JPS5930388A - Multi-purpose color television receiver - Google Patents

Abstract

PURPOSE:To speed up the detection and to keep stability after switching, by decreasing the capacitance of a capacitor at an output side of a signal detecting circuit of a color killer circuit until a chrominance subcarrier frequency is detected and a switching circuit is locked and increasing the capacitance after switching. CONSTITUTION:Capacitors 53, 54 are provided at a path on the way applying an output voltage of a color killer circuit 44 is applied to a color detecting circuit 35. Further, an output C of the circuit 35 is detected at a switching circuit 55 and only when the output C is at a high level detecting color, a switch 8 is closed. In this case, even if the electric field of a receiving signal is weak, when the switching of color demodulating state is finished, the output C is detected at a circuit 55 and the switch S8 is closed. Thus, the time constant as a filter is large and even if an output of the circuit 44 includes ripple, no detected output of the circuit 35 is changed and stable state is attained without malfunction.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a multi-system color television that receives color television signals of two systems in which the subcarrier frequencies of carrier color signals are different, such as the NTSC system and the M-NTSC system. Regarding John's receiver.

1. Structure of a conventional example and its problems FIG. 1 shows a block diagram of a conventional multi-system color television receiver. Here, the generally well-known audio carrier frequency is 6.5 and the color subcarrier frequency is 4.43.
141B with a vertical synchronizing signal frequency of 5017 and a vertical synchronizing signal frequency of 50) with an audio carrier frequency of 6.6 (zO3ECAM system and an audio carrier of 6.6
There are 3 pages with a color subcarrier frequency of 4.4 in total, a modified NTSC (hereinafter abbreviated as M-NTSC) system with a vertical synchronization signal frequency of 601-1z, and a color subcarrier frequency of 3.68 with a total of 4.5 audio carriers. (2) A case is shown in which 4 systems are received including the NTSC system with a vertical synchronization signal frequency of 60) and 12 at h.

A color television signal input to the tuner 1 passes through a filter 2, and a video signal and an audio carrier are detected by a video detection circuit 4 and output. From this output signal, only the audio carrier is input to the audio carrier frequency detection circuit 13, and the audio frequency is detected. If the audio carrier is for 6.6, switch 32.83 to 5.611Il
Switch to the l side. The audio carrier passes through a 6.6 bandpass filter 6, is subjected to FM detection by an audio detection circuit 7, is amplified by a low frequency amplification circuit 9, and is supplied to a speaker 10. If the audio carrier frequency is 4.6, switch 32
゜S3 is switched to the 4.6 side, and the 4.
．． The audio signal is demodulated through a path including a six-stone bandpass filter 6 and an audio detection circuit 8, and is supplied to a speaker 10. Also, when the detected voice carrier is 6.6 rhinoceros,
That is, when using the PAL system, SECAM system, or M-NTSC system, the switch S3 is switched to the 6.5 h side, and the video signal passes through the 6.6-th audio trap 11. This video signal is amplified by a video amplification circuit 14, matrixed, and supplied to a color cathode ray tube 16. In addition, the carrier color signal at this time is the color demodulation circuit 17.18.1 described later.
9.

Furthermore, the video signal is also supplied to a synchronization separation circuit 22, which will be described later. On the other hand, when the audio carrier is 4.5H&, the switch S3 is switched to the 4.5 side in the same way as described above, and the video signal passes through the 4.6W41Z audio trap and the audio carrier is 5.6. It is fed into the same circuit as in the case of storage.

The carrier color signal that has passed through the audio trap 11 or 12 in this manner is sent to the color demodulation circuit 1s for the color demodulation same color demodulation circuit 17 for SECAM, and the color demodulation circuit 19 for color demodulation for TSC. As a result, each color is demodulated, and a color difference signal is output for each method, which passes through the switch S4 and enters the matrix circuit @15 for six pages.

That is, first, in the case of a SECAM system signal, the demodulation circuit 17 detects that each line has 4.25M and 4.4 different color subcarriers, and determines that it is a SECAM system signal. And, the vertical synchronization signal frequency detection circuit 23 performs 50)1. If it is determined that
The color demodulation circuit for CAM is connected to the same color demodulation circuit 17, and the demodulated color difference signal is supplied to the matrix circuit 16.

In addition, in the case of a PAL system signal, the vertical synchronizing signal frequency detection circuit 23 determines 60 digits, and the output of the reception system switching circuit 21 connects the switch S4 to the PAL color recovery/demodulation circuit 18 output terminal. The color difference signals are supplied to matrix circuit 16.

