CA1275707C - Descrambling apparatus which produces a descrambling control pulse - Google Patents
Descrambling apparatus which produces a descrambling control pulseInfo
- Publication number
- CA1275707C CA1275707C CA000531147A CA531147A CA1275707C CA 1275707 C CA1275707 C CA 1275707C CA 000531147 A CA000531147 A CA 000531147A CA 531147 A CA531147 A CA 531147A CA 1275707 C CA1275707 C CA 1275707C
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- Prior art keywords
- pulse
- signal
- output signal
- detector
- descrambling
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- 230000000630 rising effect Effects 0.000 claims abstract description 9
- 239000003990 capacitor Substances 0.000 claims description 6
- 238000005070 sampling Methods 0.000 abstract 1
- 238000010586 diagram Methods 0.000 description 9
- 230000005236 sound signal Effects 0.000 description 4
- 238000006073 displacement reaction Methods 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 230000001360 synchronised effect Effects 0.000 description 2
- 230000007812 deficiency Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
- 101150112420 lnpka gene Proteins 0.000 description 1
- 239000003381 stabilizer Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K5/00—Manipulating of pulses not covered by one of the other main groups of this subclass
- H03K5/01—Shaping pulses
- H03K5/08—Shaping pulses by limiting; by thresholding; by slicing, i.e. combined limiting and thresholding
- H03K5/082—Shaping pulses by limiting; by thresholding; by slicing, i.e. combined limiting and thresholding with an adaptive threshold
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/167—Systems rendering the television signal unintelligible and subsequently intelligible
- H04N7/171—Systems operating in the amplitude domain of the television signal
- H04N7/1713—Systems operating in the amplitude domain of the television signal by modifying synchronisation signals
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- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Television Signal Processing For Recording (AREA)
- Manipulation Of Pulses (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE Disclosed is a pulse generating apparatus used in a CATV receiving adapter for descrambling the sync signal in the video signal. The pulse generating apparatus comprises a peak detector for sampling the peak in the detected video signal, a half level detector for evaluating the half level of the detected peak voltage, and a pulse generator which compares the detected video signal with the half level voltage and produces a pulse rising at a time point of coincidence of the two voltage signals.
Description
57()7 This invention relates to a pulse generating apparatus and more particularly to a pulse generating apparatus for gener-ating pulses used to descramble a scrambled video signal in a cable television system for example.
The present invention will be illustrated by way of the arcompanying drawings, in which:-Fig. 1 is a schematic block diagram showing the10 descrambling circuit embodying the present invention;
Fig. 2 iS a schematic block diagram showing the appli-cation of this invention to a cable television receiver set;
Fig. 3 is a schematic block diagram of the set-top ter-minal unit shown in Fig. 2;
ig. 4 is a schematic block diagram showing the pulse generating circuit in the set-top terminal unit;
Fig. 5 is a set of waveform diagrams used to explain the operation of the pulse generating circuit;
Fig. 6A is a graph comparing the characteristics of the inventive pulse generator with the conventional one;
Fig. 6B iS a set of wave form diagrams showing the scrambled and descrambled video signals;
Fig. 7 is a block diagram of the conventional pulse generating apparatus; and Fig. 8 is a set of waveform diagrams used to explain the operation of the conventional pulse generating apparatus.
Cable television ~CATV) is a toll broadcasting service 57~)7 and only subscribers can v~ew its programs. The CATV video sig-nal has its sync signal portlon scrambled so as to preclude non-subscribers from viewing the programs, and subscriber's CATV
receiver sets are equipped with a device for descrambling the scrambled sync signal.
A conventional descrambling circuit will be described with reference to Fig. 7. The block diagram in Fig. 7 shows only the pulse generating apparatus which produces pulses for descram-bling the scrambled sync signal, and the input signal 1 is an AMaudio signal in the television signal. In this conventional sys-tem, the audio slgnal is amplitude modulated by a signal used for descrambling the video signal, and the descrambling signal is detected from the amplitude modulated (AM) audio signal. The descrambling signal is added to the video signal so that the scrambled sync signal is descrambled, and then - la -: .
~75~(~7 1 the video signal is made nvrmally visible by an ordinary TV set. In Fig. 7, symbol 1 denotes an P~l signal input, 2 is an A~ detector, 3 is an ~I detector output, 4 is an integrator, 5 is a reference voltage, 6 is a threshold Co IrllJa f~to~ f~nd voltage, 7 is aArectangular pulse generator which compares the AM detector output with the threshold voltage, and is a rectan~ular pulse output which is delivered to the video signal processing portion of the CATV receiver to descramble the scrambled video signal.
The AM signal input 1 is detected by the AM
detector 2, and the resulting AM detector output 3 is fed to one input of the pulse generator 7. The ~r~
detector output 3 is separately integrated by the integrator 4, which output is added by the reference voltage S to form the threshold voltage 6, and it is fed to another input of the pulse generator 7. The pulse generator 7 produces a rectangular pulse when the voltaye of the 2~1 detector output 3 is higher than the threshold voltage 6. Tne integrator 4 provides an average voltage of the AM detector output 3 to shift the threshold voltage 6, thereby compen-sating the fluctuation of the rise timing of rectangular pulses caused by a change in the level of the AM signal input l due to transmission conditions or the like.
