JPH0313786B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an antenna switching device for diversity reception of a television receiver mounted on a mobile body such as an automobile.

[Prior art]

When receiving TV radio waves on a moving object such as a car, it is strongly affected by standing waves caused by interference between direct waves from the transmitting antenna and reflected waves from buildings, the ground, etc., which can cause screen flickering and synchronization problems called flutter. Disturbances occur, making it extremely difficult to view the TV screen.

In order to reduce this, JP-A No. 56-10780, 57-
As in the antenna device described in Japanese Patent No. 127339, diversity reception is performed in which a plurality of antennas are provided and automatically switched. This conventional method is
For example, antennas are installed on both sides of the roof of a car, these two antennas are switched to the vertical retrace period, and the received level of the horizontal equivalent pulse during the vertical retrace period is compared to obtain a good screen. It is.

By the way, in this case, even if the electric field is strong and a good screen is obtained, and there is no need to switch the currently selected antenna, if the reception levels of both antennas are relatively fluctuating little by little, the antenna may be switched. This has the disadvantage that flutter is noticeable due to the difference in reception conditions between the two antennas. In addition, since the level comparison is carried out spot-wise using a portion of horizontal equivalent pulses during the vertical retrace period every 1/60 seconds, there is a drawback that it is not possible to respond quickly to rapid fluctuations in the reception level.

[Summary of the invention]

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional ones, and it examines changes in the reception level of the horizontal synchronizing signal in the composite video signal after video detection during the horizontal retrace period of the television signal. To provide an antenna switching device capable of quickly responding to rapid changes in reception level and performing good television reception by switching the antenna within a horizontal retrace period only when the reception level decreases. It is.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the first invention of the present application, and FIG. 2 shows a waveform diagram of each main signal in FIG.

The device of this embodiment switches two antennas according to changes in the reception level of television signals. In FIG. Composite video signals 2 and 3 are gate pulses 4 and 3, respectively.
5 is a gate circuit which is alternately turned ON and OFF in synchronization with the horizontal synchronizing signal in the composite video signal 1 and transmits the composite video signal 1 to the next stage; 6 and 7 are reset by reset pulses 8 and 9, respectively; A peak hold circuit 12 holds the peak voltage of the horizontal synchronizing signal in the composite video signal 1 that has passed through the gate circuits 2 and 3; Compare, and if (level of peak voltage holding output 11) > (level of peak voltage holding output 10), it is “1”, and (level of peak voltage holding output 11) ≦ (level of peak voltage holding output 10). 14 is a comparator circuit that outputs a binary signal of "0", and when the gate circuit 2 is turned on by the count pulse 15 and the output of the comparator circuit 12 is "1",
and a set reset circuit which outputs the set pulse 16 when the gate circuit 3 is ON and the output of the comparator circuit 12 is "0", and outputs the reset pulse 17 under other conditions; 18 counts the number of set pulses 16; 20 is a count circuit which outputs "1" when a predetermined value n is reached, and otherwise outputs "0" when reset by the reset pulse 17 and the count reset pulse 19. The antenna switching circuit is composed of a flip-flop whose state is reversed by an antenna switching pulse 21 when the output of the antenna 18 is "1", and its two outputs 22 and 23 alternately switch between two antennas (not shown). 24
2 is a count reset pulse generation circuit that generates a count reset pulse 19 for resetting the count circuit 18 when the outputs 22 and 23 of the antenna switching circuit 20 are inverted, and 25 and 26 are synchronization circuits of a television receiver (not shown), respectively. The horizontal synchronization signal and the vertical synchronization signal after signal separation from the composite video signal 1, 27 is the vertical synchronization signal 26
After the arrival of the horizontal synchronizing signal 2 until the end of the vertical retrace period
5, and 28, 29, 30 and 31 are the horizontal synchronizing signals 3 after passing through the gate circuit 27.
2, gate pulses 4 and 5, respectively,
These are a game pulse generation circuit, a comparison pulse generation circuit, a count pulse generation circuit, and an antenna switching pulse generation circuit that generate a comparison pulse 13, a count pulse 15, and an antenna switching pulse 21. Further, 33 is a reset pulse generating circuit that generates reset pulses 8 and 9 at the leading edges of gate pulses 4 and 5, respectively.

Next, the timing of each signal waveform will be explained with reference to FIG. The gate pulses 4 and 5 are generated alternately in synchronization with the horizontal synchronization signal 32, that is, in synchronization with the horizontal synchronization signal in the composite video signal 1. Reset pulses 8, 9 occur at the leading edge of gate pulses 4, 5, respectively. Comparison pulse 13 is horizontal synchronization signal 3
2 occurs with a delay slightly longer than the rising time constant of the peak hold circuits 6 and 7. This is because the peak hold circuits 6 and 7 reset the reset pulse 8,
This is because it takes time to hold the peak voltage of the horizontal synchronizing signal in the composite video signal 1 after being reset at step 9, so that the comparison circuit 12 can compare the levels when it is sufficiently stable. The count pulse 15 is the same as the comparison pulse 13 so that the count circuit 18 can count after the comparison circuit 12 has stabilized.
Occurs slightly later than the leading edge of The antenna switching pulse 21 is further delayed than the count pulse 15,
It occurs on the lead after the horizontal sync signal 32.

