KR100278854B1 - A digital television receiver with an NTS interference detector using a comb filter that suppresses the D.V pilot carrier to extract the NTS artifact. - Google Patents

Abstract

The first comb filter combines an I- or Q-channel baseband signal, which is supplied as an input signal to an NTSC co-channel interference detector for a DTV receiver, with a signal affected by the first differential delay amount, thereby causing the co-channel interference. A first comb filter response is generated in which artifacts caused by synchronous detection of the analog television signal are suppressed. The detector includes a second comb filter that combines the input signal with a signal affected by a second differential delay amount to produce a second comb filter response that enhances the artifacts of co-channel interference. The first and second comb filters use the same type of linear combiner such that the direct terms of the input signal are similarly processed into the first comb filter response and the second comb filter response. Each amplitude of the first and second comb filter responses is respectively detected by the first and second amplitude detectors. The amplitude comparator compares the first amplitude detection response with the second amplitude detection response, and only if and when the first and second amplitude detection responses differ by more than a specified amount, co-channel interference is undesirable. Indicates that it has sufficient strength.

Description

Digital television receiver with N.S.C interference detector using a comb filter that suppresses D.V pilot carrier to extract N.C. artifacts

The present invention relates to digital television systems, and more particularly to circuitry used in digital television (DTV) receivers for determining whether co-channel interference exists from NTSC analog television signals.

In the Digital Television Standard, published by the Advanced Television Systems Committee (ATSC) on September 16, 1995, the remnants for transmitting digital television (DTV) signals on 6 MHz-bandwidth television channels. Vestigial Sideband (VSB) signals are specified. DTV signals will be transmitted on some of the microwave transmission channels currently used for over-the-air broadcasting of analog television signals from the US Television Standards Committee (hereinafter referred to as "NTSC") in the United States. The VSB DTV signal is designed such that its spectrum can be interleaved with the spectrum of an NTSC co-channel interfering analog TV signal. The symbol frequency of the DTV signal is three times the NTSC color subcarrier frequency, and the 3.58 MHz subcarrier frequency corresponds to 455/2 times the NTSC scan line rate. The main amplitude-modulated sideband frequency and the pilot carrier of the DTV signal are located at an odd multiple of the horizontal scan line speed of the NTSC analog TV signal. As a result, these DTV signal components fall between 1/4 even multiples of the horizontal scan line speed of the NTSC analog TV signal, which will be an even multiple of the luminance and chrominance component energy of the NTSC co-channel interfering analog TV signal. The video carrier of the NTSC analog TV signal is offset 1.25 MHz from the lower limit frequency of the television channel. The carrier of the DTV signal is offset from the video carrier by 59.75 times the horizontal scanning line speed of the NTSC analog TV signal so that the carrier of the DTV signal is located at about 309,877.6 kHz from the lower limit frequency of the television channel. Thus, the carrier of the DTV signal is located about 2,690,122.4 Hz from the median medium frequency of the television channel.

The exact symbol rate of the digital television standard corresponds to 684/286 times the 4.5 MHz speech carrier offset from the video carrier of the NTSC analog TV signal. The number of symbols per horizontal scan line of an NTSC analog TV signal is 684, and 286 is multiplied by the horizontal scan line speed of the NTSC analog TV signal, resulting in a 4.5 MHz speech carrier offset from the video carrier of the NTSC analog TV signal. It is an argument. The symbol rate is 10.762238 million symbols per second, which may be included in the VSB signal extended from 5.381119 MHz from the DTV signal carrier. That is, the VSB signal may be limited to a band extending from 5.690997 MHz from the lower limit frequency of the television channel.

In the United States, the ATSC standard for terrestrial broadcasting of DTV signals can transmit either of two high-resolution television (HDTV) formats having an aspect ratio (i.e., aspect ratio) of 16: 9. One HDTV display format uses 1920 effective horizontal scan lines per 30 Hz frame with 1920 samples per scan line and a 2: 1 field interlace. The other HDTV display formats use 1280 luminance samples per scan line and 720 forward scanned lines of television image per 60 Hz frame. The ATSC standard also accepts transmission of DTV display formats other than HDTV display formats, such as the parallel transmission of four television signals with normal resolution when compared to NTSC analog television signals.

During terrestrial broadcasts in the United States, DTV transmitted by Residual-Sideband (VSB) amplitude modulation (AM) is continuous in time, each consisting of 313 consecutive-in-time data segments. A succession of consecutive-in-time data fields. The data field may be regarded as successively numbered modulo-2, in which every odd data field and the subsequent even data field form a data frame. The frame rate is 20.66 frames / second. Each data segment has a duration of 77.3 microseconds. As a result, the symbol rate is 10.76 MHz, and there are 832 symbols per data segment. Each segment of data begins with a data-segment-synchronization (DSS) code group consisting of four symbols with consecutive values of + S, -S, -S, and + S. The + S value is one level below the maximum positive data excursion, and the -S value is one level above the maximum negative data excursion. The initial data segment of each data field includes a data-field-synchronization (DFS) code group that encodes a training signal for channel-equalization and multipath suppression. The training signal is a 511-sample pseudo-noise sequence (or "pseudo-noise-sequence") followed by three 63-sample PN sequences. In the field synchronization code, the center sequence of the 63-sample PN sequences is transmitted according to the first logic protocol on the first line of each odd-numbered data field and according to the second logic protocol on the first line of each even-numbered data field. The first logic protocol and the second logic protocol are complementary to each other (ie, have opposite characteristics).

Data in the data segments is trellis coded using 12 interleaved trellis codes, and each trellis code at 2/3 speed has one precoded unencoded bit. The interleaved trellis codes are Reed-Solomon forward error-correction coding to prepare for the correction of burst errors caused by noise sources such as automotive ignition systems exposed in close proximity. Go through The result of Reed-Solomon coding is 8-level (3 bits / symbol) 1-dimensional constellation symbol coding for wireless transmission without symbol precoding distinct from the trellis coding process. Is sent as. The Reed-Solomon encoding result is transmitted as 16-level (4 bits / symbol) 1-dimensional constellation symbol encoding for wired transmission without precoding. The VSB signal has its own carrier whose amplitude may vary depending on the modulation rate being suppressed.

The carrier itself is replaced with a pilot carrier of fixed amplitude corresponding to the specified modulation rate. This pilot carrier of fixed amplitude is generated by introducing a direct component shift to the modulation voltage applied to the balance modulator that generates an amplitude-modulated sideband that is supplied to a filter that supplies the VSB signal as its response. If eight levels of 4-bit symbol coding have normalized values of -7, -5, -3, -1, +1, +3, +5, and +7 in the carrier modulated signal, the pilot carrier is It has a normalization value of 1.25. The normalization value of + S is +5 and the normalization value of -S is -5.

In the early development of DTV technology, it is expected that a DTV broadcaster would be asked to determine whether or not to use a symbol precoder for the transmitter. These symbol precoders are subsequently placed in the symbol generator circuit and used in conjunction with the comb filter of each DTV signal receiver to prepare for matched filtering of symbols. The comb filter is prepositioned prior to the data slicer of the symbol decoder circuit of the DTV signal receiver and is operated as a symbol post-coder. This decision at the broadcast device depends on whether or not interference from the co-channel NTSC station is expected. The symbol precoding procedure would not have been used for a data segment or data segment synchronization code group that would allow data field synchronization data to be transmitted. Co-channel interference decreases farther away from NTSC stations, is more likely to occur when certain ionosphere conditions are established, and co-channel interference is most likely to occur during the summer months when solar activity is active. Of course, such interference will not occur where there is no co-channel NTSC station. If there is a possibility of occurrence of NTSC interference in the area of the broadcast effective viewing range, it is assumed that a symbol precoder is used for the HDTV broadcasting device so that the HDTV signal can be more easily separated from the NTSC interference. Thus, the comb filter is used as a symbol post-coder for complete matched filtering in the DTV signal receiver. If there is no possibility of NTSC interference, it is assumed that the DTV broadcaster has stopped using the symbol predecoder. The symbol postcoder of each DTV signal receiver is therefore inoperable in order to ensure that flat spectrum noise does not cause erroneous decisions regarding the symbol values of the trellis decoder.

Postcoder comb filters are optionally used in U.S. Patent No. 5,260,763, issued to R.W.Citta et al. On November 9, 1993, entitled "Receiver post coder selection circuit." The comb filter suppresses co-channel NTSC interference artifacts associated with real or in-phase baseband components (I-channels) of the complex output signal of the demodulator used in the DTV signal receiver.

The presence of these artifacts in the I-channel component of the demodulator response is detected to automatically develop the control signal to enable or disable the suppression of NTSC co-channel interference artifacts by comb filtering. During each data filter synchronization interval, the input signal to the comb filter type NTSC suppression filter of the DTV signal receiver and the output signal from the NTSC suppression filter are compared with the respective signals known a priori, and the HDTV signal receiver It is fetched from internal memory. If the minimum result compared with the input signal has weaker energy than the minimum result compared with the output signal from the NTSC suppression filter, this is the main cause of change from the expected reception is NTSC co-channel interference. Rather, it suggests random noise. As far as the special digital television receiver is concerned, it is possible to estimate that the reception rate is improved, the precoding and postcoding techniques are not used in the system, and the broadcasting apparatus does not use the precoding technique. If the minimum result compared with the input signal has a stronger energy than the minimum result compared with the output signal from the NTSC suppression filter, this means that the main cause of change from the expected reception is NTSC rather than random noise. Implies channel interference. As far as the special digital television receiver is concerned, if the precoding and postcoding techniques are used in the system, the reception rate can be improved and it can be estimated that the broadcasting apparatus has used the precoding technique.

U.S. Patent No. 5,546,132, issued to KSKim et al. On August 13, 1996, entitled "NTSC interference detector," describes the presence of the interference in response to an NTSC-extracted comb filter for an I-channel. The use of a post-coder comb filtering technique to suppress co-channel NTSC interference when detected is disclosed. U. S. Patent No. 5,546, 132 does not disclose, in particular, the imaginary or quadrature-phase baseband component (Q-channel) of a complex output signal supplied from a demodulator used in a digital DTV signal receiver. DTV signal receivers that synchronize the VSB AM signal to baseband typically supply the received I-channel signal for trellis decoding (after the post-coding process, if the pre-decoding technique is used at the transmitter). A demodulator having an in-phase synchronous detector is used. The demodulator is a quadrature-phase synchronization supplying a low pass filtered received Q-channel signal to generate an automatic frequency and phase control (AFPC) signal for a local oscillator supplying a carrier for synchro-dinning. It further comprises a quadrature-phase synchronous detector. CBPatel and ALR dated December 26, 1996, entitled "Digital VSB detector with bandpass phase tracker, as for inclusion in an HDTV receiver." The specification and accompanying drawings of US Pat. No. 5,479,449 (assigned to Samsung Electronics Co., Ltd.), published by Limberg et al., Are incorporated herein by reference. Of particular interest to the reader are components 22-27 shown in FIG. 1 of US Pat. No. 5,479,449 and the corresponding description set forth in the accompanying specification. These components are used in the DTV signal receiver to perform the complex demodulation function of the VSB AM final intermediate frequency (I-F) signal. U.S. Patent 5,479,449 discloses the demodulation of the VSB AM final IF signal, which is performed digitally, but in alternative DTV receiver designs, the complex demodulation function of the VSB AM final IF signal is performed in an analog manner instead. do.

In U.S. Pat.Nos. 5,260,793 and 5,546,132, post-coding operations are enabled during the time when substantial co-channel NTSC interference occurs, otherwise they are disabled, and such optional enable states are disabled. The control signal for the signal is developed from the received I-channel signal. The determination of the co-channel NTSC interference level is complicated by the direct bias involved in the co-channel NTSC interference, which results from the in-phase sync detection of the pilot carrier of the VSB AM DTV signal. This is particularly a problem for DTV signal receivers, where automatic gain control does not accurately adjust the amplitude of the received I-channel signal recovered by in-phase sync detection.

