JPH1141532A - Television antenna switch device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection accuracy of noise level components while including external noises and to cancel image distortion or noise sound caused by diversity operation by detecting the noise component of a pedestal in the equivalent pulse domain of a received video signal and comparatively detecting noise levels at two spots. SOLUTION: The pedestal noise at the first half section of the equivalent pulse domain after the vertical synchronizing signal of the received video signal is detected and the noise level held by a sample-and-hold(S/H) circuit 26 IS inputted to a comparator circuit 28. The pedestal noise in the latter half section is detected and inputted to the comparator circuit 28 while being lowered rather than the level held by an S/H circuit 17 by an attenuator 27. The comparator circuit 28 outputs 'L' when the level of the attenuator 27 is lower than the level of the S/H circuit 26. When the external noise is mixed, 'L' is outputted from the comparator circuit 28, a switch circuit 29 is opened and the output of a comparator circuit 28 erroneously operated by the external noise is inhibited by the switch circuit 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television antenna switching apparatus, and more particularly to an antenna switching apparatus suitable for a vehicle-mounted television receiver using a diversity receiving system.

[0002]

2. Description of the Related Art In a diversity receiving television receiver, a noise component in a pedestal portion of an equivalent pulse section after a vertical synchronizing signal in a received video signal is detected.
A television antenna switching device that controls the switching operation of the antenna switching means according to the level of the noise component is proposed in, for example, Japanese Patent Publication No. 5-42873.

[0003] As is well known, the diversity reception system is a system in which a plurality of antennas are switched to the antenna in the best reception state for reception, and various problems that occur with only one antenna, for example, fluctuation phenomenon of a reception wave. S / of the image accompanying
Disturbance of image synchronization due to deterioration of N and flutter phenomenon
This is a receiving method that can improve. In other words, in this system, in order to minimize reception disturbances in mobile reception such as vehicles, a plurality of reception antennas are arranged at intervals that do not cause mutual interference in the vehicle, and switched to the antenna with the best reception state To control.

In such a diversity receiving system, when the received image condition is good and the switching to another strong electric field receiving antenna is performed, the AG of the television receiver is changed.
There is a possibility that image disorder may occur due to a problem such as C response. The above-mentioned prior art is proposed to solve the problem of causing the image disturbance.When performing diversity reception, the pedestal part of the equivalent pulse section after the vertical synchronization signal of the video signal is input to the noise gate circuit. When the noise component is detected and the noise level exceeds a predetermined threshold, an antenna switching timing pulse is output to perform a diversity operation (that is, an antenna switching operation).

[0005]

However, in the above-mentioned prior art, there is a problem that no judgment is made on the external noise when the noise component is detected. Therefore, if there is external noise in the noise component detection section in a good reception state, the diversity operation is performed.

However, when diversity operation is performed in a good reception state, similar to the above-described image disturbance due to antenna switching at the time of a strong electric field, the antenna is switched by external noise to thereby change the AGC response of the television receiver. May cause image disturbance, and may cause noise when switching antennas.

Therefore, in order to eliminate such image disturbance and eliminate noise noise, it is necessary to minimize the diversity operation in a good reception state. Therefore, in order to minimize the diversity operation, it is necessary to consider a countermeasure against external noise in addition to the countermeasure in the above-described conventional technology. That is, it is necessary to detect a noise component in the pedestal unit in consideration of external noise.

An object of the present invention is to improve the accuracy of detecting noise level components including extraneous noise in view of the above-mentioned conventional problems, and to eliminate image disturbance and noise caused by a diversity operation.

[0009]

SUMMARY OF THE INVENTION A television antenna switching apparatus according to the present invention comprises: an antenna switching means for selecting an antenna having a maximum reception level from a plurality of antennas and connecting the antenna to a television receiver; Of the video signal received via the vertical synchronizing signal after detecting the noise component in the pedestal section of the equivalent pulse section, and providing at least two sections for detection, and comparing and detecting the noise levels of the two sections to thereby detect an extraneous signal. It is characterized by comprising detection means for determining the presence or absence of a noise component, and control means for controlling a switching operation of the antenna switching means according to the level of the noise component detected by the detection means.

