JPH0622347A - Electric field discrimination method - Google Patents

Abstract

PURPOSE:To accurately discriminate an electric field level even when a synchronizing signal level of a video signal inputted from a television receiver is fluctuated. CONSTITUTION:A video signal (a) is inversely amplified and its amplified signal (b) is inputted in a clamp circuit 3, in which the signal (b) is clamped at a peak level of a synchronizing signal. A noise gate circuit 4 samples a noise signal (d) for a vertical synchronization pulse period 6H and the sampled signal is used for discrimination of an electric field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for judging an electric field, and more particularly, for example, in a television diversity system, the deterioration of the voice S / N is suppressed by judging the received electric field and stopping the antenna switching operation in the strong electric field. The present invention relates to an electric field determination method suitable for

[0002]

2. Description of the Related Art A television diversity system is a vehicle television receiving antenna device which is mainly mounted and used in a vehicle such as an automobile. In order to eliminate the fading phenomenon that the direct wave from the broadcasting station interferes with the reflected wave from the building or the road surface, multiple TV receiving antennas mounted on the vehicle are connected to the antenna of the TV receiver via the antenna switching circuit. A vehicle television receiving antenna switching device has been proposed which is connected to an input circuit, a control circuit selects an antenna having the highest reception level, and is connected to an antenna input circuit of a television receiver (Japanese Patent Laid-Open No. Sho 56-56). -10
780).

Further, in the above system, the reception antenna is switched by using only the video signal output from the television receiver, and the reception electric field determination function is provided to stop the antenna switching operation at the time of a strong electric field. A television receiving antenna switching device for reducing signal switching noise has also been proposed (Japanese Patent Laid-Open Nos. 61-284105 and 62-6582).

FIG. 3 shows a block diagram of a conventional received electric field determination circuit. In the figure, the video signal from the television receiver 1 is inverted and amplified by the video amplifier circuit 2 and then input to the clamp circuit 3. The clamp circuit 3 controls so that the peak level of the synchronizing signal becomes a constant potential. This allows
Even if the DC level of the video signal fluctuates due to APL fluctuation,
The DC level of the noise signal input to the noise amplification circuit 6 via the noise gate circuit 4 controlled by the noise gate control signal generation circuit 5 is kept constant. The noise signal superimposed on the video signal by the clamp circuit 3 is not affected by the APL fluctuation of the video signal, and the noise amplification circuit 6
Is amplified by. The amplified noise signal is detected by the noise detection circuit 8 and then input to the sample hold circuit 10 and held as a DC voltage according to the noise level by the sampling signal from the sampling signal generation circuit 7. The noise voltage level sampled and held is compared with the threshold value set by the threshold value setting circuit 11 in the comparison circuit 12, and when the noise voltage exceeds the threshold value, the determination signal (for the antenna switching operation) ( The electric field judgment output) is output.

FIG. 4 shows the electric field judgment timing of the conventional received electric field judgment circuit. As shown in FIG. 4, when the diversity antenna switching operation is performed in the 10H period of the video signal, the received electric field determination is performed by selecting the noise component superimposed on the pedestal level in the 7-9H equivalent pulse period by the noise gate circuit. Input to the noise amplifier (Fig. 4
In the example, it is selected in the period of 9H). As a means for fixing the pedestal level during the equivalent pulse period of 7 to 9H, FIG.
As shown in (A), a clamp method (sync tip clamp method) is used in which the pedestal level is fixed by holding the peak value of the synchronizing signal inverted by the video signal amplifier circuit 2.

[0006]

However, in this method,
When the sync signal level fluctuates as shown in FIG. 5B, the pedestal level rises because the peak value of the sync signal is fixed. Therefore, the noise amplifier 6
The DC level of the noise signal input to the circuit becomes high, and a part of the inverted output signal of the noise amplification circuit 6 becomes saturated. As a result, the noise signal that has passed through the noise amplification circuit 6 has a smaller level than it actually is. That is,
The conventional electric field determination method is
There is a problem in that the noise signal detection sensitivity is lowered and the received electric field cannot be accurately determined.

It is an object of the present invention to provide a method of accurately determining an electric field level in a reception electric field determination circuit in a television diversity system or the like even if the sync signal level of a video signal input from a television receiver fluctuates. is there.

[0008]

In order to achieve the above object, an electric field determination method according to the present invention comprises inverting and amplifying a video signal,
The peak level of the sync signal of the amplified signal is clamped to a constant potential, the signal of the vertical sync pulse section of the video signal is extracted from the clamped signal for a predetermined time, and the electric field is determined using the extracted signal. Is the gist.

[0009]

Since the signal for determining the electric field is extracted in the vertical synchronizing pulse section, its DC level remains fixed at the clamp potential and does not change. Therefore, the electric field can be stably determined even if the synchronizing signal level changes. You can

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a timing chart of an embodiment of the electric field determination method according to the present invention. The electric field determination circuit for carrying out the method of the present invention may be the same as the conventional one shown in FIG. 3, but the timing for opening and closing the noise gate circuit 4 (hereinafter referred to as the noise signal sampling period) is the same as the conventional one. 7-9
The equivalent pulse section of H is changed to the vertical synchronizing pulse section of 4 to 6H, and the DC level of the noise signal input to the noise amplification circuit 6 via the clamp circuit 3 and the noise gate circuit 4 is always set to the clamp potential. It has become so. In addition, in the present embodiment, description will be given using a case where the 6H section is used. Further, it is desirable that the noise signal sampling period is sampled as short as possible from the viewpoint of preventing malfunction due to external noise.
It is set to about [μSEC].

FIG. 2 shows a change in signal level during a noise signal sampling period using the electric field determination method according to the present invention.
FIG. 2A shows a case where a video signal of a normal sync level is input. The video signal a is inverted and amplified by the video signal amplifier circuit 2 and then clamped at the peak level of the synchronizing signal by the clamp circuit 3 (waveform b). The noise signal is sampled during the 6H period, and only during this period, the noise gate circuit 4 is opened and the clamp level portion of the video signal is cut out and input to the noise amplifier circuit 6. Figure 2
When the synchronization level decreases as shown in (B), the clamp potential does not change, and the pedestal level of the video signal increases. However, the noise signal sampling period is 6
Since it is set to the H section, the DC level of the noise signal after being sampled by the noise gate circuit 4 remains fixed at the clamp potential. Therefore, since the input DC bias of the noise amplification circuit 6 does not change, the output of the noise amplification circuit 6 can amplify only the noise signal component without being saturated by the fluctuation of the synchronization signal level.

[0012]

As described above, according to the method of the present invention, even if the same electric field determination circuit as the conventional one is used, the electric field which is not affected by the fluctuation of the synchronizing signal level is changed only by changing the noise signal sample timing. The determination can be easily performed.

[Brief description of drawings]

FIG. 1 is a timing diagram for explaining an embodiment of the method of the present invention.

FIG. 2 is a diagram for explaining the operation of the method of the present invention.

FIG. 3 is a block diagram showing an example of an electric field determination circuit.

FIG. 4 is a timing chart for explaining a conventional electric field determination method by the above circuit.

FIG. 5 is a diagram for explaining the operation of the method of FIG.

[Explanation of symbols]

 a video signal b output signal of the video signal amplification circuit 2 c output signal of the noise gate circuit 4 d output signal of the noise amplification circuit 6

Claims (1)

[Claims] 1. A video signal is inverted and amplified, and a peak level of a sync signal of the amplified signal is clamped to a constant potential, and a signal in a vertical sync pulse section of the video signal is extracted for a predetermined time from the clamped signal. An electric field determination method comprising performing an electric field determination using the extracted signal.