JP3797154B2 - PAL and SECAM compatible TV receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a PAL and SECAM television receiver that receives a PAL and SECAM television signal and outputs a PAL composite video signal from a receiving circuit in any case.
[0002]
[Prior art]
FIG. 4 is a block diagram of a receiving circuit of a conventional PAL and SECAM-compatible television receiver that receives a PAL and SECAM television signal and outputs it as a PAL composite video signal. In FIG. 4, 1 is an antenna, 2 is a tuner, 3 is an intermediate frequency circuit, 4 is a PAL encoder circuit, 5 is a multi-corresponding chroma demodulation circuit, 6 is a system control microcomputer, and 7 is a SECAM / PAL discrimination circuit.
[0003]
In FIG. 4, the RF television signal received by the antenna 1 is first selected by the tuner 2, then amplified / detected by the intermediate frequency circuit 3, and output as a composite video signal at point a.
[0004]
This composite video signal is subjected to SECAM demodulation in the NTSC / PAL / SECAM multi-compatible chroma demodulation circuit 5 and outputs an RGB demodulated output signal. This RGB signal is converted into a PAL color composite video signal by the PAL encoder circuit 4 and output to a video demodulation circuit (not shown) via an output terminal d.
[0005]
Here, the multi-compatible chroma demodulation circuit 5 has a color system automatic discrimination function for the input composite video signal, and outputs a discrimination result as shown in FIG. 5A to the discrimination output terminal b. It has become. That is, when it is determined that the received signal is the NTSC color system, a voltage of “L” (0) is output, and when it is determined that the received signal is the SECAM color system, a voltage of “M” (Vs) is output. When the method is determined, a voltage of “H” (Vp) is output. Further, the automatic discrimination output signal from the chroma demodulation circuit 5 is supplied to the SECAM / PAL discrimination circuit 7, and the SECAM / PAL discrimination circuit 7 discriminates SECAM / PAL and outputs it to the point c. This is supplied to the control microcomputer 6. The system control microcomputer 6 receives the SECAM / PAL discrimination signal and controls the PAL encoder circuit 4. In the case of SECAM, the RGB input signal is encoded into the PAL signal as described above. The composite video signal, which is the output of the circuit 3, is passed through and output as it is to the point d.
[0006]
Although not described in detail, the system control microcomputer 6 performs various controls using the SECAM / PAL determination result and also performs tuning control for the tuner 2 in addition to the control of the PAL encoder circuit 4.
[0007]
FIG. 6A shows a specific circuit example of the SECAM / PAL discrimination circuit 7. An example shown here is a window comparator, which outputs only when the input is in a certain voltage range. That is, as shown in FIG. 6A, open output type comparators Q1 and Q2 are used, a high reference voltage Vref2 is applied to the + input terminal of the comparator Q1, and a low reference voltage Vref1 is applied to the − input terminal of the comparator Q2. At the same time, an input signal is collectively applied to the negative input terminal of Q1 and the positive input terminal of Q2, and the outputs of the comparators Q1 and Q2 are OR-connected to take out the output. More specifically, as shown in FIG. 6A, the two reference voltages can be generated by dividing the power supply voltage Vcc by a bleeder including resistors R1, R2, and R3, as shown in FIG. In order to perform SECAM / PAL discrimination from the automatic discrimination output from the chroma demodulation circuit 5, the higher reference voltage Vref2 is
Vref2 = (Vp + Vs) / 2
On the other hand, the lower reference voltage Vref1 is
Vref1 = Vs / 2
And the output terminals of both the comparators Q1 and Q2 are pulled up to the power source by the common resistor R4, so that a window comparator is obtained.
[0008]
Therefore, as shown in FIG. 6B, the SECAM / PAL discrimination characteristic by the window comparator is “H” level output when the input voltage is between Vref1 and Vref2, and “L” level output otherwise. Become.
[0009]
Here, the input voltage is actually an automatic determination output from the chroma demodulation circuit 5, and is “L” (0) at the time of NTSC determination, “M” (Vs) at the time of SECAM determination, and “H” at the time of PAL determination. Since there are only three states of “(Vp)”, the window comparator outputs “H” level during SECAM, and outputs “L” level otherwise. Therefore, the SECAM / PAL discrimination function can be realized.
