CA1262281A - Multi-system television receiver - Google Patents
Multi-system television receiverInfo
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- CA1262281A CA1262281A CA000581789A CA581789A CA1262281A CA 1262281 A CA1262281 A CA 1262281A CA 000581789 A CA000581789 A CA 000581789A CA 581789 A CA581789 A CA 581789A CA 1262281 A CA1262281 A CA 1262281A
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Abstract
Abstract of the Disclosure A multi-system television receiver capable of receiving television signals of a plurality of different broadcasting systems with a plurality of different subcarrier wave frequencies involves detecting the frequency of a subcarrier wave of the received television signal and producing frequency data representing the detected frequency.
Provision is also made for detecting the system of the television signal and producing system data representing the detected system. Changing of a TV channel of the receiver is also detected, and the frequency data and system data are held. The television receiver circuits are then set in a condition that complies with the broadcast system of the received television signal as determined by the frequency data and the system data.
Provision is also made for detecting the system of the television signal and producing system data representing the detected system. Changing of a TV channel of the receiver is also detected, and the frequency data and system data are held. The television receiver circuits are then set in a condition that complies with the broadcast system of the received television signal as determined by the frequency data and the system data.
Description
Multi-system television receiver This application is a division of application .;erial No. 482,033 filed May 22, 1985.
The present invention relates to a multi--system tele~ision receiver having a subcarrier generation circuit that is operable with a number of different systems.
There are a number of di~ferent types o~ television brQadcasting systems in the world, such as the PAL system, the SECAM system, the NTSC sys~em and others. In some places L0 television broadcasting with two or more systems is available.
Also, video tapes recorded under different systems are available.
To enable the reproduction of color television signals of different systems, a color television receiver that 15 can receive and reproduce color television signals o~ different systems has been developed. Such a receiver is referred to as a multi-system television receiver.
The signal formats or the NTSC system and the PAL
system are very similar to each other. Therefore,in the prior 20 art multi-system television receiver, the color signal processing circuit, particularly the subcarrier wave oscillator, an APC phase detector and a killer phase detector are used in common for both systems. Furthermore, the multi-system television receiver has means ~or detecting the type of tele-25 vision system being received so as to switch the various circuits necessary to process the television signal to a ,, 3.~, ~6~
viewable image on a CRT.
( For example, according to the PAL system, a sub-carrier wave having a frequency of 4.43 MHz is used in most places, but, in some places, a 3.58 MHz subcarrier wave is used. In the NTSC system a 3.58 MHz subcarrier wave is normally used. Furthermore, some VTR tapes recorded under the NTSC
system use a 3.58 MHz and others use a 4.43 MHz subcarrier wave.
Accordingly, a prior art multi-system television receiver that can receive television signals in the PAL
system and in the NTSC system, or can reproduce VTR tapes recorded under various systems, employs two oscillators for generating two subcarrier waves having the frequencies 4.43 MHz and 3.58 MHz. For this purpose, suitable switching ~eans is provided for selecting one of these oscillators or generating the required subcarrier wave.
The prior art multi-system television receiver thus reqùires two oscillators, resulting in a high manufacturing cost. Also, a suitab]e switching means is necessary to select one oscillator,for the particular system signal being received.
To remove this disadvan~age, a multi-system tele-vision receiver having an improved subcarrier generation circuit ha.s been proposed by the same inventor as the present invention, anA is disclosed in Japanese Patent Application laid-open publication No. 58-152070, which is assigned to the same assignee as the present application. According to this publication, only one oscillator is provided, which can generate subcarrier waves at different frequencies, and which can automatically select and produce a subcarrier wave having the appropriate frequency for the received television signal.
To enable this prior art to be described with the aid of diagrams, the figures of the drawings will first be listed.
Fig. 1 is a circuit diagram showing a subcarrier generation circuit according to the prior art;
Fig. 2 is a circuit diagram showing a subcarrier generation circuit and its associated parts, according to the preferred embodiment of the present invention;
Fig. 3 is a graph showing waveforms obtained at ( various places in the circuit of Fig. 2;
~ig. 4 is a block diagram showing a modification of a s~bcarrier generation circuit, according to the present invention; and Fig. 5 (with Fig. 3) is a circuit diagram of a low pass filter which may be replaced with the low pass filter shown in Fig. 2.
The subcarxier generation circuit disclosed in the above publication No. 58-152070 is shown in Fig. 1 where reference number 1 designates a burst gate circuit which, in accordance with the burst gate pulse in the horizontal scanning period, separates and generates a burst gate signal from the chrominance signal. Reerence number 2 is a phase detector for an automatic phase controller (APC~, 3 is a low pass filter, 4 is a voltage-controlled oscillator ~VCO). These circuits 2, 3 and 4 define the automatic phase controller (APC), the VCO 4 producing a subcarrier signal.
VCO 4 is pxovided with two crystal vibrators Sa and 5b for respectively generating a signal at a frequency of 3.58 MHz or 4.43 MHz. A switching circuit 6 is provided for selectively connecting one crystal vibrator to the VCO 4 in response to the frequency of the burst signal.
Further provided is a phase detector 7 for a killer.
When phase detector 7 stops producing the normal signal, flip-flop 8 reverses its condition upon receipt of a driving pulse having a pulse width of about 200 milliseconds. The output of flip-flop 8 is connected to the switching circuit 6 for selecting one vibrator.
The operation of this circuit is as follows. When a television signal of the NTSC system is received, a burst signal having a frequency of 3.58 MHz is separated and produced from the burst gate circuit 1. This burst signal is applied to both the phase detectors 2 and 7. In this case, the switching circuit 6 is so actuated as to connect the crystal vibrator 5a with the VCO 4 in accordance with the output signal ~6~
,, from the flip-flop 8, and, at the same time, the APC loop f operates in a synchronized relationship with the burst siynal at a frequency of 3.58 ~z. Thus, the VCO 4 produces a sub-carrier wave having a frequency 3.58 MHz. In this manner, once 5 the APC loop is synchronized, the phase detector 7 produces a phase detected signal that suspends further operation of the flip-flop 8. The VCO 4 thus produces the normal 3.58 ~z subcarrier wave in a stable condition. Then, if for some reason the control of the flip-flop 8 is delayed, the 10 switching circuit 6 can be so operated as to connect the crystal vibrator 5b (4.43 ~Hz) to the VCO 4. In such a case, the signal in the APC loop becomes mis-synchronized, so that no out-put signal is produced from the phase detector 7. The flip-flop 8 thus changes its condition upon receipt of the next 15 drive pulse, thereby switching the switching circuit 6 to connect the crystal vibrator 5a (3.58 MHz) to the VCO 4.
