JPH05191307A - Antenna changeover device - Google Patents

Abstract

PURPOSE:To improve the picture quality of a video image of an on-vehicle television receiver by selecting an antenna with an optimum condition based on each ghost level and each electric field intensity of a TV signal received by plural antennas. CONSTITUTION:An antenna selector 1 outputs selectively a TV signal received by plural antennas 2-5. A tuner section 6 detects a TV signal and outputs an IFAGC signal and a detection signal. An electric field intensity detection circuit 7 detects an electric field intensity of the detection signal and a ghost detection circuit 8 detects a ghost component from a video signal detected by the tuner section 6. Then a CPU 9 discriminates an antenna with an optimum condition from the antennas 2-5 based on each detection data signal inputted respectively from the circuits 7, 8, selects the antenna and outputs a control signal. As a result, malfunction in the antenna changeover at a weak electric field is not caused and a video image with excellent picture quality in which lateral flicker of the video image is reduced is displayed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna switching device which is added to, for example, a vehicle-mounted television receiver to input the best TV signal.

[0002]

2. Description of the Related Art In recent years, a television receiver is often mounted on a moving body such as an automobile so that the image information can be obtained while moving or while moving.

In this case, in the television receiver, the TV is selected from a plurality of antennas according to the change of the reception state of the radio wave.
An antenna switching device with the function of selecting an antenna with a good signal reception state, a so-called diversity antenna system, is attached, and this antenna switching device is capable of displaying a good quality image on the television receiver even in a weak electric field. What can do is desired.

Since the antenna of this antenna switching device is provided in the body of an automobile in consideration of the body design of the automobile, it is difficult to form an ideal diver antenna that is a combination of a plurality of unidirectional antennas.
Therefore, the TV signal received by this antenna is interfered with by multipath noise. This multipath noise is displayed on a television receiver as a so-called ghost.

In general, it is preferable to measure (detect) the electric field strength at that position as a judgment material for switching the antenna. For example, when the antenna switching device is configured to switch the antenna by detecting the electric field strength from the TV signal including the ghost, the position of the ghost of the image displayed on the television receiver changes every time the antenna is switched. A rolling phenomenon occurs and it becomes very unsightly.

Therefore, Japanese Patent Laid-Open No. 3-35624 discloses a diversity antenna system in which the ghost levels of TV signals received by a plurality of antennas are determined and the antennas are switched. in this case,
Since the antenna having the minimum ghost level is selected from the plurality of antennas, the image with less ghost is displayed on the television receiver.

By the way, such a diversity antenna system is ideal in a state where the S / N ratio of the TV signal is good, for example, in an area where the electric field strength is strong, but when the vehicle moves to a weak electric field area, noise is generated. The ghost level may be erroneously detected due to the influence of, and the antenna that is not necessarily the best may be selected.

[0008]

As described above, the above-mentioned conventional diversity antenna system has a problem that it malfunctions in a weak electric field area because it makes only the determination of the ghost level. The present invention has been made to solve such a problem, and an antenna capable of improving the image quality of an image displayed on a vehicle-mounted television receiver in an appropriate manner in response to a change in a reception state of a TV signal. An object is to provide a switching device.

[0009]

In order to achieve the above-mentioned object, the antenna switching device of the present invention provides a plurality of antennas for receiving TV signals and one TV signal among the TV signals received by these antennas. A switching means for selecting and outputting, a first control means for sequentially outputting each TV signal received by the plurality of antennas from the switching means during a blanking period of the TV signal, and a sequence for sequentially switching from the switching means. Each TV output
An electric field strength detecting means for detecting electric field strength of a signal, a ghost level detecting means for detecting a ghost level of each TV signal sequentially output from the switching means, and an electric field strength and a ghost level of each detected TV signal. Second control means for causing the switching means to output the TV signal received by the antenna under the optimum condition determined based on the above.

[0010]

In the present invention, the TV signals received by the plurality of antennas are sequentially output by the first control means to the ghost level detecting means and the electric field strength detecting means during the blanking period of the TV signal. Then, the ghost level and the electric field strength are respectively detected and input to the second control means, and the antenna is selected based on the ghost level and the electric field strength. For example, the antenna with the minimum ghost level is selected when the electric field is strong / medium, and the antenna with the strong electric field strength is selected when the electric field is weak.

That is, the output of the antenna under the optimum conditions thus selected is output to the television receiver by the switching means.

As a result, there is no malfunction in the antenna switching operation when the electric field is weak, and a high quality image in which the rolling phenomenon of the image is reduced is displayed on the television receiver.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an antenna switching apparatus according to an embodiment of the present invention.

