MXPA98005808A - Use of ntsc special receiver to detect when an ntsc signal interfering with the co-channel accompanies a digital signal of - Google Patents

Abstract

The present invention relates to a method for detecting when a digital television signal is accompanied by the NTSC signal of co-channel interference of substantial amplitude, for use in a digital television receiver. The video portion of any NTSC co-channel interference signal is sincrodined to baseband, for the generation of an in-phase demodulation result that includes first artifacts of the television signal, and for the generation of a quadrature demodulation result phase, which includes second digital television signal artifacts. The quadrature phase demodulation results are shifted in phase by 90 ° to frequencies in a prescribed frequency range before being linearly combined with the phase quadrature, in phase demodulation results to generate a linear combination result substantially free of first and second artifacts of the digital television signal in the prescribed frequency range. An indication that the digital television signal is accompanied by the NTSC signal of co-channel interference of substantial amplitude, is generated by the detection of whether the amplitude of the linear combination result exceeds or not a preset value.

Description

«^» I USE OF NTSC SPECIAL RECEIVER TO DETECT WHEN A NTSC SIGNAL THAT INTERFERES WITH THE CO-CHANNEL ACCOMPANIES A DIGITAL TV SIGNAL FIELD OF THE INVENTION The invention relates to a digital television as it is transmitted by radio waves in a broadcast television band and, more particularly, to a method for detecting in a digital television receiver when a digital television signal is accompanied by the signal of NTSC that interferes with the co-channel, of substantial amplitude.

BACKGROUND OF THE INVENTION A Digital Television Standard published on September 16, 1995 by the Advanced Television Subcommittee (Advanced Television Subcommittee) (ATSC) specifies the nature of residual sideband (VSB) signals to transmit digital television (DTV) signals on television channels of 6 MHz bandwidth such as those currently used in the Broadcasting on the air of REF signals: 27948 analogue television of the National Television Subcommittee (NTSC), within the United States. As long as the analog NTSC television signals continue to be broadcast, it will be advantageous for a DTV signal receiver to be able to determine when an NTSC analog television signal causes interference with a substantial channel in a DTV signal that is received. The DTV receiver can then be designed to change its mode of operation in response to a determination that co-channel interference is occurring, so that the undesirable effects of co-channel interference can be mitigated, which is usually done through the comb filtration. Comb filtering used in a DTV receiver for NTSC co-channel interference suppression is best discontinued when such interference is not substantial, as this may prevent additional Johnson noise arising from plural paths through the comb filter . In general, co-channel interference from an analog NTSC television signal is considered to be substantial if it has sufficient power to cause frequency errors in the splice operations of data used during the quadrature of the phase. The Ito receiver synchrods the response of the radio frequency (RF) amplifier directly to the baseband, so that an adjacent lower channel can appear as an image. The synchronous phase quadrature detection response is shifted in 90 ° phase to all video frequencies above 500-750 kHz, and linearly combined with the phase synchronous detection response to suppress the image frequency components moved to the baseband during the synchronous detection of the received NTSC signal. U.S. Patent No. 5,122,879 to Ito describes the fact that this method also cancels the video components above 750 kHz. The loss in question of high luminance frequencies is acceptable in small-screen television receivers, however, such as those used in pulse clocks. The designs of current DTV receivers use plural frequency conversion, with a first conversion to an intermediate frequency in the ultra-high frequency (UHF) band above the designated channels for television broadcast, and with a second conversion to a intermediate frequency in the very high frequency band (VHF) below the channels designated for television broadcasting. So image deletion is not a problem. In addition, the carrier of a VSB DTV signal is located only 310 kHz from the edge of the channel, so that there is very little double sideband content compared to an NTSC signal. The inventor notes that an NTSC receiver of the type that linearly combines the synchronous video detection response in phase with the synchronous video detection response in quadrature phase, transformed by inverse Hilbert, is nonetheless of interest in DTV reception, for use as an auxiliary receiver to detect when a digital television signal is accompanied by the NTSC signal of co-channel interference, of substantial amplitude. By accommodating the inverse Hilbert transformation of the phase quadrature synchronous video detection response at frequencies below 750 kHz, such an auxiliary receiver becomes substantially insensitive to the co-channel DTV signal artifacts. The suppression of DTV artifacts simplifies the measurement of the magnitude of the NTSC signal of co-channel interference.

