JPH065823B2 - Antenna switching device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an antenna switching device for a diversity receiving device of a television receiver, which is mounted on a moving body such as an automobile.

[Prior art]

When receiving TV radio waves from a moving body such as an automobile,
It is strongly affected by standing waves caused by the interference of direct waves from the transmitting antenna and reflected waves from buildings, the ground, etc., causing screen flicker called flutter and disturbance of synchronization, making the TV screen difficult to see. Become.

In order to reduce this, a plurality of antennas are provided as in the antenna devices described in JP-A-56-10780 and 57-127339, and diversity reception is performed in which the antennas are automatically switched. In this conventional method, for example, antennas are provided on both sides of the roof of an automobile, and these two antennas are switched to the vertical blanking period to compare the reception level of the horizontal equivalent pulse during the vertical blanking period to obtain a good screen. It is something to try.

By the way, in this case, the electric field is strong, a good screen is obtained, and even if it is not necessary to switch the currently selected antenna, if the reception level of both antennas fluctuates relatively in small steps, the antenna will switch off. Therefore, there is a drawback that flutter is conspicuous due to the difference in the reception state of both antennas. Further, since the level comparison is performed spotwise with a part of horizontal equivalent pulses in the vertical blanking period every 1/60 seconds, there is a drawback that it is not possible to immediately respond to a rapid fluctuation of the reception level.

By the way, an antenna switching device shown in FIG. 1 has already been developed to solve such a problem.

FIG. 1 is a block diagram of such an antenna switching device, and FIG. 2 is a waveform diagram of the operation signal of FIG. The same reference numerals in each drawing indicate the same or corresponding parts.

This device is a device that switches between two antennas according to a change in the reception level of a television signal.
Is a composite video signal after video detection of a television receiver (not shown), 2 is a horizontal sync pulse after being separated from the composite video signal 1 by a synchronizing circuit of a television receiver (not shown), and 3 is a sampling A sampling circuit for mutually extracting horizontal synchronization signals from the composite video signal 1 by the pulses 4 and 5, and 6 being a peak voltage of the horizontal synchronization signals alternately extracted by the sampling circuit 3 after being reset by the reset pulses 9 and 10. The peak hold circuit 11 holds the peak hold outputs 7 and 8 of the peak hold circuit 6 by the comparison pulse 12, and (Peak voltage peak-held this time) <(Peak voltage peak-held last time). At the time, that is, when the level of the horizontal synchronizing signal is lowered, the comparison pulse that outputs the count pulse 13 , 14 counts the time count pulse 13 in which the count pulse 13 is continuous, outputs the antenna switching request signal 16 when the number reaches a predetermined number, and resets when the count pulse is interrupted or by the count reset pulse 15. A counting circuit 17, which is based on the horizontal synchronizing pulse 2, has sampling pulses 4 and 5 and reset pulses 9 and 1.
0, a comparison pulse 12, a count reset pulse 15 are output at the timing shown in FIG. 2, and a first control circuit 18 is an antenna switching request signal 16 and an antenna switching instruction pulse 21.
Accordingly, an antenna switching circuit which outputs antenna switching signals 19 and 20 for switching between two antennas by a high frequency switch (not shown), 22 is an antenna switching instruction pulse 21 based on the horizontal synchronizing pulse 2 at the timing shown in FIG. It is a second control circuit for outputting.

Next, the operation will be described.

The composite video signal 1 is sampled by the sampling circuit 3 by the sampling pulses 4 and 5, the peak voltage is held by the peak hold circuit 6, and the peak hold outputs 7 and 8 are output as shown in FIG. The comparator circuit 11 compares the peak hold outputs 7 and 8 and outputs the count pulse 13 when the level is lowered, that is, (the output which was previously peak-held)> (the output which was later peak-held), and (first Peak hold output) Count pulse is not output when ≤ (output parked later). For example, in FIG. 2, since the voltage v0 of the peak hold output 8 at time t1 <the voltage v1 of the peak hold output 7 at time t1, the count pulse is not output, and the voltage v1 of the peak hold output 7 at time t2> the time t2. Since the voltage v2 of the peak hold output 8 is, the count pulse 13 is output, and the voltage vn-1 of the peak hold output 8 at the time tn> The voltage vn of the peak hold output 7 at the time tn is the count pulse 13 is output. It When the output count pulse 13 is continuously input to the count circuit 14 by a predetermined number, the count circuit 14 outputs the antenna switching request signal 16. Antenna switching circuit 1
8 is an antenna switching signal 19, when an antenna switching request signal 16 and an antenna switching instruction pulse 21 are simultaneously input.
Switch 20. Next, a more detailed structure and operation of this conventional device will be described with reference to FIGS. 5 and 6.