In the figure, reference numeral 1 denotes an antenna selector, which is a T selector that receives a plurality of antennas, for example, antennas 2 to 5 each having four elements.
The V signal is selectively output. A tuner 6 detects the TV signal from the antenna selector 1 and outputs an IFAGC signal and a detection signal. An electric field strength detection circuit 7 detects the electric field strength of the detection signal output from the tuner 6. A ghost detection circuit 8 detects a ghost component from the video signal detected by the tuner 6. Reference numeral 9 denotes a CPU as a diversity control unit, which determines based on each detection data signal input from the electric field strength detection circuit 7 and the ghost detection circuit 8, selects an antenna under optimum conditions, and outputs a control signal. Reference numeral 10 denotes a memory, which temporarily holds each detection data. Reference numeral 11 denotes a selector drive circuit, which receives a control signal from the CPU 9 and drives the antenna selector 1. Reference numeral 12 is a timing pulse generation circuit, which generates a timing pulse from the video detection output signal from the tuner 6.

Next, the operation of this antenna switching device will be described.

In this antenna switching device, the TV signal received by the 4-element antennas 2 to 5 is in the 4H section of 10H to 13H (273H to 276H in the even field) which is the vertical blanking period of the vertical synchronizing signal. Each antenna 2-5
The TV signal received at is output to the tuner, and the TV signal is detected by this tuner to become a video signal (video detection output). This video signal is a timing pulse generation circuit 12, a ghost detection circuit 8 and an electric field strength detection circuit 7.
Is input to each circuit.

For example, in the electric field strength detection circuit 7,
Video signals of IFAGC level and detection levels of 10H to 13H are input individually.

In this case, the timing pulse generation circuit 12
Further, by the A / D conversion clock input to the electric field strength detection circuit 7, the IFAGC level (absolute value) of the first 9H is A / D converted to become electric field strength absolute level data. Then, the signal input system is instantly switched from the IFAGC level side to the detection level side, and subsequently the detected detection levels (relative values) of 10H to 13H are similarly A / D converted and the relative level data is obtained. Becomes

Further, as shown in FIG. 2, the ghost detection circuit 8 receives a video signal having a detection level of 10H to 13H and performs a ghost level detection operation.

In the figure, the video signal Sa is supplied to the ghost detection circuit 8 at 1H (vertical synchronization pulse V) of 10H to 13H.
(between a and Vb) includes a ghost pulse Ga and Gb of about 6 dB each for positive and negative, and is a detection level video signal.

When this video signal Sa is input to the ghost detection circuit 8, this video signal Sa is differentiated, and a differential wave is generated at the rising and falling timings of each pulse to become a differential signal Sb. This differential signal Sb
Is compared with the comparator voltage (broken line) and becomes the comparator output Sc according to this level. H for masking the vertical synchronizing pulses Va and Vb on the comparator output Sc
By superimposing the d pulse Sd, the ghost count output Se that outputs only the ghost component is obtained. In addition,
This ghost count output Se has a ghost pulse G
When one of a and Gb is generated, two square waves are obtained, so if they are struck again, the ghost level can be judged from the difference in pulse width.

Further, the timing pulse generating circuit 12 receives the video detection output (the video signal actually displayed on the television receiver) from the tuner 6, and the timing pulse generating circuit 12 outputs a strobe signal to the CPU 9 or the like. Each STB is output.

Now, the diversity control operation of the CPU 9 will be described with reference to the flow chart shown in FIG.

First, the CPU 9 outputs the strobe signal STB 10
Detect the Hth pulse (leading V pulse) (step 3
01), IFA input to the electric field strength detection circuit 7 at the 9th H
Read the GC level (step 302).

After that, while the electric field strength detection circuit 7 and the ghost detection circuit 8 generate digital data (50 μse
c) Standby (step 303), reset the counter to 0 (step 304), and instruct the selector drive circuit 11 to switch to the antenna for sampling data first, for example, the antenna 2 (step 305), and then the antenna selector 1 Is driven and the output of the antenna is switched (5 μ
sec) Wait (step 306).

When the 11Hth strobe pulse from the timing pulse generating circuit 12 is detected, the CPU
9 outputs a ghost reading clock to the ghost detecting circuit 8 to read the ghost count output Se from the ghost detecting circuit 8 (step 307). Subsequently, the CPU 9 outputs a field strength level reading clock to the field strength detection circuit 7 to read the detection level as the field strength data from the field strength detection circuit 7 (step 308).

At this time, the CPU 9 raises the counter by the time the 11th strobe pulse is input (step 309) and reads the ghost count output Se and the electric field strength data four times from 10H to 13H. (Step 310), the antenna number is added to each data, and the data is temporarily stored in the memory 10. Furthermore, CP
After reading the data four times in total, U9 resets the counter to 0 (step 311), selects two antenna numbers in order (step 312), and sequentially compares these two data (step 311). 313).

The two data comparisons at this time are first judged by the absolute value level of the electric field intensity read by A / D conversion of the IFAGC level based on the IFAGC level-electric field intensity characteristic of FIG. As shown in the figure, when the electric field strength level is, for example, 20 dB or less, the IFAGC level is extremely lowered, so it is preferable to perform data comparison between 20 dB and 30 dB.