BRIEF DESCRIPTION OF THE INVENTION The invention in one of its aspects is exemplified in a method for detecting in a digital television receiver when a digital television signal is accompanied by the NTSC signal of co-channel interference of substantial amplitude, which method comprises the steps as follows. The video portion of any NTSC signal from co-channel interference is synchrodined to the baseband, to generate a phase demodulation result that includes the first artifacts of the digital television signal, and to generate a quadrature demodulation result of phase that includes second artifacts of the digital television signal. The results of the phase demodulation and phase quadrature are subsequently differentially displaced in respective phase by 90 ° at frequencies above a few kilohertz, and then linearly combined to generate a linear combination result, substantially free of first and second artifacts of the digital television signal. Subsequently, it is detected whether the amplitude of the linear combination result exceeds or not a prescribed value, to generate an indication of when the digital television signal is accompanied by the NTSC signal of co-channel interference, of substantial amplitude. The invention in another of its aspects is exemplified in a digital television receiver that includes the set of circuits for the detection of the times when the analog signal of television of substantial amplitude occupies a television broadcast channel, whose set of circuits is more particularly described as follows. The receiver has sets of input circuits for selecting from: a television broadcast channel an amplitude modulation signal, a residual sideband descriptive of a portion of the video signal of any analog television signal occupying the television channel. television broadcasting, converting the residual sideband amplitude modulation signal, and selected, to an intermediate frequency signal, and amplifying the intermediate frequency signal to provide an amplified intermediate frequency signal. The residual sideband amplitude modulation signal as originally received by the input circuitry includes a video carrier and the full lateral band in addition to a residual sideband. The video syncordination circuitry synchronously detects the amplified intermediate frequency signal with respect to the video carrier signal and with respect to a quadrature carrier with the video carrier signal, to generate a phase synchronous detection response and to generate a synchronous phase quadrature detection response. The phase shift circuitry referred to as a set of Hilbert transformation circuits, inverse, in this specification, phase-shifts all frequency components of the phase quadrature synchronous detection response in phase substantially over 90 °. of a prescribed frequency to generate the response of the phase shift circuitry. The circuit set in linear combination linearly combines the synchronous phase detection response and the phase shift circuitry response to recover the circuit set response in linear combination to a portion of the video signal written in the band complete lateral and in the residual sideband of the residual sideband amplitude modulation signal, as originally received. This linear combination of circuitry response is substantially free of response to any digital television signal that occupies the television broadcast channel that is currently received. A threshold detector is included in the receiver for determining when the first response of the linear combination circuitry exceeds a prescribed threshold value, to generate indications that the co-channel analog television signal is of substantial amplitude.

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 and 2 are each a schematic diagram of a television receiver that is capable of receiving the analog TV signals of NTSC as well as the DTV signals, whose receiver employs the method of the invention to detect the presence in the signals of DTV of NTSC analog TV signals with co-channel interference.

Figure 3 is a schematic diagram of a modification that can be made to any of the television receivers of Figures 1 and 2.