The video broadcast wave of the NTSC signal is 1.25 MHz away from the edge of the 6-MHz bandwidth broadcast channel, while the carrier wave for the DTV signal for terrestrial radio broadcast is 310 kHz away from the edge of the 6-MHz bandwidth broadcast channel. Co-channel NTSC signals do not exhibit amplitude-modulated sidebands symmetrical with respect to carriers of residual-sideband amplitude-modulated (VSB AM) carrying digital information. Therefore, artifacts of the NTSC video carrier and its sideband artifacts 940 kHz away from the DTV signal carrier are not well removed from the DTV signal as they are synchronized to the baseband. Of course, the NTSC voice carrier and its sideband artifacts, 5.44 MHz away from the DTV signal carrier, are also not well removed from the DTV signal.

The digital television standard, published on September 16, 1995 by ATSC, is a complete data symbol for DTV transmitters to compensate for the incidental post-coding of subsequent comb filtering techniques in the DTV signal receiver to eliminate NTSC co-channel interference. It does not allow the use of precoding techniques for. Instead, only the initial symbols are precoded during trellis decoding. This process itself does not facilitate the DTV signal receiver to use comb filtering to remove NTSC co-channel interference before the data slicing process is performed. DTV signal receivers that fail to remove NTSC co-channel interference artifacts before the data slicing process is performed will not have good reception under strong NTSC co-channel interference conditions. This interference condition may be caused by a DTV receiver that is away from the DTV transmitter or that the analog TV transmitter is very close to. For DTV signals that are synced to baseband, the artifact of the video carrier of the co-channel interfering NTSC color TV signal is at 59.75 f _H (f _H is the horizontal scanning frequency of such signal). The artifact of the color subcarrier is at 287.25 f _H and the artifact of the unmodulated NTSC speech subcarrier is at 345.75 f _H.

The comb filtering process is not entirely satisfactory in suppressing the artifacts of a frequency-modulated NTSC speech carrier, especially under frequency modulation with a large carrier frequency deviation range. This is because the correlation (or anti-correlation) of the FM carrier samples that are sometimes separated by some substantial fixed delay is not good. Name of invention "DTV RECEIVER WITH FILTER IN IF CIRCUITRY TO SUPPRESS FM SOUND CARRIER OF CO-CHANNEL NTSC INTERFERING SIGNAL" The contents of US Patent No. 5,748,226, issued May 5, 1998 to the inventors, are incorporated herein by reference. In U.S. Patent No. 5,748,226, the inventor recommends that the filtering used to establish the full bandwidth of the mid-frequency amplification be performed as used to remove the FM voice carrier of some NTSC co-channel interfering analog TV signals. .

The comb filtering process is more satisfactory in separating the baseband TV signal from the artifacts of the co-channel NTSC signal resulting from the image carrier, the low image frequency, and the chrominance signal frequency close to the color carrier. . The reason is that these artifacts tend not only to show good correlation between samples separated by any particular delay interval, but also to show good anti-correlation between samples separated by any other specific delay interval. .

In US Pat. No. 5,748,226, the present inventors prior to a DTV signal receiver with a comb filtering function to suppress the NTSC co-channel interference when the NTSC co-channel interference is large enough to adversely affect data-slicing operation. Support the use of data-slicing operations. The present inventors suggest a method of compensating the effects of the comb filtering operation in symbol encoding when such a comb filtering operation is selectively performed in the symbol decoding process. At that time, determine when the NTSC co-channel interference will be greater than the nominal value, named as unacceptably small, so that this decision can be used to control the selective use of the comb filtering operation to suppress NTSC co-channel interference. It is useful to decide.

NTSC co-channel interference is the imaginary of the complex output signal of the demodulator used in the DTV signal receiver whenever NTSC co-channel interference appears in the real or in-phase baseband component (I channel) of the complex output signal. Or in quadrature-phase baseband components (Q channels). Thus, the NTSC interference detector can be arranged such that its NTSC extraction filter responds to the received Q-channel signal rather than the received I-channel signal. If the NTSC co-channel interference causes too many errors in the trellis decoding process of the equalized received I-channel signal to be corrected by the Reed-Solomon decoder following the trellis decoder, the NTSC co-channel interference Channel interference is a significant amount. By determining whether a significant amount of NTSC co-channel interference is involved in the received Q-channel signal, it is speculatively determined whether a significant amount of NTSC co-channel interference is involved in the received I-channel signal. . Accurate determination of the NTSC co-channel interference level tends to be simplified further because the orthogonality of the pilot carrier of the VSB AM DTV signal after the synchronization detection device has achieved phase-lock with the pilot carrier. This is because direct bias is not fundamentally generated from phase locked detection.

NTSC co-channel interference detectors, which are not sensitive to direct bias resulting from the synchronous detection of the pilot carriers, are the object of the present invention intended by the inventors in the development of the devices disclosed herein. The above mentioned NTSC co-channel interference detector eliminates the need for an equalization filter that suppresses the direct bias resulting from the synchronous detection of pilot carriers, and whether a significant amount of NTSC co-channel interference is involved in the received I-channel signal. Allows you to determine directly whether It is more difficult to implement the equalization filter than the equalization filter responding at zero frequency. In addition, an equalization filter that does not respond at zero frequency can interfere with AGC and automatic-frequency-and-phase-control (AFPC) loops when designing a DTV signal receiver. In a DTV signal receiver responsive to the received Q-channel signal to determine whether the amount of NTSC co-channel interference is significant, NTSC co-channel interference that is not sensitive to direct bias resulting from synchronous detection of a pilot carrier. The detector is still useful. Such NTSC co-channel interference detectors provide continuity in the initial adjustment of DTV signal receiver equalization.

Accordingly, an object of the present invention is a digital television (DTV) signal for receiving a digital television signal that is received as a residual-sideband amplitude-modulated carrier and is likely to carry a co-channel interfering analog television signal of an undesired intensity in some cases. To provide a receiver.

1 is an embodiment of the present invention, which selectively operates in response to an NTSC co-channel interference detector having a comb filter for extracting NTSC artifacts from a baseband I-channel signal and suppressing a DTV pilot carrier accompanying the artifacts. Is a block diagram illustrating some circuit configurations of a digital television (DTV) receiver having a symbol decoder incorporating an NTSC co-channel interference suppression circuit according to one aspect of the present invention.

FIG. 2 is a flow chart illustrating operation in some circuitry block diagram of the digital television receiver of FIG. 1 showing how the equalization process is modified depending on the use of a comb filtering technique to suppress NTSC co-channel interference.

FIG. 3 is an embodiment of the present invention, selectively operating in response to an NTSC co-channel interference detector having a comb filter for extracting NTSC artifacts from a baseband I-channel signal and suppressing a DTV pilot carrier accompanying the artifacts. Is a block diagram illustrating some circuit configurations of a digital television (DTV) receiver having a symbol decoder incorporating an NTSC co-channel interference suppression circuit according to one aspect of the present invention.

FIG. 4 is a flowchart illustrating operation in some circuitry block diagram of the digital television receiver of FIG. 3 showing how the equalization process is modified depending on the use of comb filtering techniques to suppress NTSC co-channel interference.

FIG. 5 is a block diagram schematically showing details of some circuit configurations of the digital television (DTV) signal receiver of FIG. 1 or 3 when the NTSC-rejection comb filter uses a 12-symbol delay circuit; FIG.

FIG. 6 is a block diagram schematically showing details of some circuit configurations of the digital television (DTV) signal receiver of FIG. 1 or 3 when the NTSC-rejection comb filter uses a 6-symbol delay circuit; FIG.

FIG. 7 schematically shows the details of some circuit configurations of the digital television (DTV) signal receiver of FIG. 1 or 3 when the NTSC-rejection comb filter uses a two-image-line (1368-symbol) delay circuit. Block diagram.

FIG. 8 schematically shows the details of some circuit configurations of the digital television (DTV) signal receiver of FIG. 1 or 3 when the NTSC-rejection comb filter uses a 262-picture-line (179,208-symbol) delay circuit. Block diagram.

FIG. 9 schematically shows the details of some circuit configurations of the digital television (DTV) signal receiver of FIG. 1 or 3 when the NTSC-rejection comb filter uses a two-picture-frame (718,200-symbol) delay circuit. Block diagram.

10 is configured in accordance with the present invention, having an input signal differentially coupled with itself, such as a six-symbol differential delay in a comb filter used to extract NTSC co-channel interference artifacts that do not involve a DTV pilot carrier signal. Block diagram showing the general configuration of the NTSC co-channel interference detector.

FIG. 11 illustrates one circuit configuration of the NTSC co-channel interference detector of FIG. 10 with an input signal differentially coupled to itself, such as a 12-symbol differential delay in a comb filter used to suppress NTSC co-channel interference artifacts. A schematic block diagram.

12 illustrates the NTSC co-channel interference detector of FIG. 10 with an input signal differentially coupled to itself, such as a two-image line or 1368-symbol differential delay in a comb filter used to suppress NTSC co-channel interference artifacts. A block diagram schematically showing one circuit configuration.

FIG. 13 shows the NTSC co-channel interference detector of FIG. 10 with an input signal differentially coupled to itself, such as a 262-image line or 179,208-symbol differential delay in a comb filter used to suppress NTSC co-channel interference artifacts. A block diagram schematically showing one circuit configuration.

FIG. 14 shows the NTSC co-channel interference detector of FIG. 10 with an input signal differentially coupled to itself, such as a two-image frame or 718,200-symbol differential delay in a comb filter used to suppress NTSC co-channel interference artifacts. A block diagram schematically showing one circuit configuration.

FIG. 15 schematically illustrates one circuit configuration of the NTSC co-channel interference detector of FIG. 10 sharing elements with an NTSC-cancelling comb filter placed prior to the even-level data slicer of the DTV signal receiver of FIG. Block diagram.

FIG. 16 is a block diagram illustrating a general alternative form of circuit construction of an NTSC co-channel interference detector, constructed in accordance with the present invention, wherein the comb filter pairs in the detector of FIG. 10 each add and combine a differential-delayed detector input signal. FIG.

FIG. 17 illustrates a circuit configuration of the NTSC co-channel interference detector of FIG. 16 with an input signal that is additively coupled with itself as a six-symbol differential delay in a comb filter used to suppress NTSC co-channel interference artifacts. Schematic block diagram.

18 and 19 schematically illustrate the circuit configuration of a digital television receiver according to the present invention in which multiple comb filters and associated NTSC co-channel interference detectors are used to selectively filter for NTSC co-channel interference artifacts. Block diagram.

The present invention for achieving the above object is a digital television signal for receiving a digital television signal, which is received as a residual-sideband amplitude-modulated carrier and is likely to be accompanied by a co-channel interfering analog television signal of an undesirable intensity in some cases. In the receiver,

An amplifier circuit for supplying the amplified residual-sideband amplitude-modulated digital television signal;

Demodulation circuitry responsive to said amplified residual-sideband amplitude-modulated digital television signal to supply at least one baseband signal;

Connected to receive the I-channel baseband signal as an input signal supplied from the demodulation circuit, in order to symbol decode the I-channel baseband signal so that a symbol decoding result is generated, and a symbol decoding apparatus is equal to a significant amount of NTSC. Selectively operable upon receiving a signal indicative of the presence of channel interference and only upon receiving the signal, but optionally to suppress artifacts of the co-channel interfering analog television signal accompanying the I-channel baseband signal to be symbol decoded A symbol decoding apparatus having an operable filter;

An error correction circuit for correcting an error occurring in a symbol decoding process on a result generated in the symbol decoding apparatus;

A co-channel interference detector connected in order to receive an additional baseband input signal from said demodulation circuit and insensitive to the direct conditions of the system function of the baseband signal receiving as said input signal,

The co-channel interference detector,

The additional baseband input signal itself, such as when the first differential delay amount is generated to generate a first comb filter response, in which artifacts caused by synchronous detection of the co-channel interfering analog television signal are suppressed. A first comb filter coupled to the;

Artifacts caused by the synchronous detection of the co-channel interfering analog television signal are enhanced, and the direct condition of the system characteristic caused by the synchronous detection of the carrier is similar to the direct condition of the system characteristic of the first comb filter response. A second comb filter for coupling the additional baseband input signal with itself, such as when the second differential delay amount is to generate a second comb filter response;

A first amplitude detector for detecting an amplitude of the first comb filter response such that a first amplitude detection response is generated;

A second amplitude detector for detecting an amplitude of the second comb filter response such that a second amplitude detection response is generated; And,

The significant amount of NTSC co-channel interference exists only when and when the first amplitude detection response is compared with the second amplitude detection response and the first and second amplitude detection responses differ by more than a specified amount. And an amplitude comparator for supplying said signal.