According to the present invention, two sections for detecting a pedestal noise component in an equivalent pulse section after a vertical synchronizing signal of a received video signal are provided, and the noise levels of the two sections are compared and detected to detect extraneous pulse noise. Is determined, the accuracy of the detection of the original noise level component can be improved. As a result, since the antenna switching operation (diversity operation) is not performed in a good reception state, it is possible to effectively take measures against disturbance of received images and antenna switching noise due to voice.

[0011]

FIG. 1 is a block diagram showing a television antenna switching device according to an embodiment of the present invention. This figure shows an on-vehicle television antenna switching device suitable for a television receiver having a video output line terminal. For example, four television antennas ANT _{1 to} ANT ₄ are provided. These antennas are connected via a coaxial cable n to the antenna changeover switch circuit 1.
It is connected to the. The output of the antenna changeover switch circuit 1 is connected to an antenna input terminal (not shown) of the television receiver 2 via a coaxial cable l. The video signal detected by the television receiver 2 is output from a video output line terminal (not shown), and is connected to a video input terminal _IV of the television antenna switching device via a coaxial cable m.

The video signal from the video input terminal _IV is amplified by the video amplification circuit 3 and input to the synchronization separation circuit 5 of the control circuit 4. The synchronization separation circuit 5 performs synchronization separation of the synchronization signal, and sends the separated synchronization signal to a control signal generation circuit 6, which generates various control signals. These various control signals are supplied to the antenna switching timing pulse generation circuit 7, the noise gate pulse generation circuit 12, the sampling pulse generation circuit 18, and the reset pulse generation circuit 19.

An antenna switching timing pulse generating circuit 7
Generates a timing pulse necessary for antenna switching and supplies it to the judgment control circuit 8, which controls the reception level comparison circuit 9 and the antenna selection circuit 10. As shown, the video signal amplified by the video amplification circuit 3 is input to the clamp circuit 11. The clamp circuit 11 is for preventing the DC level of the video signal from fluctuating due to the fluctuation of the average image level (APL) and detecting the incorrect level when detecting a noise level described later.

The clamped video signal is input to the noise gate circuit 13 and the noise gate circuit 22. As shown in the timing chart of Oyobi in Figure 3 will be described later, the clamped video signal pedestal portion of the equalizing pulse interval after the vertical sync signal using the noise gate pulse P ₁ by the noise gate circuit 13 is extracted. Therefore, the noise gate pulse P ₁ is input to the noise gate circuit 13 before detecting the maximum level of antenna reception during diversity reception. Similarly, pedestal portion of the equalizing pulse interval after the vertical sync signal using the noise gate pulse P ₂ by the noise gate circuit 22 is extracted.

The pedestals extracted by the noise gate circuits 13 and 22 are amplified by the noise amplifier circuits 14 and 23 to a level required for noise level detection. The amplified pedestal unit is further provided to noise level detection circuits 15 and 24, respectively, and a DC voltage corresponding to the noise level is input to noise amplification circuits 16 and 25 at the next stage, respectively. Amplified output of the noise amplifier circuit 16 and 25 are respectively given to the sampling hold circuits 17 and 26, its level is held at the timing of the sampling pulse P ₃ and P ₄ shown in Oyobi in FIG. Moreover, the level of reset, before the above sampling as indicated by Oyobi of 3 is performed using the reset pulse P ₅ and P _6.

The noise gate pulses P ₁ and P ₂ are generated by the noise gate pulse generation circuit 12, and the sampling pulses P ₃ and P ₄ are generated by the sampling pulse generation circuit 1.
8 and the reset pulses P ₅ and P ₆ are generated from the reset pulse generating circuit 19. The outputs (1) and (2) of the generating circuits are (1) and (2)
This corresponds to (2).