Figures 4, 5, 6 and 7 are flow diagrams showing the steps of the methods for detecting in a digital television receiver when a digital television signal is accompanied by the NTSC signal of co-channel interference, of substantial amplitude, whose methods employ the invention is its various aspects.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows the portions of a television receiver that is capable of receiving the analog TV signals, of NTSC as well as the DTV signals. The television type broadcast signals over the air, as received by an antenna 1, are amplified by a radio frequency amplifier 2, ajustically tuned, and supplied to a first detector 3. The RF amplifier 2 and the first detector 3 have adjustable tuning and together they function as a tuner to select a digital television signal from one of the channels of different sites in a frequency band. The first detector 3 includes a first local oscillator that supplies the first local oscillations 11 s tunable over a frequency range above the ultra-high frequency (UHF) 'of the TV broadcast band, and a first mixer for mixing the first local oscillations with a TV signal selected by the RF amplifier 2, usable tuned, to convert the selected TV signal, to generate an intermediate frequency UHF signal in an intermediate frequency band of UHF of 6 MHz wide, located at frequencies above the assigned channels in the broadcast band of UHF TV The first detector 3 supplies the high IF band signal to an intermediate frequency amplifier 6, of UHF band, used in the NTSC audio reception. The response of the UHF IF amplifier 6 is applied to a second detector 9 used in the NTSC audio reception. The second detector 9 includes a second local oscillator that supplies them. second local oscillations of the prescribed frequency above the UHF TV broadcast band of ultra-high frequency, and a second mixer to mix the second local oscillations with the response of the UHF IF amplifier 6, to generate the signal of very high frequency intermediate frequency (VHF) 12 localized frequencies below the assigned channels in the VHF TV broadcast band. This VHF IF signal is supplied to an intermediate frequency amplifier 12, of very high frequency. The response of the IF amplifier 12 of VHF is applied to a sound detector 34, intercarrier, which supplies the intermediate frequency sound signals of the 4.5 MHz intercarrier, to an intermediate frequency, sound amplifier, intercarrier, which amplifies and in most of the The designs symmetrically limit the amplified response for amplification to an FM detector 36. The FM detector 36 reproduces the composite, baseband audio signal supplied to the remaining portions of the analogue TV receiver part of the DTV receiver. With respect to the baseband composite audio signal, these remaining portions typically include the set of decoder circuits is terephonic. If the NTSC audio signals are selected with narrow band filtering in the IF amplifiers 6 and 12 passing only the FM audio carrier as it is translated to the intermediate frequencies, the intercarrier sound detector 34 can be provided by a 13 multiplier, which multiplies the response of the IF amplifier 12 by the video carrier selected to the multiplier by a narrowband filter that responds to the response of the IF amplifier 10 or 11. If the NTSC audio signals are selected with filtering in the IF amplifiers 6 and 12 that pass through the NTSC audio and video bearers as it is transferred to the intermediate frequencies, for the implementation of "almost parallel" sound, the detector 34 sound, intercarrier can be a simple rectifier or can be a quadratic law device. The first detector 3 also supplies the high IF band signal to an intermediate frequency amplifier 37, of UHF band, used in the reception of NTSC video and in the reception of ATSC. A surface acoustic wave (SAW) filter in the UHF IF amplifier 37, which determines the total IF response for the ATSC DTV signal and for the NTSC video signal, preferably rejects the NTSC audio signal. Otherwise, the SAW filter has a substantially flat amplitude response over the remainder of the TV broadcast channel of MHz width, as it was moved to the UHF IF band, and has a 14-phase response substantially linear along its entire pass band. The SAW filter is preceded in the UHF IF amplifier 37 by an amplifying transistor designed to drive the SAW filter from a prescribed source impedance that minimizes multiple reflection. In order to better maintain this prescribed source impedance, the gain of the amplifying transistor is preferably of a fixed value and sufficient to overcome the insertion loss in the SAW filter. The response of the UHF IF amplifier 37 is applied to a second detector 38 used in the ATSC DTV reception and in the NTSC video reception. The second detector 38 includes a second local oscillator which supplies second local oscillations of the prescribed frequency above the UHF TV broadcast band, ultra high frequency, and a second mixer to mix the second local oscillations with the response of the UHF IF amplifier 37 for generating a very high frequency intermediate frequency (VHF) signal located at frequencies below the assigned channels in the VHF TV broadcast