In the foregoing conventional circuit arrangement, the fluctuation of the AM signal peak level is followed by the d.c. level of the integrator output. Therefore, the displacement of the pulse rise timing of the rectangular pulse can be corrected. However, in case the AM modulation 7~7 1 deptn differs among transmitters due to their accuracy or the li~e, only the peak level of the AM detector output varies differently on each transmission channelJ with the d.c. output voltage level of the integrator 4 being unchanged, and therefore the displacement of the pulse rise timing cannot be corrected. A significant timing displace-ment causes the video signal portion to receive the rectangular pulse output at an erroneous timing, and such inaccurate descrambling operation cannot reproduce well-synchronized pictures. The matter will further be describedin connection with Fig. 8.
Fig. 8(a) is the case of the standard ~MI modula-tion depth. For the standard AM modulation depth to have a peak-to-bottom voltage ratio (between the portions lA
and lB) of 6 d~ for example, the reference voltage is determined so that rectangular pulses are produced at a deno~es 50~ AM detector output. In the figure, symbol lC dontc~
the threshold voltage, lD is the AM detector output, and lE is the rectangular pulse.
Fig. 8tb) is the case of a greater modulation depth than standard, showing that the threshold voltage does not follow the varying AM modulation depth, and the rectangular pulses are generated at the AM detector output below 50%, resulting in a leading pulse rise timing as compared with the case of Fig. 8(a).
Fig. 8(c) is the case of a smaller modulation depth than standard, showing the generation of the rectangu-lar pulses at the AM detector output above S0~, resulting 12~S7~)7 in a lagging pulse rise timing as compared with the case of Fig.
8(a).
The cases of Figs. 8(b) and ~(c) fail to achieve the accurate descrambling and do not reproduce correct, synchronized pictures.
The present invention overcomes the foregoing prior art deficiencies and provide a pulse generating apparatus which generates pulses always at a constant timing of rising edge, even if the modulated signal input has a fluctuating modulation depth, so that the circuit receiving the pulses operates stably.
The pulse generating apparatus of the present invention comprises a peak detector which detects the peak voltage in a periodical input signal, a half level detector which detects the half level of the peak voltage, and a pulse generatGr which generates a rising pulse in response to the coincidence of the input signal with the half level. The pulse generator produces pulses always at a 50% input signal level as a threshold level, and therefore always at a constant timing even if the modulated input signal level or its modulation depth fluctuates, whereby a circuit receiving the pulses can operate stably. The invariable 50%
input threshold level also minimizes the influence of noises created by low-voltage and high-voltage circuit portions, and this is effective for the stable operation of the apparatus in constant timing.
~,....
1~7~707 Tnus, according to one aspect thereof the present invention provldes a descrambling apparatus for descrambling a scrambled signal having a signal component amplitude modulated with descrambling information, said descrambling apparatus com-prising an amplitude modulation detector for detecting the ampli-tude modulation of said signal component; a peak detector ~or peak detecting an output signal of said amplitude modulation detector; a half level detector for detecting a half level of an output signal o~ said peak detector; a comparator and pulse gen-erator recelving said output signal of said amplitude modulatorand an output signal of said half level detector and producing a pulse output signal rising at a time point of coincidence of said output signal of said amplitude modulation detector and said out-put signal of said half level detector; a mute circuit for muting the pulse output signal of said comparator and pulse generator, one input of said mute circuit being connected to the output of said peak detector and another input of said mute circuit being connec,ted to a reference voltage, said mute circuit cutting off the pulse output of said comparator and pulse generator when a non-scrambled signal is indicated by the output of said peak detector; and mPans responsive to the pulse output signal of said pulse generator for descrambling an applied scrambled signal.
Suitably the apparatus ~urther comprises a pulse width adjuster for adjusting the width of the pulse output signal of said pulse generator. Desirably said descrambling means ad~usts the level of a scrambled sync signal in a video signal in accordance with the pulse output signal of said pulse generator. Preferably the apparatus further comprises a pulse width adjuster for adjusting the width of the pulse output signal of said pulse generator.
In another aspect thereof the present invention pro-vides a descrambling apparatus for descrambling a scrambled sig-nal having a signal component amplitude modulated with descram-bling information, said descrambling apparatus comprising an amplitude modulation detector for detecting the amplitude modula-tion of said signal component; a peak detector for peak detecting ..
."~ -' ~
~ 57~7 an output signal of said amplitude modulation detector, said peak detector being formed by the parallel connection of a capacitor and a resistor; a half level detector for detecting a half level of an output signal of said peak detector; a comparator and pulse genera$or receiving said output signal of said amplitude modula-tor and an output signal of said half level detector and produc-ing a pulse output signal rising at a time point of coincidence of said output of said amplitude modulation detector and an out-put signal of said half level detector; a mutQ circuit for muting the pulse output signal of said comparator and pulse generator, one input of said mute circuit being connected to the output of said peak detector and another input of said mute circuit being connected to a reference voltage, said mute circuit cutting off the pulse output of said comparator and pulse generator when a non-scrambled signal is indicated by the output of said peak detector; and means responsive to the pulse output signal of said pulse generator for descrambling an applied scrambled signal.
