JPH06133278A - High definition television signal demodulator - Google Patents

Abstract

PURPOSE:To discriminate whether or not a supplied detection signal is a high definition TV signal stably at all times. CONSTITUTION:A switch 7 detects the connection of an external terminal to a keyed AFC output terminal 6. A 1st discrimination signal from a video demodulation circuit 1 and a 2nd discrimination signal from an audio demodulation circuit 2 are ANDed (by an AND circuit 4) at the connection and a resulting AND signal (3rd discrimination signal) selects an input changeover switch 5. On the other hand, when not connected, the input changeover switch 5 is switched by only the 1st discrimination signal from the video demodulation circuit 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-definition television signal demodulating device (hereinafter also referred to as a high-definition TV signal demodulating device).
Regarding It is an object of the present invention to provide a high-definition TV signal demodulation device that can always stably determine whether the supplied detection signal is a high-definition TV signal.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional example of a demodulator for a MUSE signal which is an example of a high definition TV signal. Further, FIG. 3 shows a connection state between the MUSE demodulation device and other devices.

In FIG. 3A, a detection signal is supplied from a BS (satellite broadcasting) tuner to a MUSE demodulator, and a video signal and an audio signal demodulated from the MUSE signal are supplied to a monitor. Further, the MUSE demodulator supplies the BS tuner with a keyed AFC output. Keed AFC
The output controls the center frequency of the carrier wave that serves as a reference when selecting a channel with the BS tuner.

In FIG. 2, the video demodulation circuit 1 is supplied with a detection signal from the BS tuner, demodulates the video signal, and determines whether or not the input detection signal is a MUSE signal, and makes a first determination. Output a signal. This judgment is M
Performed using conditions specific to the USE signal (for example, MUSE
PLL lock is applied to the synchronization signal peculiar to the signal). The first discrimination signal is supplied to the input selector switch 5 of the monitor, and the input selector switch 5 is switched to the MUSE demodulator side when the discrimination result is the MUSE signal. On the other hand, when the determination result is the non-MUSE signal, the external device that supplies the standard TV signal (here, the NTSC signal) is switched to.

Reference numeral 2a is a voice demodulation circuit, 8 is a keyed AFC output circuit, and 6 is a keyed AFC output terminal.

In the illustrated conventional MUSE demodulator, the input selector switch 5 is switched only by using the discrimination signal of the MUSE signal / non-MUSE signal obtained by the video demodulation circuit 1. Therefore, when the discrimination signal is wrong, the input changeover switch 5 is immediately switched to the wrong side. When the BS tuner is receiving the NTSC broadcast for a long time, the video demodulation circuit 1 may erroneously determine the NTSC signal as a MUSE signal with a very small probability (conversely, if the MUSE signal is The probability of misjudging an NTSC signal is small enough to ignore it. In this case, as described above, the input changeover switch 5 is momentarily switched to the MUSE signal side, which may cause noise on the screen of the monitor.

The erroneous determination in the video demodulation circuit 1 is that random noise in the NTSC signal happens to be M during reception for a long time.
This occurs when the specified conditions of the USE signal (conditions for determining MUSE signal / non-MUSE signal) are met.

[0008]

The problem to be solved by the present invention is to provide a high-definition TV signal demodulating device capable of always stably determining whether or not the supplied detection signal is a high-definition TV signal. , What kind of measures should be taken?

[0009]

In order to solve the above problems, the present invention provides

In a high-definition television signal demodulator having a keyed AFC output terminal,

A video demodulation circuit which is supplied with the detection signal and demodulates the video signal, and which determines whether or not the detection signal is a high definition television signal and outputs a first determination signal,

An audio demodulation circuit which is supplied with the detected signal and demodulates the audio signal, and which determines whether the detected signal is a high definition television signal and outputs a second determination signal.

A connection detection circuit that detects whether or not an external terminal is connected to the keyed AFC output terminal or whether or not the keyed AFC output is supplied to an external device and outputs a detection signal.

According to the first discrimination signal, the second discrimination signal and the detection signal, it is discriminated whether or not the detection signal is a high definition television signal and a third discrimination signal is outputted. The present invention provides a high-definition television signal demodulating device characterized by being provided with a discriminating circuit.

[0015]

FIG. 1 shows an embodiment of the present invention. The same parts as those in the conventional example are designated by the same reference numerals, and a detailed description of those parts will be omitted.

In this embodiment, the audio demodulation circuit 2 to which the audio detection signal is supplied from the video demodulation circuit 1 also has the same MUSE signal / non-MUSE signal discrimination function as the video demodulation circuit 1. Then, the AN of the first discrimination signal from the video demodulation circuit 1 and the second discrimination signal from the audio demodulation circuit 2
D is taken (by the AND circuit 4), and the input changeover switch 5 is switched by the AND output (third discrimination signal).
(Since the OR circuit 3 will be described later, it is assumed here that the second determination signal is directly input to the AND circuit 4.)