[0010]
[Problems to be solved by the invention]
In the PAL and SECAM compatible television receiver having the above-described configuration, there is no problem if the received television signal is a medium electric field or a strong electric field and the signal S / N is stable. In addition, there is a problem when the reception condition changes greatly and a weak electric field may occur. That is, when the S / N of the image detection output deteriorates due to such a weak electric field (especially, the color disappearance electric field or less), as shown in FIG. The discriminant function malfunctions and the output becomes indefinite. As shown in FIG. 5C, the discriminant output periodically repeats “M” and “L”. As a result, the output of the SECAM / PAL discriminating circuit 7 also repeats “H” and “L”, and the system control microcomputer 6 that receives this also frequently switches the PAL encoder 4 between the SECAM mode and the PAL mode. Therefore, when this output is displayed on a television monitor, there is a problem that a flicker-like screen becomes difficult to see. This is because it is difficult to output a composite video signal that is exactly the same when the video detection output is output through (PAL mode) and when PAL encoding is performed once after SECAM demodulation (SECAM mode).
[0011]
In this way, in a television receiver that receives a PAL and SECAM television signal and outputs it as a PAL composite video signal, when a weak signal that is less than the color disappearance electric field is received, the chroma system automatically determines the color system of the chroma demodulation circuit. As a result of the malfunction of the function, there is a problem that a stable composite video signal of the PAL system cannot be output as a composite video signal of the television receiver, and the display image on the television monitor screen becomes unstable.
[0012]
Accordingly, an object of the present invention is to provide a PAL and SECAM-compatible television receiver capable of outputting a stable composite video signal from a receiving circuit even when a weak SECAM signal having a color fading electric field or less is received. .
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention receives a PAL television signal and outputs it as a composite video signal to a video demodulation circuit. After receiving / demodulating a SECAM television signal, the PAL composite video signal is received. In a PAL and SECAM-compatible television receiver having a receiving circuit that can convert the signal into a video demodulating circuit and output it to the video demodulation circuit, the receiving circuit receives the SECAM television signal when the reception level of the SECAM television signal is high. After being demodulated, it is converted into a PAL composite video signal and output. When the reception level of the SECAM television signal is low, the SECAM television signal is processed and output as a PAL television signal. And
[0014]
In the present invention, the receiving circuit processes the SECAM signal as a PAL signal and outputs it when, for example, the reception level of the SECAM signal decreases and signal processing as the SECAM system becomes difficult.
[0015]
In the present invention, for example, when the reception level of the SECAM signal is lowered and the color disappears, the reception circuit processes and outputs the SECAM signal as a PAL monochrome broadcast signal.
[0016]
In the television receiver to which the present invention is applied, when a PAL system signal is received, the video detection output is output as it is as a composite video signal. On the other hand, when a SECAM system television signal is received, the SECAM demodulation is performed once. By encoding and outputting a PAL composite video signal, both types of television signals can be received on a PAL compatible television monitor. Further, in the present invention, when the reception level of a SECAM television signal is lowered and signal processing as the SECAM method becomes difficult, or when the weak electric field is less than the color disappearance electric field, the color of the received signal is increased. Regardless of the system, all signals are processed as PAL television signals. Therefore, even when the reception level of the SECAM television signal is lowered, it is possible to always output a stable PAL composite video signal, through which the video detection output is passed as a composite video signal, and PAL encoding after SECAM demodulation. A state in which signals are frequently switched and output does not occur. Therefore, stable video display can be realized even when receiving a weak electric field. In particular, in mobile reception such as in-vehicle television receivers, weak electric field reception is inevitable, and the quality of the received video is originally degraded due to the weak electric field, and the screen becomes more and more unstable when the screen display becomes unstable. Although it becomes difficult to see, such a problem can also be avoided according to the present invention.
