JP3599253B2 - PAL / SECAM signal discriminating circuit and television signal receiving device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a television signal receiving apparatus such as a television receiver and a video tape recorder, and more particularly, to a television signal receiving apparatus for discriminating between a PAL signal and a SECAM signal and a discrimination circuit therefor. It is.
[0002]
[Prior art]
There are a PAL system and a SECAM system as transmission systems of a color television signal. These are mainly adopted in Europe, and there are areas where both types of broadcast waves can be received. In such a region, the receiving device determines whether the signal is a signal according to the PAL system or a signal according to the SECAM system, and performs processing of the color signal according to the determination result.
[0003]
The PAL / SECAM signal is determined by utilizing the difference between the color burst signals inserted into the back porch during the horizontal blanking period in both systems. In the PAL system, the frequency of the color burst signal is fixed at 4.43 MHz and is constant. In the SECAM system, color burst signals of frequencies of 4.25 MHz and 4.41 MHz appear alternately for each line.
[0004]
FIG. 4 shows a configuration of a conventional discriminating circuit. Signals at points a, b, c, and d in the drawing are schematically shown in FIGS. 5 (a), (b), (c), and (d). Shown respectively. In FIG. 4, reference numeral 51 denotes an amplifier, 52 denotes a 4.5 MHz ceramic filter, 53 denotes an fH / 2 tuning circuit having an external capacitor C and a coil L, 54 denotes a detection circuit, and 55 denotes a comparator. The color burst signal extracted from the back porch is input to the amplifier 51. As described above, the frequency of the color burst signal differs between the PAL system and the SECAM system.
[0005]
The color burst signal shown in FIG. 5A is amplified by the amplifier 51 and provided to the ceramic filter 52. When filtered by the 4.5 MHz ceramic filter 52, the color burst signal is attenuated in the SECAM signal as compared with the 4.43 MHz PAL signal as shown in FIG. 5B. The 4.41 MHz signal is only slightly attenuated than the PAL signal, but the 4.25 MHz signal is significantly attenuated. The output of this signal processed by the fH / 2 tuning circuit 53 is as shown in (c), and the amplitude is small for the PAL signal and large for the SECAM signal. Therefore, the output voltage of the detection circuit 54 for rectifying and detecting these signals is low for the PAL signal and high for the SECAM signal as shown in (d). The comparator 55 is supplied with an intermediate reference voltage between the output voltages of the PAL signal and the SECAM signal of the detection circuit 54, and outputs an L level for the PAL signal and an H level for the SECAM signal. The PAL / SECAM signal is determined based on the output level of the comparator 55.
[0006]
[Problems to be solved by the invention]
However, the above-described discrimination circuit requires external elements such as the ceramic filter 52 and the capacitor C and the coil L of the fH / 2 circuit 3. For this reason, the mounting process becomes complicated in the manufacturing process. In addition, there is a problem that a difference in performance is likely to occur between the ceramic filter, the capacitor, and the coil due to a temperature change or a variation among elements, and the discrimination ability is not stable.
[0007]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a PAL / SECAM signal discriminating circuit having excellent temperature characteristics and a stable discriminating ability, and a television signal receiving apparatus using the same.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, in a discriminating circuit for discriminating between a PAL signal and a SECAM signal based on the frequency of a color burst signal, the color burst signal and the oscillation signal of an oscillator are compared in phase. A PLL for controlling an oscillator is provided based on the comparison output, and a PAL signal and a SECAM signal are discriminated based on the comparison output.
[0009]
Since the comparison output matches the oscillation signal of the oscillator with the color burst signal, there is a difference in the magnitude of the comparison output between the PAL system signal and the SECAM system signal having different frequencies. Therefore, it is possible to determine which of PAL / SECAM signals.