In a still further aspect thereof the invention pro-vides a descrambling apparatus for descrambling a scrambled sig-nal having component amplitude modulated with descrambling infor-mation, said descrambling apparatus comprising an amplitude rnodu-lation detector for detecting the amplitude modulation of said signal component; a peak detector for peak detecting an output signal of said amplitude modulation detector, said peak detector being formed by the parallel connection of a capacltor and a resistor; a half level detector for detecting a half level of an output signal of said peak detector, said half level detector being formed by resistors connected in parallel to said parallel connection of a resistor and capacltor forming sald peak detec-tor; a comparator and pulse generator recelving said output sig-nal of said amplitude modulator and an output signal of said half level detector and producing a pulse output signal rising at a time point of coincidence of said output signal of said amplitude modulation detector and said output signal of said half level detector, said resistors of said half level detector having a - 5a -~75707 node connected to said pulse generator, a mute circuit for muting the pulse output signal of said comparator and pulse generator, one input of said mute circuit being connected to the output of said peak detector and another input of said mute circuit being connected to a reference voltage, said mute circuit cutting off the pulse output of said comparator and pulse generator when a non-scrambled signal is indicated by the output of said peak detector; and means responsive to the pulse output signal of said pulse generator for descrambling an applied scrambled signal.
An embodiment of this invention will now be described.
It is assumed that the CATV video signal has its sync signal scrambled, and a signal for descrambling the sync signal is amplitude modulated to the audio signal.
In Fig. 2 a CATV station 10 has facillties for - 5b -''':: ~' ' 5~7~7 1 channels from channel-1 (11~ to channel-82 (12). Among the channels, channel-l is used exclusively for converting an ordinary TV radio signal into a CATV signal. In this case, the radio signal is received by an antenna 13 and demodulated by a demodulator 14. The video signal and audio signal are modulated into a CATV signal by a modulator 15, mixed with signals on other channels by a mixer lOA, amplified by an amplifier 16, and distributed through a distributer 17 to subscribers. The CATV signal is fed through a subscriber's set-top terminal unit 18 to a television receiver set 19, on which the picture and sound are reproduced. The channel-l (11) alloted to the ordinary T~ programs is not tolled, and therefore the sync signal in the video signal is not scrambled. The remaining channels from channel-2 to channel-82 (12', 12", ..., 12) are original broadcastings by the CATV station 10, and they are offered only to the subscribers. In this case, a radio signal from a program producing station is received through an antenna 21 and satellite broadcasting receiver 22, and signals are also supplied from a video tape recorder 12' and a studio 12". In each modulator 23 for these signals, the sync signal in the ~ideo signal .is scrambled using a signal produced by a scrambler 2~, and the audio signal is modulated in AM mode by the modulator 23 using a signal for reproducing the scrambled sync signal. The modulated signal is mlxed ~ith signals of other channels by the mixer lOA, amplified by the amplifier 16, and distribut-ed through the distributer 17 to subscribers. The CATV
'71)~7 1 signal is fed through the subscriber's set-top terminal unit 18 to the television receiver set 19, on which the picture and sound are repxoduced.
Next, the internal arrangement of the set-top terminal unit 18 will be described with reference to Fig.
The present invention will be illustrated by way of the arcompanying drawings, in which:-Fig. 1 is a schematic block diagram showing the10 descrambling circuit embodying the present invention;
Fig. 2 iS a schematic block diagram showing the appli-cation of this invention to a cable television receiver set;
Fig. 3 is a schematic block diagram of the set-top ter-minal unit shown in Fig. 2;
ig. 4 is a schematic block diagram showing the pulse generating circuit in the set-top terminal unit;
Fig. 5 is a set of waveform diagrams used to explain the operation of the pulse generating circuit;
Fig. 6A is a graph comparing the characteristics of the inventive pulse generator with the conventional one;
Fig. 6B iS a set of wave form diagrams showing the scrambled and descrambled video signals;
Fig. 7 is a block diagram of the conventional pulse generating apparatus; and Fig. 8 is a set of waveform diagrams used to explain the operation of the conventional pulse generating apparatus.
Cable television ~CATV) is a toll broadcasting service 57~)7 and only subscribers can v~ew its programs. The CATV video sig-nal has its sync signal portlon scrambled so as to preclude non-subscribers from viewing the programs, and subscriber's CATV
receiver sets are equipped with a device for descrambling the scrambled sync signal.
A conventional descrambling circuit will be described with reference to Fig. 7. The block diagram in Fig. 7 shows only the pulse generating apparatus which produces pulses for descram-bling the scrambled sync signal, and the input signal 1 is an AMaudio signal in the television signal. In this conventional sys-tem, the audio slgnal is amplitude modulated by a signal used for descrambling the video signal, and the descrambling signal is detected from the amplitude modulated (AM) audio signal. The descrambling signal is added to the video signal so that the scrambled sync signal is descrambled, and then - la -: .