As a result, even if either the audio demodulation circuit 2 or the video demodulation circuit 1 erroneously determines the NTSC signal as the MUSE signal, the input selector switch 5 does not switch to the MUSE side, and the monitor screen is displayed. The noise above can be prevented. The input change-over switch 5 is switched to the MUSE side when both the audio demodulation circuit 2 and the video demodulation circuit 1 make an erroneous determination, and this probability is the square of the probability that either one makes an erroneous determination. So it is a small probability that can be ignored.

However, using the second discrimination signal from the voice demodulation circuit 2 causes a new problem. This will be described.

As shown in FIG. 3B, when a MUSE type laser disc player (MUSE-LD player) is connected and the player performs fast-forwarding, special reproduction such as still image reproduction, the detection output of PCM audio is output to the player. Is often not output (such signals are referred to as non-standard MUSE signals). Therefore, in this case, the audio demodulation circuit 2 in the MUSE demodulator discriminates the non-MUSE signal, the output of the AND circuit 4 becomes low (that is, the non-MUSE signal is determined), and the input selector switch 5 is switched to the NTSC side. (In this case, it is considered that the second determination signal is directly input to the AND circuit 4). Therefore, when special reproduction is performed by the player, an inconvenience arises in which an image is not displayed on the monitor.

Here, the MUSE-LD player and the MUS
Considering the connection with the E demodulator, as shown in FIG. 3B, the keyed AFC output terminal 6 is not connected. Therefore, a mechanical switch 7 is attached to the keyed AFC output terminal 6, and the connection of an external terminal to the keyed AFC output terminal 6 is detected by turning on / off the switch 7, and a low detection signal when connected and a high detection signal when not connected. To get. And. The detection signal and the second discrimination signal from the voice demodulation circuit 2 are ORed (by the OR circuit 3) and the OR signal is supplied to the AND circuit 4. The OR circuit 3 and the AND circuit 4 form a discrimination circuit that outputs a third discrimination signal.

As a result, when the external terminal is not connected to the keyed AFC output terminal 6, the input changeover switch 5 can be controlled only by the first determination signal from the video demodulation circuit 1, so that it is special in the MUSE-LD player. Even during reproduction, the input selector switch 5 can be fixed to the MUSE side. In the case of a package medium such as MUSE-LD, unlike when receiving BS (satellite broadcast), a large amplitude noise component does not exist, and therefore a sufficiently stable discrimination can be made using only the discrimination signal of the video demodulation circuit 1. Is.

As described above, in this embodiment, the non-MUSE signal (that is, NTSC signal in this case) received by the BS tuner is always stable and non-MUSE signal (that is, NT).
SC signal). Furthermore, this embodiment is based on MUS
Non-standard MUS during special playback on E-LD player
It can always be stably discriminated from the E signal as the MUSE signal.

The input selector switch 5 is set to this MUSE.
It may be provided in the demodulation circuit.

Here, considering the case where special reproduction is performed by the MUSE-LD player while the external terminal is still connected to the keyed AFC output terminal 6, the mechanical switch 7 as described above is inconvenient. Therefore, the above-described mechanical detection of the connection may be replaced by the detection of the electric load used in the conventional automatic termination connection.

When the keyed AFC output is actually supplied to the external device from the MUSE demodulation circuit as in the BS tuner, the load from the output terminal 6 to the end is about 75 ohms, while the MUSE-LD player is used. On the other hand, when the keyed AFC output is not actually supplied from the MUSE demodulation circuit to the external device, the load beyond the output terminal 6 is infinite. Therefore, even when the external terminal is still connected to the keyed AFC output terminal 6, by detecting the electrical load of the keyed AFC output terminal 6,
A detection signal similar to that of the above-described embodiment can be obtained.

[0026]

As described above, the high-definition TV signal demodulating device according to the present invention can always stably determine whether the supplied detection signal is a high-definition TV signal.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an example.

FIG. 2 is a diagram showing a conventional example.

FIG. 3 is a diagram showing a connection state between a MUSE demodulation device and an external device.

[Explanation of symbols]

 1 Video demodulation circuit 2 Audio demodulation circuit 3 OR circuit 4 AND circuit 5 Input selector switch 6 Keyed AFC output terminal 7 switch 8 Keyed AFC output circuit

Claims (1)

[Claims] 1. A high-definition television signal demodulating device equipped with a keyed AFC output terminal, wherein a detection signal is supplied to demodulate a video signal, and whether or not the detection signal is a high-definition television signal is determined. And a video demodulation circuit that outputs a first determination signal, demodulates an audio signal to which the detection signal is supplied, and determines whether the detection signal is a high-definition television signal and a second determination signal. And a connection detection for outputting a detection signal by detecting whether or not an external terminal is connected to the keyed AFC output terminal or whether or not the keyed AFC output is supplied to an external device. A third determination is made by determining whether or not the detection signal is a high-definition television signal according to a circuit, the first determination signal, the second determination signal, and the detection signal. A high-definition television signal demodulation device, which is provided with a discrimination circuit for outputting a signal.