JPH0535664Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an in-vehicle television receiver.

BACKGROUND TECHNOLOGY In-vehicle television receivers that allow television images to be viewed inside trains, passenger cars, etc. are simply equipped with a television receiver in these vehicles and connected to an external antenna. It is not possible to obtain a good image just by leaving the camera in place. That is, the environment outside the vehicle is constantly changing as the vehicle travels, and the radio wave conditions are also changing accordingly, which may result in weak radio wave reception.

Therefore, in an in-vehicle TV receiver, multiple antennas are installed so that the directivity directions are different from each other, and the antenna that produces a good reception output is constantly detected which antenna is catching enough radio waves. It has a switching circuit.
Diversity
This is called the system control circuit.

Figure 3 shows a typical car-mounted TV receiver system using a diversity system control circuit (hereinafter referred to as a ``DSC circuit''). 1. A second antenna, which is connected to the receiver 4 via the DSC circuit 3. The receiver 4 includes a tuner 5, a video processing circuit 6, a video chroma circuit 7,
It is composed of a deflection circuit 8, a CRT (cathode ray tube) 9, and the like. Of course, the receiver 4 also has an audio system, but this is not shown. The video processing circuit 6 includes a VIF circuit 10 and a video detection circuit 1 as shown in FIG.
It consists of 1, a video amplifier 12, an AGC circuit 13, etc., and is usually composed of a 1-chip IC.

DSC circuit 3 operates during the vertical blanking period,
The first antenna 1 and the second antenna 2 are selectively switched one after another and connected to the receiver 4, and the video level when each antenna is connected is obtained from the amplifier 12 of the video processing circuit 6, and the antenna with the highest reception output is detected. do. The detection is performed by comparing the respective levels obtained above. Therefore, the antenna determined to have a high reception output is not connected to the receiver 4 until the next vertical blanking period.
Fixedly connected to. Then, in the next blanking period, antenna detection with high reception output is performed as in the previous blanking period. In this way, by switching to an antenna with a higher reception output every vertical blanking period, it is possible to reproduce good images even when driving in areas with changing environmental conditions. .

Problems to be Solved by the Invention However, in such in-vehicle TV receivers, the receiver 4 is usually not equipped with a noise removal circuit, so if a large noise that can become a pseudo synchronization signal is mixed in, synchronization will be disrupted. There is a problem that the image is unstable. To explain this point in detail, when a noise removal circuit used in a home television receiver is installed, the signal level when switching from a weak electric field antenna to a strong electric field antenna in the DSC circuit 3 during the vertical blanking period is Due to the operation of the noise removal circuit, the level becomes low and a weak electric field is generated in the DSC circuit 3 (the receiving output of the antenna is small).
This results in an incorrect determination. That is, immediately after switching the antenna, the gain control operation by the AGC circuit 13 cannot immediately follow the change in signal level, so as shown in FIG. 5, when a strong electric field signal as shown in b is input, The pedestal level L of that signal remains largely displaced downward, and therefore, if it exceeds the noise inverter threshold level _E1 set in the noise removal circuit, it is determined to be noise, and the portion exceeding level L is It is clamped to the noise clamp level _E2 . Note that in the figure, a represents a weak electric field signal. After a while, the AGC effect appears and the large signal is suppressed to a level comparable to that of the predetermined level signal, so that the undesired clamping operation by the noise removal circuit no longer occurs. However, DSC
If the aforementioned malfunction based on the operation of the noise removal circuit as described above occurs during the antenna switching operation by the circuit 3, an error will occur in the DSC circuit 3 itself, making it impossible to select an antenna with a large reception output. It becomes.

Therefore, as can be seen from FIG. 4, the in-vehicle television receiver is not provided with a noise removal circuit. However, as mentioned earlier, in-vehicle television receivers without such a noise removal function are inevitably subject to image deterioration.

The present invention was made in view of these points, and
An object of the present invention is to provide an in-vehicle television receiver that prevents false detection from occurring in a DSC circuit even if a noise removal circuit is provided.