~75~(~7 1 the video signal is made nvrmally visible by an ordinary TV set. In Fig. 7, symbol 1 denotes an P~l signal input, 2 is an A~ detector, 3 is an ~I detector output, 4 is an integrator, 5 is a reference voltage, 6 is a threshold Co IrllJa f~to~ f~nd voltage, 7 is aArectangular pulse generator which compares the AM detector output with the threshold voltage, and is a rectan~ular pulse output which is delivered to the video signal processing portion of the CATV receiver to descramble the scrambled video signal.
The AM signal input 1 is detected by the AM
detector 2, and the resulting AM detector output 3 is fed to one input of the pulse generator 7. The ~r~
detector output 3 is separately integrated by the integrator 4, which output is added by the reference voltage S to form the threshold voltage 6, and it is fed to another input of the pulse generator 7. The pulse generator 7 produces a rectangular pulse when the voltaye of the 2~1 detector output 3 is higher than the threshold voltage 6. Tne integrator 4 provides an average voltage of the AM detector output 3 to shift the threshold voltage 6, thereby compen-sating the fluctuation of the rise timing of rectangular pulses caused by a change in the level of the AM signal input l due to transmission conditions or the like.
In the foregoing conventional circuit arrangement, the fluctuation of the AM signal peak level is followed by the d.c. level of the integrator output. Therefore, the displacement of the pulse rise timing of the rectangular pulse can be corrected. However, in case the AM modulation 7~7 1 deptn differs among transmitters due to their accuracy or the li~e, only the peak level of the AM detector output varies differently on each transmission channelJ with the d.c. output voltage level of the integrator 4 being unchanged, and therefore the displacement of the pulse rise timing cannot be corrected. A significant timing displace-ment causes the video signal portion to receive the rectangular pulse output at an erroneous timing, and such inaccurate descrambling operation cannot reproduce well-synchronized pictures. The matter will further be describedin connection with Fig. 8.
Fig. 8(a) is the case of the standard ~MI modula-tion depth. For the standard AM modulation depth to have a peak-to-bottom voltage ratio (between the portions lA
and lB) of 6 d~ for example, the reference voltage is determined so that rectangular pulses are produced at a deno~es 50~ AM detector output. In the figure, symbol lC dontc~
the threshold voltage, lD is the AM detector output, and lE is the rectangular pulse.
Fig. 8tb) is the case of a greater modulation depth than standard, showing that the threshold voltage does not follow the varying AM modulation depth, and the rectangular pulses are generated at the AM detector output below 50%, resulting in a leading pulse rise timing as compared with the case of Fig. 8(a).
Fig. 8(c) is the case of a smaller modulation depth than standard, showing the generation of the rectangu-lar pulses at the AM detector output above S0~, resulting 12~S7~)7 in a lagging pulse rise timing as compared with the case of Fig.
8(a).
The cases of Figs. 8(b) and ~(c) fail to achieve the accurate descrambling and do not reproduce correct, synchronized pictures.
The present invention overcomes the foregoing prior art deficiencies and provide a pulse generating apparatus which generates pulses always at a constant timing of rising edge, even if the modulated signal input has a fluctuating modulation depth, so that the circuit receiving the pulses operates stably.
The pulse generating apparatus of the present invention comprises a peak detector which detects the peak voltage in a periodical input signal, a half level detector which detects the half level of the peak voltage, and a pulse generatGr which generates a rising pulse in response to the coincidence of the input signal with the half level. The pulse generator produces pulses always at a 50% input signal level as a threshold level, and therefore always at a constant timing even if the modulated input signal level or its modulation depth fluctuates, whereby a circuit receiving the pulses can operate stably. The invariable 50%
input threshold level also minimizes the influence of noises created by low-voltage and high-voltage circuit portions, and this is effective for the stable operation of the apparatus in constant timing.
~,....
1~7~707 Tnus, according to one aspect thereof the present invention provldes a descrambling apparatus for descrambling a scrambled signal having a signal component amplitude modulated with descrambling information, said descrambling apparatus com-prising an amplitude modulation detector for detecting the ampli-tude modulation of said signal component; a peak detector ~or peak detecting an output signal of said amplitude modulation detector; a half level detector for detecting a half level of an output signal o~ said peak detector; a comparator and pulse gen-erator recelving said output signal of said amplitude modulatorand an output signal of said half level detector and producing a pulse output signal rising at a time point of coincidence of said output signal of said amplitude modulation detector and said out-put signal of said half level detector; a mute circuit for muting the pulse output signal of said comparator and pulse generator, one input of said mute circuit being connected to the output of said peak detector and another input of said mute circuit being connec,ted to a reference voltage, said mute circuit cutting off the pulse output of said comparator and pulse generator when a non-scrambled signal is indicated by the output of said peak detector; and mPans responsive to the pulse output signal of said pulse generator for descrambling an applied scrambled signal.
Suitably the apparatus ~urther comprises a pulse width adjuster for adjusting the width of the pulse output signal of said pulse generator. Desirably said descrambling means ad~usts the level of a scrambled sync signal in a video signal in accordance with the pulse output signal of said pulse generator. Preferably the apparatus further comprises a pulse width adjuster for adjusting the width of the pulse output signal of said pulse generator.
In another aspect thereof the present invention pro-vides a descrambling apparatus for descrambling a scrambled sig-nal having a signal component amplitude modulated with descram-bling information, said descrambling apparatus comprising an amplitude modulation detector for detecting the amplitude modula-tion of said signal component; a peak detector for peak detecting ..