[0010]
Specifically, the discrimination circuit includes a burst extraction circuit that extracts a color burst signal from the television signal, and a signal having a frequency close to the frequency of the color burst signal, and a signal that oscillates according to an input control voltage. A voltage-controlled oscillator that changes frequency and phase, and a control that detects a phase difference between a color burst signal extracted by a burst extraction circuit and a signal oscillated by the voltage-controlled oscillator, and provides the voltage-controlled oscillator based on the detected phase difference. A phase comparator that generates and outputs a voltage, a sample and hold circuit that samples and holds a control voltage output from the phase comparator with a sampling pulse, and a smoothing circuit that smoothes a voltage output from the sample and hold circuit, PAL / SECAM discrimination by comparing the voltage smoothed by the smoothing circuit with a predetermined reference voltage A comparator for outputting a No. give a burst gate pulse to the burst extraction circuit, configured to include a timing circuit for providing a sampling pulse to the sample-and-hold circuit.
[0011]
In this configuration, a PLL is formed by the voltage controlled oscillator and the phase comparator, and the control voltage generated by the phase comparator changes depending on whether the color burst signal is of the PAL system or the SECAM system. Since the color burst signal of the PAL system has a single frequency, the sampled and held control voltage is substantially constant. In the SECAM system, the color burst signal has different frequencies alternately. It fluctuates for each signal. These voltages are smoothed by a smoothing circuit to have different values, and a PAL / SECAM signal can be identified by comparing with a reference voltage in a comparator. For example, when the reference voltage of the comparator is set to an intermediate value between the smoothed control voltages of the PAL system and the SECAM system, and the comparator outputs an H level or L level signal according to the comparison result, the PAL is determined by the output level. / SECAM signal is determined. The timing circuit generates a burst gate pulse and a sampling pulse based on a horizontal synchronization signal. The output timing of the sampling pulse is set according to the performance of the voltage controlled oscillator.
[0012]
The PAL / SECAM signal discriminating circuit having the above configuration is provided in a television signal receiving device such as a television receiver or a video tape recorder.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows the configuration of the PAL / SECAM signal discrimination circuit of the present invention. The PAL / SECAM signal discriminating circuit 1 includes a gate circuit 11, a limiter amplifier circuit 12, a voltage controlled oscillator 13, a phase comparator 14, a sample and hold circuit 15, a smoothing circuit 16, a comparator 17, and a timing generation circuit 5. The timing generation circuit 5 separates a horizontal / vertical synchronization signal from a video signal input from an IF demodulation circuit (not shown) and, based on the horizontal synchronization signal, a burst gate pulse supplied to the gate circuit 11 and a sample / hold circuit 15. To generate a sampling pulse to be given to.
[0014]
The gate circuit 11 extracts a color burst signal from the video signal input from the IF demodulation circuit based on the burst gate pulse. The frequency of the color burst signal is 4.43 MHz for a PAL video signal, and 4.25 MHz and 4.41 MHz for a SECAM video signal. The limiter amplifier circuit 12 amplifies the color burst signal extracted by the gate circuit 11 and provides the same to the phase comparator 14 with the same amplitude.
[0015]
The phase comparator 14 compares the phase of the color burst signal with the phase of the oscillation signal of the voltage controlled oscillator 13, and outputs a control voltage so that the frequency and phase of the oscillation signal of the voltage controlled oscillator 13 match the frequency and phase of the color burst signal. Then, it is given to the voltage controlled oscillator 13. A PLL is formed by the voltage controlled oscillator 13 and the phase comparator 14. The control voltage at the time of phase lock is correlated with the frequency of the color burst signal, and the higher the frequency, the higher the control voltage.
[0016]
The sample hold circuit 15 samples and holds the control voltage output from the phase comparator 14 when receiving the sampling pulse from the timing generation circuit 5. The timing generation circuit 5 sets the sampling pulse generation timing in advance in consideration of the performance of the PLL so as to generate the sampling pulse when the PLL has locked the phase. The smoothing circuit 16 smoothes the output voltage of the sample hold circuit 15 and supplies the smoothed output voltage to the comparator 17.
[0017]
The comparator 17 is supplied with a predetermined reference voltage, and outputs an H level signal when the voltage input from the smoothing circuit 16 is higher than the reference voltage, and outputs an L level signal when the voltage is lower than the reference voltage.