Furthermore, in the case of M-NTSC system or NTSC system signals, the NTSC color demodulation color demodulation circuit 1 is used as described later.
Since the color demodulation is carried out by switching only the 4.43M and 3.58Vh crystal oscillators at 9, when the vertical synchronizing signal 6th page frequency detection circuit 23 determines 60H2, the receiving system switching circuit 21 switches the switch S4 to NTSC. The color demodulation circuit 19 is connected to the terminal of the color demodulation circuit 19, and its color difference signal is supplied to the matrix circuit 16. The detection and switching between the NTSC system and the M-NTSC system here will be explained in detail in Figure 2, but if the correct demodulated output is output when the circuit is switched to the 4.44 M-NTSC system, then The circuit switching is fixed and M-NTSC color demodulation is performed as is. On the other hand, if the correct demodulated output is output when the circuit is switched to the 3.5J4 NTSC system,
Therefore, the circuit switching is fixed and NTSC color demodulation is performed as is.

Next, frequency detection of the vertical synchronizing signal of each method and switching of the deflection circuit will be explained.

After the video signal passes through the audio trap 11 or 12,
The signal is input to the synchronization separation circuit 22, and the vertical synchronization signal frequency detection circuit 23 determines whether it is 601 (PAL system or SECAM system) or 60)i (M-NTSC system or NTSC system). The output of this detection circuit 23 is input to the reception method switching circuit 21 described above, and the detection output switches the switch S6 to the horizontal/vertical oscillation circuit 24 or horizontal/vertical oscillation circuit 26 side. , these circuits 24.25 with 501 (z or 6
Horizontal and vertical oscillations are performed according to the 0 Hz synchronization signal and are supplied to the deflection circuit 26.

Next, the NTSC color demodulation circuit 19 for the NTSC system
Regarding the receiving method switching circuit for the M-NTSC method and M-NTSC method,
An example of a conventional circuit is shown and explained in FIG.

First, the color demodulation circuit 19 for the NTSC system will be explained. The carrier color signal supplied from the video detection circuit 4 through the audio trap 11 or 12 is switched by the switch S6 and passed through the 4.43M bandpass filter 37 or 3.
．． After being passed through the E58 & band pass filter 38,
The signal is amplified by a band amplification circuit 39. Burst gate circuit 4
A burst signal is extracted at step o, amplitude adjusted by a color saturation adjustment circuit 41, and inputted to a BY demodulator 6o and an RY demodulator 62.

The burst gate pulse generation circuit 42 generates a burst gate pulse from the horizontal synchronizing signal, and the burst gate circuit 40 extracts the burst signal and sends it to the ACC detection circuit 43. Color killer circuit 44 The ACC circuit 43 supplied to the APC circuit 46 controls the output amplitude of the band amplifier 39 to be constant.

Further, the color killer circuit 44 detects whether the received signal is a color signal or a monochrome signal based on the burst signal and the output of the color subcarrier oscillator 47, and if it is a monochrome signal, the color saturation adjustment circuit 41
Apply color killer to.

The APC circuit 46 synchronizes the oscillation phase with the burst signal when the color subcarrier oscillator 49 oscillates using the crystal oscillator 48 or 49. The synchronously controlled oscillation output is sent to the B-Y, R-Y demodulators 60, 5 together with the carrier color signal.
2, and B-Y and RY color demodulation is performed. Further, a G-Y output is obtained from the G-Y demodulator 61.

The hue adjustment circuit 46 changes the phase of the oscillator 47 to change the color 9 page phase.

Next, in the subcarrier frequency detection circuit 20, the oscillation circuit 27
A reference signal is oscillated at , the frequency of which is divided by a frequency divider circuit 28 and applied to a T-7 lip-flop 29 . The Q output of the T-7 resobflop 29 is inverted by the inverter 3o,
As shown in FIG. 3A, the level is low during the first time period T1, and the level is high during the second time period T2. This is further inverted by the inverter 31 and sent from the buffer circuit 36 to the switch S6. Added to S7. As a result, T1
), the switches S6 and S7 are switched to the 3.58vi+1 side and operate to demodulate the NTSC signal with the color subcarrier frequency of 3.58 & during the period T2. It is switched to the 4.43& side and operates to demodulate the M-NTSC signal with the color subcarrier frequency of 4.43&.

Assume now that the carrier color signal input from the video detection circuit 4 is an NTSC signal.