The DTV signal receiver has a special type of co-channel interference detector that is not sensitive to the direct conditions of the system function of the predeployed circuit. The DTV signal receiver comprises an amplifier circuit for supplying an amplified residual-sideband amplitude-modulated digital television signal and the amplified signal for supplying at least one baseband signal supplied as its input signal to a co-channel interference detector. Demodulation circuitry responsive to residual-sideband amplitude-modulated digital television (DTV) signals. The at least one baseband signal comprises an I-channel baseband signal comprising artifacts of some co-channel interfering analog television signals supplied to a symbol decoding apparatus embedded in the DTV signal receiver. The symbol decoding apparatus has a filter selectively operable to suppress artifacts of a co-channel interfering analog television signal accompanying the I-channel baseband signal to be symbol decoded. This filter receives a signal from which the symbol decoding apparatus indicates the presence of a significant amount of NTSC co-channel interference. An error correction circuit embedded in the DTV signal receiver is connected to correct an error generated in a symbol decoding result supplied from the symbol decoding apparatus. The co-channel interference detector has the following configuration.

The first comb filter differentially combines one baseband signal supplied as an input signal to the co-channel interference detector with one baseband signal, such as when a first differential delay amount is generated, to generate a first comb filter response. Let's do it. With this first comb filter response, the direct conditions of system characteristics caused by the synchronous detection of the carrier and the artifacts caused by the synchronous detection of the co-channel interfering analog television signal are suppressed. The second comb filter differentially couples one baseband signal supplied as an input signal to the co-channel interference detector with one baseband signal to generate a second comb filter response as in the case of the second differential delay amount. . With this second comb filter response, direct conditions of system characteristics caused by the synchronous detection of the carrier are suppressed, and artifacts caused by the synchronous detection of the co-channel interfering analog television signal are enhanced. A first amplitude detector detects an amplitude of the first comb filter response to generate a first amplitude detection response, and a second amplitude detector detects an amplitude of the second comb filter response to generate a second amplitude detection response. An amplitude comparator compares the first amplitude detection response with the second amplitude detection response, and the significant amount of NTSC co-channel only when and when the first and second amplitude detection responses differ by more than a specified amount. The signal is supplied to indicate that interference exists.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, and like reference numerals refer to like parts throughout the drawings. In addition, detailed descriptions of functions of known components not related to the subject matter of the present invention will be omitted herein.

As will be appreciated by those skilled in the art of electronic design, in many of the circuits shown in the accompanying drawings, shimming delays are inserted to correct the order of operation. If there is anything unusual about the specific seaming delay requirement, it will not be explicitly mentioned here.

1 shows a digital television signal receiver used to recover error-correction data suitable for recording by a digital video cassette recorder (DVCR) or MPEG-2 decoding and display in a television set. Although the DTV signal receiver of FIG. 1 is shown as receiving television broadcast signals from receive antenna 8, it may receive signals from cable networks instead of antennas. The television broadcast signal is supplied as an input signal to the "front end" 10 of the DTV receiver. The “front end” 10 of the DTV receiver is generally an intermediate-frequency (IF) which feeds a radio-frequency television signal as an input signal to an intermediate-frequency (IF) amplifier chain 12 for obtaining a residual-sideband DTV signal. And a radio-frequency amplifier and a first detector for converting the television signal. The DTV signal receiver is an intermediate-frequency (IF) amplifier for amplifying a DTV signal converted into an ultra-high-frequency (UHF) band by the first detector, and the amplified DTV signal is VHF (Very-High). A multiple conversion scheme with an IF amplifier chain 12 having a second detector for converting to a -Frequency band and another intermediate-frequency (IF) amplifier for amplifying the DTV signal converted to the VHF band. It is advantageous. If demodulation to baseband is performed digitally, the IF amplifier chain 12 will further include a third detector for converting the amplified DTV signal to the final mid-frequency band close to baseband.

Surface-acoustic-wave (SAW) filters are advantageously used in IF amplifiers for the UHF band to form channel select responses and eliminate adjacent channels. The SAW filter is quickly cut off at a distance of at least 5.38 MHz from the suppressed carrier frequency of the pilot carrier and the VSB DTV signal having a similar frequency and a fixed amplitude. Thus, the SAW filter removes a large amount of frequency-modulated (FM) speech carriers of any co-channel interfering analog TV signal. By eliminating the FM voice carrier of any co-channel interfering analog TV signal in the IF amplifier chain 12, artifacts of the carrier generated when the final IF signal is detected to recover baseband symbols are avoided and the symbol during symbol decoding The artifacts that interfere with data-slicing of baseband symbols can be predicted. The prevention of artifacts that interfere with the data-slicing of the baseband symbols during the symbol decoding is a comb filtering process which is a step before the data-slicing process, especially when the differential delay in the comb filter is more than several symbol periods. Better than achieved by dependence

The final IF output signal generated in the IF amplifier chain 12 is subjected to the residual sideband amplitude modulated DTV signal in the final mid-frequency band to recover the real baseband signal and the virtual baseband signal. The demodulator is fed to a complex demodulator 14. Such demodulation may be performed digitally after analog-to-digital conversion of the final mid-frequency band of the low megacycle range, such as described in US Pat. No. 5,479,449, for example. Alternatively, the demodulation may be performed in an analog manner, in which case the result is typically subjected to analog-to-digital conversion to facilitate another process. Complex demodulation is preferably performed by in-phase (I) synchronous demodulation and quadrature-phase (Q) synchronous demodulation. The digital result of the demodulation process generally has an 8-bit accuracy and describes a 2N-level symbol that encodes N-bits of data. Recently, 2N is 8 when the DTV signal receiver of FIG. 1 receives through-the-air broadcast through the antenna 8, and the DTV signal receiver of FIG. 1 receives a cable broadcast. In case it is 16. The present invention relates to terrestrial over-the-air broadcast reception, and FIG. 1 does not illustrate some circuits of a DTV signal receiver that provides symbol and error-correction decoding functions for the received wired transmission.

The symbol synchronization and equalization circuit 16 receives at least digitized real samples of the in-phase (I-channel) baseband signal of the complex demodulator 14. The symbol synchronization and equalization circuit 16 of the DTV signal receiver of FIG. 1 also receives digitized imaginary samples of quadrature-phase (Q-channel) baseband signals. The symbol synchronization and equalization circuit 16 includes a digital filter having adjustable weighting coefficients that compensate for ghost and tilt of the received signal. The symbol synchronization and equalization circuit 16 provides symbol synchronization or "de-rotation" as well as amplitude equalization and ghost cancellation. Symbol synchronization and equalization circuitry in which symbol synchronization is achieved prior to amplitude equalization is known from US Pat. No. 5,479,449. In such a design, the complex demodulator 14 will supply an oversampled demodulator response to the symbol synchronization and equalization circuit 16 including a real baseband signal and a virtual baseband signal. After symbol synchronization, the oversampled data is decimated to extract the baseband I-channel signal at normal symbol rate and reduce the sample rate through digital filtering used for amplitude equalization and ghost cancellation. . In symbol synchronization and equalization circuits where the amplitude equalization process precedes the symbol synchronization process, "de-rotation" or "phase tracking" is also known to those skilled in the art of digital signal receiver design.

Each sample of the output signal of the symbol synchronization and equalization circuit 16 is decomposed to about 10 bits and, in fact, describes in analog form an analog symbol representing one of the (2N = 8) levels. The output signal of the symbol synchronization and equalization circuit 16 is carefully gain-controlled by any of several known methods so that the ideal step levels for the symbol are known. Since the response speed of such gain control is very fast, by one gain control method, the direct component of the real baseband signal supplied from the complex demodulator 14 is adjusted to a normalization level of +1.25. Such a gain control method is generally described in US Pat. No. 5,479,449, and CB Patel et al., "Automatic Gain Control of Radio Receiver for Receiving Digital High-Definition Television Signals," published June 3, 1997. Automatic gain control of a wireless receiver for receiving a resolution television signal) is described in more detail in US Pat. No. 5,573,454, which is also incorporated herein by reference.

The output signal of the symbol synchronization and equalization circuit 16 is supplied as its input signal to the data synchronization detection circuit 18 which recovers the data field synchronization information DFS and the data segment synchronization information DSS from the equalized baseband I-channel signal. Alternatively, the input signal of the data synchronization detecting circuit 18 can be obtained before the equalization process.

The equalized I-channel signal sample of normal symbol rate supplied as an output signal from the symbol synchronization and equalization circuit 16 is applied as its input signal to an NTSC-rejection comb filter 20. The NTSC-rejection comb filter 20 is a first delay 201 for generating a differential delay stream pair of 2N-level symbols and a first for linearly combining the differential delay symbol streams so that a response of the comb filter 20 is generated. A linear combiner 202. As described in US Pat. No. 5,260,793, the first delay unit 201 provides a delay equal to the period of twelve 2N-level symbols, and the first linear combiner 202 is a subtractor (first and second linear). One of the combiners is a subtractor and the other is an adder). Each sample of the output signal of the NTSC-rejection comb filter 20 is decomposed by about 10 bits and, in fact, describes in analog form an analog symbol representing one of (14N-1) = 15 levels.

It is contemplated that the symbol synchronization and equalization circuit 16 is designed to suppress the direct bias component of the input signal (i.e., the direct term of a system function expressed in digital samples). Each sample of the output signal of the symbol synchronization and equalization circuit 16, which is supplied as an input signal of the comb filter 20, is in fact a normalization level of -7, -5, -3, -1, +1, +3, +5 and +7. An analog symbol representing one of them is described in digital form. These symbol levels are named “odd” symbol levels and detected by odd-level data slicer 22, resulting in intermediate symbol decoding results of 000, 001, 010, 011, 100, 101, 110 and 111, respectively.

Each sample of the output signal of the comb filter 20 is in effect a normalization level of -14, -12, -10, -8, -6, -4, -2, 0, +2, +4, +6, +8, Analog symbols representing one of +10, +12 and +14 are described in digital form. These symbol levels are named "even" symbol levels and are detected by the even-level data-slicer 24 to detect 001, 010, 011, 100, 101, 110, 111, 000, 001, 010, 011, 100, 101, 110 And precoded symbol decoding results of 111 are respectively generated.

The data slicers 22 and 24 are configured in a so-called "hard decision" form that is considered in this respect in the description, or are used in a so-called "soft decision" used to perform a Viterbi decoding scheme. soft odd-number data-slicer 22 and even-level data-slicer 24 using a multiplexer connection to change the position of the circuit and provide a bias to modify its slicing range. Arrangements that can be replaced with data-slicers are possible, but such placement is undesirable due to the complexity of the operation.

The symbol synchronization and equalization circuit 16 is thought to be designed to suppress the direct bias component of the input signal (i.e., the direct term of the system function expressed in digital samples), the direct bias component being a normal level of +1.25. And appears in the real baseband signal supplied from the complex demodulator 14 due to the detection of the pilot carrier. In practice, the symbol synchronization and equalization circuit 16 is designed to preserve the direct bias component of its input signal, thereby at least in part simplifying the design of the equalization filter of the symbol synchronization and equalization circuit 16. Thus, the data-slicing level of the odd-level data-slicer 22 is offset with its input signal to account for the direct bias component involved in the data step. If the first linear combiner 202 is a subtractor, whether the symbol synchronization and equalization circuit 16 is designed to suppress or preserve the direct term of the system function of its input signal is determined by the data of the even-level data slicer 24. Not so important when it comes to slicing levels. However, if the differential delay provided by the first delay 201 is selected so that the first linear combiner 202 becomes an adder, then the data slicing level of the even-level data slicer 24 is applied to the data step with its input signal. It should be offset to account for the entailed double direct bias component.

An intersymbol-interference suppression comb filter 26 is applied to the data slicers 22 and 24 to generate a filter response in which intersymbol interference (ISI) introduced by the comb filter 20 is suppressed. Subsequently deployed and used. The ISI-suppression comb filter 26 comprises a three-input multiplexer 261, a second linear combiner 262, and a second delay 263 having a delay equal to that of the first delay 201 of the NTSC-removing comb filter 20. Equipped. The second linear combiner 262 is a modulo-8 adder if the first linear combiner 202 is a subtractor, and a modulo- if the first linear combiner 202 is an adder. 8 Subtractor. The first linear combiner 202 and the second linear combiner 262 may be configured with respective read-only memories (ROMs) to enhance the linear coupling operation to fully support the associated sample rate. The output signal of the multiplexer 261 provides the response of the ISI-suppression comb filter 26 and is delayed by the second delay 263. The second linear combiner 262 combines the result of symbol decoding precoded from the even-level data slicer 24 with the output signal of the second delay 263.