Further, a comparison circuit 20, a threshold setting circuit 21, an attenuator 27, a comparison circuit 28, a switch circuit 2
9 and the like will be described later with reference to FIGS. 3 and 4. FIG.
Is a timing chart of the antenna switching pulse. From the antenna selection circuit 10, the antenna switching pulses PT _{1 to} P
T ₄ is selectively output in accordance with the best reception state. The dotted line of PT _{4 in} the figure indicates that the fourth antenna ANT ₄ has been selected. The mark in the video signal indicates the timing of horizontal synchronization, and each number indicates the number of horizontal synchronization in an odd field.

In the vertical blanking interval shown in the drawing, the antenna selection circuit 10 drives the antenna switching switch circuit 1 to continuously switch each antenna once in one field of the pedestal section during the horizontal scanning period. . The antenna switching pulse generation circuit 7 generates a timing detectable by the reception level comparison circuit 9 in order to detect the reception level of each antenna, and determines this timing via the judgment control circuit 8 and the reception level comparison circuit 9 and the antenna selection circuit. Output to the circuit 10.

As described above, according to the present invention, each reception antenna is switched to detect the maximum reception level, and the diversity reception that holds the antenna having the maximum reception level is performed.
Further, in the present invention, as described below, two detection sections of the pedestal noise component in the equivalent pulse section after the vertical synchronization signal are provided, and the noise levels of the two sections are compared and examined to determine whether there is any extraneous pulse noise. And the diversity reception is controlled so as to improve the detection accuracy of the original noise level component.

FIG. 3 is a timing chart of the noise gate pulse, the sampling pulse, and the reset pulse. FIGS. 4A, 4B, and 4C show the comparison circuit 28.
(A) is a case where there is no pulsed external noise, (B) is a case where there is a pulsed external noise (No. 1), and (C) is a case where there is a pulsed external noise ( Part 2).

The noise level sampled and held by the sample and hold circuit 17 is compared with a threshold value set by a threshold value setting circuit 21 in a comparison circuit 20. The noise level sampled and held by the sample and hold circuit 26 is input to the comparison circuit 28. The reset pulse (1) (ie, P ₅ in FIG. 3) from the reset pulse generation circuit 19 is supplied to the comparison circuit 20 and the attenuator 27 by the reset pulse (2) (ie, P ₅ in FIG. 3).
₆ ) are input to the comparison circuits 28, respectively.

In the present invention, the pedestal noise in the first half of the 9H line in the equivalent pulse section is detected at the timings shown in FIG. 3 and the noise level (voltage) sampled and held by the sample and hold circuit 26 is compared with the comparison circuit 28. To enter. On the other hand, the pedestal noise in the latter half of the 9H line is detected at the timing of, in FIG. In the attenuator 27, the level is lowered from the level held by the sample and hold circuit 17, input to the comparison circuit 28 from the attenuator 27, and compared with the level of the sample and hold circuit 26 described above.

As shown in FIG. 4, the comparison circuit 28 compares the level of the attenuator 27 with the level from the sample-and-hold circuit 26, and when the level of the attenuator 27 is lower than the level of the sample-and-hold circuit 26, "high". (H), and outputs “low” (L) when the level of the attenuator 27 is higher than the level of the sample-and-hold circuit 26.
Is input to

The switch circuit 29 is "high" and short-circuited (on)
Then, the operation of opening (off) is performed at “low”. Therefore, the comparison circuit 20 outputs the result of determining whether or not to perform the diversity operation in the same manner as in the related art.
By the operation described above, the final decision of the diversity operation as to whether or not to pass the judgment result of the comparison circuit is made. More specifically, as shown in FIG. 4A, when there is no pulsed external noise on the 9H line, the level (dotted line) of the sample and hold circuit 17 is
8 is set lower than the noise level (solid line). For this purpose, an attenuator 27 is used. This is set so that the comparison circuit does not malfunction due to random noise.

