JPH0727732Y2 - Television receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention relates to a television receiver including a reception level detecting device, such as a vehicle-mounted television receiver.

(Prior Art) Conventionally, in a television receiving device such as a vehicle-mounted device, a signal level of a receiving channel changes depending on a receiving place, so that the receiving level detecting device detects the receiving signal level and displays it on a screen.

FIG. 4 is a block diagram showing a television receiving device provided with a conventional reception level detecting device, and FIG. 5 is a characteristic diagram showing frequency characteristics of the surface wave filter (hereinafter referred to as SAW filter) of FIG. .

In FIG. 4, a high frequency television signal (referred to as an RF signal) induced in the antenna 1 is controlled by a system control microcomputer (hereinafter referred to as a system control microcomputer) 12 and an electronic tuning tuner (hereinafter referred to as an ET tuner). ) 2, the channel is selected and converted into a video intermediate frequency signal (hereinafter referred to as an IF signal).

The IF signal from the ET tuner 2 is supplied to a video intermediate frequency circuit (hereinafter, referred to as PIF circuit) 4 via a SAW filter 3 having a frequency characteristic as shown in FIG. 5, for example. Fifth
In the figure, the horizontal axis represents frequency and the vertical axis represents output response. P is the desired video intermediate frequency, S is the audio intermediate frequency, C is the color subcarrier, P ″ is the video intermediate frequency of the upper adjacent channel, and S ′ is the audio intermediate frequency of the lower adjacent channel.

As shown in FIG. 4, the PIF circuit 4 includes a PIF amplifier circuit,
It is composed of a video detection circuit and an automatic gain control circuit (hereinafter referred to as AGC circuit), amplifies and detects the IF signal, and outputs a video detection output and a 4.5 MHz audio intermediate frequency signal (hereinafter referred to as SIF signal). To do. The video detection output is supplied to a demodulation circuit 5 and demodulated into R, G, B primary color signals, and then supplied to a picture tube (hereinafter referred to as CRT) 7 via a switching circuit 6 to display an image.

On the other hand, the 4.5 MHz SIF signal is an audio intermediate frequency circuit (hereinafter, SIF
The audio signal is amplified by limiter amplification and FM detection by a circuit 9 and is amplified by an amplifier circuit 10 and supplied to a speaker 11.

Further, the AGC voltage in the PIF circuit 4 is supplied to the system control microcomputer 12 via a voltage detection circuit (not shown). The voltage detection circuit is composed of, for example, a plurality of comparators, each comparator compares with a reference voltage, and the comparison result output is supplied to the microcomputer 12. Alternatively, the voltage detection circuit may be one that performs analog-digital conversion on the AGC voltage and compares the digital data with the ROM data in the microcomputer 12. That is, the system control microcomputer 12
The input signal level is determined conversely from the AGC voltage that changes according to the antenna input signal level. Then, the result of the determination is output to the switching circuit 6 as a character or pattern signal by the R, G, B primary color signals. These judgment output signals (R ', G', B'signals) are controlled by a switching signal (SW signal) output from the microcomputer 12 at the same time in the switching circuit 6, so that the state of the received signal level is the same as that of the video or Color display on CRT7 separately. In this case, it is also possible to determine the received signal level for each channel and display the received signal levels of all channels on the CRT 7 at once.

By the way, in such a television receiver,
If the antenna input signal level is high in a strong electric field area, the reception level display as if the signal channel is received occurs not only when the signal channel is received but also when the adjacent non-signal channel is received. This is because the band characteristic of the ET tuner 2 and the SAW filter 3 is a wide band for video, so that the adjacent channel exclusion performance is limited. That is, there is a problem that an error occurs in the detection and display of the received signal level using the AGC voltage from the PIF circuit 4. In particular, when the channels are separated from each other by 4 MHz and the frequency bands are partially overlapped with each other, such as the VHF channels 7 to 8, the above-mentioned problems are remarkable.

FIG. 6 shows an example of the frequency spectrum of the television broadcast wave in the VHF high band (channels 4 to 12). In this figure, P and S are video carrier and audio carrier of each channel, and the numbers attached to P and S indicate channel numbers. Channels 5,7,9,11 are non-signal channels, and frequency bands between channels 7 and 8 overlap as shown.

(Problems to be solved by the invention) As described above, in the conventional television receiving device, since the received signal level is detected and displayed by using the AGC voltage of the PIF circuit, the adjacent no-signal channel is input when a strong electric field is input. However, there is a problem that an erroneous display is likely to occur.