The output signal of the multiplexer 261 receives one of three input signals applied to the multiplexer 261, such that the output signal of the multiplexer 261 is selected in response to the multiplexer control signals of the first, second, and third states supplied from the controller 28 to the multiplexer 261. Play it. The first input port of the multiplexer 261 is configured to be stored in the memory in the controller 28 while data field synchronization information DFS and data segment synchronization information DSS from the equalized baseband I-channel signal are restored by the data synchronization detection circuit 18. Receive the ideal symbol decoding result supplied. The controller 28 supplies the multiplexer control signal of the first state to the multiplexer 261 during the restoration time so that the ideal symbol decoding result supplied from the memory in the controller 28 is supplied as the final coding result as the output signal. Adjust The odd-level data-slicer 22 supplies the intermediate symbol decoding result as its output signal to the second input port of the multiplexer 261. The multiplexer 261 is adjusted by the multiplexer control signal in the second state to reproduce the intermediate symbol decoding result as the final coding result supplied from the multiplexer 261. The second linear combiner 262 supplies an ISI-suppressed comb filtered symbol decoding result as an output signal to a third input port of the multiplexer 261. The multiplexer 261 is adjusted by the multiplexer control signal in the third state to reproduce the ISI-suppressed comb filtered symbol decoding result as the final coding result supplied from the multiplexer 261. Running errors occurring in the ISI-suppressed filtered symbol decoding result of the ISI-suppressed comb filter 26 may occur when the data synchronization detection circuit 18 restores the data field synchronization information DFS and the data segment synchronization information DSS. It can be reduced by feedback processing the ideal symbol decoding results supplied from the memory within.

The output signal of the multiplexer 261 of the ISI-suppression comb filter 26 is a 3-parallel-bit group assembled by the data assembler 30 for application to a trellis decoder dircuitry 32. group) includes the final symbol decoding result. The trellis decoder circuit 32 generally uses twelve trellis decoders. The trellis decoding result is supplied from the trellis decoder circuit 32 to the data de-interleaver circuit 34 for de-commutation. BYTE BUILDING circuit 36 converts the output signal of the data deinterleaver 34 into a Reed-Solomon error-corrected coded byte and applies it to the Reed-Solomon decoder circuit 38, and the Reed-Solomon decoder circuit 38 reads Perform a Solomon decoding operation to generate an error-corrected byte stream which is supplied to a data de-randomizer 40. The data de-randomizer 40 supplies reproduction data to the remaining components (not shown) of the receiver. The remaining components of a complete DTV receiver will include components such as a packet classifier, voice decoder, MPEG-2 decoder, and the like. The remaining components of the DTV receiver built into the digital tape recorder / player will include circuitry for converting data into a recording format.

Insensitive to the direct bias component of the input signal, the NTSC co-channel interference detector 44 detects the strength of artifacts arising from NTSC co-channel interference in its input signal, which is the baseband I-channel signal of the DTV signal receiver of FIG. It is used to

The NTSC co-channel interference detector 44 displays an indication indicating whether NTSC co-channel interference has sufficient strength to cause an incorrect error in the data-slicing process performed by the odd-level data-slicer 22. Supply to controller 28. If the NTSC co-channel interference detector 44 indicates that the NTSC co-channel interference does not have the strength described above, the controller 28 will supply the multiplexer control signal of the second state to the multiplexer 261 most of the time. will be. The only time this does not occur is when data field synchronization information DFS and data segment synchronization information DSS are restored by the data synchronization detection circuit 18, so that the controller 28 sends the multiplexer control signal of the first state to the multiplexer. Supply to 261. The multiplexer 261 is adjusted by the multiplexer control signal in the second state to reproduce the intermediate symbol decoding result supplied from the odd-level data-slicer 22 as its output signal.

If the NTSC co-channel interference detector 44 indicates that the NTSC co-channel interference has sufficient strength to cause an incorrect error in the data-slicing process performed by the odd-level data-slicer 22, The controller 28 will supply the multiplexer control signal of the third state to the multiplexer 261 most of the time. The only time this does not occur is when data field synchronization information DFS and data segment synchronization information DSS are restored by the data synchronization detection circuit 18, so that the controller 28 sends the multiplexer control signal of the first state to the multiplexer. Supply to 261. The multiplexer 261 is coupled to the multiplexer control signal of the third state to reproduce, as its output signal, an ISI-suppressed-filtered symbol decoding result generated by the second linear combiner 262 and supplied as a second linear combination result. Is adjusted by

FIG. 2 shows a flowchart showing how the equalization process is modified in the DTV signal receiver of FIG. 1 according to whether or not the comb filtering process for suppressing co-channel NTSC interference is used. The present inventors have found that artifacts of co-channel NTSC interference exist in the baseband symbol coding process, and if no special measures are taken to remove these artifacts, errors may occur in the calculation of equalization filter kernel coefficients. It is pointed out that.

In an initial step S1, the complex demodulation process of the digital television signal is successively performed by the complex demodulator 14 of the DTV signal receiver of FIG. 1 to orthogonally relate to the received I-channel baseband signal and the received I-channel baseband signal. The received Q-channel baseband signal at is separated. In decision step S2, which is subsequently performed on the NTSC co-channel interference detector 44 of the DTV signal receiver of FIG. 1, it is determined whether a significant amount of NTSC co-channel interference is involved in the received I-channel baseband signal. .

Significant amounts of co-channel NTSC interference in DTV signal receivers are at levels where the error correction capability of the two-dimensional Reed-Solomon decoding process after the trellis decoding process is greatly exceeded due to the number of errors incurred during the trellis decoding process. to be. Under reception conditions where normal background noise is mixed, a significant number of bit errors will eventually result in the recovered data. The substantial amount of co-channel NTSC interference of a specially designed DTV signal receiver can be easily determined through experiments conducted on its prototype.

If it is determined in step S2 that a small amount of co-channel NTSC interference is involved in the received I-channel baseband signal, then adjusting kernel weights of the digital equalization filter, step S3, and step S3. Subsequent step S4 of symbol decoding the equalization filter response generated at is performed. Adjusting the kernel weights step S3 is performed such that the digital equalization filter supplies a matched response to the I-channel baseband signal. The symbol decoding step S4 of the equalization filter response is performed to generate a symbol decoding result used in a subsequent step S5 of trellis decoding the symbol decoding result for error correction. Step S5 of performing the trellis decoding process is followed by step S6 of performing the Reed-Solomon decoding process for error correction as a result of the trellis decoding, and then deformatting the result of the Reed-Solomon decoding process. Step S7 is performed.

On the other hand, in the determination step S2, a large amount of co-channel NTSC interference is performed by comb filtering the received I-channel baseband signal and the received I-channel baseband signal using an appropriate comb filter. The kernel weight of the digital equalization filter is adjusted to match the response of the serialized digital equalization filter and the comb filter to the ideal response for the filter cascade. After step S10 for symbol decoding the response of the filter cascade is performed, step S11 for postcoding the symbol decoding response is performed to perform the corrected symbol decoding result to be used in step S5 for performing the trellis decoding process. You can get it. Performing a trellis decoding process as a result of trellis decoding following the step S5 of performing the trellis decoding process; This is done continuously.

The auxiliary method used to adjust the kernel weight of the digital equalization filter in step S3 for equalizing the digital equalization filter response is similar to the adjustment of the kernel weight of the digital equalization filter used in the prior art. This adjustment calculates a discrete Fourier transform (DFT) of the received data field synchronization code or its prescribed code portion and synchronizes the discrete Fourier transform (DFT) of the received data field synchronization code or its prescribed code portion to an ideal data field synchronization. The DFT of the DTV transmission channel can be determined by dividing by the DFT of the code or its prescribed code part. The DFT of the DTV transmission channel is normalized to the largest term to characterize the channel, and the kernel weights of the digital equalization filter are selected to compensate for the normalized DFT to characterize the channel. This method of adjustment is published July 19, 1994, in the name of the invention, "METHODS FOR OPERATING GHOST-CANCELATION CIRCUITRY FOR TV RECEIVER OR VIDEO RECORDER." This is described in more detail in US Pat. No. 5,331,416 to CB Patel et al. This method is preferred for the initial adjustment of the kernel weight of the digital equalization filter because the initial adjustment is faster than using adaptive synchronization. After initial adjustment of the kernel weight of the digital equalization filter, the adaptive equalization method is preferentially selected.

The block LMS method for performing adaptive equalization is called RAPID-UPDATE ADAPTIVE CHANNEL-EQUALIZATION FILTERING FOR DIGITAL RAPID RECEIVERS, SUCH AS HDTV RECEIVERS. US Patent No. 5,648,987 to J. Yang et al., Published July 15, 1997, under the name of the invention. The continuous LMS method for performing the adaptive equalization process is a U.S. patent application issued by ALRLimberg et al., Issued April 4, 1997, entitled "DYNAMICALLY ADAPTIVE EQUALIZER SYSTEM AND METHOD." 08 / 832,674.

In step S9, a DTF may be used to perform an auxiliary method for adjusting the kernel weight of the digital equalization filter to match the response of the serially connected digital equalization filter and the comb filter with the ideal response for the filter cascade. The DTF is particularly useful when performing a fast initial equalization process based on the use of its prescribed portion, which is a DFS code or training signal, before converting to an adaptive equalization process. The DFT (Discrete Fourier Transform) of the receiving DFS code or its prescribed code portion is calculated as comb filtered by a comb filter 20 for removing NTSC artifacts. Then, the DFT can determine the DFT indicating the characteristics of the DTV transmission channel by dividing the DFT of the ideal DFS code or its prescribed code by the DFT of the ideal data field synchronization code or its prescribed code by comb filtered. . The DFT of the DTV transmission channel is normalized to the largest term to characterize the channel, and the kernel weights of the digital equalization filter are selected to compensate for the normalized DFT to characterize the channel. After the initial adjustment of the kernel weight of the digital equalization filter, it is preferable to use an adaptive equalization method. These adaptive equalization methods differ from the methods used when the artifacts of NTSC co-channel interference are minor in that the number of possible valid signal states is doubled using the comb filter 20 to remove NTSC artifacts.

FIG. 3 shows the configuration of a DTV signal receiver different from the DTV signal receiver of FIG. 1 in that a baseband Q-channel signal other than a baseband I-channel signal is applied to the NTSC co-channel interference detector 44 as an input signal. It is a block diagram. The NTSC co-channel interference detector 44 is used to detect the strength of artifacts resulting from NTSC co-channel interference of the baseband Q-channel signal. The detection response of the NTSC co-channel interference detector 44 is not sensitive to some direct bias components appearing in the baseband Q-channel signal for the time that phase-lock of the synchronous detector of the complex demodulator 14 is to be established. Accordingly, there is no switching between the baseband signal and the comb filtering baseband signal in calculating weighting coefficients for equalization filtering in the symbol synchronization and equalization circuit 16. Some direct bias components appearing in the baseband Q-channel signal after the DTV signal receiver that acquires a DTV signal (e.g. due to poor phase-synchronization upon receiving a weak signal) are also subject to the NTSC co-channel interference. It will not affect the detection response of detector 44. In the DTV signal receiver of FIG. 3, a determination as to whether a significant amount of co-channel NTSC interference is involved in a received I-channel baseband signal is such that a significant amount of co-channel NTSC interference is caused by the received Q-channel baseband signal. Inferred from the determination as to whether or not

FIG. 4 is a flowchart showing how the equalization process is modified in the DTV signal receiver of FIG. 3 according to whether the comb filtering process for suppressing NTSC co-channel interference is used. The flowchart of FIG. 4 for the DTV signal receiver of FIG. 3 shows that a decision step S02 that determines whether a significant amount of NTSC co-channel interference is involved in the received Q-channel baseband signal results in a significant amount of co-channel interference. The content differs from the flowchart of FIG. 2 for the DTV signal receiver of FIG. 1 in that it replaces the determination step S2 for determining whether or not it is accompanied by a received I-channel baseband signal.

