JP2002369088A - Secam-l system television receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a television receiver of an SECAM-L system capable of hardly generating a buzz sound even in an on-vehicle television receiver whose receiving condition is largely changed. SOLUTION: In a television receiver in an SECAM-L system, a PIF trap circuit 6 for attenuating a video signal frequency is added to the output part of an SAW filter 4 for an SIF for extracting an SIF signal from an IF signal to be outputted from a tuner 2 so that the signal can be amplified/detected in a state that video signal components are sufficiently removed. Thus, it is possible to prevent the generation of any buzz sound due to a video signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver capable of receiving a television signal of a broadcasting system (SECAM-L system) adopted in France.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a receiving circuit up to video and audio detection in a television receiver capable of receiving the conventional SECAM-L system. In FIG. 4, 1 is an antenna, 2 is a tuner, 3 is a video intermediate frequency (hereinafter PI).
F) SAW (surface acoustic wave) filter, 4 is a SAW filter for audio intermediate frequency (hereinafter referred to as SIF), 5
Is an intermediate frequency amplification / detection circuit.

[0003] In FIG. 4, R
The F television signal is tuned / frequency-converted by the tuner 2, and then output as an intermediate frequency (hereinafter referred to as IF) signal having frequency characteristics as shown in FIG. In FIG. 5, “P” indicates PIF (38.9 MHz).
z), “C” is the color carrier frequency (about 34.5 MH)
z) and "S" are SIF (32.4 MHz), which have characteristics such that a video signal band for one channel is extracted.

Referring again to FIG. 4, the IF signal output from the tuner 2 includes a PIF SAW filter 3 for eliminating a television signal on an adjacent channel, and an SIF SIF filter.
It is supplied to the AW filter 4. Examples of the characteristics of the SAW filter are as shown in FIGS.
As shown in FIG. 6A, the AW filter 3 has such a characteristic that only the video signal is extracted.
The signal is dropped. On the other hand, S for SIF
As shown in FIG. 6B, the AW filter 4 has such a characteristic that only the SIF signal is extracted, and reduces unnecessary video signal components as much as possible.

[0005] Therefore, by passing through the SAW filter, only the video signal component is obtained at point b in FIG.
Only the audio signal component is obtained at the point c. As a result of the intermediate frequency amplification / detection circuit 5 amplifying / detecting the signal under optimal conditions by the dedicated circuits, the video detection output is output at the point d and the audio signal is output at the point e. A detection output is obtained. Thereafter, the video detection output is chroma-demodulated, and the video is reproduced on the display element by the synchronization signal processing, while the audio detection output is amplified and output from the speaker. here,
Since the configurations of the chroma demodulation circuit and the audio circuit are well known, a detailed description is omitted.

By the way, in such a receiving circuit, the video signal and the audio signal are separately amplified / detected under the optimum conditions. Therefore, in principle, the audio detection output should not be affected by the video signal at all. Actually, since the rejection performance of the SAW filter is limited, it is difficult to completely eliminate the influence of the video signal.

Further, since the sound signal of the SECAM-L system television signal is amplitude modulated (AM) like the video signal, it is destined to be more susceptible to the video signal than the frequency modulation (FM). In order to cope with such a fate of the broadcasting system, the transmission power ratio of the video signal and the audio signal of the broadcast wave is set to be larger than that of the NTSC or PAL television signal of the FM audio, and the operation is shown in FIG. As shown, the spectrum of the received television signal also has a so-called P
The -S ratio is about 6 to 10 dB in the NTSC / PAL system, whereas the SECAM-L system is about 10 to 20 dB.
B is bigger.

[0008] When the television receiver is used in a vehicle,
Multipath deteriorates the reception condition, and adds an element in which the PS ratio fluctuates, which deteriorates the reception condition as compared with the reception by the stationary television receiver.

When the audio signal is affected by the video signal, the S / N of the audio detection output deteriorates, but the biggest deterioration phenomenon is the occurrence of video buzz. If the frequency components that are adversely affected by the video signal are high,
Although the sound quality can be reduced by the pass filter (LPF) without significantly impairing the sound quality, it is difficult to remove the buzz including the 50 Hz vertical synchronization component after the detection output.

[0010]

As described above, the SEC
In AM-L television broadcasting, since both video and audio are AM, the audio signal is easily affected by the video signal in principle, and the PS ratio of the broadcast signal is large. It has a fate that buzz is likely to occur due to video signals.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a SECAM-L television receiver in which buzzing sound is unlikely to occur even in a vehicular vehicle where the receiving conditions vary greatly under such disadvantageous conditions. .