Accordingly, the APC loop is synchronized at a frequency of 3.58 MHz, so that the VCO 4 produces a normal subcarrier wave at this frequency.
When a television signal of the PAL system is received, upon a change o channel, a burst signal having a frequency 4.43 MHz is separated and produced from the burst gate circuit 1. Accordingly, by the output signal from the flip-flop 8, the switching circuit 6 is actuated to connect the crystal vibrator Sb to the VCO 4. The APC loop thus operates in a synchronized relationship with the burst signal at a frequency of 4.43 ~Iz, and the VCO 4 produces a sub-carrier wave having this frequency. In this manner, once the APC loop is synchronized at frequency 4.43 MHz, the phase detector 7 produces a phase detected signal that suspends further operation of the flip-flop 8. The VCO 4 thus produces the normal 4.43 MHz subcarrier wave in a stable condition.
However, this circuit has a number of disadvantages.
The first disadvantage is an erroneous operation that may take place if a television signal of the SECA~I
system is received.
According to the SECAM system, the chrominance signal contains a subcarrier wave at a frequency of 4.25 MHz or 28~
4.406 ~z, which is very close to the frequency 4.43 MUIz of S the burst signal Accordingly, if the signal component ~t the trailing edge of the horizontal sync signal, where the burst signal of the PAL system or the NTSC system is located, 5 should come in while a television signal of the SECAM system is being received~ the APC circuit makes a retraction operation, resulting in an error operation as if a burst signal at 4.43 ~lz had been received.
The second disadvantage relates to an erroneous 10 operation that may take place upon changing from a channel in one broadcasting system, such as a PAL system, to a channel in another broadcasting system, such as a SECAM system.
More specifically, according to the prior art sub-carrier generation circuit, the low pass filter defining the 15 APC loop has a relatively long time constant. Therefore, when a channel change between two different broadcasting systems is effected/ it takes a relatively long time to detect the broadcasting system of the newly selected channel and to switch the switching circuit 6 to generate the proper subcarrier 20 wave from the VCO 4. ~During this period of time, the image on the screen is often distorted.
The last disadvantage relates to an erroneous operation caused by a noise signal produced from the flip-flop circuit 8 or a system detection circuit for detecting the type 25 of broadcasting system being received.
Specifically, according to the prior art multi-system television receiver, the system detection circuit detects and produces a signal representing the type of broadcasting system being received~ However, the system detection circuit 30 makes an error detection by the noise signal. The noise signal is, for example, contained in the received broadcasting signal, or produced upon reproduction of a tape recorded under poor conditions, or is produced when a video search signal is added.
The present invention has been developed with a view to substantially solving the above described disadvantages and has for its essential object to provide an improved multi-system television receiver that will not operate erroneously when a noise signal is caused by a change of channel between two different broadcasting systems or for any other of the reasons described above.
It is also an essential object of the present invention to provide an improved multi-system television receiver that can immediately provide a stable image after a channel change, particularly between two different broadcasting systems.
The invention also consists of a multi-system television receiver capable of receiving television signals of a plurality of different broadcasting systems with a plurality of different subcarrier wave frequencies comprising: frequency detecting means for detecting the frequency of a subcarrier wave of the received television signal and produci~g frequency data representing the detected frequency; system detecting means for detecting the system of the television signal and pro~ucing system data representing the detected system; channel change detecting means for detecting the changing of a ~V channel of said receiver; holding means for holding said frequency data and system data upon said changing of the channel detected by said detecting means; and television receiver circuits set in a condition in compliance with the broadcast system of said received television signal as determined by said frequency data and said system data.
~z~
- 6~ -Referring to Fig. 2, a tuner 29 for receiving television signals and producing a tuned television signal is connected to a sound-trap 30 and then to a picture intermediate frequency (PIF) 31. The output o~ the PIF
31 is connected to each of a SECAM circuit 26, a PAL/NTSC
detector 27 and a video trap 32. The video trap 32, which is also coupled to a video circuit (not shown), is connected to a band pass filter (BPF) 19 and hence to a band pass amplifier 20. The band pass amplifier 20 produces a chrominance signal that is applied to a burst gate circuit 1. The burst gate circuit 1 operates in response to a bur~t gate pulse. The output of burst gate circuit 1 is connected to a phase detector 2 for use in an automatic phase controller (APC). A low pass filter 3 is connected to the phase detector 2 and to a voltage controlled oscillator 4 which is coupled via a switching circuit 6 to crystal vibrators 5a and Sb for ( oscillation at di~ferent frequencies, i.e. 3.58 MHz and 4.43 MHz, respectively. An automatic phase controller (APC) is defined by a feed back loop containing the phase detector 2, the low pass filter 3 and the VC0 4. Accordingly, the VC0 4 produces a subcarrier signal at a frequency of 3.58 MHz or 4043 MHz depending on the frequency of the burst signal, in a manner that will be described in detail later.
According to the preferred embodiment, the low pass filter 3 comprises a capacitor 9 connected between a hot line, through which the signal transmits, and ground. Also, a series connection of a resistor 11 and a capacitor 10 is conneeted parallel to the capacitor 9. Furthermore, a series connection of a capacitor 12 and a normally-closed switch 13 is connected parallel to the capacitor 10. Normally-closed switch 13 is controlled by a pulse from a pulse generator 15 in a manner that will be described later.
The output of the VC0 4 is applied to a PAL/NTSC
demodulator 33 which produees an R-Y signal or a B-Y signal.
The output of the VC0 4 is also applied to a phase detector 7 whieh also reeeives the output signal from the burst gate circuit 1.
According to a preferred embodiment, the phase detector 7 is eonnected with ~ capacitor 16 which is grounded.
Also, a series connection of a capacitor 17 and a normally-closed switch 18 is connected parallel to the capacitor 16.Normally-closed switch 18 is also controlled by a pulse from the pulse generator 15 in a manner described below.