5 shows an NTSC-removing comb filter 120 of one modified configuration of the NTSC-removing comb filter 20 and an ISI-suppression comb filter 126 of a modified configuration of the ISI-suppression comb filter 26. A block diagram showing details of some circuit configurations of a digital television (DTV) signal receiver. A subtractor 1202 performs the function of the first linear combiner of the NTSC-removing comb filter 120 and the modulo-8 adder 1262 performs the function of the second linear combiner of the ISI-suppression comb filter 126. In the NTSC-removing comb filter 120, a 12-symbol delayer 1201 indicating a delay of 12 symbol periods is used as the first delay, and in the ISI-suppression comb filter 126, a delay indicating a delay of 12 symbol periods as the second delay is also used. 1263 is used. The 12-symbol delay represented by each of the delayers 1201 and 1263 is close to one cycle delay of the artifact of the analog TV video carrier at 59.75 times the analog TV horizontal scanning frequency f _H. The 12-symbol delay is close to the five cycle delay of the artifact of the analog TV chrominance subcarrier 287.25 times the analog TV horizontal scanning frequency f _H. The 12-symbol delay is close to the 6 cycle delay of the artifact of an analog TV voice carrier 345.75 times the analog TV horizontal scanning frequency f _H. The reason is that the differential combined response of the subtractor 1202 for frequencies close to the voice carrier, video carrier and chrominance subcarriers differentially delayed by the first delayer 1201 tends to reduce co-channel interference. to be. However, in the portion of the image signal having an edge that crosses the horizontal scanning line, the amount of correlation of the analog TV image signal spaced apart in the horizontal space direction is very small.

The multiplexer 1261 of one variation of the multiplexer 261 of FIG. 1 is determined that there is a small amount of NTSC co-channel interference present, most of the time causing an uncorrectable error in the output signal generated in the data-slice 22. The multiplexer control signal being in the second state and being in the third state most of the time it is determined that a large amount of NTSC co-channel interference is present and causes an uncorrectable error in the output signal generated at the data-slice 22. Is controlled by The multiplexer 1261 is coupled to the multiplexer control signal in its third state to feed back the modulo-8 summation of the adder 1262 as an addee to the adder 1262, delayed by the 12-symbol delayer 1263 by 12 symbol periods. Is adjusted by This is called a modular accumulation procedure in which a single error is conveyed as an execution error that is repeated every 12 symbol periods. The execution error of the ISI-suppression-filtering symbol decoding result generated by the ISI-suppression comb filter 126 is not only over the entirety of each data segment containing a DFS code but also for the four symbol periods at the beginning of each data segment. Decreased by the multiplexer 1261 in the 1 state. When this control signal is in its first state, the multiplexer 1261 reproduces, as its output signal, the ideal symbol decoding result supplied from the memory of the controller 28 of FIG. By applying an ideal symbol decoding result into the multiplexer 1261, generation of execution errors is stopped. Since there are 4 + 69 (12) symbols per data segment, the ideal symbol decoding result slips back four symbol periods in phase for each data segment, so that execution errors do not last longer than three data segments. Does not.

6 shows an NTSC-removing comb filter 220 of one modified configuration of the NTSC-removing comb filter 20 and an ISI-suppression comb filter 226 of a modified configuration of the ISI-suppression comb filter 26. A block diagram showing details of some circuit configurations of a digital television (DTV) signal receiver. In the NTSC-removing comb filter 220, a first delayer 2201 indicating a delay of 6 symbol periods is used, and a second delayer 2263 representing a delay of 6 symbol periods is also used in the ISI-suppression comb filter 226. Each of the retarder 6-symbol delay is shown by 2201 and 2263 are of the analog TV horizontal scan frequency f of 59.75 times the analog TV video carrier of the _H artifacts close to the delay of 0.5 cycles, the analog TV horizontal scan frequency f _H 287.25 It is close to the 2.5 cycle delay of the artifact of the double analog TV chrominance subcarrier, and close to the three cycle delay of some artifact of the analog TV voice carrier 345.75 times the analog TV horizontal scanning frequency f _H. The adder 2202 performs the function of the first linear combiner of the NTSC-removing comb filter 220 and the modulo-8 subtractor 2262 performs the function of the second linear combiner of the ISI-suppression comb filter 226. Since the delays indicated by each of the delayers 2201 and 2263 are shorter than the delays indicated by the respective delayers 1201 and 1263, good anti-correlation of the signal added by the adder 2202 is good. Is more likely to be good correlation of the signal differentially coupled by the subtractor 1202. Artifacts converted from frequencies close to analog TV video carriers and chroma subcarriers are trapped across the reject-frequency band of the NTSC-rejected comb filter 220 response, which is wider than the reject-frequency band of the NTSC-rejected comb filter 120 response. trap-filtered). The NTSC voice carrier artifact is trap filtered by the NTSC-rejection comb filter 120 rather than the NTSC-rejection comb filter 220. However, if the voice carrier of the co-channel interfering analog TV signal is suppressed by the SAW filtering or voice trap of the IF amplifier chain 12, insufficient speech rejection of the NTSC-rejection comb filter 220 is not a problem. The response to sync tips is continually reduced using the NTSC-rejection comb filter 220 of FIG. 6 rather than the NTSC-rejection comb filter 120 of FIG. 5, thereby reducing the trellis decoding and Reed-Solomon. The tendency to overwhelm error-correction during coding is substantially reduced.

The multiplexer 2261 of one modified configuration of the multiplexer 261 of FIG. 1 is determined to have a small amount of NTSC co-channel interference present at most times when an uncorrectable error occurs in the output signal generated in the data-slice 22. By the multiplexer control signal being in the second state and being in the third state most of the time it is determined that there is a large amount of NTSC co-channel interference causing an uncorrectable error in the output signal generated in the data-slice 22 Controlled. The multiplexer 2261 is controlled by a control signal in its third state to feed back the modulo-8 summation result of the subtractor 2262 as an addend to the subtractor 2262, delayed by the 6-symbol delayer 2263 by 6 symbol periods. Adjusted. This is called a modular accumulation procedure in which a single error is conveyed as an execution error repeated every six symbol periods. The execution error of the ISI-suppression-filtering symbol decoding result generated by the ISI-suppression comb filter 226 is not only over the entirety of each data segment including data field synchronization but also for the first four symbol periods at the beginning of each data segment. Reduced by multiplexer 2261 in the state. When this control signal is in its first state, the multiplexer 2261 reproduces the ideal symbol decoding result supplied from the memory of the controller 28 of FIG. 1 as its output signal. By inserting the ideal symbol decoding result into the output signal of the multiplexer 2261, occurrence of execution error is stopped. Since there are 4 + 138 (6) symbols per data segment, the ideal symbol decoding results in four symbol periods of phase slip back in each data segment, so that execution errors cannot last longer than two data segments. The possibility of prolonging the period of execution error in the ISI-suppression comb filter 226 may affect the trellis code, although the execution error is more frequently regenerated and this execution error is twice the 12 interleaved trellis codes. Although insane, it is actually less than in the case of the ISI-suppression comb filter 126.

7 shows an NTSC-removing comb filter 320 of one modified configuration of the NTSC-removing comb filter 20 and an ISI-suppression comb filter 326 of a modified configuration of the ISI-suppression comb filter 26. A block diagram showing details of some circuit configurations of a digital television (DTV) signal receiver. In the NTSC-removing comb filter 320, a first delay 3201 indicating a delay of 1368 symbol periods almost equal to that of two horizontal scan lines of an analog TV signal is used, and a delay of 1368 symbol periods is also used in the ISI-suppressed comb filter 326. A second delay 3263 is used. The first linear combiner of the NTSC-removing comb filter 320 is a subtractor 3202 and the second linear combiner of the ISI-suppressing comb filter 326 is a modulo-8 adder 3262.

The multiplexer 3261 in one variant of the multiplexer 261 is in a state of 2 at most times when it is determined that a small amount of NTSC co-channel interference is present, causing an uncorrectable error in the output signal generated at the data-slice 22. And is controlled by the multiplexer control signal, which is determined to be in a third state most of the time when it is determined that a large amount of NTSC co-channel interference is present and causes an uncorrectable error in the output signal generated in the data-slice 22. The DTV signal receiver preferably includes circuitry for detecting a change that has occurred between alternate scan lines within the NTSC co-channel interference, so that the controller 28 under the condition is a third of the multiplexer 3261. Supply of the state control signal can be suppressed.

The multiplexer 3261 is coupled to a control signal in its third state to feed back the modulo-8 summation of the adder 3262 as an addee to the adder 3262, which is delayed by 1368 symbol periods by the two-image line delayer 3263. Is adjusted by This is called a modular accumulation procedure in which a single error is conveyed as an execution error repeated every 1368 symbol periods. Since this symbol code length is longer than the length of a single block of the Reed-Solomon code, a single execution error is easily corrected during the Reed-Solomon decoding process. The execution error of the ISI-suppressed filtering symbol decoding result generated by the ISI-suppressed comb filter 326 is not only applied to the first state for the four symbol periods at the beginning of each data segment but also throughout each data segment including field synchronization. Which is reduced by the multiplexer 3261. When this control signal is in its first state, the multiplexer 3261 reproduces, as its output signal, the ideal symbol decoding result supplied from the memory of the controller 28 of FIG. By inserting the ideal symbol decoding result into the output signal of the multiplexer 3261, the occurrence of execution error is stopped. Since the duration of 16.67 milliseconds of the NTSC video field represents a phase slippage over 24.19 milliseconds of the DTV data field, the DTV data segment containing field sync eventually scans the entire NTSC frame raster. do. The 525 lines of the NTSC frame raster each comprise 684 symbol periods for a total of 359,100 symbol periods. Since the 359,100 symbol periods are slightly less than 432 times the 832 symbol periods of the DTV data segment with field synchronization, longer error duration execution errors than 432 data fields are ideal symbol decoding during the DTV data segment containing data field synchronization. You can speculate with confidence that it will be eliminated by the multiplexer 3261 that reproduces the result. In addition, in the case of an NTSC video scan line and a start code group that can use the ideal symbol decoding result, there is a phase difference between the data segments. It can be assumed that 359,100 symbol periods, which are 89,775 times the four symbol periods of the code start group, are scanned during 89,775 consecutive data segments. Since there are 313 data segments per DTV data field, it is possible to assume with conviction that execution errors of longer duration than 287 data fields will be eliminated by the multiplexer 3261 which reproduces the ideal symbol decoding result during the code start group. have. Since the two sources for suppressing execution errors are independent of each other, it is very unlikely that execution errors of longer duration than 200 data fields will occur. Furthermore, if the execution error reoccurs, NTSC co-channel interference drops low at once, adjusting the multiplexer 3261 to reproduce the data-slice 22 response as its output signal. Errors can be corrected faster than if.

For the NTSC-removing comb filter 320 of FIG. 7, the performance is very good in suppressing demodulation artifacts generated in response to analog TV horizontal sync pulses and many demodulation artifacts generated in response to analog TV vertical sync pulses and equalization pulses. Do. These artifacts are co-channel interference with the highest energy. The NTSC-rejection comb filter 320 differs from its color, except that scan-line-to-scan-line change occurs in the image content of an analog TV signal over two scan-line periods. It provides an excellent function that can suppress the video content regardless. The FM audio carrier of the analog TV signal is suppressed fairly well if it is not suppressed by the tracking rejection filter of the symbol synchronization and equalization circuit 16 of FIG. Artifacts of most analog TV color bursts are also suppressed in response to the NTSC-removing comb filter 320. Moreover, the filtering function provided by the NTSC-removal comb filter 320 is in an "orthogonal" relationship to the NTSC-interference cancellation function built into the trellis decoding process.

FIG. 8 shows an NTSC-removal comb filter 420 of one modified configuration of the NTSC-removing comb filter 20 and an ISI-suppression comb filter 426 of a modified configuration of the ISI-suppression comb filter 26. A block diagram showing details of some circuit configurations of a digital television (DTV) signal receiver. In the NTSC-removing comb filter 420, a first delayer 4201 is used which exhibits a delay of 179,208 symbol periods which is approximately equal to the period of 262 horizontal scan lines of the analog TV signal. A second delay 4263 is used. A subtractor 4202 performs the function of the first linear combiner of the NTSC-removing comb filter 420, and the modulo-8 adder 4262 performs the function of the second linear combiner of the postcoding comb filter 426.