[0012]

According to the present invention, there is provided a tuner for outputting an intermediate frequency signal of a desired channel band, and a video intermediate frequency signal extraction for extracting a video intermediate frequency signal from the intermediate frequency signal. For SA
In a SECAM-L television receiver having a W filter and an audio intermediate frequency signal extraction SAW filter for extracting an audio intermediate frequency signal from the intermediate frequency signal, the output signal from the audio intermediate frequency signal extraction SAW filter is On the other hand, a video intermediate frequency trap circuit for attenuating the video intermediate frequency is provided.

According to the present invention, in a SECAM-L television receiver, a video signal is output to an output section of a SAW filter for extracting an audio intermediate frequency signal from an intermediate frequency signal output from a tuner. A video intermediate frequency trap circuit for attenuating the frequency is added, and the video signal component is sufficiently removed before amplification / detection. Therefore, when receiving a TV signal of the SECAM-L system in which the audio signal is amplitude-modulated similarly to the video signal,
Generation of buzz sound due to the influence of the video signal can be effectively reduced. Therefore, especially when the PS ratio of the transmission signal is large, or when the PS
This is effective when the ratio increases.

In the present invention, the video intermediate frequency trap circuit is composed of, for example, a SAW filter element.

In the present invention, it is preferable that an impedance element is interposed between the audio intermediate frequency signal extracting SAW filter and the video intermediate frequency trap circuit. With this configuration, even when the audio intermediate frequency signal extraction SAW filter and the video intermediate frequency trap circuit are both configured by SAW filters,
Since these SAW filters are connected via an impedance element, it is possible to eliminate an influence on characteristics due to mutual interference between the SAW filters.

In the present invention, the video intermediate frequency trap circuit may be constituted by, for example, a series resonance circuit including an inductor and a capacitor.

In the present invention, the attenuation band of the video intermediate frequency trap circuit may include a video intermediate frequency signal band excluding an audio intermediate frequency, or the attenuation band of the video intermediate frequency trap circuit may be a video image excluding an audio intermediate frequency. A configuration in which the Q of the video intermediate frequency trap circuit is set so as to include the intermediate frequency signal band can be adopted.

In the present invention, a plurality of trap circuits including at least the video intermediate frequency trap circuit may be provided so that the attenuation band of the video intermediate frequency trap circuit includes a video intermediate frequency signal band excluding an audio intermediate frequency. Good.

In this case, it is preferable to use a trap element in which the plurality of trap circuits are integrated.

[0020]

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

FIG. 1 is a block diagram of a receiving circuit of a television receiver to which the present invention is applied. Note that the basic configuration of a receiving circuit of a television receiver to which the present invention is applied is the same as that of a conventional television receiver, and thus, portions having common functions are denoted by the same reference numerals.

In FIG. 1, the television receiver of the present embodiment has
An antenna 1, a tuner 2 for outputting an intermediate frequency (hereinafter, referred to as IF) signal of a desired channel band, and a video intermediate frequency (hereinafter, referred to as PIF) signal from an IF signal. Filter for extracting PIF (SAW filter for extracting PIF signal) 3 from the IF signal to an audio intermediate frequency (hereinafter SIF)
SIF SAW filter (SI
SAW filter for F signal extraction) 4 and IF amplification / detection circuit 5.

In the television receiver of the present embodiment, as in the prior art, the RF television signal received by the antenna 1 is selected / frequency-converted by the tuner 2 and the frequency characteristic described with reference to FIG. Is output. In FIG. 5, “P” indicates PIF (38.9 MHz).
z), “C” is the color carrier frequency (about 34.5 MH)
z) and "S" are SIF (32.4 MHz), which have characteristics such that a video signal band for one channel is extracted.

Referring again to FIG. 1, the IF signal output from the tuner 2 includes a PIF SAW filter 3 and an SIF SA for eliminating a television signal of an adjacent channel.
It is supplied to the W filter 4.

Here, the characteristics of the SAW filter are shown in FIG.
As described with reference to (a) and (b), the PIF S
As shown in FIG. 4A, the AW filter 3 has such a characteristic that only the video signal is extracted.
The signal is down. On the other hand, as shown in FIG. 4B, the SIF SAW filter 4 has such a characteristic that only the SIF signal is extracted, and unnecessary video signal components are reduced as much as possible.