."~ -' ~
~ 57~7 an output signal of said amplitude modulation detector, said peak detector being formed by the parallel connection of a capacitor and a resistor; a half level detector for detecting a half level of an output signal of said peak detector; a comparator and pulse genera$or receiving said output signal of said amplitude modula-tor and an output signal of said half level detector and produc-ing a pulse output signal rising at a time point of coincidence of said output of said amplitude modulation detector and an out-put signal of said half level detector; a mutQ circuit for muting the pulse output signal of said comparator and pulse generator, one input of said mute circuit being connected to the output of said peak detector and another input of said mute circuit being connected to a reference voltage, said mute circuit cutting off the pulse output of said comparator and pulse generator when a non-scrambled signal is indicated by the output of said peak detector; and means responsive to the pulse output signal of said pulse generator for descrambling an applied scrambled signal.
In a still further aspect thereof the invention pro-vides a descrambling apparatus for descrambling a scrambled sig-nal having component amplitude modulated with descrambling infor-mation, said descrambling apparatus comprising an amplitude rnodu-lation detector for detecting the amplitude modulation of said signal component; a peak detector for peak detecting an output signal of said amplitude modulation detector, said peak detector being formed by the parallel connection of a capacltor and a resistor; a half level detector for detecting a half level of an output signal of said peak detector, said half level detector being formed by resistors connected in parallel to said parallel connection of a resistor and capacltor forming sald peak detec-tor; a comparator and pulse generator recelving said output sig-nal of said amplitude modulator and an output signal of said half level detector and producing a pulse output signal rising at a time point of coincidence of said output signal of said amplitude modulation detector and said output signal of said half level detector, said resistors of said half level detector having a - 5a -~75707 node connected to said pulse generator, a mute circuit for muting the pulse output signal of said comparator and pulse generator, one input of said mute circuit being connected to the output of said peak detector and another input of said mute circuit being connected to a reference voltage, said mute circuit cutting off the pulse output of said comparator and pulse generator when a non-scrambled signal is indicated by the output of said peak detector; and means responsive to the pulse output signal of said pulse generator for descrambling an applied scrambled signal.
An embodiment of this invention will now be described.
It is assumed that the CATV video signal has its sync signal scrambled, and a signal for descrambling the sync signal is amplitude modulated to the audio signal.
In Fig. 2 a CATV station 10 has facillties for - 5b -''':: ~' ' 5~7~7 1 channels from channel-1 (11~ to channel-82 (12). Among the channels, channel-l is used exclusively for converting an ordinary TV radio signal into a CATV signal. In this case, the radio signal is received by an antenna 13 and demodulated by a demodulator 14. The video signal and audio signal are modulated into a CATV signal by a modulator 15, mixed with signals on other channels by a mixer lOA, amplified by an amplifier 16, and distributed through a distributer 17 to subscribers. The CATV signal is fed through a subscriber's set-top terminal unit 18 to a television receiver set 19, on which the picture and sound are reproduced. The channel-l (11) alloted to the ordinary T~ programs is not tolled, and therefore the sync signal in the video signal is not scrambled. The remaining channels from channel-2 to channel-82 (12', 12", ..., 12) are original broadcastings by the CATV station 10, and they are offered only to the subscribers. In this case, a radio signal from a program producing station is received through an antenna 21 and satellite broadcasting receiver 22, and signals are also supplied from a video tape recorder 12' and a studio 12". In each modulator 23 for these signals, the sync signal in the ~ideo signal .is scrambled using a signal produced by a scrambler 2~, and the audio signal is modulated in AM mode by the modulator 23 using a signal for reproducing the scrambled sync signal. The modulated signal is mlxed ~ith signals of other channels by the mixer lOA, amplified by the amplifier 16, and distribut-ed through the distributer 17 to subscribers. The CATV
'71)~7 1 signal is fed through the subscriber's set-top terminal unit 18 to the television receiver set 19, on which the picture and sound are repxoduced.
Next, the internal arrangement of the set-top terminal unit 18 will be described with reference to Fig.
3. The signal from the distributer 17 is selected in a tuner 25 to extract only a channel specified through a remote control photosensor 26 or keyboard 27. The video signal with the scrambled sync signal is reproduced correctly by a descrambler 28 and fed to the television receiver set 19, on which the picture and sound are reproduced. In this case, implementation of descrambling the sync signal is dependent on as to whether the pertinent channel has been set in a memory 29 at the subscripti.on contract. When the channel is allowed by the contract, the channel allowance information is set to the memory 29 by way of an address receiver 30, decoder 31 and CPU 32, and based on the information the tuner 25 is operated through a PLL 33 to select the station and, at the same time, the CPU 32 issues a command for reproducing the video signal b~ descrambling the sync signal. Reference number 34 in Fig. 3 denotes a power supply circuit.
The following describes scrambling and descrambllng of the sync signal. In Fig. 6B, a sync signal K protruding downward as shown in (a) is turned upwaxd by scrambling as shown in (b). When the signal is descrambled, the sync signal K protruding downward is restored as shown in (c), allowing correct reproduction ~'~757~?'7 of the sync signal, and censequently well synchronized pictures are reproduced. Symbol L in the waveforms (c) denotes the output of the AM detector 40, and M denotes the output of the comparator and pulse generator 41.
