JP3091338B2 - Automatic antenna switching device for automobiles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic antenna for selecting one antenna having the best reception condition from a plurality of antennas mounted on an automobile or combining a plurality of antennas and connecting the antenna to a television receiver. Regarding the switching device, in particular,
Even when the reception state is poor, the bar noise caused by the antenna search is prevented from appearing on the screen.

[0002]

2. Description of the Related Art In a television receiver mounted on an automobile, the reception state changes remarkably as the vehicle travels. Therefore, a plurality of antennas are provided on the automobile, and an antenna in the best reception state is selected or a plurality of antennas are selected. A diversity receiving method for combining the signals and connecting the signals to a television receiver has been conventionally known.

[0003] A conventional automatic antenna switching device for performing diversity reception by a television receiver mounted on an automobile, as shown in FIG.
To 1d, and an antenna in a good reception state is connected to the television receiver 4 via the antenna switching circuit 3 controlled by the control circuit 2.

In order to control the switching operation of the switching circuit 3, a video signal output from a television receiver 4 is applied, and a clamp circuit 5 for fixing a DC component of the video signal, and a clamp circuit 5 A synchronizing signal separating circuit 8 which separates a synchronizing signal from a video signal output from the control circuit 2 and guides the synchronizing signal to the control circuit 2, and an output of the clamp circuit 5
Sample-and-hold circuits 6a to 6d for sampling and holding every 1a to 1d, and sample-and-hold circuits 6a to 6d
A maximum level detection circuit 7 for transmitting sample and hold circuits 6a to 6d holding the highest reception level among the reception levels held in 6d to the control circuit 2 as detection signals.

As shown in FIGS. 4A and 4B, in a short period between the horizontal synchronizing pulses P ₁ and P ₂ existing in the vertical blanking period for each field or frame, the control circuit 2 The circuit 3 is controlled so that the antennas 1a to 1d are switched one by one and connected to the television receiver 4 sequentially.

At this time, the waveform of the video signal output from the television receiver 4 and having the DC component fixed by the clamp circuit 5 is, as shown in FIG. 4B, the connected antennas 1a to 1d. The signals of the peak values 11a to 11d whose reception levels fluctuate in accordance with the reception state of the above are output, and these peak values 11a to 11d are held in the sample and hold circuits 6a to 6d, respectively.

In the maximum level detection circuit 7, each of the peak values 11a to 11d held in the sample and hold circuits 6a to 6d
Is detected, the antenna having the highest reception level is selected based on the detected reception level, and is transmitted to the control circuit 2 as a detection signal.

The control circuit 2 continues to connect the antenna having a high reception level selected by the detection signal to the television receiver 4 until the next field or frame.

[0009]

In order to perform diversity reception, signals received by a plurality of antennas 1a to 1d are selected and supplied to a television receiver 4 via an automatic antenna switching device 3. In such a case, even if synchronization is not continuously obtained due to the fading phenomenon, a pseudo-synchronous signal is internally generated, and timing such as an antenna search time is set based on the pseudo-synchronous signal.

However, when the synchronization is lost several times or more consecutively, the timing error of the pseudo-synchronous signal is accumulated and increases, and the timing of the antenna search deviates from the vertical blanking period and the timing of the video signal is shifted. There is a problem that the period shifts to a period, and a bar noise in a white line shape due to an antenna search appears on the screen, making it difficult to see the image.

Accordingly, the present invention has been conceived to prevent the appearance of white-line-shaped bar noise based on an antenna search on a screen.

[0012]

According to the present invention, there is provided an automatic antenna switching apparatus for a vehicle which performs diversity reception, comprising: an antenna switching circuit for switching a plurality of antennas to a television receiver for connection; and an output from the television receiver. A synchronizing signal separating circuit for separating a synchronizing signal from a video signal to be transmitted. In the automatic antenna switching apparatus for performing an antenna search based on the synchronizing signal separated by the synchronizing signal separating circuit, A pseudo synchronizing signal generating means for generating a pseudo synchronizing signal serving as a reference for antenna search timing when a synchronizing signal cannot be obtained; the pseudo synchronizing signal generating means is built in the microcomputer; It uses a timer to count the number of times the vertical sync
Equipped with a counter to count, vertical sync signal missing
When detected by the above microcomputer,
Combination capable of generating periodic in time series Te, the average period of said pseudo-sync signals to approximate the correct period of the synchronizing signal.

When the synchronization signal cannot be obtained many times from the synchronization signal separation circuit, the antenna
The search is configured to stop.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the basic structure of an automatic antenna switching apparatus for performing diversity reception according to the present invention is substantially the same as that of the conventional apparatus shown in FIG. 3, but as shown in FIG. A synchronization signal detection circuit in the control circuit 2 for detecting the presence or absence of the synchronization signal separated by the synchronization signal separation circuit 8 using a microcomputer in the control circuit 2 and a timer built in the microcomputer. Prepared,
Further, a missing counter 21 is provided for counting the number of times the vertical synchronizing signal is continuously lost.

Each time a vertical synchronizing signal is detected, the time until the next vertical synchronizing signal arrives (16.68 m) is set by a timer.
sec), calculate a longer time (16.68 msec + Δt)
If the vertical synchronization signal is not detected even after the calculated time has elapsed, the missing counter 21 is incremented.
The count value of the missing counter 21 is reset to 0 every time a vertical synchronization signal is detected. When the first vertical synchronization signal is not detected, the pseudo synchronization signal is generated with a period of time (16.68 msec + Δt).