By passing through such a SAW filter, a video signal component is obtained at the point b in FIG. 1, while an audio signal component is obtained at the point c in the intermediate frequency amplification / detection circuit 5. As a result of the amplification / detection under the optimum conditions by the dedicated circuits, a video detection output is obtained at point d and an audio detection output is obtained at point e. Thereafter, although not shown, the video detection output is chroma-demodulated,
While video is reproduced on the display element by the synchronization signal processing, the audio detection output is amplified and output as audio from the speaker.

The difference between the television receiver of this embodiment and the conventional one is that the SIF SAW filter 4
A PIF trap circuit 6 is provided between the output of the IF amplifier and the IF amplification / detection circuit 5. Here, the trap circuit is
The PIF trap circuit 6 resonates with a signal of a predetermined frequency to remove or sufficiently reduce the signal.
Attenuates the video frequency signal from the SIF output from the SIF SAW filter 4.

Conventionally, in TV broadcasting of the SECAM-L system, since both video and audio are AM, the audio signal is easily affected by the video signal in principle, and the P-
Since the S ratio was large, the sound detection output was destined to easily generate buzz due to the video signal. However, the television receiver of the present embodiment has such disadvantageous conditions, Even in the case of a vehicle-mounted device having a large change, a high-level video signal component that cannot be completely removed by the SIF SAW filter 4 can be further reduced by the PIF trap circuit 6. For this reason, as a result, it is possible to reduce the detection of the video signal component being superimposed on the audio detection output, and thus it is possible to reduce the occurrence of the buzz sound due to the video signal component.

(Specific Example 1 of PIF Trap Circuit 6) FIG.
(A) and (b) are circuit diagrams each showing a specific example of a PIF trap circuit 6 (video intermediate frequency trap circuit) shown in FIG. 1 in a television receiver to which the present invention is applied, and FIG. FIG. 4 is an explanatory diagram showing trap characteristics.

As shown in FIG. 2A, in this embodiment, P
SAW filter element 61 as IF trap circuit 6
(SAW trap). Where SIF
The IF signal output from the tuner 2 (see FIG. 1) is input to the unbalanced input terminal a of the SAW filter 4 for
The balanced output terminal c _a and c _b, resistors R1 and capacitor C1, resistor R2 and the capacitor C2 are connected in series, are input to the SIF differential input terminals f and g of the IF amplifier / detector circuit 5 .

[0031] The connection point c _c of the resistor R1 and the capacitor C1, and between the connection point c _d of the resistor R2 and the capacitor C2, is connected to the SAW filter device 61 as a PIF trap circuit 6, the PIF Trap circuit 6
Has a trap characteristic as shown in FIG.

For this reason, in the television receiver of this embodiment, the level of the video signal component (P) that cannot be completely removed by the SIF SAW filter 4 as illustrated in FIG. 6B can be further reduced. . Therefore, the amplification of the audio signal and the AM detection can be performed in a state where the influence of the video signal is further eliminated, so that the buzz sound caused by the video signal can be suppressed.

In this embodiment, both the SIF SAW filter 4 and the PIF trap circuit 6 are composed of SAW filters.
And R2, it is possible to eliminate the influence of the mutual interference between the SAW filters on the characteristics.

In order to eliminate the influence of the mutual interference between the SAW filters on the characteristics, the impedance is not limited to the resistance, and may be replaced with another impedance element.

(Specific Example 2 of PIF Trap Circuit 6) FIG.
(A) and (b) are a circuit diagram showing a specific example of the PIF trap circuit 6 shown in FIG. 1 and an explanatory diagram showing a trap characteristic of the PIF trap circuit 6 in a television receiver to which the present invention is applied. is there.

In this embodiment, as shown in FIG.
To the unbalanced input terminal a of the IF SAW filter 4, IF signal output from the tuner 2 (see FIG. 1) is input to the balanced output terminal c _a and c _b, a capacitor C1, and C2, respectively They are connected in series and input to the SIF differential input terminals f and g of the IF amplification / detection circuit 5, respectively.

In this embodiment, the PIF trap circuit 6
A series resonance circuit 62 including an inductor Lp and a capacitor Cp is used.

In the series resonance circuit 62 having such an LC configuration, as shown in FIG.
Although it is difficult to obtain a steep trap characteristic as compared with the SAW trap described with reference to (b), since an arbitrary Q trap can be configured depending on the setting of the LC constant, the purpose can be relatively easily achieved with general-purpose components. It is possible to do.

