JPS6338609Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to a color television receiver, which is capable of simultaneously receiving television signals of different systems.

(b) Prior Art There are various television systems currently in use, and neighboring countries in Europe and the Middle East in particular may use different systems. In such adjacent areas, a color television receiver is desired that can receive not only the television broadcasts of the home country but also the television broadcasts of neighboring countries with different systems. For example, there are so-called dual-type receivers for Spain and Switzerland (both PAL-B systems) that can receive French broadcasts (SECAM-L system).

By the way, in the above PAL-B system, the video carrier frequency _P , the color subcarrier frequency _C ,
The frequency relationship of the voice carrier frequency _S is V _L (VHF
low band), V _H (high band of VHF), U
(UHF band) is as shown in Figure 1. Therefore, general PAL-B
In the receiver for this system, by setting the tuner's local oscillation frequency ₀ in each of the above bands to the frequency position shown by the broken line in Figure 1, the IF (IF) where _P , _C , and _S are respectively the intermediate frequencies shown is set. intermediate frequency) signal.

On the other hand, in the French SECAM system, _P , _C ,
The frequency relationship of _S is different between the V _L band and the V _H and U bands, and in the V _H and U bands, as in the previous PAL-B system, _C and _S have higher frequencies than _P , as shown in Figure 2b. However, in the _VL band, as shown in Figure 2a, _C and _S are located on the lower frequency side. Therefore, in a general receiver for the French SECAM system, the local oscillation frequency ₀ of the tuner is selected at each position shown in Figure 2 a and b, and V _L
By performing upper heterodyne detection for the band and lower heterodyne detection for the _VH and U bands, an IF signal with _P , _C , and _S having the frequencies shown in the figure is obtained. There is.

Therefore, PAL-B system and French SECAM
In order to receive both systems, a dedicated VIF (video intermediate frequency) filter and VIF signal processing circuit should be installed in parallel for each of the IF signals shown in Figures 1 and 2. Such a method requires additional switching circuits for the two processing circuits, resulting in high costs and is not a good idea.

Therefore, as an alternative method,
For SECAM television signals, PAL
A method of performing VIF amplification, detection, etc. with a single VIF signal processing circuit designed for the -B method and having the band characteristics as shown in Figure 3 is considered.In this case, the local oscillation frequency ₀ of the tuner is It is sufficient to set it at each position shown in Figures a and b. i.e. France
When receiving SECAM V _H and U bands (Fig. 2b), tuner ₀ is set to the high side as shown in the figure to perform upper heterodyne detection, and when receiving V _L band (Fig. 2 a), it is set _{to 0.} When set to the lower side as shown in the figure to perform lower heterodyne detection, a VIF signal with 38.9MHz as the IF video carrier frequency and 34.47MHz as the IF color subcarrier frequency is derived from the tuner at the time of each of the above receptions. , above VIF
It can be processed by a signal processing circuit (Fig. 3).

However, with this method, France
Since the video carrier frequency of the lowest channel of SECAM's V _L band is 47.75MHz, the tuner's local oscillation frequency ₀ for this channel is ₀ =
47.75-38.9=8.85MHz, which is considerably low. This means that the considerable change in ₀ in the V _L band becomes large. Therefore, it is difficult to always obtain an oscillation output of a constant magnitude for each channel within this band, and there is a problem in that a sufficient oscillation output cannot be obtained particularly at low frequencies such as those mentioned above. For this reason, the aforementioned dual-type receivers for Spain and the like were designed to be able to receive only the French U-band.

(c) Purpose of the invention This invention was created in view of the above points,
It is an object of the present invention to realize a color television receiver with a simple configuration and at low cost, which can receive television signals of mutually different systems such as the above-mentioned PAL-B system and the French SECAM system.

(d) Structure of the invention The color television receiver of the invention has a relationship between the television signal of the first method in which there is always a constant frequency difference between _P and _C in each band and the frequency difference between _P and _C. In a color television receiver that receives a television signal of a second system which is the same as the first system in one band and reversed in the other band, when the first system is received and the second system is When receiving one band, the tuner performs intermediate frequency conversion so that _P becomes frequency ₁ and _C becomes frequency ₂ , and when receiving the other band in the second method, the tuner performs intermediate frequency conversion so that _P becomes ₂ above and _C becomes ₁ above. Each signal after intermediate frequency conversion is input to a single video intermediate frequency signal processing circuit through a video intermediate frequency filter set so that the amount of attenuation for frequencies ₁ and ₂ is approximately the same. This is a configuration designed to do this.

(E) Embodiment FIG. 5 shows an embodiment of a color television receiver according to the present invention, and 1 is the same as described above.
A composite tuner capable of receiving television signals in each band of the PAL-B system and the French SECAM system, 2 is a VIF filter, 3 is a VIF signal processing IC, and 4 is for PAL for 5.5MHz intercarrier signals. SIF amplification and FM detection circuit, 5 is
A SIF filter, 6 is an SIF amplification/AM detection circuit for SECAM operating in the IF band, and 7 is an audio amplification circuit. Each of these circuits has the following configuration.

First, tuner 1 will be explained. That is, for PAL-B television signals, this tuner 1 uses upper heterodyne detection to detect the IF video carrier frequency at 38.9MHz and the IF color subcarrier frequency, just as in the case shown in FIG. 34.47MHz, IF audio carrier frequency
Local oscillation frequency ₀ is set to 33.4MHz. Also, as shown in Figure 6b, for the _VH and U bands of the French SECAM system, upper heterodyne detection is used in the same way as when receiving the PAL-B system.
₀ is set so that the IF video carrier frequency is 38.9MHz and the IF color subcarrier frequency is 34.47MHz, and the IF video carrier frequency is further set by upper heterodyne detection for the _VL band.
The IF color subcarrier frequency is 34.47MHz.
₀ is set to 38.9MHz.