band. The second detectors 9 and 38 preferably share the same second local oscillator. fifteen The VHF IF signal from the second detector 38 is supplied to a very high frequency intermediate frequency amplifier 41, which includes the steps of the controlled gain amplifier which provides up to 60 dB or more of amplification. The VHF IF amplifier 41 is provided with the reverse automatic gain control, derived in response to its output signal level, with the inverse AGC preferred by the gain linearity it provides. The RF amplifier 2 is provided with the reverse automatic gain control, delayed, in response to the output signal level of the IF amplifier 47. The output signal from the VHF IF amplifier 47 is applied to a detector 13 of the ATSC symbol code, which detects the codes of the baseband symbol therefrom. The symbol code detector 13 is one that uses a synchronous phase detector to detect the residual sideband amplitude modulation of the data carrier, and uses a phase quadrature synchronous detector to develop the automatic frequency and the control signal phase (AFPC) for a controlled oscillator 16 which provides synchronous signals to the synchronous detectors. The phase synchronous detector operates in the analog mode and its output signal is digitized with 10 bits or a similar resolution by an analog-to-digital converter 14. Alternatively, the symbol code detector 13 and the subsequent ADC 14 can be replaced by a third detector for converting the VHF band response of the IF amplifier 47 to an intermediate frequency band., final, just above the base band, an analog to digital converter for the digitization of the response of the third detector, and the set of digital synchrodination circuits to synchronize the digitized response of the third detector, to the baseband. Such a set of alternative circuits are described in CB Patel et al. In U.S. Patent No. 5,479,449, issued December 26, 1995 and entitled "VSB DIGITAL DETECTOR WITH PASS BAND PHASE TRACER, FOR INCLUSION WITHIN A RECEIVER HDTV ", and US Patent No. 5,548,617, issued August 20 and entitled" DIGITAL VSB DETECTOR WITH STEP BAND PHASE TRACER USING RADER FILTERS, FOR USE IN AN HDTV RECEIVER ", 17 by means of examples. When a DTV signal is being received, a direct signal resulting from the synchronous detection of the pilot signal, accompanies the symbol codes as they are reproduced in the baseband, and is detected by a pilot carrier detector 15, to generate a signal DTV CAPAZ, which conditions the portions of the DTV receiver screen to display DTV images instead of NTSC television images. The pilot carrier detector 15 can, as shown in Figure 1, be of a type to respond to the digital input signal, or alternatively be of a type to respond to the analog input signal as supplied directly from the detector 13 of symbol code. Figure 1 shows the digitized baseband symbol codes, which are supplied from the ADC 14 to a symbol decoder 20 of the type described in greater detail in U.S. Patent Application Serial No. 08 / 746,520 filed by the inventor on November 12, 1996 and entitled "DIGITAL TELEVISION RECEIVER WITH SET OF ADAPTIVE FILTER CIRCUITS TO SUPPRESS NTSC CO-CHANNEL INTERFERENCE". The symbol decoder 20 comprises an 18 data switch 21 for the data sectioning of the input signal of the symbol decoder 20, to produce a first response of the symbol decoder, a NTSC artifact reject comb 22 filter that supplies a response to the input signal of the symbol decoder 20, the response of which suppresses any NTSC co-channel interference signal, a data switch 23 for severing data from the response of the comb filter 22, to generate a wrong symbol decoder response, an adaptation filter or balance to correct that error decoder response of bad symbols, to produce a second response of the symbol decoder, and a multiplexer 25 to select one of the first and second responses of the symbol decoder, as the last response of the symbol decoder, supplied by the symbol decoder 20 to a typical Trellis 16 type decoder for a DTV receiver. In the absence of an indication of the substantial NTSC co-channel interference signal, which is received, the multiplexer 25 selects the first response of the symbol decoder from the data switch 21, to provide the output signal 20 of the decoder 19. of symbols for the trellis decoder 16. In the presence of the indication of the substantial NTSC co-channel interference signal that is received, except during the initialization intervals of the symbol decoder, the multiplexer 25 selects the second response of the symbol decoder from the adaptive comb filter 24, to provide the symbol decoder 20 with the output signal for the trellis decoder 16. The symbol decoder 20 can be improved by modifying the multiplexer 25 to provide ideal symbol decoding results. extracted from the memory inside the television receiver, at the times in which the synchronization of data segments and the groups of field synchronization codes appear, in a received DTV signal. Such improvement is described in detail in U.S. Patent Application Serial No. 08 / 839,690 filed by the inventor on April 15, 1997 and entitled "DIGITAL TELEVISION RECEIVER WITH ADAPTIVE FILTER CIRCUIT ASSEMBLY TO ELIMINATE CO-CHANNEL