Here, as an example for comparing only two antennas A and B, the CPU 9 is shown in FIG.
A comparison determination is made based on a comparison chart as shown in FIG.

In this case, according to the IFAGC level-electric field strength characteristic of FIG. 4, it is divided into a medium / strong electric field and a weak electric field at the boundary of 30 dB, and the CPU 9 first determines the absolute electric field strength level (IFAGC level). Judge whether it is 30 dB or more or 30 dB or less. Then, the CPU 9 performs more detailed individual comparison based on the respective electric field strength and ghost level data, and as a result, determines which one of the antennas A and B is the antenna under the optimum condition.

When the antenna under the optimum condition is selected as described above, the data of this antenna is held in the memory 10 (step 314) and the counter is incremented (step 315). In this embodiment, since the antenna has four elements, the data comparison is repeated three times (step 316) and the comparison is performed on all the sampled data. That is, the data having the best value among the sampled data is held in the memory 10. And CPU9
Selects the antenna of the optimum condition from the antenna number of the finally held data (step 317).

At this time, if the difference between the data of the selected antenna and the data of the current antenna is not more than the predetermined value, the current antenna can be held.

Further, the CPU 9 outputs a control signal to the selector drive circuit 11 for switching the antenna to this selected antenna. The selector drive circuit 11 drives the antenna selector 1 to switch the antenna, and holds this antenna for one field section.

Next, the antenna switching operation of the embodiment will be described with reference to the timing chart of FIG.

First, the CPU 9 causes the strobe signal ST
When the 10th H strobe pulse (leading V pulse) of B is detected, the CPU 9 displays the 9th I Ith as electric field strength data.
FAGC level (AGC) is read. Then, CPU
When the 11th strobe pulse is detected by 9,
The ghost and the detection level detected by each circuit are read into the CPU 9 at the 10th H. At this time, 11
7 μsec after the H-th strobe pulse is output, C
A ghost reading clock is output from PU9 to read the ghost. Further, 12 μsec after the 11th H strobe pulse is output, the CPU 9 outputs the electric field strength level reading clock to read the detection level as electric field strength data. Then, the CPU 9 compares the antennas as described above based on the read data. This is repeated up to 13H and 14H
When the strobe pulse for the eye is output, 100
After a delay of μsec, the current antenna is switched to the one with the optimum conditions, and this antenna is held for one field section.

As described above, according to the diversity antenna system of the present embodiment, the antenna is selected based on the electric field strength and the ghost level with respect to the change in the reception state of the TV signal. For example, an antenna with a small ghost level is selected when the electric field is medium or strong, and an antenna with a higher electric field strength is selected when the electric field is weak. Then, the TV being received by the antenna under the optimum condition thus selected
Since the image detection output of the signal is input to the television receiver, the malfunction of the antenna switching operation is eliminated even when the automobile moves to the weak electric field area.

As a result, it is possible to display on the television receiver an image with good image quality in which the rolling phenomenon is reduced.

[0039]

As described above, according to the antenna switching device of the present invention, the optimum antenna is selected based on each ghost level and each electric field strength of the TV signal received by the plurality of antennas. For example, when the electric field is weak, there is no malfunction in the antenna switching operation, and it is possible to display a high quality image on the television receiver in which the rolling phenomenon is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an antenna switching device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a ghost detection operation of the antenna switching device of FIG.

FIG. 3 is a flowchart showing the diversity control operation in this embodiment.

FIG. 4 is an IFAGC level-electric field strength characteristic diagram used in this example.

FIG. 5 is a comparison chart of the ghost level and the electric field strength when, for example, two antennas A and B are compared.

6 is an antenna switching timing chart of the antenna switching device of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Antenna selector, 2-5 ... Antenna, 6 ... Tuner, 7 ... Electric field intensity detection circuit, 8 ... Ghost detection circuit, 9
... CPU, 10 ... Memory, 11 ... Selector drive circuit, 1
2 ... Timing pulse generation circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Tomizawa 3-3-9 Shimbashi, Minato-ku, Tokyo Toshiba Abu E. Co., Ltd.

Claims (1)

[Claims] 1. A plurality of antennas for receiving a TV signal, a switching means for selecting and outputting one TV signal from the TV signals received by these antennas, and a switching means for blanking the TV signal. First control means for sequentially outputting each TV signal received by a plurality of antennas from the switching means, electric field strength detection means for detecting electric field strength of each TV signal sequentially output from the switching means, and the switching The ghost level detecting means for detecting the ghost level of each TV signal sequentially output from the means, and the TV signal received by the antenna of the optimum condition judged based on the electric field strength and the ghost level of each detected TV signal are switched. Second output by means
An antenna switching device, comprising: