JPS6321397B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a system switching device for a multi-system color television receiver, and particularly to a system switching device for a multi-system color television receiver, which can receive signals of the same color of color television in one of at least two systems. The present invention relates to a system switching device for a multi-system color television receiver.

As is well known, there are two types of color signals for color television: the PAL system and the SECAM system. Here, the PAL method is a method in which a color subcarrier is quadrature-two-phase modulated with two color signals and transmitted, and the color signal is demodulated by synchronous detection on the receiving side. In the SECAM method, color signals are sequentially FM-modulated and transmitted, so a color order determination signal is inserted into the vertical retrace period. By the way, in some countries or regions, the color signal of color television is
Two types are used: PAL and SECAM, and depending on the location, you may be able to receive either one. When color television is sold in such a wide area (eg, Europe), a multi-system color television receiver capable of receiving both systems is sold.

FIG. 1 is a block diagram of a conventionally known system switching device for a multi-system color television receiver. In the figure, the chroma signal input terminal 1 has
Chroma signal is input. This chroma signal may be a PAL chroma signal or
Or is it a SECAM chroma signal? The chroma signal input to the input terminal 1 is applied to a PAL chroma signal processing circuit 2 and a SECAM chroma signal processing circuit 3 (hereinafter these chroma signal processing circuits will be simply referred to as processing circuits). Processing circuit 2
operates when a PAL chroma signal is input to input terminal 1, and derives a PAL chroma signal discrimination output a and a demodulated signal d. On the other hand, if the chroma signal input to input terminal 1 is a SECAM chroma signal, processing circuit 3 operates to
The signal discrimination output b is derived, and its demodulated signal e is derived. The discrimination output a is input to the discrimination changeover switch 5. The discrimination signal b is inverted by the inverter 7 and inputted to the discrimination changeover switch 5 as a signal b'.

By the way, normal PAL chroma signal or
When the SECAM chroma signal is being received, the decision outputs a and b appear in opposite logic states. However, in the playback output of a VTR of poor quality, especially during special playback, the discrimination output becomes different as shown in FIG. 3, which will be described later. Therefore, in such a case, the discrimination changeover switch 5 is manually switched. When the PAL chroma signal and SECAM chroma signal are received as normal signals,
The switching signal c output from the discrimination switch 5 is used to control the mode switching switch 4. That is, when the processing circuit 2 derives the discrimination output a, the system switching switch 4 provides the demodulated output d demodulated by the processing circuit 2 to the output terminal 6. On the other hand, when the processing circuit 3 derives the discrimination output b, the mode changeover switch 4 derives the demodulated output e demodulated by the processing circuit 3 to the output terminal 6.

On the other hand, if either the PAL chroma signal or the SECAM chroma signal is an abnormal signal, the customer (or user) must operate the discrimination switch 5 to change the system selection switch so that a normal screen can be obtained. 4 had to be switched to the correct state.
Therefore, when there is an abnormality in the PAL chroma signal or the SECAM chroma signal, a manual switch must be used to switch, and there is a problem in that the switching cannot be done automatically.

Therefore, it is an object of the present invention to prevent the system changeover switch from entering an incorrect switching state due to the arrival of an abnormal signal, without requiring the customer to operate a manual switch, even when an abnormal signal is being received. An object of the present invention is to provide a system switching device for a multi-system color television receiver.

To summarize, the present invention is a PAL/SECAM automatic discrimination switching device for a multi-system color television receiver, in which a normal operating state is memorized using an RS flip-flop, so that the system switching switch is prevented from erroneously receiving an abnormal signal. This prevents the device from switching to the closed state.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram of a system switching device for a multi-system color television receiver according to an embodiment of the present invention. This embodiment differs from the conventional one shown in FIG. 1 in that an RS flip-flop 8 is used in place of the manual changeover switch 5.
The RS flip-flop 8 is constructed by combining two NAND gates 8a and 8b, for example. Then, the discrimination output a of the processing circuit 2 is applied to the reset input terminal R of the RS flip-flop. The discrimination output b is applied to the set input terminal S of the RS flip-flop 8. The output Q (ie, signal c) of the RS flip-flop 8 is given as a switching signal to the mode switching switch 4. Method selection switch 4
selects processing circuit 2 when signal c is at high level, and selects processing circuit 3 when signal c is at low level.

FIG. 3 is a diagram schematically showing the logical states of the discrimination outputs of the two methods for the received signal to explain the operations of FIGS. 1 and 2. FIG. In Figure 3, the abnormal PAL chroma signal and the abnormal SECAM chroma signal are signals in which one of the discrimination outputs is normal, but the other discrimination output makes a misjudgment, and both discrimination outputs make a misjudgment. It does not mean that it is. That is, the abnormal PAL chroma signal refers to a signal that the processing circuit 3 misidentifies as a SECAM chroma signal. Abnormal SECAM
The chroma signal refers to a signal that the processing circuit 2 misidentifies as a PAL signal.