FIG. 5 is a block diagram showing the detailed structure of the conventional device, and FIG. 6 is a waveform diagram of each main signal of FIG.

In FIG. 5, the same reference numerals as those in FIG. 1 indicate the same things, and in the figure, 3a and 3b are alternately turned on and off in synchronization with the horizontal synchronizing signal in the composite video signal 1 by the gate pulses 4 and 5, respectively. The gate circuits 6a and 6b for transmitting the composite video signal 1 to the next stage are set by the reset pulses 9 and 10, respectively, and then the gate circuits 3a and 3b.
The peak hold circuit for holding the peak voltage of the horizontal synchronizing signal in the composite video signal 1 that has passed through the reference numeral 43, the set pulse 13a when the gate circuit 3a is turned on by the count pulse 115 and the output of the comparison circuit 11 is "0". A set / reset circuit that outputs and outputs a reset pulse 13b under the conditions other than these, and a reference numeral 44 generates a count reset pulse 119 that resets the count circuit 14 when the outputs 19 and 20 of the antenna switching circuit 18 are inverted. The reset pulse generation circuits 48, 29, 30 and 31 are based on the horizontal synchronizing signal 32 after passing through the gate circuit 47, and the gate pulses 4 and 5 and the comparison pulse 1 respectively.
2, a gate pulse generation circuit that generates a count pulse 15 and an antenna switching pulse 21, a comparison pulse generation circuit,
The count pulse generating circuit and the antenna switching pulse generating circuit, the gate pulse generating circuit 48, the comparison pulse generating circuit 29, and the count pulse generating circuit 30 are the control circuit 17.
The antenna switching pulse generation circuit 30 constitutes the control circuit 22. Reference numeral 33 is a reset pulse generation circuit which generates reset pulses 9 and 10 at the leading edges of the gate pulses 4 and 5, respectively.

Next, the timing of each signal waveform will be described with reference to FIG. The reset pulses 9 and 10 occur at the leading edges of the gate pulses 4 and 5, respectively. The comparison pulse 12 is generated with a slight Nagai delay from the leading edge of the horizontal synchronizing signal 32. This is because the peak hold circuits 6a and 6b have reset pulses 9,
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 10, so that the comparison circuit 12 can perform level comparison in a sufficiently stable time. The count pulse 115 is the comparison circuit 1
Is generated slightly later than the double edge of the comparison pulse 12 so that it can be counted by the counting circuit 14 after being stabilized. The antenna switching pulse 21 is generated at the trailing edge of the horizontal synchronizing signal 32 with a further delay from the count pulse 115.

In this antenna switching device, the antennas are switched during the horizontal blanking period as described above.
When the antenna is switched and the reception level changes abruptly, the response time of the AGC of the television receiver is correct, so that the AGC is not stable within the horizontal blanking period and a part of the screen is disturbed. .

[Outline of Invention]

The present invention has been made in order to improve the above-mentioned drawbacks of the above-mentioned device, and in the horizontal blanking period of a television signal, the change in the receiving level of the horizontal synchronizing signal in the composite video signal after video detection is examined, and the receiving level is When it comes down, a signal to switch the antenna is generated, this signal is held until the next vertical blanking period, and the antenna is switched within this vertical blanking period, whereby the disturbance of the screen can be removed, It is an object of the present invention to provide an antenna switching device capable of performing stable television reception.

Example of Invention

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

FIG. 3 is a block diagram of an antenna switching device according to an embodiment of the present invention, and FIG. 4 is a waveform diagram of the operation signal of FIG. 3, and the same reference numerals in each drawing indicate the same or corresponding parts. To do. In the figure, 23 is a latch reset pulse 2
Antenna switching request signal 16 until reset by 4
, 25 is a latch output held by the latch circuit 23, 26 is a vertical synchronous antenna switching instruction pulse for operating the antenna switching circuit 18, 2
Reference numeral 7 is a third circuit for outputting a latch reset pulse 24 and a vertical synchronization antenna switching instruction pulse 26 based on the vertical synchronization pulse 28 after being separated from the composite video signal 1 by a synchronizing circuit of a television receiver (not shown). The present invention is characterized in that a latch circuit 43 for holding the output of the count circuit until the next vertical blanking period is added to the conventional circuit of FIG. Therefore, the detailed structure of the control circuit is basically the same as that of the conventional example shown in FIG. However, the antenna switching circuit 18 and the latch circuit 23 in FIG. 3 are not switched in the horizontal blanking period as in FIG. 5, but are switched in the vertical blanking period, and therefore the control circuit 27 is vertical. The antenna switching signal 19 and the latch reset pulse 24 are generated based on the synchronizing signal and its twice the cycle.