A channel seleetor 14 is eoupled to the puls~
generator 15. Whenever the broadcasting channel is changed by the channel selector 14, the pulse generator 15 generates a short pulse, such as shown by waveform d in Fig. 3. This short pulse is applied to each of the normally-closed switches 13 and 18 to open them temporarily during the duration of the pulse. When the switch 13 opens, the capacitor 12 is disconnected from the capacitor 10, thereby making tile time constant of the low pass filter 3 short.
Similarly, when the switch 18 opens the time constant of ~z~
( the phase detector 7 is shortened. When the time constant is ( shortened, the retraction operation of the APC loop occurs faster, whereby the subcarrier wave for the newly selected channel can be produced very fast from the VCO. This quick response can be accomplished even when the channel change is effected between two different broadcasting systems having different subcarrier wave frequencies. Accordingly, a stable subcarrier ~ave can be obtained immediately after the change lQ of the channel.
The phase detector 7 is provided to produce a color killer output which is applied to both a band pass amplifier 20 and the flip-flop circuit 8. When th~ VCO 4 is producing a subcarrier signal having a frequency of 3.5~ ~z, the flip-flop 8 generates HIG~ in response to the signal obtained fromthe phase detector 7. Similarly, when the VCO 4 is producing a subcarrier signal having a frequency of 4.43 MHzl the flip-flop 8 generates LOW. The output of the flip-flop 8, such as shown in Fig. 3 at waveform a, is appli~d to an AND gate 22a provided in a detection control circuit 22.
The detection control circuit 22 further includes AND gates 22b and 22c and a pulse generator 22d. One input of the AND gate 22b is connected to a SECAM circuit 26 which produces HIGH when the received television signal is in the SECAM system~ and LOW when it is not, such as indicated in Fig. 3, waveform b. One input of the AND gate 22c is connected to a PAL/NTSC detector 27 which produces HIGH when the received television signal is in the NTSC system and LOW
when it is in either the PAL system or the SECAM system, such as indicated in Fig. 3, waveform c. The other inputs of AND
gates 22a, 22b and 22c are connected to the pulse generator 22d. The pulse generator 22d has its input connected to an OR gate 22e having two inputs. One input of the OR gate 22e - is connected to the pulse generator 15 and the other input thereof is connected to a television signal detector 28.
Details of the pulse generator 22d will be described later.
The television signal detector 28 has two inputs:
one for receiving the horizontal pulse; and the other for receiving the sync-pulse. Accordingly, ~henever a television signal, which may be obtained through an antenna (not shown), cable (not shown), or from a video tape, is being received, the television signal detector 28 generates a HIGH output, such as shown in Fig. 3 at waveform e. The television signal detector 28 produces LOW while the channel is being changed.
From this viewpoint, the signal produced from the television signal detector 28 is similar to the signal produced from the pulse generator 15, except that these two signals are in opposite phase~ Furthermore, the signal from the television signal detector 28 has the feature that, when a video tape is being reproduced, the channel change recorded in the tape can also be detected. Therefore, whenever there is a channel change in the reproduced video tape, no pulse will be produced from the pulse generator 15, but a pulse will be produced from the television signal detector 28.
Accordingly, the OR gate 22e produces a signal not only when the channel is actually changed, but also when a channel change recorded in a video tape is detected.
As indicated in Fig. 3, waveform f, the pulse generator 22d detects a step up of the waveform d or a step up of the waveform e, and produces a one-shot pulse having a pulse duration of t or t'. The AND gates 22a, 22b and 22c are enabled only when a one-shot pulse is present, that is a short period of time immediately after the channel change is effected, which may be an actual channel change or a channel change recorded in a video tape.
The AND gates 22a, 22b and 22c are connected to a hold circuit 23 which is coupled to a reset circuit 25. The reset circuit Z5 receives the signal from the television signal detector 28 and produces a reset signal when the channel is changed. Accordingly, when a new channel is selected, the output signal from the AND gate 22a is h~ld in the hold circuit 23, and is produced from the output terminal 24A of the hold circuit 23. Similarly, the output signal ~rom the AND gate 2Zb is held and produced from the output terminal 24B, and the output signal from the AND gate 22c is held and ~a62æ3~:~
produced from the output terminal 24C. Once the hold circuit holds various data from the AND gates 22a, 22b and 22c ( immediately after the channel selection, this data is main-tained as long as the selected channel is on.
Output terminal 24A, carrying data of the subcarrier frequency, is connected to the switching circuit 6 for selecting either one of the crystal vibrators 5a and 5b, and also to the band pass filter 19, video trap 32 and sound trap 30.
Output terminal 24B, carrying data representing the SECAM system, is connected to the SECAM circuit 26 for rlain-taining the SECA~1 circuit operative while the received tele-vision signal is in the SECAM system.
Output terminal 24C, carrying data representing the PAL system or the NTSC system, is connected to the PAL/NTSC
demodulator 33 for actuating the demodulator 33. When the received television signal is in the PAL system, the output terminal 24C will produce LOW, thereby setting the demodulator 33 as a PAL demodulator. On the other hand, when the received television signal is in the NTSC system, the output terminal 24C will produce HIGH, thereby setting the demodulator 33 as an NTSC demodulator.
The operation of the circuit of Fig. 2 will now be described. This circuit is operable with five different broadcasking systems, namely: the PAL system with a 3.58 M~Iz subcarrier wave; the PAL system with a 4.43 MHz subcarrier wave; the NTSC syste~ with a 3.58 MHz subcarrier wave; the NTSC system with a 4.43 MHz subcarrier wave; and the SECAM
system with 4.43 MHz.
It is assumed that the channel selector 14 is actuated to select a television signal of the NTSC system with the 3.58 ~z subcarrier wave. When the channel selector 14 is actuated, the pulse generator 15 produces a pulse (first pulse in waveform d) which affects the pulse generator 22d to produce a one-shot pulse tfirSt pulse in waveform f). While the one-shot pulse is pxesent, the flip-flop 8 produces HIGH
indicating that the subcarrier wave has a frequency of 3.58MHz.
Also, the SECAM circuit 26 produces LOW indicating that the received television signal is not in the SECA~I system, and the PAL/NTSC detector 27 produces HIGH indicating that the ( received television signal is in the NTSC system.