[0017]
In the present invention, the receiving circuit includes a multi-compatible video demodulating circuit, an integrating circuit for integrating the color system discrimination output output from the video demodulating circuit, and an integrated output from the integrating circuit compared with a reference voltage. And a discriminating means for discriminating the SECAM / PAL of the received signal.
[0018]
In the present invention, the SECAM / PAL discriminating means includes a window comparator that discriminates a broadcast system of a received signal by comparing an integrated output from the integrating circuit with a reference voltage.
[0019]
In the present invention, it is preferable that the reference voltage of the window comparator is set to a value different from an intermediate value of the color system discrimination output output from the video demodulation circuit.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram regarding a receiving circuit of a PAL system and SECAM system compatible television receiver to which the present invention is applied. 2A and 2B are explanatory diagrams showing the basic principle of the color system discrimination operation in the receiving circuit shown in FIG. 1, and the color system discrimination output from the chroma demodulation circuit in the receiving circuit shown in FIG. It is explanatory drawing which shows the effect which performed the integration. FIG. 3 is an explanatory diagram showing the result of identifying and specifying the color system by the receiving circuit shown in FIG. Note that the basic configuration of a television receiver to which the present invention is applied is the same as that of the conventional example, and therefore equivalent parts are denoted by the same reference numerals.
[0021]
In the receiving circuit of the PAL system and SECAM system television receiver shown in FIG. 1, 1 is an antenna, 2 is a tuner, 3 is an intermediate frequency circuit, 4 is a PAL encoder circuit, 5 is a multi-corresponding chroma demodulation circuit, and 6 is A system control microcomputer, 7 is a SECAM / PAL discrimination circuit, and 8 is an integration circuit.
[0022]
In the television receiver to which the present invention is applied, the RF television signal received by the antenna 1 is selected by the tuner 2 and then amplified / detected by the intermediate frequency circuit 3 as in the case of referring to FIG. A point is output as a composite video signal. The composite video signal is subjected to SECAM demodulation in the NTSC / PAL / SECAM multi-compatible chroma demodulation circuit 5 and outputs an RGB demodulated output signal. This RGB signal is converted into a PAL color composite video signal by the PAL encoder circuit 4 and output to a video demodulation circuit (not shown) via an output terminal d.
[0023]
The chroma demodulation circuit 5 has a color system automatic discrimination function for the input composite video signal, and outputs a discrimination output as shown in FIG. 2A to the discrimination output terminal b. That is, when it is determined that the received signal is the NTSC color system, a voltage of “L” (0) is output, and when it is determined that the received signal is the SECAM color system, a voltage of “M” (Vs) is output. When the method is determined, a voltage of “H” (Vp) is output.
[0024]
The SECAM / PAL discriminating circuit 7 discriminates SECAM / PAL based on the automatic discrimination output signal from the chroma demodulation circuit 5 and outputs the discrimination result to the point c to be supplied to the system control microcomputer 6. ing. The system control microcomputer 6 receives the SECAM / PAL discrimination signal and controls the PAL encoder circuit 4. In the case of SECAM, the RGB input signal is encoded into the PAL signal as described above, while in the case of PAL. Is designed to pass through the composite video signal output from the intermediate frequency circuit 3 and output it to the point d. Therefore, a PAL-compatible TV monitor can receive both PAL and SECAM TV signals.
[0025]
Here, also in this embodiment, the window comparator shown in FIG. 6A is used as the SECAM / PAL discriminating circuit 7, and outputs only when the input is in a certain voltage range. That is, as shown in FIG. 6A, open output type comparators Q1 and Q2 are used, a high reference voltage is applied to the + input terminal of the comparator Q1, and a low reference voltage is applied to the-input terminal of the comparator Q2. At the same time, input signals are collectively applied to the negative input terminal of the comparator Q1 and the positive input terminal of the comparator Q2, and the outputs of the comparators Q1 and Q2 are ORed to extract the output. Here, the two reference voltages can be generated by dividing the power supply voltage Vcc by a bleeder including resistors R1, R2, and R3 as shown in FIG. 6A. In this embodiment, the higher reference voltage Vref2 is generated. Like the conventional example,
Vref2 = (Vp + Vs) / 2
The lower reference voltage Vref1 ′ is set as described later,
Vref1′≈3Vs / 4
And different values from the conventional ones.