Next, the operation will be described. As in the device of FIG. 1, the sampling circuit 3 has sampling pulses 4, 5
The horizontal sync signal is extracted from the composite video signal 1 by the peak hold circuit 6
The peak voltage is held at, the peak hold outputs 7 and 8 are compared as shown in Fig. 2, and when the level is lowered, that is, (first peak-held output)> (later-peak-held output) When the pulse 13 is output and the output count pulse is continuously input to the count circuit 14 by a predetermined number, the count circuit 14 outputs the antenna switching request signal 16 as shown in FIG. The antenna switching request signal 16 is composed of two vertical synchronizing pulses 28 as shown in FIG.
And is held by the latch circuit 23 until the next vertical blanking period. The latch circuit 23 stores the antenna switching request signal 16 until the next vertical blanking period and latches the output 25.
Is output. Control circuit 2 based on vertical synchronizing pulse 28
When the latch circuit 23 holds the antenna switching request signal 16 when the vertical synchronization antenna switching instruction pulse 26 output by the signal 7 is input to the antenna switching circuit 18,
The antenna switching circuit 18 switches the antenna switching signals 19 and 20, and if not, the antenna switching signals 19 and 2
Do not switch 0. When the antenna switching signal is switched, the third control circuit 27 outputs the latch reset pulse 24 and resets the latch circuit 23.

As described above, in this embodiment, the reception level of the horizontal synchronizing signal is checked during the horizontal blanking period, and when the reception level is lowered and the antenna is switched, the signal for switching the antenna is held until the next vertical blanking period. Since the antennas are switched within the vertical blanking period, the AGC stabilizes within a vertical blanking period longer than the horizontal blanking period even when the antennas switch and the reception level changes rapidly. Do not disturb.

In the above embodiments, the count value of the count circuit 14 is set to a predetermined fixed number, but it can be set from the outside so that the optimum switching state can be set according to the reception situation.

Also, in the above description, switching of two antennas has been described, but switching of a plurality of antennas of three or more can be similarly configured.

〔The invention's effect〕

As described above, according to the present invention, the reception level of the horizontal synchronizing signal is checked during the horizontal retrace period of the television signal, and when the reception level is lowered and the antenna is switched, the signal for switching the antenna is changed to the next vertical signal. Since the antenna is switched during the vertical blanking period while holding until the blanking period, even if the reception level changes abruptly due to switching of the antenna, the AGC does not exceed the horizontal blanking period within the vertical blanking period. There is an effect that it is possible to receive a stable television without disturbing the screen.

[Brief description of drawings]

FIG. 1 is a block diagram of an antenna switching device which eliminates the drawbacks of the conventional antenna switching device, FIG. 2 is a waveform diagram of the operation signal of FIG. 1, and FIG. 3 is an antenna switching device according to an embodiment of the present invention. A block diagram and FIG. 4 are waveform diagrams of the operation signals of FIG. In the figure, 1 is a composite video signal, 2 is a horizontal sync pulse,
6 is a peak hold circuit, 11 is a comparison circuit, 14 is a count circuit, 18 is an antenna switching circuit, 23 is a latch circuit, and 28 is a vertical synchronizing pulse. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

[Claims] 1. An antenna switching device for switching a plurality of antennas according to a reception level of a television signal, and two or more antennas for sequentially holding the reception levels of adjacent horizontal synchronizing signals in a horizontal blanking period of the television signal. A peak hold circuit, a comparison circuit that compares the outputs of the peak hold circuit with each other, and the number of times the reception level of the horizontal synchronizing signal continuously decreases according to the comparison result of the comparison circuit. A count circuit for outputting, a latch circuit for holding the output of the count circuit until the next vertical blanking period, and an antenna switching circuit for switching the antenna within the vertical blanking period by the output of the latch circuit are provided. An antenna switching device characterized by. 2. The antenna switching device according to claim 1, wherein the count value of the count circuit can be arbitrarily set.