Accordingly, when the one-shot pulse (first pulse in waveform f) is produced from the pulse generator 22d, each of the AND gates 22a and 22c produces HIGH (waveforms g and i), and the AND gate 22b produces no pulse (waveform h). The signals from AND gates 22a, 22b and 22c are produced in response to the one-shot pulse, and are held in the holding circuit 23 which accordingly produces HIGH, LOW and HIGH, respectively, from its output terminals 24A, 24B and 24C. These signals from output terminals 24A, 24B, and 24C are maintained until the reset circuit produces a reset signal, that is until the next channel change.
The HIGH from output terminal 24A is applied to the switching circuit 6 for selecting the crystal vibrator 5a for oscillation at the frequency of 3.58 MXz. The HIG~ from output terminal 24A is also applied to the band pass filter 19 for selecting a band appropriate for the 3.58 MHz subcarrier wave, and further to the video trap 32 and to the sound trap 30.
The LOW from output terminal 24B is applied to the SEC~M circuit 26 to disable it.
The HIGH from output terminal 24C is applied to the PAL/NTSC demodulator 33 to set it as a NTSC demodulator.
Since the data representing the system of the tele-vision signal and the data representing the frequency o~ the subcarrier wave are applied to the hold circuit 23 only when the AND gates 22a, 22b and 22c are enabled, that is a short period of time iINmediately after the change of channel, any undesirable change or fluctuation in these data will not be transmitted to the hold circuit 23 and to various other circuits, such as the switching circuit 6. Accordingly, once the hold circuit 23 holds the data of the received television signal at the beginning of the channel selection, such data will not be changed, even if the television signal fluctuates or noise appears in the signal. Accordingly, the television receiver not only automatically sets the circuit in a condition suitable for the system of the received signal, but also maintains this ~2~æ~
set condition as long as the channel is maintained the same.
When a channel change is effected by the channel selector 14, ( or when a ch ~ el change signal recorded in a video tape is reproduced, new data will be set and held in the hold circuit S 23.
Signals produced from the output terminals 24A, 24B
and 24C for television signals received in different systems are shown in the Table below.
Received Television Signal 24A 24B 24C
10 PAL 3.58 MHz subcarrier LOW LOW LOW
PAL 4.43 MHz subcarrier HIGH LOW LOW
NTSC 3.58 MHz subcarrier LOW LOW HIGH
NTSC 4.43 MHz subcarrier HIGH LOW HIGH
SECAM 4.43 MHz subcarrier LOW HI~H LOW
According to the embodiment shown in Fig. 2, the detection control circuit 22 employs A~D gates 22a, 22b and 22c, but these AND gates can be replaced by other logic gates, such as NOR gates, when the pulses applied to the gates are in negative form.
Referring to Fig. 4, a modification of a subcarrier generation circuit according to the present invention is shown.
The output of the flip-flop 8 is connected to an OR gate 34 which also receives a signal from a SECAM killer 35 in a SECAM circuit. The output of the OR gate 34 is connected to the switching circuit 6. Operation of this circuit is as ~ollows.
When a television signal of the NTSC system is received, the flip-Xlop 8 produces HIGH in the manner described above. This HIGH is applied through the OR gate 34 to the switching circuit 6 to cause oscillation at 3.58 MHz by the crystal vibrator 5a. Accordingly, the APC loop synchronizes at the frequency of 3.58 MHz and the VCO therefore generates a suhcarrier wave at 3.58 MHz.
When a television signal of the PAL system is received, the flip-flop 8 produces LOW in the manner described above. This LOW is applied through the OR gate 34 to the switching circuit 6 to cause oscillation at 4.43 MHz by the crystal vibrator Sb. ~ccordingly, the APC loop synchronizes at the frequency 4.43 ~ and the VCO therefore generates a subcarrier wave at 4.43 MHz.
( When a television signal of the SECAM system is received, the SECAM KILLER 35 for the SECAM color killer produces HIGH. Therefore, regardless of the signal from the flip-flop 8, the OR gate 34 produces HIGH. Accordingly, the switching circuit 6 is so turned as to oscill~ate at 3.58 MHz.
In this case, a subcarrier wave component at the frequency of 4.25 MHz or 4.406 MHz contained in the chrominance signal can be applied to the phase detector 2. Since such frequencies are much different from 3.58 MHz, the VCO 4 generates the sub-carrier wave at 3.58 MHz without making any retraction operation by the APC lo~p.
In this case, the color killer output produced from the phase detector 7 can beused for disabling a color processing circuit for the NTSC/PAL system and for enabling a color processing circuit for the SECAM system.
Referring to Fig. 5, a circuit diagram of a low pass filter is shown. According to the low pass filtar 3 shown in Fig. 2, a series connection of capacitor 12 and normally-close switch 13 is connected in parallel with the capacitor 10 to shorten the time constant when the switch 13 opens.
According to the modification shown in Fig. 5, a series connection of a resistor 36 and a normally-open switch 13' is connected parallel to the capacitor 10. Accordinyly, when a channel change i5 effected, the switch 13' closes to shorten the time constant. Accordingly, the low pass filter 3 shown in Fig. 2 can be replaced by the low pass filter 3 shown in Fig. 5.
Although the present invention has been fully described with reference to a preferred embodiment, many modifications and variations thereof will now be apparent to those skilled in the art, and the scope of the present invention is therefore to be limited not by the details of the preferred embodiment described above, but only by the terms of the appended claims.
The present invention relates to a multi--system tele~ision receiver having a subcarrier generation circuit that is operable with a number of different systems.
There are a number of di~ferent types o~ television brQadcasting systems in the world, such as the PAL system, the SECAM system, the NTSC sys~em and others. In some places L0 television broadcasting with two or more systems is available.
Also, video tapes recorded under different systems are available.
To enable the reproduction of color television signals of different systems, a color television receiver that 15 can receive and reproduce color television signals o~ different systems has been developed. Such a receiver is referred to as a multi-system television receiver.
The signal formats or the NTSC system and the PAL
system are very similar to each other. Therefore,in the prior 20 art multi-system television receiver, the color signal processing circuit, particularly the subcarrier wave oscillator, an APC phase detector and a killer phase detector are used in common for both systems. Furthermore, the multi-system television receiver has means ~or detecting the type of tele-25 vision system being received so as to switch the various circuits necessary to process the television signal to a ,, 3.~, ~6~
viewable image on a CRT.