Therefore, the present invention is to eliminate the above problems,
It is an object of the present invention to provide a television receiving device capable of reducing erroneous display of a received signal level on an adjacent non-signal channel.

[Structure of the Invention] (Means for Solving the Problems) A television receiver of the present invention has a frequency conversion means for receiving a television signal and converting it into an intermediate frequency signal, and a predetermined video frequency characteristic, A first inputting an intermediate frequency signal from the frequency converting means to obtain an output signal for video detection;
Image signal from the first filter means, and second filter means having predetermined audio frequency characteristics, receiving the intermediate frequency signal from the frequency conversion means, and obtaining an output signal for audio detection. It has a first intermediate frequency amplifying means for amplifying and detecting the detection output signal, and a function for amplifying and detecting the sound detection output signal from the second filter means, and has an AGC voltage corresponding to the received signal level. Second intermediate frequency amplifying means having a function of creating, means for detecting the level of the AGC voltage from the second intermediate frequency amplifying means, and determining the magnitude of the received signal level, and the determination result of this means And display means for displaying.

The audio frequency characteristic of the second filter means is preferably a narrow-band frequency characteristic centered on the audio intermediate frequency so that the second intermediate frequency amplifying means performs separate detection.

Alternatively, the audio frequency characteristic of the second filter means may be a narrow-band frequency characteristic centered on the video intermediate frequency and the audio intermediate frequency so that intercarrier detection is performed by the second intermediate frequency amplifying means. desirable.

(Operation) In the present invention, the AGC voltage for detecting the received signal level is obtained from the second intermediate frequency amplifying means for audio instead of the conventional image intermediate frequency amplifying circuit. Since the narrow band audio detection output signal that has passed through the second filter means is supplied to the second intermediate frequency amplifying means for audio, the level of the AGC voltage obtained from the second intermediate frequency amplifying means. Is less likely to be affected by adjacent channels, and therefore erroneous display of the received signal level can be prevented.

(Embodiment) Hereinafter, the present invention will be described based on an embodiment shown in the drawings.

FIG. 1 is a block diagram showing a television receiver according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing frequency characteristics of the SAW filter shown in FIG.

In FIG. 1, parts having the same functions as those in FIG. 4 are designated by the same reference numerals. That is, antenna 1, ET tuner 2,
PIF circuit 4, demodulation circuit 5, switching circuit 6, CRT 7, SIF circuit 9, amplification circuit 10, speaker 11, system control microcomputer
12 has the same circuit function as that in FIG.

The difference between this embodiment and the conventional example shown in FIG. 4 is that in this embodiment, a method called a Kwoji parallel detection method is basically used, and the IF signal from the ET tuner 2 is used for video and audio. It is supplied to a two-output type SAW filter 3A having frequency characteristics of two systems, and the video detection output signal IFp and the audio detection output signal IFs are extracted from the SAW filter 3A. The video detection output signal IFp is the PIF. The first SIF circuit 8 that inputs to the circuit 4 and amplifies the output signal IFs for voice detection and 4.5 MHz detection
To the SI, and further performs limiter amplification and FM detection.
The configuration is such that it is supplied to the F circuit (referred to as the second SIF circuit) 9. The first SIF circuit 8 outputs a voice detection output signal I
It is composed of a SIF amplification circuit that amplifies Fs, a 4.5 MHz detection circuit, and an AGC circuit. And for detection of received signal level
Unlike the conventional example, the AGC voltage is obtained from the first SIF circuit 8 and supplied to the system control microcomputer 12 via a voltage detection circuit (not shown). Other configurations are similar to those of the conventional example (FIG. 4).

Regarding the SAW filter 3A, the video detection output signal IFp has a frequency characteristic as shown in FIG. That is, the band of P (video intermediate frequency) to C (color subcarrier) necessary for video detection has a small loss and is 92
The S (sound intermediate frequency) that interferes with the 0 kHz beat or the like is attenuated as much as possible. On the other hand, output signal for voice detection
IFs has a frequency characteristic as shown in FIG. 2 (b), and only S (sound intermediate frequency) is taken out. The audio detection output signal IFs from the SAW filter 3A is the first
Supplied to the SIF circuit 8 of the
It is supplied to the IF circuit 9 and FM detected.

In the above configuration, the IF signal from the tuner 2 is passed through the SAW filter 3 to lower the audio signal level as much as possible, and the video signal is detected under the optimum condition for the video signal detection. Voice detection is performed under the optimum conditions for voice detection by lowering as much as possible to improve performance such as voice sensitivity and voice / buzz.