Further, even if the absolute attenuation at the trap frequency is small, the modulated video signal components around the carrier frequency can also be effectively removed at the same time, so that the influence of the video signal on the audio detection output can be reduced. As a result, the occurrence of buzz can be prevented.

(Other Configuration Examples) Since the PIF band may be widened, the attenuation band of the PIF trap circuit 6 may be configured to include the PIF signal band excluding the SIF or the PIF signal band excluding the SIF. A configuration in which the Q of the PIF trap circuit 6 is set so as to cover the band may be adopted.

Further, a plurality of trap circuits including at least the PIF trap circuit 6 may be provided so that the attenuation band of the PIF trap circuit 6 encompasses the PIF signal band excluding the SIF. It is preferable to use an integrated trap element.

[0042]

As described above, according to the present invention,
SECAM in which the audio signal is amplitude-modulated similarly to the video signal
-When receiving an L-type television signal, it is possible to effectively reduce the occurrence of buzzing sound due to the influence of a video signal, especially when the transmission signal has a large PS ratio, or during mobile reception. Is effective when the PS ratio is increased due to the multipath.

[Brief description of the drawings]

FIG. 1 is a block diagram related to a receiving circuit of a television receiver to which the present invention is applied.

FIGS. 2A and 2B are circuit diagrams each showing a specific example of the video intermediate frequency trap circuit shown in FIG. 1 in a television receiver to which the present invention is applied, and a trap of the video intermediate frequency trap circuit; FIG. 4 is an explanatory diagram showing characteristics.

FIGS. 3A and 3B are circuit diagrams showing another specific example of the video intermediate frequency trap circuit shown in FIG. 1 in a television receiver to which the present invention is applied, and FIG. FIG. 4 is an explanatory diagram showing the trap characteristics of FIG.

FIG. 4 is a block diagram related to a receiving circuit of a conventional television receiver.

FIG. 5 is an explanatory diagram illustrating an example of a frequency characteristic of a tuner output.

FIGS. 6A and 6B are explanatory diagrams showing examples of characteristics of a video intermediate frequency SAW filter and an audio intermediate frequency SAW filter, respectively.

FIG. 7 is an explanatory diagram showing an example of a spectrum of a television signal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Antenna 2 Tuner 3 SAW filter for PIF (SAW for video intermediate frequency
4 SIF SAW filter (SAW for audio intermediate frequency)
5) Intermediate frequency amplification / detection circuit 6 PIF trap circuit (video intermediate frequency trap circuit) 61 SAW filter element constituting PIF trap circuit 62 Series resonance circuit constituting PIF trap circuit Lp Inductor constituting PIF trap circuit Cp PIF Capacitors that make up the trap circuit

Claims (8)

[Claims] 1. A tuner for outputting an intermediate frequency signal of a desired channel band, and a video intermediate frequency signal extracting SAW for extracting a video intermediate frequency signal from the intermediate frequency signal.
In a SECAM-L television receiver having a filter and an audio intermediate frequency signal extracting SAW filter for extracting an audio intermediate frequency signal from the intermediate frequency signal, a video intermediate signal is output from the audio intermediate frequency signal extracting SAW filter. A SECAM-L television receiver comprising a video intermediate frequency trap circuit for attenuating the frequency. 2. An image intermediate frequency trap circuit comprising:
2. The SECAM-L television receiver according to claim 1, wherein the television receiver comprises a W filter element. 3. An impedance element is interposed between the audio intermediate frequency signal extracting SAW filter and the video intermediate frequency trap circuit.
The described SECAM-L television receiver. 4. The SECAM-L television receiver according to claim 1, wherein said video intermediate frequency trap circuit is constituted by a series resonance circuit comprising an inductor and a capacitor. 5. The SECAM-L television receiver according to claim 1, wherein the attenuation band of the video intermediate frequency trap circuit includes a video intermediate frequency signal band excluding an audio intermediate frequency. Machine. 6. The Q of the video intermediate frequency trap circuit is set so that the attenuation band of the video intermediate frequency trap circuit includes a video intermediate frequency signal band excluding an audio intermediate frequency. SECAM-
L-type television receiver. 7. A plurality of trap circuits including at least the video intermediate frequency trap circuit so that an attenuation band of the video intermediate frequency trap circuit includes a video intermediate frequency signal band excluding an audio intermediate frequency. The SECAM-L television receiver according to claim 5. 8. The SECAM-L television receiver according to claim 7, wherein a trap element in which the plurality of trap circuits are integrated is used.