is at the "H" level, but the transistor 12 is connected to the resistor 17 similarly to the transistor 11.
and 18, the emitter potential is reverse biased with respect to the base potential, and when the switch 23 is on the b side, it is on, and when it is on the a side, it is off, and the diode 22 is also turned on and off accordingly, and the switch 23 is on the b side. In either case, the decoding function of the decoder 2 is stopped, but the decoding function of the decoder 3 is not stopped in either case, and is ultimately not affected by the switching of the discrimination changeover switch 23. As mentioned above,
When a normal signal is received, the discrimination changeover switch 23 has no effect, and the correct output is always automatically switched and taken out.

Next, a description will be given of when an abnormal signal is received.
Thinking about when a PAL abnormal signal arrives,
Assuming that the changeover switch 23 is not present, the discrimination outputs 6 and 7 become "H" level at the same time, and the demodulated outputs from both decoders 2 and 3 appear at both switched terminals of the switch 4. Next, if the switch 23 is turned to side a, the transistor 11 is turned on, the diode 21 is turned on, and the function of the decoder 3 is stopped.
The output of is not applied to switch 4.

Furthermore, if the switch 23 is turned to the b side, the transistor 12 is turned on, the diode 22 is turned on, and the function of the decoder 2 is stopped.
The determination output 6 becomes "L" level. Therefore, since switch 4 operates on the decoder 3 side, the output of decoder 2 is not applied to switch 4. However, in the latter state, the correct demodulated output cannot be obtained at the output 5, so the switch 23 may be set to the a side. Operation in case of SECAM abnormal signal
It is the same as PAL, and after all, the discrimination changeover switch 2
3 functions as a selection switch for the demodulated outputs of decoders 2 and 3 when an abnormal signal is received, and also functions to stop the decoding function of the decoder that is not selected.

In the above embodiment, the switch 4 is configured to be switched by the discrimination output 6 of the decoder 2, but it may be configured to be switched by the discrimination output 7 of the decoder 3.

As described above, according to the present invention, by applying a signal to only one of the switched terminals of the changeover switch, the changeover switch does not need to require special accuracy against crosstalk. This has the effect of providing an inexpensive multi-system color television receiver.

[Brief explanation of drawings]

Figure 1 is a block diagram of an automatic discrimination switching circuit for a multi-system color television receiver, Figure 2 is a block diagram of a conventional automatic discrimination switching circuit that can correct automatic switching malfunctions when an abnormal signal is received, and Figure 3 1 and 2, FIG. 4 is a block diagram showing an embodiment of the present invention, and FIG. 5 is an explanatory diagram of the operation of the circuit shown in FIG. 4. 2, 3...decoder, 4...changeover switch,
6, 7...Method discrimination output, 23...Discrimination changeover switch. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1 A first decoder for demodulating a color signal of a first method, a second decoder for demodulating a color signal of a second method different from the first method, and these first or second decoders. a changeover switch that receives a method discrimination output based on a color signal input to the decoder, and selectively outputs a demodulated output from the first or second decoder based on the method discrimination output;
a discrimination changeover switch that switches the state of the first decoder, and when the method discrimination output from the first decoder indicates a color signal of the first method and the discrimination changeover switch is in the first state, the second decoder The demodulation operation is stopped, and when the method discrimination output from the second decoder indicates a color signal of the second method and the discrimination changeover switch is in a second state, the demodulation operation of the first decoder is stopped. A multi-format color television receiver equipped with means.