Next, the band characteristic of the VIF filter 2 is set as shown in Fig. 3 mentioned above, and in particular, the attenuation amount at 38.9 MHz and the attenuation amount at 34.47 MHz are equal (6 dB from the peak value). It is characterized in that it is set to have a band characteristic that is substantially symmetrical with respect to the peak value within the range of 34.47 MHz to 38.9 MHz.

On the other hand, the SIF filter 5 is for separating the AM modulation type SIF signal from the output signal of the tuner 1 when receiving the French SECAM. When the tuner 1 is operated as described above for each SECAM band, the IF audio carrier frequency is 40.97MHz in the _VL band (see Figure 6a), and 32.4MHz in the _VH and U bands (see Figure 6a). (see Figure b). Therefore, this SIF filter 5
When receiving each band, the bandpass characteristics can be switched to have bandpass characteristics centered at each of the above frequencies.

The VIF signal processing IC 3 includes a VIF amplifier circuit 8, a synchronous detection circuit 9 for video detection, a video carrier signal extraction circuit 10, a quadrature phase detection circuit 11 for AFT, a video amplification/polarity switching circuit 12,
This IC is a general-purpose IC with wide-band characteristics and includes an AGC voltage generation circuit 13, etc., and the configuration of this IC itself has no noteworthy features.

According to such a receiver, as can be seen from the above explanation, the VIF signal derived from the VIF filter 2 when receiving each band of PAL-B system and French SECAM has the same bandwidth and corresponding frequency band. The signals have similar attenuation characteristics within the bandwidth. Therefore, for each VIF signal, a single VIF signal processing IC 3 performs VIF amplification, video detection, AGC voltage generation,
It is also possible to perform various operations such as creating an AFT voltage.

By the way, the video carrier signal extraction circuit 1 supplied to the synchronous detection circuit 9 and the phase detection circuit 11
It is necessary to switch the tuning frequency of 0 between when receiving the French SECAM _VL band and when receiving other signals. However, it is not necessary to change the detection characteristic (so-called S-shaped characteristic) of the phase detection circuit 11 itself.
This is because the tuner 1 performs upper heterodyne detection for both bands of the PAL-B system and the French SECAM system. Of course, since the synchronous detection circuit 9 performs AM detection,
There is no need to change the detection operation itself.

The video amplification/polarity switching circuit 12 in the VIF signal processing IC 3 operates as follows. That is, since the video signal is a negative modulation type in the PAL system and a positive modulation type in the SECAM system, the polarity of the video signal output from the synchronous detection circuit 9 is inverted only when one of them is received. Video signals of the same polarity are derived during both types of reception.

Also, the IF voice carrier frequency is
When receiving SECAM V _L band, it is 40.97MHz (Figure 6a), and when receiving _VH and U band, it is 32.4MHz (6th MHz).
Figure b), and both of these are located well outside the band characteristics of the VIF filter 2. Therefore, the trap circuit for removing the IF audio carrier mentioned above is connected to the VIF.
There is no need to make any special arrangements in the circuit system or to switch them.

(F) Effects of the invention According to the invention, the relationship between the frequency difference between _P and _C is constant throughout the entire band, and the difference between the frequency difference between _P and _C depending on the broadcast band. It is possible to conduct VIF amplification and video detection by guiding the second type of television signal, in which the relationship is reversed, to a single VIF signal processing circuit, and furthermore, the tuner is always the same for all bands of both types. Since directional heterodyne detection is performed, the relative change in the local oscillation frequency is small, so a stable oscillation output can always be obtained and IF conversion can be performed reliably. Therefore, the configuration of the receiver is simpler than when a dedicated VIF filter and VIF processing circuit are provided for each of the above systems and each signal processing circuit is operated by switching. A dual-type color television receiver for reception can be realized at low cost.

[Brief explanation of drawings]

Figure 1 is a diagram showing the frequency relationship of _P , _C , and _S in the PAL-B system, and Figure 2 a and b are French SECAM
Figure 3 shows the band characteristics of the VIF _filter for the _PAL - _B system. Figures 4a and b show the French SECAM system television signal. Figure 5 is a block diagram showing an embodiment of the color television receiver of the present invention, and Figures 6a and b are diagrams illustrating the prior art for converting into an IF signal compatible with the VIF filter shown in the figure. FIG. 3 is a diagram for explaining the IF conversion operation of the French SECAM system in an example. 1: Tuner, 2: VIF filter, 3 : VIF signal processing IC, 4: SIF amplification and detection circuit for PAL,
5: SIF filter, 6: SIF amplification for SECAM
Detection circuit.

Claims (1)

[Claims for Utility Model Registration] (1) Relationship between the first system television signal having a certain frequency difference between the video carrier frequency _P and the color subcarrier frequency _C in each band, and the frequency difference between _P and _C. is a color television receiver that receives a television signal of a second system in which one band is the same as the first system and the other band is reversed; When receiving one band, the tuner performs intermediate frequency conversion so that _P becomes frequency ₁ and _C becomes frequency ₂ , and when receiving the other band in the second method, the tuner performs intermediate frequency conversion so that _P becomes ₂ above and _C becomes ₁ above. Each signal after intermediate frequency conversion is input to a single video intermediate frequency signal processing circuit through a video intermediate frequency filter set so that the amount of attenuation for frequencies ₁ and ₂ is approximately the same. A color television receiver characterized by: (2) The color television receiver according to claim 1, wherein the intermediate frequency conversion in the tuner is performed by upper heterodyne detection during each reception.