At that time, when the T-flip-flop 29 enters the reset state of 10 pages and enters the T1 period, the burst signal and the oscillation output of the oscillator 47 have a constant phase relationship, and the output phase-detected by the color killer circuit 44 is the third As shown in Figure B, a color signal of <3.68 is detected and becomes a high level.

Then, the output of the color detection circuit 36 to which this detection output is applied also becomes high level as shown in FIG. 3C, and T
Since the output A of the -7 flip-flop 29 is at a low level, the output of the AND gate 34 becomes a high level as shown in FIG. 3E, and the R (reset l-) terminal of the T-flip-flop 29 remains at a high level. , the T-flip 70 knob 29 is locked in the recent state, and its output A
is locked to a low level. Therefore, the switches S6 and 37 are locked to the 3.581i side by the output of the buffer amplifier 32, and the NTS of the color subcarrier frequency 3.68■h is
A state is reached in which the carrier color signal of the C system is continuously received and demodulated. The capacitor 36 smoothes the output B of the color killer circuit 44 in order to stabilize the switching state.

Next, the carrier color signal 1 I inputted from the video detection circuit 4
Zuji is M-NTS whose color subcarrier frequency is 4.4316.
Consider the case of method C. At this time, as in the case where the color subcarrier frequency is 3.68 h, the output of the T-flip-flop 29 is shown in FIG. The time will be at a high level. In this state, when the T-7 reset flop 29 enters the seven state state and the T2 period begins, the high level output from the buffer circuit 32 causes the switch S6. S7 is switched to the 4.43 side to demodulate a signal with a color subcarrier frequency of 4.43M. Therefore, the phase detection output of the color killer circuit 44 as shown in FIG. 4B detects a color signal of <4.44 and becomes high level, and the output of the color detection circuit 36 becomes as shown in FIG. 4C. Become a high level. This is no good,
This time, the output of the AND gate 33 goes to a high level as shown in the fourth diagram, and the S (set) terminal of the T-flip-flop 29 goes to a high level of 1, and the T-7 flip-flop 29 is locked in the set state. , its output A is locked to a high level. Therefore, switch S6. S7 is 4.
Color subcarrier frequency 4 locked to 43■111111
．． This means that 43 M-NTSC carrier color signals are continuously demodulated.

However, in such a conventional circuit, the capacitance of the capacitor 36 of the output I11 of the color killer circuit 44 is made large in order to stabilize the switching state.
As shown by the broken line in the figure, when the electric field strength of the received color television signal becomes weaker, the time it takes for the output voltage of the color killer circuit 44 to reach a certain voltage indicating color detection (hereinafter referred to as color detection time) increases. It's getting long. Therefore, even under such a weak electric field strength, the color detection circuit 3
In order to generate a detection output in 5, T1, O': and T2 in FIGS. 3 and 4 must be made longer than the color detection time.

For example, in FIG. 6, if the detection limit is up to electric field strength E2, T1. T2 may be equal to or greater than T1, but the electric field strength of the weaker signal E2. If you try to detect color with a camera, the color detection time will be T2, so T1. T2
must be thickened to 72 or higher and must be 13 pages. However, doing so has the disadvantage that it takes a long time for the color to appear on the screen after reaching a predetermined color demodulation state, such as when switching channels. vice versa,
As is clear from FIG. 6, when T1°T2 is reduced to about T1, color demodulation cannot be performed correctly unless the received signal has an electric field strength of El or more.

On the other hand, the capacitor 36 on the output side of the color killer circuit 44
If the capacitance is made smaller, the voltage rises faster, so the fifth
The characteristics are as shown by the solid line in the figure, and color detection is possible up to the electric field strength E2 even with T1, but the color killer circuit 44
The disadvantage is that the filtering effect is reduced against ripples such as sag contained in the output voltage of the device, resulting in unstable operation and a tendency to cause malfunctions.

OBJECTS OF THE INVENTION The present invention eliminates such conventional drawbacks and provides a method for receiving a carrier color signal using a color demodulation circuit, which allows quick color detection even when the electric field strength of a received color television signal is weak. It is an object of the present invention to provide a multi-system color television receiver that can quickly switch to a demodulated 14-page state in accordance with the 14-page state, and that operates stably and does not cause malfunctions after switching.

Structure of the Invention In the present invention, in the above-mentioned device that detects and locks the frequency of the carrier color signal by alternately switching the reception frequency, the color subcarrier frequency is detected and the switching circuit is locked. By reducing the capacitance of the capacitor installed on the output side of the signal detection means such as the killer circuit, and switching to a larger capacitance in the normal state after switching, high-speed detection and stability after switching can be achieved. It is designed to satisfy both contradictory characteristics.