The multiplexer 4261 of one modified configuration of the multiplexer 261 of FIG. The multiplexer control signal being in the second state and being in the third state most of the time it is determined that a large amount of NTSC co-channel interference is present and causes an uncorrectable error in the output signal generated at the data-slice 22. Is controlled by The DTV signal receiver preferably includes circuitry for detecting field-to-field changes within the NTSC co-channel interference, so that the controller 28 is configured to operate the multiplexer 4261 under such conditions. Supply of the third state control signal can be suppressed.

The multiplexer 4261 feeds the modulo-8 summation of the adder 4262 into the control signal in its third state to be fed back to the adder 4262 as delayed by 179,208 symbol periods by the 262-image line delayer 4263. Is adjusted by This is called a modular accumulation process in which a single error is conveyed as an execution error repeated every 179,208 symbol periods. Since this symbol code length is longer than the length of a single block of the Reed-Solomon code, a single execution error is easily corrected during the Reed-Solomon decoding process. The execution error of the ISI-suppressed filtering symbol decoding result generated by the ISI-suppressed comb filter 426 is not only applied to the first state for the four symbol periods at the beginning of each data segment but also throughout each data segment including field synchronization. Which is reduced by the multiplexer 4261. When this control signal is in its first state, the multiplexer 4261 reproduces, as its output signal, an ideal symbol decoding result supplied from the memory of the controller 28 of FIG. By inserting the ideal symbol decoding result into the output signal of the multiplexer 4261, the occurrence of execution error is stopped. It can be estimated that the maximum number of data fields necessary to remove the execution error of the output signal of the multiplexer 4261 is approximately equal to the maximum number of data fields required to eliminate the execution error of the output signal of the multiplexer 3261. However, the number of times the error is repeated in this period is reduced by the factor 131.

The NTSC-removing comb filter 420 of FIG. 8 suppresses all demodulation artifacts generated in response to analog TV horizontal sync pulses and most demodulation artifacts generated in response to analog TV vertical sync pulses and equalization pulses. These artifacts are co-channel interference with the highest energy. In addition, the NTSC-removing comb filter 420 suppresses artifacts caused in the video content of an analog TV signal that does not change from field-to-field or line-to-line, thereby irrespective of its horizontal spatial frequency or color. The stop pattern can be removed. Artifacts of most analog TV color bursts are also suppressed in response to the NTSC-removing comb filter 420.

FIG. 9 shows the NTSC-removal comb filter 520 of one modified configuration of the NTSC-removing comb filter 20 and the ISI-suppression comb filter 526 of the modified configuration of the ISI-suppression comb filter 26. A block diagram showing details of some circuit configurations of a digital television (DTV) signal receiver. In the NTSC-removing comb filter 520, a first delay 5201 indicating a delay of 718,200 symbol periods which is approximately equal to a period of two frames of an analog TV signal is used, and the ISI-suppression comb filter 526 also exhibits a delay of 718,200 symbol periods. Second delay 5263 is used. The subtractor 5202 performs the function of the first linear combiner of the NTSC-removing comb filter 520, and the modulo-8 adder 5262 performs the function of the second linear combiner of the postcoding comb filter 526.

The multiplexer 5261 of one modified configuration of the multiplexer 261 of FIG. 1 is determined to have a small amount of NTSC co-channel interference present at most times when an uncorrectable error occurs in the output signal generated in the data-slice 22. By the multiplexer control signal being in the second state and being in the third state most of the time it is determined that there is a large amount of NTSC co-channel interference causing an uncorrectable error in the output signal generated in the data-slice 22 Controlled. The DTV signal receiver preferably comprises circuitry for detecting a change between alternating frames within the NTSC co-channel interference, so that the controller 28 is in such a state the third state control signal of the multiplexer 5261. The supply of can be suppressed.

The multiplexer 5261 feeds the modulo-8 summation of the adder 5262 into the control signal in its third state to be fed back to the adder 5262 as delayed by 718,200 symbol periods by the two-image frame delayer 5263. Is adjusted by This is called a modular accumulation process in which a single error is conveyed as an execution error repeated every 718,200 symbol periods. Since this symbol code length is longer than the length of a single block of the Reed-Solomon code, a single execution error is easily corrected during the Reed-Solomon decoding process. The execution error of the ISI-suppressed filtering symbol decoding result generated by the ISI-suppressed comb filter 526 is not only applied to the first state for the four symbol periods at the beginning of each data segment but also throughout each data segment including field synchronization. Which is reduced by the multiplexer 5261. When this control signal is in its first state, the multiplexer 5261 reproduces the ideal symbol decoding result supplied from the memory of the controller 28 in Fig. 1 as its output signal. By inserting the ideal symbol decoding result into the output signal of the multiplexer 5261, occurrence of execution error is stopped. It can be estimated that the maximum number of data fields required to remove the execution error of the output signal of the multiplexer 5261 is approximately equal to the maximum number of data fields required to eliminate the execution error of the output signal of the multiplexer 5261. However, the number of times the error is repeated in this period is reduced by the factor 525.

The NTSC-removing comb filter 520 of FIG. 9 suppresses all demodulation artifacts generated in response to analog TV horizontal sync pulses and most demodulation artifacts generated in response to analog TV vertical sync pulses and equalization pulses. These artifacts are co-channel interference with the highest energy. In addition, the NTSC-removing comb filter 520 can eliminate such a still pattern regardless of its spatial frequency or color by suppressing artifacts resulting from the video content of an analog TV signal that does not change over two frames. Artifacts of all analog TV color bursts are also suppressed in response to the NTSC-removing comb filter 520.

FIG. 10 is a block diagram illustrating a general configuration of the NTSC co-channel interference detector 44 in the DTV signal receivers of FIGS. 1 and 3. Node 440 receives an input signal for the NTSC co-channel interference detector 44, which is an equalized I-channel or Q supplied from symbol synchronization and equalizer circuit 16 of the DTV signal receivers of FIGS. Can be a channel baseband signal. Further, the input signal may instead be an I-channel or Q-channel baseband signal supplied without equalization from the complex demodulator 14 of the modified DTV signal receiver of FIG. 1 or 3. In the NTSC cancellation comb filter in the NTSC co-channel interference detector 44, the third delayer 441 differentially delays the input signal applied to the node 440 to generate the subtracted and subtracted input signals for the digital subtractor 442. The difference output signal generated by the subtractor 442 is an NTSC-rejection comb filter response R where artifacts resulting from synchronous detection of the co-channel interfering analog television signal are suppressed. In the NTSC-selected comb filter in the NTSC co-channel interference detector 44, the fourth delay 443 differentially delays the input signal applied to the node 440 to generate the subtracted and subtracted input signal for the digital subtractor 444. The difference output signal generated by the subtractor 444 is an NTSC-selected comb filter response S with enhanced artifacts resulting from synchronous detection of the co-channel interfering analog television signal. The direct term of the system characteristic resulting from the synchronization detection of the pilot carriers is suppressed by the NTSC-rejection comb filter response R and the NTSC-selection comb filter response S.

The amplitude of the NTSC-rejected comb filter response R from the subtractor 442 is detected by an amplitude detector 445 and the amplitude of the NTSC-selected comb filter response S from the subtractor 444 is detected by an amplitude amplifier 446. Amplitude comparator 447 compares the results of amplitude detection by amplitude detectors 445 and 446 to generate an output bit that indicates whether the response of amplitude detector 446 substantially exceeds the response of amplitude detector 445. This output bit is used to select the state between the second and third states of multiplexer 261 operation. For example, the output bit generated from the amplitude comparator 447 may be one of two control bits supplied to the multiplexer 261 of the ISI-suppression comb filter 26 of FIG. 1 or 3. The other control bits indicate whether the signal supplied from the controller 28 is to be reproduced in the multiplexer 261 response.

Since the amplitude detectors 445 and 446 can be envelope detectors with a time constant equal to, for example, multiple data sample intervals, the difference in the data components of the input signal is a low value that makes the input signal guess random. Tends to average. Amplitude differences in random noise associated with the difference output signals of the subtractors 442 and 444 also tend to be averaged to zero. Thus, when amplitude comparator 447 indicates that the amplitude detection responses of the amplitude detectors 445 and 446 differ by more than a prescribed amount, this is a significant level or more in the baseband signal where the artifacts of some co-interference analog television signal are supplied to node 440. Indicates that This significant level corresponds to the significant level for the equalized I-channel baseband signal applied to the odd-level data slicer 22. Errors occurring in symbol decoding performed through simple data slicing of the I-channel baseband signal are subject to the teleless and read-out as long as the artifacts of some co-channel interfering analog television signals remain below a significant level. Can be corrected by the Solomon error-correction coding process.

NTSC co-channel interference artifacts are removed with the comb filter response R generated in the subtractor 442 and NTSC co-channel interference artifacts are selected with the comb filter response S generated in the subtractor 444. If the amplitude of the comb filter response S is actually greater than the amplitude of the comb filter response R, this difference can be assumed to be caused by the presence of NTSC co-channel interference artifacts in the signal at node 440. For this situation, due to the output bits supplied by the amplitude comparator 447, the multiplexer 261 is adjusted so that it is not operated in its second state, so that the intermediate symbol decoding result from the odd-level data slicer 22 results in the multiplexer. It does not appear as the result of the final symbol decoding from 261.

If the amplitude of the comb filter response S is not actually greater than the amplitude of the comb filter response R, this lack of difference is assumed to be caused by the absence of NTSC co-channel interference artifacts in the signal at node 440. Can be. For this situation, due to the output bits supplied by the amplitude comparator 447, the multiplexer 261 is adjusted such that it is not operated in its third state, thereby decoding the ISI-suppressed filtering symbol generated from the second linear combiner 262. The result does not appear as the final symbol decoding result generated from the multiplexer 261.

In a preferred embodiment of the NTSC co-channel interference detector 44 shown in Figs. 11-14, the 6-symbol delayer 1443 is used as the fourth delayer 443.

FIG. 11 is a block diagram illustrating an NTSC co-channel interference detector 144 of a modified configuration of the NTSC co-channel interference detector 44 of FIG. 10, specifically for use in the symbol decoding apparatus of FIG. 5. The third delay 1441 provides a 12-symbol differential delay between the subtracted input signal and the subtracted input signal to the subtractor 442 of the comb filter that suppresses NTSC co-channel interference artifacts associated with the baseband signal supplied to the node 440. to provide. These artifacts result from analog TV signal components having frequencies close to the frequencies of the video carrier, color subcarrier, and audio carrier. In some unfavorable embodiments of the invention, the third delayer 441 is configured to suppress NTSC co-channel interference caused by analog TV signal components having frequencies close to the frequencies of the image carrier and color subcarriers. It is chosen to have a delay slightly longer or slightly shorter than the duration of the horizontal scan line.

FIG. 12 is a block diagram illustrating an NTSC co-channel interference detector 344 of a modified configuration of the NTSC co-channel interference detector 44 of FIG. 10, specifically for use in the symbol decoding apparatus of FIG. 7. At the NTSC co-channel interference detector 344, the 1368-symbol third delay 3434 provides a two-image line duration differential delay in the NTSC-cancelled comb filter used to suppress the NTSC co-channel interference artifacts.

FIG. 13 is a block diagram illustrating an NTSC co-channel interference detector 444 of one modified configuration of the NTSC co-channel interference detector 44 of FIG. 10, specifically for use in the symbol decoding apparatus of FIG. 8. At NTSC co-channel interference detector 444, 179,208-symbol third delayer 4441 provides a 262-picture line duration differential delay in the NTSC-rejection comb filter used to suppress NTSC co-channel interference artifacts.

FIG. 14 is a block diagram illustrating an NTSC co-channel interference detector 544 of a modified configuration of the NTSC co-channel interference detector 44 of FIG. 10, in particular for use in the symbol decoding apparatus of FIG. 9. In the NTSC co-channel interference detector 544, the 718,200-symbol delay 5454, which provides a two-picture-frame duration differential delay, is the third delay in the NTSC-rejection comb filter used to suppress NTSC co-channel interference artifacts. Used.