( For example, according to the PAL system, a sub-carrier wave having a frequency of 4.43 MHz is used in most places, but, in some places, a 3.58 MHz subcarrier wave is used. In the NTSC system a 3.58 MHz subcarrier wave is normally used. Furthermore, some VTR tapes recorded under the NTSC
system use a 3.58 MHz and others use a 4.43 MHz subcarrier wave.
Accordingly, a prior art multi-system television receiver that can receive television signals in the PAL
system and in the NTSC system, or can reproduce VTR tapes recorded under various systems, employs two oscillators for generating two subcarrier waves having the frequencies 4.43 MHz and 3.58 MHz. For this purpose, suitable switching ~eans is provided for selecting one of these oscillators or generating the required subcarrier wave.
The prior art multi-system television receiver thus reqùires two oscillators, resulting in a high manufacturing cost. Also, a suitab]e switching means is necessary to select one oscillator,for the particular system signal being received.
To remove this disadvan~age, a multi-system tele-vision receiver having an improved subcarrier generation circuit ha.s been proposed by the same inventor as the present invention, anA is disclosed in Japanese Patent Application laid-open publication No. 58-152070, which is assigned to the same assignee as the present application. According to this publication, only one oscillator is provided, which can generate subcarrier waves at different frequencies, and which can automatically select and produce a subcarrier wave having the appropriate frequency for the received television signal.
To enable this prior art to be described with the aid of diagrams, the figures of the drawings will first be listed.
Fig. 1 is a circuit diagram showing a subcarrier generation circuit according to the prior art;
Fig. 2 is a circuit diagram showing a subcarrier generation circuit and its associated parts, according to the preferred embodiment of the present invention;
Fig. 3 is a graph showing waveforms obtained at ( various places in the circuit of Fig. 2;
~ig. 4 is a block diagram showing a modification of a s~bcarrier generation circuit, according to the present invention; and Fig. 5 (with Fig. 3) is a circuit diagram of a low pass filter which may be replaced with the low pass filter shown in Fig. 2.
The subcarxier generation circuit disclosed in the above publication No. 58-152070 is shown in Fig. 1 where reference number 1 designates a burst gate circuit which, in accordance with the burst gate pulse in the horizontal scanning period, separates and generates a burst gate signal from the chrominance signal. Reerence number 2 is a phase detector for an automatic phase controller (APC~, 3 is a low pass filter, 4 is a voltage-controlled oscillator ~VCO). These circuits 2, 3 and 4 define the automatic phase controller (APC), the VCO 4 producing a subcarrier signal.
VCO 4 is pxovided with two crystal vibrators Sa and 5b for respectively generating a signal at a frequency of 3.58 MHz or 4.43 MHz. A switching circuit 6 is provided for selectively connecting one crystal vibrator to the VCO 4 in response to the frequency of the burst signal.
Further provided is a phase detector 7 for a killer.
When phase detector 7 stops producing the normal signal, flip-flop 8 reverses its condition upon receipt of a driving pulse having a pulse width of about 200 milliseconds. The output of flip-flop 8 is connected to the switching circuit 6 for selecting one vibrator.
The operation of this circuit is as follows. When a television signal of the NTSC system is received, a burst signal having a frequency of 3.58 MHz is separated and produced from the burst gate circuit 1. This burst signal is applied to both the phase detectors 2 and 7. In this case, the switching circuit 6 is so actuated as to connect the crystal vibrator 5a with the VCO 4 in accordance with the output signal ~6~
,, from the flip-flop 8, and, at the same time, the APC loop f operates in a synchronized relationship with the burst siynal at a frequency of 3.58 ~z. Thus, the VCO 4 produces a sub-carrier wave having a frequency 3.58 MHz. In this manner, once 5 the APC loop is synchronized, the phase detector 7 produces a phase detected signal that suspends further operation of the flip-flop 8. The VCO 4 thus produces the normal 3.58 ~z subcarrier wave in a stable condition. Then, if for some reason the control of the flip-flop 8 is delayed, the 10 switching circuit 6 can be so operated as to connect the crystal vibrator 5b (4.43 ~Hz) to the VCO 4. In such a case, the signal in the APC loop becomes mis-synchronized, so that no out-put signal is produced from the phase detector 7. The flip-flop 8 thus changes its condition upon receipt of the next 15 drive pulse, thereby switching the switching circuit 6 to connect the crystal vibrator 5a (3.58 MHz) to the VCO 4.
Accordingly, the APC loop is synchronized at a frequency of 3.58 MHz, so that the VCO 4 produces a normal subcarrier wave at this frequency.
When a television signal of the PAL system is received, upon a change o channel, a burst signal having a frequency 4.43 MHz is separated and produced from the burst gate circuit 1. Accordingly, by the output signal from the flip-flop 8, the switching circuit 6 is actuated to connect the crystal vibrator Sb to the VCO 4. The APC loop thus operates in a synchronized relationship with the burst signal at a frequency of 4.43 ~Iz, and the VCO 4 produces a sub-carrier wave having this frequency. In this manner, once the APC loop is synchronized at frequency 4.43 MHz, the phase detector 7 produces a phase detected signal that suspends further operation of the flip-flop 8. The VCO 4 thus produces the normal 4.43 MHz subcarrier wave in a stable condition.
However, this circuit has a number of disadvantages.
The first disadvantage is an erroneous operation that may take place if a television signal of the SECA~I
system is received.
According to the SECAM system, the chrominance signal contains a subcarrier wave at a frequency of 4.25 MHz or 28~
4.406 ~z, which is very close to the frequency 4.43 MUIz of S the burst signal Accordingly, if the signal component ~t the trailing edge of the horizontal sync signal, where the burst signal of the PAL system or the NTSC system is located, 5 should come in while a television signal of the SECAM system is being received~ the APC circuit makes a retraction operation, resulting in an error operation as if a burst signal at 4.43 ~lz had been received.
The second disadvantage relates to an erroneous 10 operation that may take place upon changing from a channel in one broadcasting system, such as a PAL system, to a channel in another broadcasting system, such as a SECAM system.