DESCRIPTION OF THE EMBODIMENTS FIG. 6 shows a circuit diagram of essential parts of a multi-system color television receiver according to an embodiment of the present invention. In FIG. 6, parts that are the same as those in the prior art are given the same reference numerals as in FIG. 2, and their explanations will be omitted.

15 A: - In this circuit, two capacitors 53 and 64 are provided as filter capacitors provided in the middle of supplying the output voltage of the color killer circuit 44 to the color detection circuit 35, and a switch S8 is connected in series to the capacitor 54. connect and
The output C of the color detection circuit 35 is detected by the switching circuit 66, and the switch S8 is closed only when the output C is at a high level as compared to the color detection.

According to this configuration, the switching polarity of the switches SS and S7 by the output A of the T-flip-flop 29 does not match the color subcarrier frequency of the received carrier color signal, so that the output voltage of the color killer circuit 44 is at a low level. At certain times, and even if they match, if the output voltage B applied from the color killer circuit 44 to the color detection circuit 36 has not yet risen sufficiently, the detection output C of the color detection circuit 36 is at a low level. Therefore, the switching circuit 65 switches the switch S8.
is open, so the time constant as a filter is small, and the detection characteristics are as shown by the broken line in FIG. In this case, even if the electric field strength of the received signal is weak, if the color demodulation method matches, the color detection time τ will be shortened, and the color detection circuit 35 will promptly generate the detection output C, which will be the color subcarrier frequency of the received carrier color signal. The color demodulation state can be quickly switched to match the color demodulation state. Further, when the color detection circuit 36 outputs the detection output C and the switching of the color demodulation state is completed, the detection output C is detected by the switching circuit 56 and the switch S8 is closed. Therefore, from now on, the time constant of the filter becomes large, and even if the output voltage of the color killer circuit 44 contains ripples, there is no longer any risk that the detection output of the color detection circuit 35 will change, and malfunctions may occur. The fear disappears.

In this way, it is possible to increase the operating speed while locking to a predetermined color demodulation state according to the received carrier color signal, and it is possible to promptly perform predetermined color demodulation, and furthermore, after locking, The predetermined color demodulation state can be stably maintained.

Page 17 Note that in the above explanation, the time constant of the filter is changed by changing the capacitor.
It goes without saying that other filter components such as resistors may also be switched.

Effects of the Invention As described above, according to the present invention, when receiving carrier color signals having different color subcarrier frequencies and switching the color demodulation circuit to match the color subcarrier frequency, the detection and switching can be weakened. It is possible to realize a receiver that can perform switching quickly even when there is an input electric field, and that can operate stably without causing malfunctions after switching.

[Brief explanation of the drawing]

Fig. 1 is an overall block diagram of an example of a multi-scheme color television receiver, Fig. 2 is a circuit diagram of the main parts of an example of a conventional multi-scheme color television receiver, and Figs. 3 and 4 are its circuit diagrams. FIG. 6 is a waveform diagram for explaining the operation, FIG. 6 is a characteristic diagram for explaining the operation, and FIG. 6 is a circuit diagram of a main part of a multi-system color television receiver according to an embodiment of the present invention. 18 page 19...NTSC color demodulation circuit, 2o...
...Color subcarrier frequency detection circuit, 27...Oscillation circuit, 28...Divide circuit, 29...T
-Flip-flop, 33.34...AND gate, 35...River/color detection circuit, 37,38...mark/band pass filter, 44...color killer circuit, 48.49 ...Crystal oscillator, 53.54.
Old... capacitor, 65... switching circuit, 86,
87. Ss old... switch.

Claims (1)

[Scope of Claims] First color synchronization means for reproducing a first reference color subcarrier in synchronization with a first carrier color signal having different color subcarrier frequencies and a burst signal in the first carrier color signal. and second color synchronization means for regenerating a second reference color subcarrier in synchronization with a burst signal in the second carrier color signal, and a received carrier color signal of the two carrier color signals. The first color synchronizing means reproduces the burst signal extracted from the first
and a second reference color subcarrier reproduced by the second color synchronization means during a second period, and a filter having a switchable time constant. and a switch means for switching the time constant of the output voltage of the signal detection means is connected to the filter, and when the voltage of the filter reaches a predetermined threshold, the operating state of the time zone switching means of the signal detection means is locked. 2 pages, the switch means is controlled to increase the time constant of the filter, and the output signal of the time zone switching means of the signal detection means causes the receiving circuit to switch between the first and second carriers. A multi-system color television receiver that can switch which color signal to receive.