Means for Solving the Problems In order to achieve the above object, the in-vehicle television receiver of the present invention includes a plurality of antennas, a receiver, and a plurality of antennas that are sequentially switched within a vertical blanking period to connect the receiver to the receiver. and a diversity system control circuit that detects an antenna with a large reception output based on the video detection output obtained from the video detection output and fixedly connects the antenna to the receiver every vertical blanking period. A noise removal circuit operates with a level set in a region exceeding a horizontal synchronizing pulse of a predetermined video signal as a noise inverter threshold level, and clamps large noise reaching the level to a small level, and the operation of the noise removal circuit is controlled. Means is provided for inactivating at least the detection operation period by the diversity system control circuit during the vertical blanking period.

Operation Since the noise removal circuit is inactive while the DSC circuit is detecting an antenna with a high reception output, a high level signal is directly applied to the DSC circuit as a high level signal. Sideways
The DSC circuit enables correct detection. on the other hand,
Since the noise removal circuit is enabled to operate except during the detection operation period, synchronization disturbance does not occur and high-quality video can be reproduced.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, etc. In FIG. 1, the same parts as in FIG. 4 are given the same reference numerals, and redundant explanation will be omitted. In the figure, reference numeral 14 denotes a noise removal circuit, which operates as a noise inverter threshold level with a level _E1 set in a region exceeding the synchronization pulse of a predetermined video signal as shown in FIG. Noise clamp level E ₂ reaches the noise of ₁
15 is a control circuit for controlling the operation period of this noise eliminating circuit 14, and 15 is a control circuit for controlling the operation period of the noise eliminating circuit 14, and is a control circuit for controlling the vertical blanking line obtained from the vertical deflection output circuit 16. Based on the pulses, a control pulse P as shown in FIG. This pulse P corresponds to a certain period within the vertical blanking period V of the video signal shown in FIG. 2A, and during this pulse period _T1 , the DSC circuit 3 shown in FIG. This includes the operating period t ₁ [Fig. 2 C]. Note that the period T ₁ may be the same as the detection period t ₁ and may be the same as the maximum vertical blanking period V. The noise removal circuit 14 is turned off during this period T ₁ and turned on during the other period T ₂ .

Therefore, during the period _T1 , when the DSC circuit 3 switches the antennas one after another, the signal from the antenna with a large reception output is not judged as noise, but is sent from the video amplifier 12 as a large signal.
Since it is fed back to DSC circuit 3, the DSC
No error occurs in the detection operation in the circuit 3.

On the other hand, during a period T ₂ (a period in which the DSC circuit does not operate) other than the period T ₁ , large noise components are removed by the operation of the noise removal circuit 14, so that a stable image can be obtained without synchronization disturbance. can be played.

Effects of the invention As described above, according to the invention, the noise removal circuit is inactive at least during the operation of detecting an antenna with a high reception output in the DSC circuit, so when switching between antennas with a high signal level
In addition to preventing false detections in the DSC circuit, the noise removal circuit is activated and removes large noises during normal image reception periods when the detected antenna is fixedly connected, so stable images with no synchronization disturbance are produced. The present invention is extremely useful because it has the effect of being reproducible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of an in-vehicle television receiver embodying the present invention, and FIG. 2 is an explanatory diagram thereof. FIG. 3 is a schematic diagram of a general in-vehicle television receiver. FIG. 4 is a block diagram of the main part of the conventional example, and FIG. 5 is an explanatory diagram thereof. 1, 2...Antenna, 3...DSC circuit, 4...
...Receiver, 14...Noise removal circuit, 15...Control circuit, _E1 ...Noise inverter threshold level,
E ₂ ... Noise clamp level, t ₁ ... Detection operation period.

Claims (1)

[Scope of utility model registration request] A plurality of antennas and a receiver; the plurality of antennas are sequentially switched within a vertical blanking period, an antenna with a large reception output is detected based on the video detection output obtained from the receiver, and the antenna is connected to the receiver; A diversity system that performs a fixed connection operation every vertical blanking period.
a noise removal circuit that operates with a level set in a region exceeding a synchronization pulse of a predetermined video signal as a noise inverter threshold level, and clamps large noise reaching the level to a small level; An in-vehicle television receiver comprising means for disabling the operation of the noise removal circuit at least during the detection operation period by the diversity system control circuit during the vertical blanking period.