More specifically, according to the prior art sub-carrier generation circuit, the low pass filter defining the 15 APC loop has a relatively long time constant. Therefore, when a channel change between two different broadcasting systems is effected/ it takes a relatively long time to detect the broadcasting system of the newly selected channel and to switch the switching circuit 6 to generate the proper subcarrier 20 wave from the VCO 4. ~During this period of time, the image on the screen is often distorted.
The last disadvantage relates to an erroneous operation caused by a noise signal produced from the flip-flop circuit 8 or a system detection circuit for detecting the type 25 of broadcasting system being received.
Specifically, according to the prior art multi-system television receiver, the system detection circuit detects and produces a signal representing the type of broadcasting system being received~ However, the system detection circuit 30 makes an error detection by the noise signal. The noise signal is, for example, contained in the received broadcasting signal, or produced upon reproduction of a tape recorded under poor conditions, or is produced when a video search signal is added.
The present invention has been developed with a view to substantially solving the above described disadvantages and has for its essential object to provide an improved multi-system television receiver that will not operate erroneously when a noise signal is caused by a change of channel between two different broadcasting systems or for any other of the reasons described above.
It is also an essential object of the present invention to provide an improved multi-system television receiver that can immediately provide a stable image after a channel change, particularly between two different broadcasting systems.
The invention also consists of a multi-system television receiver capable of receiving television signals of a plurality of different broadcasting systems with a plurality of different subcarrier wave frequencies comprising: frequency detecting means for detecting the frequency of a subcarrier wave of the received television signal and produci~g frequency data representing the detected frequency; system detecting means for detecting the system of the television signal and pro~ucing system data representing the detected system; channel change detecting means for detecting the changing of a ~V channel of said receiver; holding means for holding said frequency data and system data upon said changing of the channel detected by said detecting means; and television receiver circuits set in a condition in compliance with the broadcast system of said received television signal as determined by said frequency data and said system data.
~z~
- 6~ -Referring to Fig. 2, a tuner 29 for receiving television signals and producing a tuned television signal is connected to a sound-trap 30 and then to a picture intermediate frequency (PIF) 31. The output o~ the PIF
31 is connected to each of a SECAM circuit 26, a PAL/NTSC
detector 27 and a video trap 32. The video trap 32, which is also coupled to a video circuit (not shown), is connected to a band pass filter (BPF) 19 and hence to a band pass amplifier 20. The band pass amplifier 20 produces a chrominance signal that is applied to a burst gate circuit 1. The burst gate circuit 1 operates in response to a bur~t gate pulse. The output of burst gate circuit 1 is connected to a phase detector 2 for use in an automatic phase controller (APC). A low pass filter 3 is connected to the phase detector 2 and to a voltage controlled oscillator 4 which is coupled via a switching circuit 6 to crystal vibrators 5a and Sb for ( oscillation at di~ferent frequencies, i.e. 3.58 MHz and 4.43 MHz, respectively. An automatic phase controller (APC) is defined by a feed back loop containing the phase detector 2, the low pass filter 3 and the VC0 4. Accordingly, the VC0 4 produces a subcarrier signal at a frequency of 3.58 MHz or 4043 MHz depending on the frequency of the burst signal, in a manner that will be described in detail later.
According to the preferred embodiment, the low pass filter 3 comprises a capacitor 9 connected between a hot line, through which the signal transmits, and ground. Also, a series connection of a resistor 11 and a capacitor 10 is conneeted parallel to the capacitor 9. Furthermore, a series connection of a capacitor 12 and a normally-closed switch 13 is connected parallel to the capacitor 10. Normally-closed switch 13 is controlled by a pulse from a pulse generator 15 in a manner that will be described later.
The output of the VC0 4 is applied to a PAL/NTSC
demodulator 33 which produees an R-Y signal or a B-Y signal.
The output of the VC0 4 is also applied to a phase detector 7 whieh also reeeives the output signal from the burst gate circuit 1.
According to a preferred embodiment, the phase detector 7 is eonnected with ~ capacitor 16 which is grounded.
Also, a series connection of a capacitor 17 and a normally-closed switch 18 is connected parallel to the capacitor 16.Normally-closed switch 18 is also controlled by a pulse from the pulse generator 15 in a manner described below.
A channel seleetor 14 is eoupled to the puls~
generator 15. Whenever the broadcasting channel is changed by the channel selector 14, the pulse generator 15 generates a short pulse, such as shown by waveform d in Fig. 3. This short pulse is applied to each of the normally-closed switches 13 and 18 to open them temporarily during the duration of the pulse. When the switch 13 opens, the capacitor 12 is disconnected from the capacitor 10, thereby making tile time constant of the low pass filter 3 short.
Similarly, when the switch 18 opens the time constant of ~z~
( the phase detector 7 is shortened. When the time constant is ( shortened, the retraction operation of the APC loop occurs faster, whereby the subcarrier wave for the newly selected channel can be produced very fast from the VCO. This quick response can be accomplished even when the channel change is effected between two different broadcasting systems having different subcarrier wave frequencies. Accordingly, a stable subcarrier ~ave can be obtained immediately after the change lQ of the channel.
The phase detector 7 is provided to produce a color killer output which is applied to both a band pass amplifier 20 and the flip-flop circuit 8. When th~ VCO 4 is producing a subcarrier signal having a frequency of 3.5~ ~z, the flip-flop 8 generates HIG~ in response to the signal obtained fromthe phase detector 7. Similarly, when the VCO 4 is producing a subcarrier signal having a frequency of 4.43 MHzl the flip-flop 8 generates LOW. The output of the flip-flop 8, such as shown in Fig. 3 at waveform a, is appli~d to an AND gate 22a provided in a detection control circuit 22.
The detection control circuit 22 further includes AND gates 22b and 22c and a pulse generator 22d. One input of the AND gate 22b is connected to a SECAM circuit 26 which produces HIGH when the received television signal is in the SECAM system~ and LOW when it is not, such as indicated in Fig. 3, waveform b. One input of the AND gate 22c is connected to a PAL/NTSC detector 27 which produces HIGH when the received television signal is in the NTSC system and LOW
when it is in either the PAL system or the SECAM system, such as indicated in Fig. 3, waveform c. The other inputs of AND
gates 22a, 22b and 22c are connected to the pulse generator 22d. The pulse generator 22d has its input connected to an OR gate 22e having two inputs. One input of the OR gate 22e - is connected to the pulse generator 15 and the other input thereof is connected to a television signal detector 28.