The level (a) of the sample-and-hold circuit 17 thus set and the level (b) of the sample-and-hold circuit 28 are compared by the comparison circuit 28. At this time, the output of the comparison circuit 28 is "H" when a <b, as shown in FIG.
Is output. As a result, the switch circuit 29 is short-circuited, and therefore depends on the judgment result of the comparison circuit 20.

Next, as shown in FIG. 4 (B), when pulsed external noise is present in the latter half of the 9H line, that is, external noise is present in the timing portion for determining the diversity operation based on the noise level. In this case, the level (a) of the sample-and-hold circuit 17 to the comparison circuit 28 and
The level (b) of the sample and hold circuit 28 becomes a> b, and the output of the comparison circuit 28 becomes “L” as such. Therefore, the switch circuit 29 is in the open state, and the result of the judgment by the comparison circuit 20 is not output to the judgment control circuit 8.

Further, as shown in FIG. 4C, when there is a pulsed external noise in the first half of the 9H line,
That is, when there is a pulsed external noise in FIG. 3, the level (a) of the sample and hold circuit 17 to the comparison circuit 28 and the level (b) of the sample and hold circuit 28
Becomes a <b, and the output of the comparison circuit 28 becomes “H” like that. This indicates that the comparison circuit 20 that determines the diversity operation is not affected. That is, at this time, the switch circuit 29 is in a short-circuit state, and as a result, it depends on the judgment of the comparison circuit 20.

When external noise is mixed in the noise gate period of FIG. 3 by the above operation, "L" is output from the comparison circuit 28, and the switch circuit 29 is opened. Therefore, the output malfunctioned by the external noise in the comparison circuit 20 is prohibited by the switch circuit 29, and the signal is not sent to the judgment control circuit 8, so that the diversity operation by the external noise is not performed, and the good reception is achieved. In the state, a state in which the diversity operation is not performed for the external noise can be maintained.

[0029]

As described above, according to the present invention,
Since the pedestal noise component detection section of the equivalent pulse section after the vertical synchronization signal of the received video signal is set at two places, the noise levels at these two places are compared to determine the presence or absence of extraneous pulse noise. It is possible to improve the detection accuracy of the original noise level component. as a result,
Since no diversity operation is performed in a good reception state, disturbance of received images and antenna switching noise due to voice can be effectively eliminated.

[Brief description of the drawings]

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

FIG. 2 is a timing chart of an antenna switching pulse.

FIG. 3 is a timing chart of a noise gate pulse, a sampling pulse, and a reset pulse.

FIG. 4 is a timing chart in the comparison circuit (2), where (A) shows a case where there is no pulsed external noise;
(B) is a case where pulsed external noise is present (part 1), and (C) is a case where pulsed external noise is present (part 2).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Antenna changeover switch circuit 2 ... TV receiver 3 ... Video amplifier circuit 4 ... Control circuit 5 ... Synchronization separation circuit 6 ... Control signal generation circuit 7 ... Antenna changeover timing pulse generation circuit 8 ... Judgment control circuit 9 ... Reception level comparison circuit DESCRIPTION OF SYMBOLS 10 ... Antenna selection circuit 11 ... Clamp circuit 12 ... Noise gate pulse generation circuit 13, 22 ... Noise gate circuit 14, 23 ... Noise amplification circuit 15, 24 ... Noise level detection circuit 16, 25 ... Noise amplification circuit 17, 26 ... Sample Hold circuit 18 Sampling pulse generation circuit 19 Reset pulse generation circuit 20, 28 Comparison circuit 21 Threshold circuit 27 Attenuator 29 Switch circuit

Claims (1)

[Claims] 1. An antenna switching means for selecting an antenna having a maximum reception level from a plurality of antennas and connecting the antenna to a television receiver, and after a vertical synchronizing signal of a video signal received via the antenna switching means. Detecting means for detecting a noise component in the pedestal portion of the equivalent pulse section and providing at least two sections for detecting, and comparing and detecting the noise levels of the two places to determine the presence or absence of an external noise component; Control means for controlling a switching operation of the antenna switching means according to a level of a noise component detected by the means.