Next, the operation of the above configuration will be explained with reference to FIGS. 1 and 2. Now, the antenna switching circuit 20
It is assumed that one of the antennas is selected and receiving signals based on the outputs 22 and 23 of the antenna. If the gate circuit 2 is turned on by a certain horizontal synchronization signal 25, the composite video signal 1 is applied to the peak hold circuit 6 through the gate circuit 2. The peak hold circuit 6 holds the peak voltage of the horizontal synchronizing signal in the composite video signal 1 after being reset by the reset pulse 8 at the leading edge of the gate pulse 4. The comparison circuit 12 uses a comparison pulse 13 to compare this peak voltage with the level held in the peak hold circuit 7 by the previous horizontal synchronization signal, and finds that (level of peak voltage holding output 11) > (level of peak voltage holding output 10) If so, output “1”, otherwise output “0”. Next, the reset circuit 14 uses the count pulse 15 to output the gate pulses 4 and 5 and the comparison circuit 12.
Examine the output of . In this case, since gate circuit 2 is turned on by gate pulse 4, comparison circuit 12
If the output is "1", (previous level) > (current level), the level is decreasing, and set pulse 16 is output, otherwise the level is the same or higher. Therefore, a reset pulse 17 is output. That is, by checking the states of the gate circuits 2 and 3 and the output of the comparator circuit 12 in the reset circuit 14, the composite video signal 1
This means that it is possible to determine whether the level of the horizontal synchronization signal in the image has decreased.

Next, if the level is decreasing, the count circuit 18 counts the set pulses 16. If it has not decreased, the count circuit 18 is reset by the reset pulse 17 and the counting result is set to zero.

The next horizontal synchronizing signal 25 operates in the same manner as above, but this time, the peak voltage of the horizontal synchronizing signal in the composite video signal 1 is newly held in the peak hold circuit 7, and the set-reset circuit 14 holds the peak voltage of the horizontal synchronizing signal in the composite video signal 1.
If the output is "0", it is determined that the level has decreased from the previous time, a set pulse 16 is output, and the count circuit 18 counts.

At time t1 in Figure 2, the peak voltage holding output 11
level v0 is the level of peak voltage holding output 10
Since it is smaller than V1 and the gate circuit 2 is turned on, the level has not decreased, and the reset pulse 17 is generated. Similarly, t2,
At tn, the level is decreasing and a set pulse 16 is generated.

This device performs the above operation for each horizontal synchronizing signal, but when the count of the count circuit 18 reaches a certain predetermined value n, that is, the horizontal When it is determined that the level of the synchronization signal has decreased, the output of the count circuit 18 becomes "1", the flip-flop of the antenna switching circuit 20 is inverted by the antenna switching pulse 21, the outputs 22 and 23 are inverted, and the antenna is switched. At the same time as the antenna is switched, the count reset pulse generating circuit 24 generates a count reset pulse 19 to reset the count circuit 18 and prepare for the next counting.

Note that if the antenna is switched during the vertical retrace period, the vertical synchronization may be disrupted, so the gate circuit 27 briefly cuts off the horizontal synchronization signal 25 during the vertical retrace period using the vertical synchronization signal 26, so that the antenna is switched off. This is to prevent switching.

In summary, this embodiment compares the received level of the horizontal synchronizing signal in the composite video signal with the previous one in each horizontal retrace period, and only when it has decreased a certain number of times in succession, The antenna can be switched.

Although the above embodiment uses two peak hold circuits, an arbitrary number of peak hold circuits may be provided to sequentially circulate and hold the newly held level and the previously held level. A similar configuration can be made such that the comparison circuit 12 compares the two.

Further, in the embodiment described above, the count value n of the count circuit 18 is a predetermined fixed number, but it can also be set externally, and the optimum state can be changed depending on the reception situation.

In addition, in the above embodiment, the level drop is checked every time during each horizontal retrace period, but if the electric field fluctuates little by little, the antenna may switch many times during one vertical scanning period, causing the screen to disappear. It may be difficult to see. In such a case, by subtracting the horizontal synchronizing signal 25 at a constant rate, the frequency of switching can be reduced and this problem can be alleviated.

FIG. 3 shows a second embodiment of the present invention as described above, and only shows the addition to FIG. 1 and a part of its surroundings. That is, the device of this embodiment has a gate circuit 34 and a count circuit 3 in addition to the circuit shown in FIG.
5 has been added.

The counting circuit 35 counts the horizontal synchronizing signals 25 and starts the gate circuit 34 only when a certain number is reached.
It is turned on and allows the horizontal synchronization signal 25 to pass through, thereby making it possible to thin out the horizontal synchronization signal. Note that this count circuit 35 is reset by a horizontal synchronizing signal passed through the gate circuit 34. In this case, the number to be counted may be set externally depending on the reception situation.