Details of the pulse generator 22d will be described later.
The television signal detector 28 has two inputs:
one for receiving the horizontal pulse; and the other for receiving the sync-pulse. Accordingly, ~henever a television signal, which may be obtained through an antenna (not shown), cable (not shown), or from a video tape, is being received, the television signal detector 28 generates a HIGH output, such as shown in Fig. 3 at waveform e. The television signal detector 28 produces LOW while the channel is being changed.
From this viewpoint, the signal produced from the television signal detector 28 is similar to the signal produced from the pulse generator 15, except that these two signals are in opposite phase~ Furthermore, the signal from the television signal detector 28 has the feature that, when a video tape is being reproduced, the channel change recorded in the tape can also be detected. Therefore, whenever there is a channel change in the reproduced video tape, no pulse will be produced from the pulse generator 15, but a pulse will be produced from the television signal detector 28.
Accordingly, the OR gate 22e produces a signal not only when the channel is actually changed, but also when a channel change recorded in a video tape is detected.
As indicated in Fig. 3, waveform f, the pulse generator 22d detects a step up of the waveform d or a step up of the waveform e, and produces a one-shot pulse having a pulse duration of t or t'. The AND gates 22a, 22b and 22c are enabled only when a one-shot pulse is present, that is a short period of time immediately after the channel change is effected, which may be an actual channel change or a channel change recorded in a video tape.
The AND gates 22a, 22b and 22c are connected to a hold circuit 23 which is coupled to a reset circuit 25. The reset circuit Z5 receives the signal from the television signal detector 28 and produces a reset signal when the channel is changed. Accordingly, when a new channel is selected, the output signal from the AND gate 22a is h~ld in the hold circuit 23, and is produced from the output terminal 24A of the hold circuit 23. Similarly, the output signal ~rom the AND gate 2Zb is held and produced from the output terminal 24B, and the output signal from the AND gate 22c is held and ~a62æ3~:~
produced from the output terminal 24C. Once the hold circuit holds various data from the AND gates 22a, 22b and 22c ( immediately after the channel selection, this data is main-tained as long as the selected channel is on.
Output terminal 24A, carrying data of the subcarrier frequency, is connected to the switching circuit 6 for selecting either one of the crystal vibrators 5a and 5b, and also to the band pass filter 19, video trap 32 and sound trap 30.
Output terminal 24B, carrying data representing the SECAM system, is connected to the SECAM circuit 26 for rlain-taining the SECA~1 circuit operative while the received tele-vision signal is in the SECAM system.
Output terminal 24C, carrying data representing the PAL system or the NTSC system, is connected to the PAL/NTSC
demodulator 33 for actuating the demodulator 33. When the received television signal is in the PAL system, the output terminal 24C will produce LOW, thereby setting the demodulator 33 as a PAL demodulator. On the other hand, when the received television signal is in the NTSC system, the output terminal 24C will produce HIGH, thereby setting the demodulator 33 as an NTSC demodulator.
The operation of the circuit of Fig. 2 will now be described. This circuit is operable with five different broadcasking systems, namely: the PAL system with a 3.58 M~Iz subcarrier wave; the PAL system with a 4.43 MHz subcarrier wave; the NTSC syste~ with a 3.58 MHz subcarrier wave; the NTSC system with a 4.43 MHz subcarrier wave; and the SECAM
system with 4.43 MHz.
It is assumed that the channel selector 14 is actuated to select a television signal of the NTSC system with the 3.58 ~z subcarrier wave. When the channel selector 14 is actuated, the pulse generator 15 produces a pulse (first pulse in waveform d) which affects the pulse generator 22d to produce a one-shot pulse tfirSt pulse in waveform f). While the one-shot pulse is pxesent, the flip-flop 8 produces HIGH
indicating that the subcarrier wave has a frequency of 3.58MHz.
Also, the SECAM circuit 26 produces LOW indicating that the received television signal is not in the SECA~I system, and the PAL/NTSC detector 27 produces HIGH indicating that the ( received television signal is in the NTSC system.
Accordingly, when the one-shot pulse (first pulse in waveform f) is produced from the pulse generator 22d, each of the AND gates 22a and 22c produces HIGH (waveforms g and i), and the AND gate 22b produces no pulse (waveform h). The signals from AND gates 22a, 22b and 22c are produced in response to the one-shot pulse, and are held in the holding circuit 23 which accordingly produces HIGH, LOW and HIGH, respectively, from its output terminals 24A, 24B and 24C. These signals from output terminals 24A, 24B, and 24C are maintained until the reset circuit produces a reset signal, that is until the next channel change.
The HIGH from output terminal 24A is applied to the switching circuit 6 for selecting the crystal vibrator 5a for oscillation at the frequency of 3.58 MXz. The HIG~ from output terminal 24A is also applied to the band pass filter 19 for selecting a band appropriate for the 3.58 MHz subcarrier wave, and further to the video trap 32 and to the sound trap 30.
The LOW from output terminal 24B is applied to the SEC~M circuit 26 to disable it.
The HIGH from output terminal 24C is applied to the PAL/NTSC demodulator 33 to set it as a NTSC demodulator.
Since the data representing the system of the tele-vision signal and the data representing the frequency o~ the subcarrier wave are applied to the hold circuit 23 only when the AND gates 22a, 22b and 22c are enabled, that is a short period of time iINmediately after the change of channel, any undesirable change or fluctuation in these data will not be transmitted to the hold circuit 23 and to various other circuits, such as the switching circuit 6. Accordingly, once the hold circuit 23 holds the data of the received television signal at the beginning of the channel selection, such data will not be changed, even if the television signal fluctuates or noise appears in the signal. Accordingly, the television receiver not only automatically sets the circuit in a condition suitable for the system of the received signal, but also maintains this ~2~æ~
set condition as long as the channel is maintained the same.
When a channel change is effected by the channel selector 14, ( or when a ch ~ el change signal recorded in a video tape is reproduced, new data will be set and held in the hold circuit S 23.
Signals produced from the output terminals 24A, 24B
and 24C for television signals received in different systems are shown in the Table below.