FIG. 15 shows an NTSC co-channel interference detector 044 of one modified configuration of the NTSC co-channel interference detector 44 of FIG. 5 replaces the fourth delayer 443 with an NTSC- of one modified configuration of the NTSC-removal comb filter 20 of FIG. A block diagram showing how to share as the first delay portion of the cancellation comb filter 020. The remaining component 0201 of the first delay unit is connected in series with the fourth delay unit 443 to generate a subtracted and a subtracted input signal for the digital subtractor 0202 by differentially delaying the input signal supplied to the node 440. The subtractor 0202 serves as a first linear combiner in the NTSC-removing comb filter 20. Due to the difference output signal of the subtractor 0202, the NTSC-rejection comb filter response is supplied as its input signal to the even-level data slicer 24 as well as the input signal to the amplitude detector 445. The third delayer 441 is provided by the series connected components 443 and 0201 providing a first delay in the NTSC-removing comb filter 020, and the subtractor 442 is provided by a subtractor 0202 of the NTSC-removing comb filter 020. Is provided. Thus, in Figure 15 the components 441 and 442 are included in the NTSC-rejection comb filter 020 and do not exist separately. Intersymbol interference introduced by the NTSC-removing comb filter 020 is characterized by an ISI-suppression comb filter 026 of a modified configuration of an ISI-suppression comb filter 26 using a modulo-8 digital adder 0262 as a second linear combiner. Are suppressed by

FIG. 16 is a block diagram illustrating a general configuration of the NTSC co-channel interference detector 46 in the DTV signal receivers of FIGS. 1 and 3. Node 460 receives an input signal for the NTSC co-channel interference detector 44, which is an equalized I-channel or Q- supplied from the symbol synchronization and equalization circuit 16 of the DTV signal receivers of FIGS. It can be a channel baseband signal. Further, the input signal may instead be an I-channel or Q-channel baseband signal supplied without equalization from the complex demodulator 14 of the modified DTV signal receiver of FIG. 1 or 3. In the NTSC cancellation comb filter in the detector 46, the fifth delayer 461 differentially delays the input signal applied to the node 460 to generate a singular input signal for the digital adder 462. The sum output signal generated from the adder 462 is the NTSC-rejection comb filter response R where artifacts resulting from synchronous detection of the co-channel interfering analog television signal are suppressed. In the NTSC-selected comb filter in the NTSC co-channel interference detector 46, the sixth delay 463 differentially delays the input signal applied to the node 460 to generate an additional input signal for the digital adder 464. The summing output signal generated from the adder 464 is an NTSC-selected comb filter response S with enhanced artifacts resulting from synchronous detection of the co-channel interfering analog television signal. In the NTSC co-channel interference detector 46, the direct term of the system characteristic resulting from the synchronous detection of a pilot carrier is rather than suppressed as in the NTSC co-channel interference detector 44, rather than the NTSC-cancelled comb filter response R and the NTSC-selected comb filter boosted by response S.

The amplitude of the NTSC-rejected comb filter response R from the adder 462 is detected by an amplitude detector 465 and the amplitude of the NTSC-selected comb filter response S from the adder 464 is detected by an amplitude amplifier 466. Amplitude comparator 467 compares the results of amplitude detection by amplitude detectors 465 and 466 to generate an output bit that indicates whether the response of amplitude detector 466 substantially exceeds the response of amplitude detector 465. This output bit is used to select the state between the second and third states of multiplexer 261 operation. For example, the output bit generated from the amplitude comparator 467 may be one of two control bits supplied by the controller 28 to the multiplexer 261 of the ISI-suppression comb filter 26 of FIG. 1 or 3. The other control bits indicate whether the signal supplied from the controller 28 is to be reproduced in the multiplexer 261 response.

Since the amplitude detectors 465 and 466 can be envelope detectors with a time constant equal to, for example, multiple data sample intervals, the difference in the data components of the input signal is a low value that makes the input signal guess random. Tends to average. The amplitude difference between the random noise and the direct term associated with the summation output signal of the adders 462 and 464 also tends to average to zero. Thus, when amplitude comparator 467 indicates that the amplitude detection responses of the amplitude detectors 465 and 466 differ by more than a prescribed amount, this is a significant level above the baseband signal where the artifacts of some co-interfering analog television signals are supplied to node 460. Indicates that This significant level corresponds to the significant level for the equalized I-channel baseband signal applied to the odd-level data slicer 22. Errors occurring in symbol decoding performed through simple data slicing of the I-channel baseband signal are subject to the teleless and read-out as long as the artifacts of some co-channel interfering analog television signals remain below significant levels. Can be corrected by the Solomon error-correction coding process.

NTSC co-channel interference artifacts are removed with the comb filter response R generated at the adder 462 and NTSC co-channel interference artifacts are selected with the comb filter response S generated at the adder 464. If the amplitude of the comb filter response S is actually greater than the amplitude of the comb filter response R, this difference can be assumed to be caused by the presence of NTSC co-channel interference artifacts in the signal at node 460. For this situation, due to the output bits supplied by the amplitude comparator 467, the multiplexer 261 is adjusted so that it is not operated in its second state, whereby the intermediate symbol decoding result generated from the odd-level data slicer 22 results in the multiplexer. It does not appear as the final symbol decoding result from 261.

If the amplitude of the comb filter response S is not actually greater than the amplitude of the comb filter response R, this lack of difference is assumed to be caused by the absence of NTSC co-channel interference artifacts in the signal at node 460. Can be. For this situation, due to the output bits supplied by the amplitude comparator 467, the multiplexer 261 is adjusted such that it is not operated in its third state, thereby decoding the ISI-suppressed filtering symbol generated from the second linear combiner 262. The result does not appear as the final symbol decoding result generated from the multiplexer 261.

FIG. 17 is a block diagram illustrating an NTSC co-channel interference detector 244 of a modified configuration of the NTSC co-channel interference detector 46 of FIG. 10, in particular for use in the symbol decoding apparatus of FIG. 6. The fifth delayer 2461 provides a six-symbol differential delay between the subject input signals to the adder 462 of the comb filter that suppresses NTSC co-channel interference artifacts associated with the baseband signal supplied to the node 460. These artifacts result from analog TV signal components having frequencies close to those of the video carrier, color subcarrier. The sixth delay 2463 is added to the adder 462 of the comb filter for enhancing NTSC co-channel interference artifacts arising from frequencies close to the frequencies of the image carrier and color subcarriers, accompanied by the baseband signal supplied to the node 460. Provides 12-symbol differential delay between the input signal.

FIG. 18 illustrates a modified embodiment of the DTV signal receiver of FIG. 1 in the manner described above, configured in accordance with another aspect of the present invention, for utilizing multiple even-level data slicers A24, B24 and C24 operating in parallel. The block diagram shown. Each data slicer is placed after the NTSC-removing comb filter and placed before the ISI-suppression comb filter. The even-level data slicer A24 converts the response of the NTSC-rejection filter A20 of the first scheme to the first precoded symbol decoding result and applies it to the ISI-suppressed comb filter A26 of the first scheme. The even-level data slicer B24 converts the response of the NTSC-rejection filter B20 of the second scheme into a second comb filtered symbol decoding result and applies it to the ISI-suppressed comb filter B26 of the second scheme. The even-level data slicer C24 converts the response of the third type NTSC-rejection filter C20 into a third comb filtered symbol decoding result and applies it to the third type ISI-suppressed comb filter C26. The odd-level data-slicer 22 supplies intermediate symbol decoding results to the ISI-suppressed comb filters A26, B26 and C26. The prefixes A, B and C added to the identification numbers for the components of FIG. 18 are integers 1,2,3,4 and 5 when the receiver portion as shown in any of FIGS. 5 to 9 is used. Different integer values to correspond to either.

The co-channel interference detector A44 of the first scheme determines how the NTSC-cancellation comb filter A20 of the first scheme effectively reduces the co-channel interference of the analog TV signal presently in the equalized I-channel signal. Judge from the signal. A second mode co-channel interference detector B44 determines how the NTSC-rejection comb filter B20 of the second method effectively reduces the co-channel interference of the analog TV signal presently in the equalized I-channel signal. Judge from the signal. A third mode co-channel interference detector C44 determines how the third mode NTSC-rejection comb filter C20 effectively reduces the co-channel interference of the analog TV signal presently in the equalized I-channel signal. Judge from the signal. By suppressing the pilot carrier of the Q-channel signal, the co-channel interference detectors A44, B44 and C44 can easily provide an indication of the relative effectiveness of the NTSC-removing comb filters A20, B20 and C20.

The symbol decoding selection circuit 90 generates and applies the best estimate of the correction symbol decoding to the data assembler 30. This best estimate is the ideal symbol decoding result generated in the controller 28, the intermediate symbol decoding result generated in the odd-level data slicer 22, and the ISI-suppressed filtering symbol decoding generated in the ISI-suppressed comb filters A26, B26, and C26. Generated by selecting from the results. The symbol decoding selection circuit 90 responds to an indication of validity from the co-channel interference detectors A44, B44 and C44 if the controller 28 does not supply additional symbol selection information to the symbol decoding selection circuit 90. Formulate the best estimate above. The additional symbol selection information supplied from the controller 28 includes an indication as to when the synchronization code occurs, such that the best estimate is estimated based on the ideal symbol decoding result generated at the controller 28. Adjusted. The best estimate of the symbol decoding result is used to correct the summing process with matching comb filters A26, B26 and C26 in the preferred embodiment of the DTV signal receiver of FIG.

If all of the co-channel interference detectors A44, B44, and C44 indicate a lack of substantial artifacts from NTSC co-channel interference outside the time of occurrence of the synchronization code, then the symbol decoding selection circuitry 90 is said odd- Answer to select the intermediate symbol decoding result generated at level data slicer 22 as the best estimate of the correction symbol decoding result. This minimizes the effect of Johnson noise in symbol decoding.

If the at least one co-channel interference detector of the co-channel interference detectors A44, B44, and C44 indicates substantial artifacts from NTSC co-channel interference at a time other than when the synchronization code is generated, the symbol decoding selection circuit 90 is placed subsequent to one of the NTSC-rejection comb filters A20, B20 and C20 that best suppresses artifacts resulting from NTSC co-channel interference as determined by the co-channel interference detectors A44, B44 and C44. Respond to select the ISI-suppressed filtering symbol decoding result generated in the ISI-suppressed comb filter A26, B26 or C26.

High-energy demodulation artifacts generated in response to analog TV sync pulses, equalization pulses, and color bursts are all suppressed when the NTSC-rejection comb filter A20 adds and combines alternating picture frames. In addition, artifacts occurring in the video content of an analog TV signal that does not change two frames are suppressed, so that a still pattern is removed regardless of its spatial frequency or color. The co-channel interference detector A44 of FIG. 14 is used with the symbol decoding circuit of FIG.

The remaining problem with suppressing demodulation artifacts is related to suppressing the demodulation artifacts that result from the frame-to-frame difference at any pixel location in the analog TV signal raster. These demodulation artifacts can be suppressed by intra-frame filtering techniques. The NTSC-removing comb filter B20 and ISI-suppression comb filter B26 circuit may be selected to suppress residual demodulation artifacts depending on the correlation in the horizontal direction, and the NTSC-removal comb filter C20 and ISI-suppression comb filter C26 circuit may be selected. Can be selected to suppress residual demodulation artifacts depending on the correlation in the vertical direction. Consider further how such design decisions are made.

Assuming that the voice carrier of the co-channel interfering analog TV signal is suppressed through sound traps or SAW filtering of DTV IF-amplifier chain 12, the NTSC-rejection comb filter B20 and the ISI-suppression comb filter B26 circuit are It is advantageously chosen to be in the same manner as the NTSC-removing comb filter 220 and the ISI-suppression comb filter 226 circuit of FIG. 6. The reason is that the anti-correlation between image components that are only 6 symbol periods apart from one another is usually superior to the correlation between image components that are only 12 symbol periods apart from each other. The co-channel interference detector B44 of FIG. 17 is used with the symbol decoding circuit of FIG.

The optimal selection for the NTSC-removing comb filter C20 and the ISI-suppressing comb filter C26 circuit is not straightforward. NTSC co-channel interference signals are field-parallel scanned. Therefore, in the NTSC-removing comb filter C20, an alternative should be made as to whether the current scan line is to be combined with the temporally closer scan line in the same field or the spatially closer scan line in the preceding field. In general, it is a better choice to select a temporally closer scan line in the same field. The reason is that jump cuts between fields reduce the possibility of NTSC removal by the comb filter C20. In such a selection, the NTSC-rejection comb filter C20 and the ISI-suppression comb filter C26 circuit are configured in the same manner as the NTSC-rejection comb filter 320 and the ISI-suppression comb filter 326 circuit of FIG. 7. The co-channel interference detector C44 of FIG. 12 is used with the symbol decoding circuit of FIG.