Next, the descrambler 28 will be described with reference to Fig.
1. The scrambled television signal tuned by the tuner 25 is split into two parts at the entry of the descrambler 28. One part is delivered to an RF amplifier 35 which raises the signal amplitude in response to pulses supplied from the outside, while another part is fed through a band-pass filter 36 for band confinement to an amplifier 37, by whlch the signal is amplified, and the video signal is detected by a video detector 38, A band-pass filter 39 extracts only the 4.5 MHz beat from the output signal of the video detector 38, and it is subjected to AM
detection by an AM detector 40. The AM detector output is split into two parts, one being fed to a comparator and pulse generator 41, while the other being fed to a peak detector 42, by which the peak voltage of the output waveform from the AM detector 40 is detected. A half level detector 43 evaluates the half level of the peak voltage, and it is supplied to the comparator and pulse generator 41. The comparator and pulse generator 41 compares the AM detect output with the half level detector output, and produces a pulse when the AM detector output voltage is higher.
The output pulse has its width ad~usted by a pulse width ad~uster 42a to the duration of a compressed sync signal, and it is delivered to the RF amplifier 35. The RF amplifier 35 operates to : - 8 -, . . .
~X~75707 1 raise the signal amplitude only during the period of pulse application, and consequently the scrambled sync signal can be descrambled.
Fig. 5(a3 is the case o~ the standard AM
modulation depth. The threshold voltage 44 is half the output of the peak detector 42 as determined by the half level detector 43, and therefore rectangular pulses are produced at a 50~ level of the output 45 of the AM detector 40.
Fig. 5(b) is the case of a greater modulation depth than standard. The threshold voltage 44a which represents the half level of the peak voltage 45a rises with the rise of the peak voltage 45a, producing rectangular pulses at a 50% level of the ~1 detector output~ and the rise timing of rectangular pulses is identical to the case of the standard modu]ation depth shown in Fig. 5(a).
Fig. 5(c~ is the case of a smaller modulation depth than standard. The threshold voltage 44b falls with the fall in the peak voltage 45b, and the rise timing of rectangular pulses is identical to the case of the standard modulation depth shown in Fig. 5(a). Accordingly, the rise timing of rectarlgular pulses is invariable irrespective of the modulation depth.
Fig. 6A shows in graph the variation in the rise timing according to the conventional pulse qenerating apparatus as indicated by 16 and that of the inventive pulse generating apparatus as indicated by 17. The graph shows that the inventive pulse generating apparatus retains ~L~7S7~37 1 a constant rise timing of rectangular pulses against the variation in the ~ modulation depth.
Fig. 4 shows the arrangement of the peak hold circuit (peak detector) 42 and its periphery. The circuit 42 consists of a diode D and a parallel connection of a capacitor C and resistor Rl connected in parallel to the diode D. The half level detector 43 consists of resistors R2 and R3 connected in parallel to the parallel connection of the capacitor C and resistor Rl, with the node of R2 C~lnpa~*f ~d and R3 being connected to the~pulse generator 41. The AM
detector 40 consists of a limiter amplifier 40a and a multiplier 40b. Reference number 46 denotes a current mirror circuit which produces a reference voltage for a mute circuit 47 which cuts off the pulse output when a non-scrambled channel, e.g., channel-l in this embodiment, is tuned. A constant voltage circuit (voltage stabilizer) 48 is used to stabilize the voltage at the lower end of the resistor R3, and the circuit may be replaced with the ground wirin~.
The following describes scrambling and descrambllng of the sync signal. In Fig. 6B, a sync signal K protruding downward as shown in (a) is turned upwaxd by scrambling as shown in (b). When the signal is descrambled, the sync signal K protruding downward is restored as shown in (c), allowing correct reproduction ~'~757~?'7 of the sync signal, and censequently well synchronized pictures are reproduced. Symbol L in the waveforms (c) denotes the output of the AM detector 40, and M denotes the output of the comparator and pulse generator 41.
Next, the descrambler 28 will be described with reference to Fig.
1. The scrambled television signal tuned by the tuner 25 is split into two parts at the entry of the descrambler 28. One part is delivered to an RF amplifier 35 which raises the signal amplitude in response to pulses supplied from the outside, while another part is fed through a band-pass filter 36 for band confinement to an amplifier 37, by whlch the signal is amplified, and the video signal is detected by a video detector 38, A band-pass filter 39 extracts only the 4.5 MHz beat from the output signal of the video detector 38, and it is subjected to AM
detection by an AM detector 40. The AM detector output is split into two parts, one being fed to a comparator and pulse generator 41, while the other being fed to a peak detector 42, by which the peak voltage of the output waveform from the AM detector 40 is detected. A half level detector 43 evaluates the half level of the peak voltage, and it is supplied to the comparator and pulse generator 41. The comparator and pulse generator 41 compares the AM detect output with the half level detector output, and produces a pulse when the AM detector output voltage is higher.
The output pulse has its width ad~usted by a pulse width ad~uster 42a to the duration of a compressed sync signal, and it is delivered to the RF amplifier 35. The RF amplifier 35 operates to : - 8 -, . . .