Received Television Signal 24A 24B 24C
10 PAL 3.58 MHz subcarrier LOW LOW LOW
PAL 4.43 MHz subcarrier HIGH LOW LOW
NTSC 3.58 MHz subcarrier LOW LOW HIGH
NTSC 4.43 MHz subcarrier HIGH LOW HIGH
SECAM 4.43 MHz subcarrier LOW HI~H LOW
According to the embodiment shown in Fig. 2, the detection control circuit 22 employs A~D gates 22a, 22b and 22c, but these AND gates can be replaced by other logic gates, such as NOR gates, when the pulses applied to the gates are in negative form.
Referring to Fig. 4, a modification of a subcarrier generation circuit according to the present invention is shown.
The output of the flip-flop 8 is connected to an OR gate 34 which also receives a signal from a SECAM killer 35 in a SECAM circuit. The output of the OR gate 34 is connected to the switching circuit 6. Operation of this circuit is as ~ollows.
When a television signal of the NTSC system is received, the flip-Xlop 8 produces HIGH in the manner described above. This HIGH is applied through the OR gate 34 to the switching circuit 6 to cause oscillation at 3.58 MHz by the crystal vibrator 5a. Accordingly, the APC loop synchronizes at the frequency of 3.58 MHz and the VCO therefore generates a suhcarrier wave at 3.58 MHz.
When a television signal of the PAL system is received, the flip-flop 8 produces LOW in the manner described above. This LOW is applied through the OR gate 34 to the switching circuit 6 to cause oscillation at 4.43 MHz by the crystal vibrator Sb. ~ccordingly, the APC loop synchronizes at the frequency 4.43 ~ and the VCO therefore generates a subcarrier wave at 4.43 MHz.
( When a television signal of the SECAM system is received, the SECAM KILLER 35 for the SECAM color killer produces HIGH. Therefore, regardless of the signal from the flip-flop 8, the OR gate 34 produces HIGH. Accordingly, the switching circuit 6 is so turned as to oscill~ate at 3.58 MHz.
In this case, a subcarrier wave component at the frequency of 4.25 MHz or 4.406 MHz contained in the chrominance signal can be applied to the phase detector 2. Since such frequencies are much different from 3.58 MHz, the VCO 4 generates the sub-carrier wave at 3.58 MHz without making any retraction operation by the APC lo~p.
In this case, the color killer output produced from the phase detector 7 can beused for disabling a color processing circuit for the NTSC/PAL system and for enabling a color processing circuit for the SECAM system.
Referring to Fig. 5, a circuit diagram of a low pass filter is shown. According to the low pass filtar 3 shown in Fig. 2, a series connection of capacitor 12 and normally-close switch 13 is connected in parallel with the capacitor 10 to shorten the time constant when the switch 13 opens.
According to the modification shown in Fig. 5, a series connection of a resistor 36 and a normally-open switch 13' is connected parallel to the capacitor 10. Accordinyly, when a channel change i5 effected, the switch 13' closes to shorten the time constant. Accordingly, the low pass filter 3 shown in Fig. 2 can be replaced by the low pass filter 3 shown in Fig. 5.
Although the present invention has been fully described with reference to a preferred embodiment, many modifications and variations thereof will now be apparent to those skilled in the art, and the scope of the present invention is therefore to be limited not by the details of the preferred embodiment described above, but only by the terms of the appended claims.
Claims (2)
1. A multi-system television receiver capable of receiving television signals of a plurality of different broadcasting systems with a plurality of different subcarrier wave frequencies comprising:
frequency detecting means for detecting the frequency of a subcarrier wave of the received television signal and producing frequency data representing the detected frequency;
system detecting means for detecting the system of the television signal and producing system data representing the detected system;
channel change detecting means for detecting the changing of a TV channel of said receiver;
holding means for holding said frequency data and system data upon said changing of the channel detected by said detecting means; and television receiver circuits set in a condition in compliance with the broadcast system of said received television signal as determined by said frequency data and said system data.
frequency detecting means for detecting the frequency of a subcarrier wave of the received television signal and producing frequency data representing the detected frequency;
system detecting means for detecting the system of the television signal and producing system data representing the detected system;
channel change detecting means for detecting the changing of a TV channel of said receiver;
holding means for holding said frequency data and system data upon said changing of the channel detected by said detecting means; and television receiver circuits set in a condition in compliance with the broadcast system of said received television signal as determined by said frequency data and said system data.
2. A multi-system television receiver as claimed in claim 1, wherein said frequency detecting means comprises a phase detector and an oscillator, said phase detector detecting a phase difference between a burst signal of the received television signal and a subcarrier signal produced from said oscillator, and producing an output signal corresponding thereto, and a flip-flop connected to said phase detector and responsive to said output signal for producing said frequency data.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000581789A CA1262281A (en) | 1984-05-23 | 1988-10-31 | Multi-system television receiver |
Applications Claiming Priority (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP75991/1984 | 1984-05-23 | ||
| JP1984075991U JPS60189187U (en) | 1984-05-23 | 1984-05-23 | Subcarrier automatic switching circuit |
| JP81275/1984 | 1984-05-30 | ||
| JP8127584U JPS60192578U (en) | 1984-05-30 | 1984-05-30 | Subcarrier automatic switching circuit |
| JP17199384U JPS6188378U (en) | 1984-11-13 | 1984-11-13 | |
| JP171993/84 | 1984-11-13 | ||
| CA000482033A CA1252880A (en) | 1984-05-23 | 1985-05-22 | Multi-system television receiver |
| CA000581789A CA1262281A (en) | 1984-05-23 | 1988-10-31 | Multi-system television receiver |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000482033A Division CA1252880A (en) | 1984-05-23 | 1985-05-22 | Multi-system television receiver |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1262281A true CA1262281A (en) | 1989-10-10 |
Family
ID=27426414
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000581789A Expired CA1262281A (en) | 1984-05-23 | 1988-10-31 | Multi-system television receiver |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1262281A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117156084B (en) * | 2023-10-30 | 2024-01-09 | 中孚安全技术有限公司 | System identification and restoration method for television signals |
-
1988
- 1988-10-31 CA CA000581789A patent/CA1262281A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117156084B (en) * | 2023-10-30 | 2024-01-09 | 中孚安全技术有限公司 | System identification and restoration method for television signals |
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