INTERFERENCE. OF NTSC ". twenty The output signal from the VHF IF amplifier is applied to the circuit set 46 to synchronize the modulation of the NTSC video carrier to the baseband. A phase synchronous detector and a phase quadrature synchronous detector are used in the circuit set 46 to synchrodate the modulation of the NTSC video carrier to the baseband; it is presumed that synchronization will be carried out in the digital regime after converting to a final intermediate frequency band just above the baseband, so that the final intermediate frequency can be digitized. Alternatively, the synchronization of the modulation of the NTSC video carrier to the baseband can be performed in the analog regime, and the responses of a phase synchronous detector and a phase quadrature synchronous detector, used for this purpose, can be digitized using the respective analog to digital converters. The Q response of the phase quadrature synchronous detector is the Hilbert transformation of the simple sideband components of the NTSC signal (for example, those components above 750 kHz in frequency) plus the artifacts of. the signal of DTV 21 as these appear in the response I of the synchronous detector in phase. This Hilbert transformation provided by the Q response of the phase quadrature synchronous detector is shifted in phase to provide 90 ° delay at all frequencies (except possibly the lowest at which there should be little response) by the circuit set 47 of Hilbert transformation. Addition and subtraction are considered as alternative forms of the linear combination. One of the linear combiners 47 and 48 is an adder and the other is a subtracter. The Hilbert inverse transform response of the circuit set 47 is linearly combined with the response of the in-phase synchronous detector in the linear combiner 48, to generate a composite video signal with the intensified high frequencies to correct the levels for the application of the rest of the set of analog television receiver circuits. With respect to the baseband composite video signal, these remaining portions typically include the synchronous separation circuit set, the color signal reproduction circuit set, and the set of circuits for the adaptation of the NTSC image of 4: 3 aspect ratio for presentation on a 16: 9 screen used to display DTV images. The inverse transformation response of Hilbert of the circuitry 47 is linearly combined in the linear combiner 49 with the in-band base-band I response of the synchro-tuning circuitry 46, to generate a luminance signal cutoff approximately above 750 kHz, whose luminance signal It is free of DTV artifacts. Whether the linear combiners 48 and 49 are respectively an adder and a subtracter, or if the linear combiners 48 and 49 are respectively a subtracter and an adder, this depends on whether the operation of the phase quadrature synchronous detector is chosen to drive the operation of a synchronous detector in phase or to delay it. Figure 1 shows the band -limited luminance signal from the linear combiner 46 which is further filtered using a low pass filter 50 with a cutoff frequency of 1 MHz or the like and then square by a quadrat 31 to generate an indication of the energy of the signal 23 of NTSC co-channel interference during DTV reception. The 31st square could be constructed from a digital multiplier that receives that signal as a multiplier and as a multiplier, but it is more practical to do it in the read-only memory (rom). The output signal of the quadrature 31 is an indication of the energy of the NTSC co-channel interference signal during DTV reception. A digital threshold detector 32 determines when this indication is strong enough to exceed a threshold value below which it is considered that the NTSC co-channel interference signal will not be sufficiently substantial to be likely to introduce non-correctable error within of the operation of the data disconnector 21. The response of the threshold detector 32 is supplied to the circuit set 33 of the multiplexer control. The multiplexer control circuitry 33 controls the selection by the multiplexer 25 between the first and second responses of the symbol decoder, which determines the ultimate response of the symbol decoder supplied as the output signal 20 of the symbol decoder. The circuit set 24 33 multiplexer control conditions the multiplexer 25 to select the first response of the symbol decoder as the output signal of the symbol decoder 20 during the initialization intervals of the symbol decoder. At other times the set of control circuits 33 of the multiplexer conditions the multiplexer 25 to select the first response of the symbol decoder as the output signal of the symbol decoder.as long as the response of the threshold detector 32 indicates that the NTSC co-channel interference signal is considered as not substantial enough to be likely to introduce non-correctable error in the operation of the data disconnector 21, unless the conditioning of the multiplexer 25 select the response of the second symbol decoder as the output signal of the symbol decoder 20. Figure 2 shows the apparatus of Figure 1 modified to supply the response of the linear combiner 49 to the digital threshold