Furthermore, in the above embodiment, peak voltage holding and level comparison are performed using one horizontal synchronization signal, but the responsiveness of the peak hold circuit, that is, the variation in the rise time constant and the fluctuation of the horizontal synchronization signal during the horizontal retrace period, Due to disturbances in the rising edge, the level comparator may not be stable and accurate comparison may not be possible. In such cases, peak voltage holding and level comparison are not performed using the same horizontal sync signal, but the horizontal sync signal is All you have to do is separate them.

FIG. 4 shows an embodiment of the second invention of the present application in which peak voltage holding and level comparison are performed using separate horizontal synchronizing signals. Only the additional part and a part of its surroundings are shown. Further, FIG. 5 shows the waveform diagram.

That is, the device of this embodiment has a distribution circuit 3 in the circuit shown in FIG.
6 is added, and each horizontal synchronizing signal 32 after passing through the gate circuit 27 is sent to the gate pulse generation circuit 28, the comparison pulse generation circuit 29, the count pulse generation circuit 30, and the antenna switching pulse generation circuit 31.
The signals are distributed like signals 37 and 38 in FIG. 5, and peak voltage holding, level comparison, counting, and antenna switching are performed using separate horizontal synchronizing signals. In this embodiment, the particles are distributed one by one, but it goes without saying that the particles can be distributed at appropriate intervals.

Further, in the above description, switching between two antennas has been described, but a similar configuration can be applied to switching between three or more antennas.

〔Effect of the invention〕

As described above, according to the present invention, the reception level of the horizontal synchronization signal of the composite video signal is checked during the horizontal retrace period of the television signal, and the horizontal retrace is performed only when the reception level has decreased and it is truly necessary to switch the antenna. Since the antenna is switched within the line period, a screen with less flicker can be obtained, and it is also possible to quickly respond to rapid fluctuations in the reception level.
In addition, by appropriately distributing the horizontal synchronization signal, it can operate effectively even when the response of the peak hold circuit is poor or when there is disturbance in the rising edge of the horizontal synchronization signal in the composite video signal. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an antenna switching device according to an embodiment of the first invention of the present application, FIG. 2 is a waveform diagram of each main signal in FIG. 1, and FIG. FIG. 4 is a block diagram showing only a part added to FIG. 1 of the embodiment and a part of its surroundings, and FIG. 4 is a block diagram showing only a part added to FIG. FIG. 5 is a waveform diagram of each main signal in FIG. 4. In the figure, 1 is a composite video signal, 6 and 7 are peak hold circuits, 12 is a comparison circuit, 18 is a count circuit, 20 is an antenna switching circuit, 25 is a horizontal synchronization signal, 34 is a gate circuit, 35 is a count circuit, 36 is a distribution circuit.

Claims (1)

[Scope of Claims] 1. In an antenna switching device that switches a plurality of antennas according to the reception level of a television signal, at least two or more antennas sequentially maintain the reception level of a horizontal synchronization signal during a horizontal retrace period of the television signal. The output of one newly held peak hold circuit is compared with the output of the next peak hold circuit that was held last time, and this comparison is performed when the one peak hold circuit newly held. A comparison circuit that performs the operation during the horizontal retrace period at a time; a count circuit that counts the number of times the reception level of the horizontal synchronization signal has continuously decreased based on the comparison result of the comparison circuit and outputs when a certain count value is reached; An antenna switching device comprising: an antenna switching circuit that switches antennas based on the output of the circuit. 2. The antenna switching device according to claim 1, wherein the count value of the counting circuit can be set arbitrarily. 3. The antenna switching according to claim 1 or 2, wherein each of the peak hold circuits holds the reception level of the horizontal synchronization signal every horizontal retrace period at predetermined intervals. Device. 4. The antenna switching device according to claim 3, wherein the predetermined interval can be set arbitrarily. 5. An antenna switching device that switches a plurality of antennas according to the reception level of a television signal, comprising at least two or more peak hold circuits that sequentially hold the reception level of a horizontal synchronization signal during a horizontal retrace period of the television signal; A comparator circuit that compares the output of one peak hold circuit newly held with the output of the next peak hold circuit held previously, and performs this comparison during the horizontal retrace period when the peak hold circuit does not hold. and an output count circuit that counts the number of times the reception level of the horizontal synchronization signal has continuously decreased based on the comparison result of the comparison circuit and when a certain count value is reached, and an antenna switching circuit that switches the antenna based on the output of the count circuit. An antenna switching device characterized by comprising a circuit. 6. The antenna switching device according to claim 5, wherein the count value of the counting circuit can be set arbitrarily. 7. The antenna switching according to claim 5 or 6, wherein each of the peak hold circuits holds the reception level of the horizontal synchronization signal every horizontal retrace period at predetermined intervals. Device. 8. The antenna switching device according to claim 7, wherein the predetermined interval can be set arbitrarily.