FIG. 4 is a diagram schematically showing the logic states of each input and output of the RS flip-flop.

Figure 5 shows the RS for the discrimination output of the circuit in Figure 3.
This is a time chart for explaining the output state of a flip-flop.

Next, the specific operation of this embodiment will be explained with reference to FIGS. 2 to 5.

(1) Operation when a normal PAL chroma signal is received When a normal PAL chroma signal is received,
Both the determination output a determined by the processing circuit 2 and the determination output b determined by the processing circuit 3 are correct determination outputs. Therefore, the discrimination output a becomes high level, and the discrimination output b becomes low level. This high level discrimination output a is RS
Since it is applied to the reset input terminal of flip-flop 8, the output Q (ie, signal c) of RS flip-flop 8 becomes low level. Therefore, the system selector switch 4 selects the processing circuit 2 and derives the demodulated output d at the output terminal 6.

(2) Operation when receiving an abnormal PAL chroma signal When receiving an abnormal PAL chroma signal,
Although the discrimination output a is normal, the discrimination output b is in an erroneous discrimination state (that is, a high level; indicated by an asterisk in the figure). For this reason, the RS flip-flop 8
Since both the set and reset inputs of the RS flip-flop are at a high level, the RS flip-flop remains in its previous state. Therefore,
The output Q remains at a low level and does not change. Therefore, even when an abnormal PAL chroma signal is received, the demodulated output d of the PAL chroma signal is derived from the output terminal 6.

(3) Operation of B/W signal reception status B/W signal indicating flanking period or writing period
When receiving the W signal (monochrome broadcasting), both discrimination outputs a and b are at low level. Therefore, the output Q and the output of the RS flip-flop 8 both become high level, so that the demodulated output d of the PAL chroma signal is derived from the output terminal 6.
However, in this case, since the color killer is operating, no demodulated signal appears in the first place, and there is no problem.

(4) Operation when a normal SECAM chroma signal is received When a normal SECAM chroma signal is received, the discrimination output a becomes low level and the discrimination output b
becomes high level. Therefore, the output Q of the RS flip-flop 8 becomes high level, and the output becomes low level. Therefore, since the system changeover switch 4 is switched to the processing circuit 3 side, the demodulated output e of the SECAM chroma signal is derived from the output terminal 6.

(5) Operation when an abnormal SECAM chroma signal is received When an abnormal SECAM chroma signal is received, both discrimination outputs a and b become high level. In this case, the discrimination output a represents an erroneous discrimination. Therefore, both the set input terminal and reset input terminal of the RS flip-flop 8 are given a high level. However, in response to both inputs being at high level, RS flip-flop 8 maintains its previous state and does not change its output at all, so that output Q remains at low level. Therefore, the mode selector switch 4 is not switched at all, and the processing circuit 3 continues to be in the selected state. Therefore, from output terminal 6
A demodulated output e of the SECAM chroma signal is derived.

By the way, in the embodiment shown in FIG. 2, as an example of the configuration of the RS flip-flop 8, a case was described in which it was configured with two NAND gates 8a and 8b.
It may also be constructed by combining various other logic circuits. For example, by combining two Noah gates, RS
A flip-flop can also be constructed.

As described above, according to the present invention, in a multi-system color television receiver that displays images based on signals of two systems, even when an abnormal signal is received, the system switching switch can be manually switched. This eliminates the need to operate a manual switch every time an abnormal screen occurs, and provides unique effects such as being able to reproduce the same screen as when normal chroma signals are always being received.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional system switching device for a multi-system color television receiver. FIG. 2 is a block diagram of a system switching device for a multi-system color television receiver according to an embodiment of the present invention. Third
The figure is a diagram schematically showing the discrimination state of each type of chroma signal in FIGS. 1 and 2. Fourth
The figure is a diagram schematically showing the logic state of an RS flip-flop. FIG. 5 is a time chart showing the output state of the RS flip-flop with respect to the discrimination output of the circuit of FIG. In the figure, 1 is an input terminal, 2 is a PAL chroma signal processing circuit, 3 is a SECAM chroma signal processing circuit, 4 is a system selection switch, 5 is a discrimination selection switch, 6 is an output terminal, 7 is an inverter, and 8 is an RS flip-flop. show.

Claims (1)

[Scope of Claims] 1. A multi-system color television receiver that displays images based on either a chroma signal of a first system or a chroma signal of a second system, comprising: a first chroma signal processing means that operates when a chroma signal is received; a second chroma signal processing means that operates when a chroma signal of the second method is received; a chroma signal that is a chroma signal of the first method; a first method determining means for determining whether the chroma signal is a chroma signal of the second method; an output of the first method determining means is given as one input; an RS flip-flop that derives an output of the first or second logic state when the output of the second method determining means is given as the other input;
and a switching means for switching and deriving the output of the first chroma signal processing means or the output of the second chroma signal processing means based on the first or second logic state of the RS flip-flop. System switching device for color television receivers.