detector 32 without quadrature on the part of the square 31. The response of the linear combiner 49 is essentially of band-width iuminance extending up to 750 kHz, since it is always of the same polarity. In 25 consequently, the square 31 can be omitted, and the digital threshold detector 32 can be replaced with a digital threshold detector 032 with a prescribed threshold that is the square root of the prescribed threshold of the digital threshold detector 32. That is, the threshold The prescribed threshold of the digital threshold detector 32 is the square of the prescribed threshold of the digital threshold detector 032. In the television receivers of Figure 1 and Figure 2, the inclusion of the low pass filter 50 facilitates the requirements on the Hilbert inverse transform circuit set 47, since the exact 90 ° delay does not need to be provided to frequencies above the cutoff frequency of the low pass filter 50, in order to suppress the DTV artifacts in that portion of the frequency spectrum. Where the Hilbert reverse transform circuit set 47 provides the reasonably accurate 90 ° delay, up to 4.2 MHz or the like, it is possible to replace the low pass filter 50 by a direct connection. Whenever the combination of the Hilbert reverse transform filter 47 in the linear combiner 48 is compromised with the in-band base-band I response of the synchro-skew circuitry 46. to intensify the high composite video signal frequencies, the Hilbert reverse transform circuit set 47 does not need to provide the exact 90 ° delay for frequency clearing up to 4.2 MHz, since the video circuitry can be used to compensate for the progressive attenuation of high composite video signal frequencies that explains the incorrect delay if the error in the delay is not too severe. Figure 3 shows a modification that can be made to either of the television receivers of Figures 1 and 2. In the modification of Figure 3, instead of the set of circuits 47 of Hilbert's inverse transformation, the displacement of the phase quadrature baseband Q-response of the synchro-skew circuitry 46 for the application to the linear combiners 48 and 49, the circuit set 51 of the Hilbert inverse transformation shifts the baseband Q-response in quadrature of the phase set of synchrodynamic circuits 46, for the right application to the linear combiner 48; and another circuit set 52 of Hilbert inverse transform shifts the baseband Q response in 27 phase quadrature of the synchro-skew circuitry 46 for the right application to the linear combiner 49. The Hilbert inverse transform circuitry 51 provides accurate 90 ° delay from 0.5 MHz to 4.2 MHz to optimize the spectral response of the composite video signal, but does not have to provide 90 ° delay at frequencies well below 0.5 MHz. This avoids the very many bifurcation (FIR) finite impulse responses needed to provide the 90 ° delay at frequencies well below 0.5 MHz at the high digital sampling rates also required to provide the 90 ° recoup at frequencies up to 4.2 MHz. Due to the use of the low pass filter 50, the Hilbert reverse transform circuit set 52 needs to provide delay of reasonably accurate 90 ° only up to 1.0 MHz or similar, but circuit set 52 provides the 90 ° delay at very high frequencies below 0.5 MHz, preferably below a fraction of the NTSC scan line proportion. These requirements can be met at a digital sampling rate or rate, converted to decimals, four times lower than the speed of 28 digital sample taken in the circuit set 51 of the Hilbert inverse transformation, substantially reducing the temporary storage requirements to provide differentially delayed samples for the FIR filtration in the Hilbert inverse circuit array 52. Of course, the low pass filter 50 can be designed to have an even lower cutoff frequency below 0.5 MHz, so that the digital sampling rate converted to a decimal used in the Hilbert reverse transformation circuit set 52 it may be 8 times lower than the digital sampling rate used in circuit set 51 of the Hilbert inverse transformation. Or the cut-off frequency of the low-pass filter 50 can be further reduced by half again more or a few times, so that the digital sample-taking speed converted to a decimal, used in the reverse transformation circuit set 52 of Hilbert, can also be converted to decimal from the digital sampling rate used in the circuit set 51 of inverse transformation of Hiibert. 29 Figure 4 is a flowchart of the method of operation implemented by the TV receiver of Figure 1. An initial step SO of receiving a digital television signal suitable for times to be accompanied by an analog signal of interference television co -channel, which has a portion of video, is carried out by elements 1, 2, 3, 37, 38 and 41 of the television receiver of Figure 1. The set of synchro-skew circuits 46 carries out a subsequent step Si of syncrodination of the video portion of any analog television signal, of co-channel interference, to the base band to generate a phase demodulation result that includes first artifacts of the DTV signal, and for the generation of a result of quadrature phase demodulation that includes second artifacts of the DTV signal. The circuitry 47 inverse Hilbert transformer implements