[0018]
The waveforms of the signals at points A to F in FIG. 1 are shown in FIGS. 2A to 2F for the PAL signal and the SECAM signal, respectively. The shaded portion in the signal of FIG. 2 is a color burst signal. The burst gate pulse shown in (B) is applied to the gate circuit 11, and a color burst signal is extracted from the video signal in (A) as shown in (C). The color burst signal is amplified by the limiter amplifier circuit 12 to enhance the discrimination ability.
[0019]
(D) shows the PLL control voltage output from the phase comparator 14. In the PAL signal, the control voltage has substantially the same waveform, and the output voltage of the sample and hold circuit 15 shown in (E) becomes substantially constant. The output voltage of the smoothing circuit 16 shown in (F) is also constant.
[0020]
On the other hand, in the SECAM signal, since the color burst signals of different frequencies appear alternately, the level also appears alternately in the PLL control voltage. The PLL control voltage for the 4.41 MHz color burst signal is slightly lower than the control voltage for the 4.43 MHz PAL color burst signal, and the control voltage for the 4.25 MHz signal drops significantly. Therefore, in the SECAM signal, the output of the sample-and-hold circuit 15 is a rectangular wave with two lines as one cycle, and the voltage smoothed by the smoothing circuit 17 is lower than that of the PAL signal.
[0021]
The reference voltage supplied to the comparator 17 is set to an intermediate value between the smoothed voltage in the PAL signal and the smoothed voltage in the SECAM signal. Accordingly, the output of the comparator 17 is at the H level when the PAL signal is being received, and is at the L level when the SECAM signal is being received, and the PAL / SECAM signal is determined.
[0022]
The PAL / SECAM signal discriminating circuit 1 having the above configuration does not require an external element such as a ceramic filter or a coil, unlike the conventional discriminating circuit shown in FIG. Further, since the PLL is hardly affected by a temperature change, excellent temperature characteristics are obtained, and the discrimination ability is stabilized.
[0023]
FIG. 3 shows a configuration of a television receiver provided with the PAL / SECAM signal discrimination circuit 1 described above. In the figure, reference numeral 2 denotes a tuner that extracts a signal of a desired reception channel from a television signal received by the antenna ANT and converts the signal into an intermediate frequency signal. Reference numeral 3 denotes an IF demodulation circuit that amplifies the intermediate frequency signal and separates the signal into a video signal and an audio signal. Reference numeral 4 denotes an audio processing circuit which processes an audio signal input from the IF demodulation circuit 3 and drives the speaker 22.
[0024]
Reference numeral 5 denotes the aforementioned timing generation circuit. Here, the configuration is independent of the PAL / SECAM signal discrimination circuit 1. The timing generation circuit 5 receives the video signal from the IF demodulation circuit 3 and separates horizontal and vertical synchronization signals from the video signal. Further, based on the horizontal synchronizing signal, a burst gate pulse and a sampling pulse to be applied to the discrimination circuit 1 and other timing signals to be applied to other circuits are generated.
[0025]
Reference numeral 6 denotes a PAL chroma processing circuit, which performs color demodulation of a video signal according to the PAL method. Reference numeral 7 denotes a SECAM chroma processing circuit which performs color demodulation of a video signal according to the SECAM method. Both of these chroma processing circuits 6 and 7 always operate regardless of the type of the received video signal, and output color signals. When the video signal is of the PAL type, the output of the PAL chroma processing circuit 6 is a correct color signal, and when the video signal is of the SECAM type, the output of the SECAM chroma processing circuit 7 is a correct color signal.
[0026]
Reference numeral 8 denotes a luminance signal processing circuit that extracts a luminance signal from a video signal. The operations of the chroma processing circuits 6 and 7 and the luminance signal processing circuit 8 are controlled by a timing signal provided from the timing generation circuit 5. Reference numeral 9 denotes a deflection circuit that generates a sawtooth wave based on the horizontal synchronization signal and the vertical synchronization signal supplied from the timing generation circuit 5 and outputs the sawtooth wave to the horizontal / vertical deflection coils of the CRT 21.