~X~75707 1 raise the signal amplitude only during the period of pulse application, and consequently the scrambled sync signal can be descrambled.
Fig. 5(a3 is the case o~ the standard AM
modulation depth. The threshold voltage 44 is half the output of the peak detector 42 as determined by the half level detector 43, and therefore rectangular pulses are produced at a 50~ level of the output 45 of the AM detector 40.
Fig. 5(b) is the case of a greater modulation depth than standard. The threshold voltage 44a which represents the half level of the peak voltage 45a rises with the rise of the peak voltage 45a, producing rectangular pulses at a 50% level of the ~1 detector output~ and the rise timing of rectangular pulses is identical to the case of the standard modu]ation depth shown in Fig. 5(a).
Fig. 5(c~ is the case of a smaller modulation depth than standard. The threshold voltage 44b falls with the fall in the peak voltage 45b, and the rise timing of rectangular pulses is identical to the case of the standard modulation depth shown in Fig. 5(a). Accordingly, the rise timing of rectarlgular pulses is invariable irrespective of the modulation depth.
Fig. 6A shows in graph the variation in the rise timing according to the conventional pulse qenerating apparatus as indicated by 16 and that of the inventive pulse generating apparatus as indicated by 17. The graph shows that the inventive pulse generating apparatus retains ~L~7S7~37 1 a constant rise timing of rectangular pulses against the variation in the ~ modulation depth.
Fig. 4 shows the arrangement of the peak hold circuit (peak detector) 42 and its periphery. The circuit 42 consists of a diode D and a parallel connection of a capacitor C and resistor Rl connected in parallel to the diode D. The half level detector 43 consists of resistors R2 and R3 connected in parallel to the parallel connection of the capacitor C and resistor Rl, with the node of R2 C~lnpa~*f ~d and R3 being connected to the~pulse generator 41. The AM
detector 40 consists of a limiter amplifier 40a and a multiplier 40b. Reference number 46 denotes a current mirror circuit which produces a reference voltage for a mute circuit 47 which cuts off the pulse output when a non-scrambled channel, e.g., channel-l in this embodiment, is tuned. A constant voltage circuit (voltage stabilizer) 48 is used to stabilize the voltage at the lower end of the resistor R3, and the circuit may be replaced with the ground wirin~.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A descrambling apparatus for descrambling a scram-bled signal having a signal component amplitude modulated with descrambling information, said descrambling apparatus comprising an amplitude modulation detector for detecting the amplitude mod-ulation of said signal component; a peak detector for peak detec-ting an output signal of said amplitude modulation detector; a half level detector for detecting a half level of an output sig-nal of said peak detector; a comparator and pulse generator receiving said output signal of said amplitude modulator and an output signal of said half level detector and producing a pulse output signal rising at a time point of coincidence of said out-put signal of said amplitude modulation detector and said output signal of said half level detector; a mute circuit for muting the pulse output signal of said comparator and pulse generator, one input of said mute circuit being connected to the output of said peak detector and another input of said mute circuit being con-nected to a reference voltage, said mute circuit cutting off the pulse output of said comparator and pulse generator when a non-scrambled signal is indicated by the output of said peak detec-tor; and means responsive to the pulse output signal of said pulse generator for descrambling an applied scrambled signal.
2. A descrambling apparatus according to claim 1, fur-ther comprising a pulse width adjuster for adjusting the width of the pulse output signal of said pulse generator.
3. A descrambling apparatus according to claim 1, wherein said descrambling means adjusts the level of a scrambled sync signal in a video signal in accordance with the pulse output signal of said pulse generator.
4. A pulse generating apparatus according to claim 3, further comprising a pulse width adjuster for adjusting the width of the pulse output signal of said pulse generator.
5. A descrambling apparatus for descrambling a scram-bled signal having a signal component amplitude modulated with descrambling information, said descrambling apparatus comprising an amplitude modulation detector for detecting the amplitude mod-ulation of said signal component; a peak detector for peak detec-ting an output signal of said amplitude modulation detector, said peak detector being formed by the parallel connection of a capac-itor and a resistor; a half level detector for detecting a half level of an output signal of said peak detector; a comparator and pulse generator receiving said output signal of said amplitude modulator and an output signal of said half level detector and producing a pulse output signal rising at a time point of coinci-dence of said output of said amplitude modulation detector and an output signal of said half level detector; a mute circuit for muting the pulse output signal of said comparator and pulse gen-erator, one input of said mute circuit being connected to the output of said peak detector and another input of said mute cir-cuit being connected to a reference voltage, said mute circuit cutting off the pulse output of said comparator and pulse genera-tor when a non-scrambled signal is indicated by the output of said peak detector; and means responsive to the pulse output sig-nal of said pulse generator for descrambling an applied scrambled signal.
6. A descrambling apparatus according to claim 5, fur-ther comprising a pulse width adjuster for adjusting the width of the pulse output signal of said pulse generator.
7. A descrambling apparatus according to claim 5, wherein said descrambling means adjusts the level of a scrambled sync signal in a video signal in accordance with the pulse output signal of said pulse generator.