a subsequent step S2 shift differential demodulation in phase and quadrature phase, resulting in the respective phase by 90 ° at frequencies in a frequency range prescribed extending well below 750 kilohertz. The linear combiner 49 carries out a subsequent step S3 of combination 30 line of the phase and phase quadrature demodulation results, after their differential displacement in the respective phase by 90 °, at frequencies in the prescribed frequency range, to generate a linear combination result substantially free of the first and second artifacts of the digital television signal in the prescribed frequency range. (The low pass filter cut 50 determines the upper limit of this prescribed frequency range). The square 31 performs a step S4 of quadrature or square of the linear combination result; and the digital threshold detector 32 then performs a final step S5 to detect whether the square resulting from said linear combination result exceeds or not the square of the prescribed value, for the determination of whether the digital television signal is accompanied by the Analog television signal, interference, co-channel of substantial amplitude. Figure 5 is a flow chart of the method of operation implemented by the television receiver of Figure 1, differing from the flow diagram of Figure 4 in which step S2 is implemented by the Hilbert inverse transform circuit set 47 , it's more 31 particularly shown as the step S2 'of the phase shift of the phase quadrature demodulation results by 90 ° at frequencies in a prescribed frequency range extending below 750 Kilohertz. Figure 6 is a flow chart of the method of operation implemented by the TV receiver of Figure 2. The method described in the flow diagram of Figure 6 uses the same steps SO, Si, S2 and S3 described in the diagram of flow of Figure 4. The quadrature step S4 implemented by the square 31 in the receiver of Figure 1 is omitted in the operation of the television receiver of Figure 2, of course. The step S5 performed by the digital threshold detector 32 in the TV receiver of Figure 1 is supplanted in the operation of the TV receiver of Figure 2 by a step S5 'of detecting whether the amplitude of the linear combination result in the prescribed frequency range exceeds or not a prescribed value, for the generation of an indication of when the DTV signal is accompanied by the analog television signal, interference, co-channel of substantial amplitude. This step S5 'is carried out by the 32 digital threshold detector 032 in the television receiver of Figure 2. Figure 7 is a flowchart of the method of operation implemented by the television receiver of Figure 6, differing from the flow chart of Figure 4 in that the step S2 implemented by the circuitry 47 of the inverse Hilbert transformer, is more particularly shown as step S2 'phase shift results quadrature demodulation of phase by 90 ° at frequencies in a frequency range prescribed that extends well below the 750 ki lohercios.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (8)

1. A method, characterized in that it comprises the steps of: receiving a time-dependent digital television signal to be accompanied by an analog television signal, of co-channel interference having a video portion; the syncrodination of the video portion of any. analog signal of co-channel interference television, to the base band, to generate a phase demodulation result that includes first artifacts of the digital television signal, and for the generation of a phase quadrature demodulation result that includes seconds artifacts of the digital television signal; the differential displacement of the demodulation results in phase and quadrature phase in the respective phase by 90 °, at frequencies in a prescribed frequency range extending well below 750 Kilohertz. the linear combination of the phase and phase quadrature demodulation results after the differential displacement in the respective phase 34 by 90 ° at frequencies in the prescribed frequency range, to generate a linear combination result substantially free of the first and second artifacts of the digital television signal in the prescribed frequency range; and the detection of whether the amplitude of the linear combination result in the prescribed frequency range exceeds or not a prescribed value, for the generation of an indication of when the digital television signal is accompanied by the analog signal of interference television. channel, of substantial amplitude.
2. 2. The method according to claim 1, characterized in that the differential displacement step of the demodulation results in phase and quadrature phase, in the respective phase by 90 ° at frequencies in the described frequency range, comprises a sub-step of: the inverse Hilbert transformation of the quadrature phase demodulation result.
3. 3. The method according to claim 1, characterized in that the step of detecting whether the absolute amplitude of the result of linear combination exceeds or not the prescribed value, comprises the substeps of: quadrature of the linear combination result; and the detection of whether the square resulting from the linear combination result exceeds or not the square of the prescribed value.