[0027]
Reference numeral 10 denotes a matrix circuit, which generates R, G, and B signals based on the luminance signal from the luminance signal processing circuit 8 and the color signals from the PAL chroma processing circuit 6 or the SECAM chroma processing circuit 7, and outputs the generated signals to the CRT 21. The color signal given to the matrix circuit 10 is switched between the output of the PAL chroma processing circuit 6 and the output of the SECAM chroma processing circuit 7 by the switch circuit 23.
[0028]
This switching is performed based on the output signal of the comparator 17 of the PAL / SECAM signal discriminating circuit 1. The switch circuit 23 supplies the output signal of the PAL chroma processing circuit 6 to the matrix circuit 10 when the signal supplied from the comparator 17 is at the H level, and performs the SECAM chroma processing when the signal input from the comparator 17 is at the L level. The output signal of the circuit 7 is provided to the matrix circuit 10. In this way, an appropriate color signal is selected according to the format of the received television signal, and a color image whose color has been correctly restored is always displayed on the CRT 21.
[0029]
Although the television receiver has been described here, the PAL / SECAM signal discrimination circuit 1 of the present invention can also be applied to a video tape recorder.
[0030]
【The invention's effect】
According to the determination circuit of the present invention, the PAL / SECAM signal is determined based on the control voltage of the PLL, so that the circuit configuration is simplified. Further, since it is not necessary to use a ceramic filter or a tuning circuit having a coil and a capacitor which are easily affected by a temperature change, the temperature characteristics are improved, the stability is improved, and a reliable PAL / The SECAM signal can be determined.
[0031]
Further, in the television signal receiving apparatus provided with this discriminating circuit, when a television signal of the PAL system or the SECAM system is received, it is possible to automatically determine which system signal is being received. is there.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of a PAL / SECAM signal discrimination circuit according to the present invention.
FIG. 2 is a diagram showing signals of main parts of a PAL / SECAM signal discrimination circuit according to the present invention.
FIG. 3 is a configuration diagram showing an embodiment of a television receiver provided with a PAL / SECAM signal discrimination circuit of the present invention.
FIG. 4 is a diagram showing a configuration of a conventional PAL / SECAM signal discriminating circuit.
FIG. 5 is a diagram showing signals in a conventional PAL / SECAM signal discriminating circuit.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 PAL / SECAM signal discriminating circuit 2 Tuner 3 IF demodulation circuit 4 Audio processing circuit 5 Timing generation circuit 6 PAL chroma processing circuit 7 SECAM chroma processing circuit 8 Luminance signal processing circuit 9 Deflection circuit 10 Matrix circuit 11 Gate circuit 12 Limiter amplification circuit 13 Voltage controlled oscillator 14 Phase comparator 15 Sample hold circuit 16 Smoothing circuit 17 Comparator 21 CRT
22 speaker 23 switch circuit

Claims (2)

A discriminating circuit for discriminating between a PAL signal and a SECAM signal based on a frequency of a color burst signal of a television signal;
A burst extraction circuit for extracting a color burst signal from a television signal,
A voltage-controlled oscillator that oscillates a signal having a frequency close to the frequency of the color burst signal, and changes the frequency and phase of the oscillating signal according to an input control voltage,
A phase comparison that detects a phase difference between a color burst signal extracted by the burst extraction circuit and a signal oscillated by the voltage-controlled oscillator, and generates and outputs a control voltage to be applied to the voltage-controlled oscillator based on the detected phase difference. Vessels,
A sample and hold circuit that samples the control voltage output from the phase comparator with a sampling pulse, and holds the sampled control voltage;
A smoothing circuit for smoothing a voltage output from the sample and hold circuit;
A comparator that compares the voltage smoothed by the smoothing circuit with a predetermined reference voltage and outputs a PAL / SECAM determination signal;
A timing circuit that provides a burst gate pulse to the burst extraction circuit and provides the sampling pulse to the sample and hold circuit;
A discriminating circuit comprising: A television signal receiving apparatus comprising the PAL / SECAM signal discriminating circuit according to claim 1 .

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