Moreover, since the first SIF circuit 8 amplifies and detects only the narrow band signal centered on S (sound intermediate frequency) shown in FIG. 2 (b) (separate detection by only the sound signal), it is obtained here. The AGC voltage to be determined is determined only based on the signal level of S (audio intermediate frequency), and P (video intermediate frequency) of the same channel, P ″ (video intermediate frequency of the upper adjacent channel) or S ′ (lower side of the adjacent channel) It is hardly affected by the audio intermediate frequency of the adjacent channel.Therefore, by using the AGC voltage of the first SIF circuit 8 for detecting the reception signal level, the erroneous display on the adjacent non-signal channel is eliminated. can do.

FIG. 3 is a SAW filter 3A for explaining another embodiment of the present invention.
It is a characteristic view showing the frequency characteristics of.

This figure shows the P (video intermediate frequency) and S (audio intermediate frequency) beat components (4.5 MHz) for detection in the first SIF circuit 8.
SA when using the inter-carrier detection method that uses
The frequency characteristic of W filter 3A is shown. The video detection output signal IFp has the same frequency characteristic as that of FIG. 2A as shown in FIG. 3A, but the audio detection output signal IFp.
As shown in FIG. 3B, s has a narrow band characteristic centered on P and S. In this case, the AGC of the first SIF circuit 8
The voltage is affected by P (video intermediate frequency), but since the high frequency component of the modulated video signal is scarcely included, the voltage is less affected than before and erroneous display may occur on a non-signal channel adjacent to a signal channel. Can be reduced.

Although the PIF circuit 4 and the SIF circuits 8 and 9 are shown as separate blocks in FIG. 1, it goes without saying that these circuits may be arbitrarily combined to form a one-chip IC.

Further, in FIG. 1, the SAW filter 3A has a configuration in which two filter elements for video and audio are combined, but the configuration may be such that a video SAW filter and an audio SAW filter are provided separately. Of course.

[Advantage of Device] As described above, according to the present invention, the AGC voltage for detecting the received signal level is replaced with the conventional video intermediate frequency amplifier circuit,
Since it is obtained from the audio intermediate frequency amplifier circuit, it is possible to reduce the erroneous display of the received signal level in the channel adjacent to the signal channel. In particular, if there is a signal channel with every other channel, 7
When receiving in a high electric field area where there is a signal on channel 8 or channel 8, erroneous display on adjacent channels can be greatly improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a television receiver according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing frequency characteristics of the SAW filter shown in FIG. 1, and FIG. 3 is another embodiment of the present invention. FIG. 4 is a characteristic diagram showing frequency characteristics of the SAW filter, FIG. 4 is a block diagram showing a conventional television receiver, and FIG. 5 is a block diagram showing frequency characteristics of the SAW filter of FIG.
FIG. 6 is an explanatory diagram showing an example of the frequency spectrum of a television broadcast wave in the VHF high band. 2 ... ET tuner, 3A ... SAW filter, 4 ... PIF circuit, 5 ... demodulation circuit, 6 ... switching circuit, 7 ... CRT, 8 ...
… First SIF circuit, 9 …… Second SIF circuit, 12 …… System control microcomputer.

Claims (3)

[Scope of utility model registration request] 1. A frequency conversion means for receiving a television signal and converting it into an intermediate frequency signal, and a predetermined video frequency characteristic, wherein the intermediate frequency signal is inputted from the frequency conversion means, and an output signal for video detection is provided. A first filter means for obtaining an output signal for audio detection, which has a predetermined audio frequency characteristic and which receives an intermediate frequency signal from the frequency conversion means, and the first filter A first intermediate frequency amplification means for amplifying and detecting the video detection output signal from the means, and a function for amplifying and detecting the audio detection output signal from the second filter means, and depending on the received signal level. Second intermediate frequency amplifying means having a function of generating an AGC voltage, means for detecting the level of the AGC voltage from the second intermediate frequency amplifying means, and determining the magnitude of the received signal level, Television receiver, characterized by comprising a display means for displaying the determination result of the means. 2. The television receiving apparatus according to claim 1, wherein said second filter means has a narrow band centering on an audio intermediate frequency so that said second intermediate frequency amplifying means carries out a separate detection. A television receiver having the following audio frequency characteristics. 3. The television receiver according to claim 1, wherein the second filter means is centered on a video intermediate frequency and an audio intermediate frequency so as to perform intercarrier detection by the second intermediate frequency amplifying means. And a narrow band audio frequency characteristic.