Instead of another choice, the NTSC-rejection comb filter C20 and the ISI-suppression comb filter C26 circuit are configured in the same manner as the NTSC-rejection comb filter 420 and the ISI-suppression comb filter 426 circuit of FIG. 8. The co-channel interference detector C44 of FIG. 13 is used with the symbol decoding circuit of FIG.

19 shows that the co-channel interference detectors A44, B44 and C44 detect the presence of NTSC co-channel interference artifacts of the Q-channel baseband DTV signal rather than detecting the presence of artifacts of the I-channel baseband DTV signal. 18 is a block diagram showing a modified embodiment of the DTV signal receiver of FIG. By detecting the presence of NTSC co-channel interference artifacts of the I-channel baseband DTV signal, as performed by the DTV signal receiver of FIG. The delay elements can be shared with the filters A20, B20 and C20.

Those skilled in the art of designing a DTV receiver will appreciate that the present invention may be obtained by understanding the foregoing description, which may design other embodiments of the present invention, and the following claims, which are intended to include such embodiments within the scope of the present invention. Could be done.

As described above, according to the present invention, an equalization suppressing direct bias resulting from synchronous detection of a pilot carrier is used by using an NTSC co-channel interference detector which is not sensitive to direct bias generated from synchronous detection of the pilot carrier. Aside from the need for a filter, one can directly determine whether a significant amount of NTSC co-channel interference occurs simultaneously with the received I-channel signal. Also, in a DTV signal receiver, indirectly determining, by an NTSC co-channel interference detector responsive to the received Q-channel signal, whether or not a significant amount of NTSC co-channel interference is involved in the received I-channel signal. The use of an NTSC co-channel interference detector, which is not sensitive to direct bias resulting from the synchronous detection of C, provides continuity in the initial adjustment of the DTV signal receiver equalization.

So far, the present invention has been described in connection with specific embodiments, but the above disclosure is merely an application of the present invention, and is limited to the specific embodiments disclosed herein as the best mode for carrying out the present invention. It doesn't happen.

In addition, one of ordinary skill in the art can easily understand that the present invention can be variously modified and changed without departing from the spirit or the field of the present invention provided by the scope of the following claims. There will be.

Claims (27)

A digital television signal receiver for receiving a digital television signal received as a residual-sideband amplitude-modulated carrier, which is in some cases likely to carry undesired intensity co-channel interfering analog television signals: An amplifier circuit for supplying the amplified residual-sideband amplitude-modulated digital television signal; Demodulation circuitry responsive to said amplified residual-sideband amplitude-modulated digital television signal to supply at least one baseband signal; A symbol decoding apparatus for symbol decoding an I-channel baseband signal for generating a symbol decoding result, the apparatus being connected to receive an I-channel baseband signal as an input signal at the demodulation circuit, wherein the device is the I to be symbol decoded. A filter that is selectively operative for suppressing certain artifacts of the co-channel interference analog television signal accompanying the channel baseband signal, the filter further comprising a significant amount of co-channel NTSC interference A symbol decoding device configured to be operable only when receiving a predetermined signal indicating existence; An error correction circuit for correcting an error generated in a symbol decoding result in the symbol decoding apparatus; A co-channel interference detector coupled to receive an additional baseband input signal from the demodulation circuit and insensitive to the direct condition of the system function of the baseband signal receiving as the input signal; The co-channel interference detector, The additional baseband input signal whose artifact caused by the synchronous detection of the co-channel interfering analog television signal is suppressed with its own signal affected by a first differential delay amount to generate a first comb filter response. A first comb filter to be coupled; Artifacts caused by synchronous detection of the co-channel interfering analog television signal are enhanced, and the direct conditions of system characteristics resulting from synchronous detection of the carrier signal are similar to the corresponding conditions in the first comb filter response. A second comb filter for combining the additional baseband input signal with its own signal affected by a second differential delay amount to generate a second comb filter response; A first amplitude detector for detecting an amplitude of the first comb filter response such that a first amplitude detection response is generated; A second amplitude detector for detecting an amplitude of the second comb filter response such that a second amplitude detection response is generated; Compare the first amplitude detection response to the second amplitude detection response and indicate that the significant amount of co-channel NTSC interference is present only if the first and second amplitude detection responses differ by more than a specified amount. And an amplitude comparator for supplying a signal. The method of claim 1, wherein the demodulation circuit, The amplified residual to supply a Q-channel baseband signal comprising additional artifacts of an I-channel baseband signal and any co-channel interfering analog television signal used to apply the input signal to the symbol decoding apparatus. A complex demodulator responsive to sideband amplitude-modulated digital television signals. 3. The digital television signal receiver of claim 2, wherein the Q-channel baseband signal supplied from the complex demodulator is used to apply the additional baseband signal as its input signal to the co-channel interference detector. 3. The digital television signal receiver of claim 2, wherein the I-channel baseband signal supplied from the complex demodulator is used to apply the additional baseband signal as its input signal to the co-channel interference detector. The method of claim 1, wherein the first comb filter, Differentially combine the additional baseband input signal with its own signal affected by the first differential delay amount to produce the first comb filter response, wherein the second comb filter comprises: And digitally combine the additional baseband input signal with its own signal affected by the second differential delay amount to produce a two-comb filter response. 6. The digital television signal receiver of claim 5, wherein the second differential delay amount is six symbol epochs. 7. The digital television signal receiver of claim 6, wherein the first differential delay amount is 12 symbol epochs. 7. The digital television signal receiver of claim 6, wherein the first differential delay amount is 1368 symbol periods or the duration of two NTSC video scan lines. 7. The digital television signal receiver of claim 6, wherein the first differential delay amount is 179,208 symbol periods or durations of 262 NTSC video scan lines. 7. The digital television signal receiver of claim 6, wherein the first differential delay amount is 718,200 symbol periods or the duration of two NTSC video frames. 4. The first comb filter of claim 1, wherein the first comb filter further combines the additional baseband input signal with its own signal affected by the first differential delay amount to produce the first comb filter response. And wherein the second comb filter adds and combines the additional baseband input signal with its own signal affected by the second differential delay amount to produce the second comb filter response. And a digital television signal receiver. 12. The digital television signal receiver of claim 11 wherein the first differential delay amount is six symbol periods. 13. The digital television signal receiver as claimed in claim 12, wherein the second differential delay amount is 12 symbol periods. A digital television signal receiver for receiving a digital television signal received as a residual-sideband amplitude-modulated carrier, which is in some cases likely to carry undesired intensity co-channel interfering analog television signals: An amplifier circuit for supplying the amplified residual-sideband amplitude-modulated digital television signal; Demodulation circuitry responsive to said amplified residual-sideband amplitude-modulated digital television signal to supply at least one baseband signal; A symbol decoding device coupled to receive an I-channel baseband signal comprising artifacts of any co-channel interfering analog television signal as an input signal supplied from the demodulation circuit; A first data slicer embedded in said symbol decoding apparatus for symbol decoding said I-channel baseband signal to produce a first symbol decoding result; To combine the I-channel baseband signal affected by the first differential delay amount with itself to produce a first comb filter response that suppresses artifacts caused by the synchronous detection of the co-channel interfering analog television signal. The first comb filter embedded in the symbol decoding apparatus; A second data slicer embedded in said symbol decoding apparatus for symbol decoding said first comb filter response during a second period such that a second symbol decoding result is generated; Corresponding to the first symbol decoding result during a first time period and corresponding to the second symbol decoding result during a second time period, so that each of the first and second delay amounts is different from the other one so that a final symbol decoding result is generated. The second comb filter embedded in the symbol decoding apparatus for combining the selected symbol decoding result, the same symbol period number, with the final symbol decoding result dependent on the second delay amount; Errors generated in the first symbol decoding result selected as the final symbol decoding result, as long as the artifact of any co-channel interfering analog television signal has a strength that is weaker than the undesirable strength in the I-channel baseband signal. An error correction circuit having an ability to correct an error and connected to correct an error occurring in the final symbol decoding result; And A co-channel interference detector connected in order to receive an additional baseband input signal from said demodulation circuit and in a manner insensitive to the direct conditions of the system function of the baseband signal receiving as said input signal; The co-channel interference detector, The additional baseband input signal is affected by a third differential delay amount to generate a third comb filter response in which artifacts caused by synchronous detection of the co-channel interfering analog television signal are suppressed. A third comb filter coupled differentially with the third comb filter; The fourth comb, wherein the artifacts caused by the synchronous detection of the co-channel interfering analog television signal are enhanced, and the direct conditions of the system characteristics resulting from the synchronous detection of the carrier are similar to the corresponding conditions in the first comb filter response. A fourth comb filter for differentially combining the additional baseband input signal with its own signal affected by a fourth differential delay amount to generate a filter response; A first amplitude detector for detecting an amplitude of the third comb filter response such that a first amplitude detection response is generated; A second amplitude detector for detecting an amplitude of the fourth comb filter response such that a second amplitude detection response is generated; And A co-channel interfering analog television signal of the I-channel baseband signal when the first amplitude detection response is compared with the second amplitude detection response and the first and second amplitude detection responses differ by more than a specified amount. The error correction circuit includes an amplitude comparator for indicating that the error correction circuit has sufficient strength to be unable to continuously correct an error of the first symbol decoding result generated by the first data slicer, and thus the final display. Is supplied to the second comb filter as a command for selecting a symbol decoding result other than the first symbol decoding result as the final symbol decoding result. 15. The apparatus of claim 14, wherein the demodulation circuit; The amplified signal for supplying a Q-channel baseband signal comprising an I-channel baseband signal used to apply the input signal to the symbol decoding device and additional artifacts of any co-channel interfering analog television signal; And a complex demodulator responsive to the residual-sideband amplitude-modulated digital television signal. 16. The digital television signal according to claim 15, wherein the Q-channel baseband signal supplied from the complex demodulator is used to apply the additional baseband signal to the co-channel interference detector as its input signal. receiving set. 16. The digital television signal according to claim 15, wherein the I-channel baseband signal supplied from the complex demodulator is used to apply the additional baseband signal to the co-channel interference detector as its input signal. receiving set. 16. The apparatus of claim 15, wherein the second comb filter of a defined third time period selects an ideal symbol decoding result as the final symbol decoding result, wherein the amplitude comparator is other than the first symbol decoding result. Obtained at a time other than the third time of supplying the command to the second comb filter to select a symbol decoding result as the final symbol decoding result, wherein the first time is a time other than the second and third time periods. Digital television signal receiver, characterized in that obtained in. 15. The apparatus of claim 14, wherein the third comb filter differentially combines the additional baseband input signal with its own signal affected by the first differential delay amount to produce the third comb filter response. While the fourth comb filter differentially combines the additional baseband input signal with its own signal affected by the second differential delay amount to produce the fourth comb filter response. And a digital television signal receiver. 20. The digital television signal receiver of claim 19 wherein the fourth differential delay amount is six symbol periods. 21. The digital television signal receiver of claim 20, wherein the first, second and third differential delay amounts are each 12 symbol periods. 21. The digital television signal receiver of claim 20, wherein the first, second, and third differential delay amounts are 1368 symbol periods or durations of two NTSC video scan lines, respectively. 21. The digital television signal receiver of claim 20, wherein the first, second, and third differential delay amounts are 179,208 symbol periods or durations of 262 NTSC video scan lines, respectively. 21. The digital television signal receiver of claim 20, wherein the first, second and third differential delay amounts are 718,200 symbol periods or duration of two NTSC video frames, respectively. 15. The method of claim 14, wherein the first comb filter is further to combine the additional baseband input signal with its own signal affected by the first differential delay amount to produce the first comb filter response. The second comb filter, on the other hand, additively combining the additional baseband input signal with its own signal affected by the second differential delay amount to produce the second comb filter response. And a digital television signal receiver. 27. The digital television signal receiver of claim 25, wherein the first differential delay amount is six symbol periods. 27. The digital television signal receiver of claim 26, wherein the second differential delay amounts are each 12 symbol periods.