4. 4. A method characterized in that it comprises the steps of: receiving a time-dependent digital television signal to be accompanied by an analog co-channel interference television signal having a portion of video; the syncrodination of the video portion of any analog signal from co-channel interference television, to the baseband, to generate a phase demodulation result that includes first artifacts of the digital television signal, and to generate a result phase-shifting demodulation including second artifacts of the digital television signal; the phase shift of the demodulation results in quadrature phase by 90 ° to 36 frequencies in a prescribed frequency range well below 750 kilohertz; the linear combination of phase quadrature demodulation results, phase shifted, resulting with phase quadrature demodulation results, and in phase, to generate a linear combination result substantially free of the first and second signal artifacts digital television in the prescribed frequency range; and detecting the amplitude of the linear combination result in the prescribed frequency range, exceeding a prescribed value, for the generation of an indication that said digital television signal is accompanied by an analog television signal of co-channel interference, of substantial amplitude.
5. 5. The method according to claim 4, characterized in that the step of detecting the amplitude of the linear combination result in the prescribed frequency range exceeding a prescribed value for generating an indication that the digital television signal is accompanied by the analog TV signal of 37 Co-channel interference of substantial amplitude, comprises the substeps of: quadrature of the linear combination result; and detecting when the square resulting from the linear combination result exceeds the square of the prescribed value, for the generation of said indication that the digital television signal is accompanied by the NTSC signal of co-channel interference, of substantial amplitude.
6. 6. A digital television receiver that includes a set of circuits for detecting the times when the analog signal of television of substantial amplitude occupies a television broadcast channel, characterized the set of circuits because it comprises: the set of input circuits to select from of a television broadcast channel a residual sideband amplitude modulation signal, descriptive of a video signal portion of any analog television signal occupying the television broadcast channel, converting the bandwidth modulation signal residual lateral, selected, at 38 an intermediate frequency signal and amplifying said intermediate frequency signal to provide a simplified intermediate frequency signal, the residual sideband amplitude modulation signal as originally received by the set of input circuits including a video carrier and the band full lateral, in addition to a residual sideband; the set of video syncordination circuits for synchronously detecting said amplified intermediate frequency signal, with respect to the video carrier signal and with respect to a quadrature carrier with the video carrier signal, for generating a response of synchronous detection in phase and for the generation of a phase quadrature synchronous detection response; the first phase displacement circuitry for shifting all frequency components of the phase quadrature synchronous detection response above a prescribed frequency in phase substantially 90 [deg.] to generate a first displacement circuitry response of phase; 39 the first linear combination circuitry linearly combines the phase-synchronous detection response and the first phase displacement circuitry response to recover the first response of the linear combination circuitry to a portion of the video signal described in the full sideband and in the residual sideband, whose first response of the linear combination circuitry is substantially free of response for any television signal occupying the television broadcast channel; and a threshold detector to determine when the first response of the combination circuitry. linear exceeds a prescribed threshold value, for the generation of indications that the co-channel analog television signal is of substantial amplitude.
7. 7. The digital television receiver according to claim 6, further characterized in that it comprises: the second set of linear combination circuits, which linearly combines the synchronous detection response in phase and the first response of the phase shift circuitry, to recover the second response of the circuitry in linear combination for all video signals.
8. 8. The digital television receiver according to claim 6, further characterized in that it comprises: the second set of phase shift circuits for shifting virtually all the frequency components of the phase quadrature synchronous detection response by 90 ° in phase. up to 500 kilohertz, to generate a second response of the phase shift circuitry; and the second set of linear combination circuits which linearly combines the phase synchronous detection response and the second phase shift circuitry response to recover the second response of the linear combination circuitry for all video signals. 41 SUMMARY OF THE INVENTION A method is described for detecting when a digital television signal is accompanied by the NTSC signal of co-channel interference of substantial amplitude, for use in a digital television receiver. The video portion of any NTSC signal of co-channel interference is sincrodined to baseband, for the generation of an in-phase demodulation result that includes first artifacts of the digital television signal, and for the generation of a demodulation result in Phase quadrature, which includes second digital television signal artifacts. The quadrature phase demodulation results are shifted in phase by 90 ° to frequencies in a prescribed frequency range before being linearly combined with the quadrature phase, in phase demodulation results to generate a substantially free linear combination result of the first and second artifacts of the digital television signal in the prescribed frequency range. An indication that the digital television signal is accompanied by the NTSC signal of co-channel interference of substantial amplitude, is 42 generated by detecting whether the amplitude of the linear combination result exceeds or not a prescribed value.