[0026]
In the television receiver configured as described above, the present embodiment is characterized in that an integrating circuit 8 is first provided between the color system discrimination output terminal b of the chroma demodulation circuit 5 and the SECAM / PAL discrimination circuit 7. . In accordance with this, although it does not appear in the block diagram, as shown in FIGS. 2A and 2B, it is also characterized in that the discrimination condition (reference voltage) of the SECAM / PAL discrimination circuit 7 is changed. Have.
[0027]
Hereinafter, the features of the present invention will be described in detail with reference to FIGS. 1, 2, and 3. FIG. Also in this embodiment, the color system discrimination output voltage output from the chroma demodulation circuit 5 at the time of color system misjudgment below the color disappearance electric field, which is a problem in the conventional example, is 4H ( The output of “M” and “L” is repeated every horizontal synchronization cycle).
[0028]
However, in this embodiment, the integration circuit 8 is provided between the color system discrimination output terminal b of the chroma demodulation circuit 5 and the SECAM / PAL discrimination circuit 7, and the output of the chroma demodulation circuit 5 is sufficiently large compared to 4H. Since integration is performed by the constant integration circuit 8, a voltage close to a direct current with a slight ripple remaining is obtained as an integrated output waveform at point e in FIG. 1 as indicated by a solid line L1 in FIG. The output is input to the SECAM / PAL discrimination circuit 7.
[0029]
Here, as the integration time constant in the integration circuit 8 is increased, the residual ripple is reduced. However, if the integration time constant is large, the SECAM / Since the response of the discrimination output of the PAL discrimination circuit 7 is deteriorated, it is not preferable to make it too large.
[0030]
Further, as shown in FIG. 2B, when the output of “M” and “L” is repeated every 4H (horizontal synchronization period), the integrated output voltage Va is naturally Va≈Vs. / 2
Thus, in the detection window of the window comparator in the conventional SECAM / PAL discriminating circuit 7, the lower reference voltage Vref1 and the integrated output voltage Va are substantially matched. As a result, the window comparator detects residual ripple of the integrated output, and outputs a signal having a waveform that repeats “H” and “L” in the 4H cycle as the SECAM / PAL discrimination output as in the conventional case. become.
[0031]
Therefore, in this embodiment, the lower reference voltage Vref1 ′ of the window comparator is a value intermediate between the SECAM detection output voltage Vs and the integrated output voltage Va, that is, Vref1′≈3Vs / 4.
It is set to.
[0032]
Accordingly, the SECAM / PAL discrimination characteristic by the window comparator is “H” level output when the input voltage is between Vref1 ′ and Vref2, and “L” level output otherwise. As a result, as shown in FIG. 3, when the color disappearance point or less, it always becomes “L” level, and based on this discrimination result, the system control microcomputer 6 can detect the PAL even if it is a SECAM television signal. It is processed in the same way as a standard television signal. That is, in the case of the color disappearance point or less, the system control microcomputer 6 passes through the composite video signal that is the output of the intermediate frequency circuit 3 even if it is a SECAM television signal, and d Output to a point.
[0033]
Thus, in the television receiver to which the present invention is applied, the reference voltage Vref1 ′ is set to a value intermediate between the SECAM detection output voltage Vs and the integrated output voltage Va. Even if a signal with a ripple as indicated by a solid line L1 is output in 2 (b), the window comparator does not detect this in the SECAM / PAL discriminating circuit 7, and the output of the SECAM / PAL discriminating circuit 7 at the point c. A stable “L” (PAL mode) level is output. Therefore, since the microcomputer 6 controls the through operation for the PAL encoder 4, the composite video signal of the television receiver does not process any composite video signal that is the detection output of the intermediate frequency circuit 3. The output is continued as it is, and a stable image display can be realized while a weak electric field image.