8. A pulse generator apparatus according to claim 7, further comprising a pulse width adjuster for adjusting the width of the pulse output signal of said pulse generator.
9. A descrambling apparatus for descrambling a scram-bled signal having component amplitude modulated with descram-bling information, said descrambling apparatus comprising an amplitude modulation detector for detecting the amplitude modula-tion of said signal component; a peak detector for peak detecting an output signal of said amplitude modulation detector, said peak detector being formed by the parallel connection of a capacitor and a resistor; a half level detector for detecting a half level of an output signal of said peak detector, said half level detec-tor being formed by resistors connected in parallel to said par-allel connection of a resistor and capacitor forming said peak detector; a comparator and pulse generator receiving said output signal of said amplitude modulator and an output signal of said half level detector and producing a pulse output signal rising at a time point of coincidence of said output signal of said ampli-tude modulation detector and said output signal of said half level detector, said resistors of said half level detector having a node connected to said pulse generator, a mute circuit for mut-ing the pulse output signal of said comparator and pulse genera-tor, one input of said mute circuit being connected to the output of said peak detector and another input of said mute circuit being connected to a reference voltage, said mute circuit cutting off the pulse output of said comparator and pulse generator when a non-scrambled signal is indicated by the output of said peak detector; and means responsive to the pulse output signal of said pulse generator for descrambling an applied scrambled signal.
10. A descrambling apparatus according to claim 9, fur-ther comprising a pulse width adjuster for adjusting the width of the pulse output signal of said pulse generator.
11. A pulse generating apparatus according to claim 9, wherein said descrambling means adjusts the level of a scrambled sync signal in a video signal in accordance with the pulse output signal of said pulse generator.
12. A pulse generating apparatus according to claim 11, further comprising a pulse width adjuster for adjusting the width of the pulse output signal of said pulse generator.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP46358/86 | 1986-03-05 | ||
| JP4635886 | 1986-03-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1275707C true CA1275707C (en) | 1990-10-30 |
Family
ID=12744925
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000531147A Expired - Lifetime CA1275707C (en) | 1986-03-05 | 1987-03-04 | Descrambling apparatus which produces a descrambling control pulse |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4852164A (en) |
| JP (1) | JP3047238B2 (en) |
| CA (1) | CA1275707C (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH05160691A (en) * | 1991-12-04 | 1993-06-25 | Nikon Corp | Binarization threshold setting circuit |
| US20030213001A1 (en) | 1994-11-07 | 2003-11-13 | Index Systems, Inc. | Method and apparatus for transmitting and downloading setup information |
| US6583825B1 (en) * | 1994-11-07 | 2003-06-24 | Index Systems, Inc. | Method and apparatus for transmitting and downloading setup information |
| US5694427A (en) * | 1995-02-21 | 1997-12-02 | Advanced Micro Devices Inc. | Pseudo-AUI line driver and receiver cells for ethernet applications |
| AU6864898A (en) * | 1997-03-17 | 1998-10-12 | Macrovision Corporation | Method and apparatus for adaptively enhancing a scrambled television signal |
| US6169584B1 (en) * | 1997-12-05 | 2001-01-02 | Motorola, Inc. | Automatic modulation control of sync suppressed television signals |
| US20100311399A1 (en) * | 2005-03-31 | 2010-12-09 | United Video Properties, Inc. | Systems and methods for generating audible reminders on mobile user equipment |
| JP2009124514A (en) * | 2007-11-15 | 2009-06-04 | Sony Corp | Solid-state imaging device and camera system |
| US20090165049A1 (en) | 2007-12-19 | 2009-06-25 | United Video Properties, Inc. | Methods and devices for presenting and interactive media guidance application |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3461390A (en) * | 1964-11-25 | 1969-08-12 | Xerox Corp | Dicode decoder translating dicode or three-level digital data signal into two level form |
| US4071781A (en) * | 1976-11-15 | 1978-01-31 | Northern Telecom Limited | Pulse duration correction circuit |
| US4241455A (en) * | 1977-12-29 | 1980-12-23 | Sperry Corporation | Data receiving and processing circuit |
| JPS6012826B2 (en) * | 1980-01-07 | 1985-04-03 | 株式会社日立製作所 | receiving circuit |
| US4567517A (en) * | 1983-02-15 | 1986-01-28 | Scientific-Atlanta, Inc. | Descrambler for sync-suppressed TV signals |
| US4635142A (en) * | 1983-11-22 | 1987-01-06 | Storage Technology Corporation | Amplitude sensor with adaptive threshold generation |
| JPS6016722A (en) * | 1984-06-26 | 1985-01-28 | Matsushita Electric Ind Co Ltd | Waveform shaping device |
-
1987
- 1987-03-02 US US07/020,739 patent/US4852164A/en not_active Expired - Lifetime
- 1987-03-04 CA CA000531147A patent/CA1275707C/en not_active Expired - Lifetime
- 1987-03-05 JP JP62048961A patent/JP3047238B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6323415A (en) | 1988-01-30 |
| JP3047238B2 (en) | 2000-05-29 |
| US4852164A (en) | 1989-07-25 |
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| Date | Code | Title | Description |
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| MKLA | Lapsed | ||
| MKLA | Lapsed |
Effective date: 20041101 |