If the pseudo synchronizing signal is generated with a period of a regular time (16.68 msec) when no second or later vertical synchronizing signal is detected, the timing error of the pseudo synchronizing signal does not accumulate, and the vertical synchronizing signal does not accumulate. If a signal is detected, it should be able to follow immediately.

However, since the pseudo synchronizing signal is generated by the timer of the microcomputer, for example, 1
Even if it can be generated with a cycle such as 6.40, 16.60, 16.80, 17.00 msec, it is difficult to generate it with a cycle of 16.68 msec.

Therefore, when the second or later vertical synchronizing signal is not detected, the periods that can be generated by the timer of the microcomputer are combined in a time series so that the average period becomes 16.68 msec, which is almost the same as the vertical synchronizing signal. To generate a pseudo sync signal.

Even if the power of the television receiver 4 is turned on, if the reception condition of the antenna is poor, if a channel without broadcasting is selected, or if the broadcasting is finished, the television receiver 4 is turned off. The output video signal becomes an irregular noise signal, and a random signal is output from the synchronizing signal separation circuit 8 due to this noise, so that a synchronizing signal cannot be obtained.

If the code for transmitting the video signal from the television receiver 4 is abnormal, such as poor contact or disconnection, the output signal from the synchronizing signal separation circuit 8 is high or low. The state is fixed at the level, and the synchronization signal cannot be obtained.

As described above, when the vertical synchronizing signal is continuously lost many times (for example, 15 times), the power of the television receiver 4 is turned off or the cable for guiding the video signal is abnormal. Thus, the antenna search is stopped to prevent the appearance of white linear bar noise on the screen.

Using the computer of the control circuit 2, the operation shown in the flowchart of FIG. 2 is performed.

Step 1: Check the presence / absence of a vertical synchronizing signal. Step 2: Determine how many times the vertical synchronizing signal is continuously lost. Step 3a: If the first loss is detected, the first time Set the timing of the pseudo-synchronous signal with a cycle corresponding to the lack of, and proceed to step 4, step 3b:
If the second loss is detected, the timing of the pseudo-synchronous signal having a cycle corresponding to the second loss is set, and the process proceeds to Step 4. Step 3b: If the third loss is detected, 3 The timing of the pseudo-synchronous signal having a cycle corresponding to the second missing is set, and the process proceeds to Step 4. Step 4: An antenna search process is performed, and the process returns to Step 1.

Step 5: If it is determined in step 1 that a vertical synchronizing signal is present, the missing counter is reset to 0, and the process proceeds to step 4.

Step 6: If N or more (for example, 15) missings are detected in step 2, the antenna search is stopped and the process returns to step 1.

Even if a synchronizing signal is not obtained by performing such a series of operations, a pseudo synchronizing signal having a cycle similar to the cycle of the synchronizing signal can be generated. -When a search is performed, white bar noise does not appear on the screen. Moreover,
When the synchronizing signal cannot be obtained many times, the antenna search is forcibly stopped, so that white bar noise does not appear on the screen.

[0027]

As is apparent from the description based on the above embodiment, according to the automatic antenna switching apparatus for a vehicle which performs diversity reception according to the present invention, even if the reception state is poor and the synchronization signal cannot be obtained, the synchronization signal can be obtained. The antenna search is performed based on the timing of a pseudo-synchronous signal having a cycle similar to the cycle of the antenna search, so that the antenna search timing is shifted from the vertical blanking period to the video signal period, and the antenna search is displayed on the screen. It is possible to avoid a situation in which a white line-shaped bar noise appears and the image becomes difficult to see.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a vehicle antenna automatic switching device according to the present invention;

FIG. 2 is a flowchart used to explain the operation of the device of the present invention;

FIG. 3 is a block diagram showing an example of a conventional automobile antenna automatic switching device.

FIG. 4 is a waveform diagram of a video signal used to explain the operation of the device of the present invention and the conventional device.

[Explanation of symbols]

 1a-1d Antenna 2 Control Circuit 21 Missing Count Counter 3 Antenna Switching Circuit 4 Television Receiver 5 Clamp Circuit 6a-6d Sample / Hold Circuit 7 Maximum Level Detection Circuit 8 Synchronization Signal Separation Circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/44 H04B 7/08

Claims (1)

(57) [Claims] An antenna switching circuit for switching and connecting a plurality of antennas to a television receiver, and a synchronization signal separation circuit for separating a synchronization signal from a video signal output from the television receiver, In the automatic antenna switching device for performing antenna search based on the synchronization signal separated by the synchronization signal separation circuit, when the synchronization signal cannot be obtained from the synchronization signal separation circuit, the antenna search timing reference and comprising pseudo sync signal comprising a pseudo sync signal generating means for generating,該疑similar synchronizing signal generating means is adapted to use a timer built in the microcomputer, the vertical same
Equipped with a counter that counts the number of consecutive
When the lack of the vertical sync signal is detected twice or more,
An automatic antenna switching device for an automobile, wherein the periods that can be generated by the microcomputer are combined in a time series so that the average period of the pseudo synchronization signal is approximated to the correct period of the synchronization signal.