[0034]
Here, when the received weak electric field television signal is a signal of the SECAM system, the video detection output is output through though the SECAM signal is received. The next SECAM and PAL systems are only differences in color signal processing systems, so there is no significant difference between the two systems when the color killer is in operation and color disappearance occurs. Therefore, there is no inconvenience even if it is processed as a PAL signal. Rather, it becomes more advantageous in terms of S / N than performing PAL encoding again on the SECAM signal that has undergone some signal processing in the chroma demodulation circuit 5 to become an RGB signal.
[0035]
【The invention's effect】
As described above, according to the present invention, in a television receiver circuit that receives a PAL and SECAM television signal and outputs it as a PAL composite video signal, even when a weak signal equal to or less than the color disappearance electric field is received, It prevents the SECAM / PAL processing from being disturbed by the malfunction of the color system automatic discrimination function, and outputs a stable composite video signal of the PAL system. For this reason, stable video display can be realized on the television monitor screen. In addition, when a SECAM television signal is received, a weak electric field in which a malfunction occurs is processed as a PAL monochrome signal without performing a SECAM demodulation process. N can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram of a receiving circuit of a PAL and SECAM compatible television receiver to which the present invention is applied.
2A and 2B are explanatory diagrams showing the basic principle of the color system discrimination operation in the receiving circuit shown in FIG. 1, and the color system discrimination from the chroma demodulation circuit in the receiving circuit shown in FIG. It is explanatory drawing which shows the effect which performed the integration to the output.
FIG. 3 is an explanatory diagram showing a result of identifying and specifying a color system by the receiving circuit shown in FIG. 1;
FIG. 4 is a block diagram of a receiving circuit of a conventional PAL and SECAM television receiver.
FIGS. 5A, 5B, and 5C are respectively an explanatory diagram showing the principle of a color system discrimination operation in the conventional method shown in FIG. 4, an explanatory diagram showing discrimination results, and problems thereof; It is explanatory drawing.
FIGS. 6A and 6B are equivalent circuit diagrams of a window comparator used as a SECAM / PAL discriminating circuit, and an explanation showing a result of discriminating a color system by a conventional method using the comparator. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Antenna 2 Tuner 3 Intermediate frequency circuit 4 PAL encoder circuit 5 Chroma demodulation circuit 6 System control microcomputer 7 SECAM / PAL discrimination circuit 8 Integration circuit

Claims (6)

A PAL television signal is received and output as a composite video signal to a video demodulation circuit. A SECAM television signal is received and demodulated, then converted to a PAL composite video signal and output to the video demodulation circuit. In a PAL and SECAM compatible television receiver having a simple receiving circuit,
When the reception level of the SECAM television signal is high, the receiving circuit demodulates the SECAM television signal, converts it to a PAL composite video signal, and outputs it, while receiving the SECAM television signal. When the signal is low, the SECAM television signal is processed and output as a PAL television signal. The receiving circuit processes and outputs a SECAM television signal as a PAL television signal when the reception level of the SECAM television signal decreases and signal processing as the SECAM method becomes difficult. 2. A PAL and SECAM receiver according to claim 1 characterized in that The receiving circuit processes and outputs a SECAM television signal as a PAL monochrome broadcast signal when the reception level of the SECAM television signal is lowered and the color disappears. 1. A PAL and SECAM-compatible television receiver according to 1. The reception circuit includes a multi-compliant video demodulation circuit, an integration circuit that integrates the broadcast system discrimination output output from the video demodulation circuit, and an SECAM of a received signal by comparing the integration output from the integration circuit with a reference voltage. 4. A PAL and SECAM-compatible television receiver according to claim 1, further comprising: discrimination means for performing / PAL discrimination. 4. The PAL and SECAM according to claim 3, wherein said SECAM / PAL discriminating means comprises a window comparator for discriminating a broadcasting system of a received signal by comparing an integrated output from said integrating circuit with a reference voltage. Compatible TV receiver. 6. The PAL and SECAM-compatible television receiver according to claim 5, wherein the reference voltage of the window comparator is set to a value different from an intermediate value of the broadcast system discrimination output output from the video demodulation circuit. .

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