Television – Receiver circuitry
Reexamination Certificate
1999-06-22
2004-10-12
Harvey, David E. (Department: 2614)
Television
Receiver circuitry
Reexamination Certificate
active
06803970
ABSTRACT:
The invention relates to detection of synchronizing signals in the digital data received by digital television receivers, for acquiring data field and line synchronization, and for acquiring symbol synchronization.
BACKGROUND OF THE INVENTION
Vestigial sideband (VSB) signals that are used in terrestrial through-the-air transmissions of digital high-definition television (HDTV) signals have their natural carrier wave, which would vary in amplitude depending on the percentage of modulation, replaced by a pilot carrier wave of fixed amplitude, which amplitude corresponds to a prescribed percentage of modulation. This percentage modulation has been standardized as being ⅝ times as large as the smallest change in symbol code level in symbol codes having eight levels. Such VSB signals have been chosen for over-the-air broadcasting within the United State and can be used in over-the-air narrowcasting systems or in cable-casting systems. However, certain cable-casting is likely to be done using suppressed-carrier quadrature amplitude modulation (QAM) signals instead, rather than VSB signals.
Radio receivers for receiving digital television signals, in which receiver the final intermediate-frequency signal is somewhere in the 1-8 MHz frequency range rather than at baseband, are described by C. B. Patel et alii in U.S. Pat. No. 5,479,449 issued 26 Dec. 1995, entitled DIGITAL VSB DETECTOR WITH BANDPASS PHASE TRACKER, AS FOR INCLUSION IN AN HDTV RECEIVER, and included herein by reference. The use of infinite-impulse response filters for developing complex digital carriers in such receivers is described by C. B. Patel et alii in U.S. Pat. No. 5,548,617 issued 20 Aug. 1996, entitled DIGITAL VSB DETECTOR WITH BANDPASS PHASE TRACKER USING RADER FILTERS, AS FOR USE IN AN HDTV RECEIVER, and incorporated herein by reference. The use of finite-impulse response filters for developing complex digital carriers in such receivers is described by C. B. Patel et alii in U.S. Pat. No. 5,731,848 issued 24 Mar. 1998, entitled DIGITAL VSB DETECTOR WITH BANDPASS PHASE TRACKER USING NG FILTERS, AS FOR USE IN AN HDTV RECEIVER, and incorporated herein by reference. The design of receivers for both VSB and QAM signals in which both types of signal are processed through the same intermediate-frequency amplifiers receivers is described by C. B. Patel et alii in U.S. Pat. No. 5,506,636 issued 9 Apr. 1996, entitled HDTV SIGNAL RECEIVER WITH IMAGINARY-SAMPLE-PRESENCE DETECTOR FOR QAM/VSB MODE SELECTION, and incorporated herein by reference. U.S. Pat. No. 5,606,579 issued 25 Feb. 1997 to C. B. Patel et alii and entitled DIGITAL VSB DETECTOR WITH FINAL I-F CARRIER AT SUBMULTIPLE OF SYMBOL RATE, AS FOR HDTV RECEIVER is incorporated herein by reference. The detection of data segment synchronization code groups in an HDTV receiver is described by J. Yang in U.S. No. 5,594,506 issued 14 Jan. 1977, entitled LINE SYNC DETECTOR FOR DIGITAL TELEVISION RECEIVER, and incorporated herein by reference. In U.S. Pat. No. 5,511,099 issued 23 Apr. 1996, entitled PASSBAND SYNC BLOCK RECOVERY, and incorporated herein by reference J. W. Ko et alii describe the use of match filters for detecting prescribed digital sequences having high auto-correlation properties that modulate a radio-frequency carrier in digital recording. These patents are all assigned to Samsung Electronics, Co., Ltd. pursuant to employee invention agreements already in force at the time the inventions disclosed in these patents were made.
In the radio receivers described in U.S. Pat. No. 5,506,636 the final IF signal is digitized and synchrodyne procedures to obtain baseband samples are carried out in the digital regime. In radio receivers that are to have the capability of receiving digital TV signals no matter whether they are transmitted using VSB or QAM, conversion of the signals to final IF signals just above baseband permits the frequencies of the local oscillators in the tuner to remain the same no matter whether VSB or QAM transmissions are being received. The differences in carrier frequency location within the channel are accommodated in the synchrodyning procedures carried out in the digital regime.
A problem that is encountered in the design of digital TV receivers is acquiring carrier synchronization, then symbol synchronization, and then data line and field synchronization rapidly enough that tuning across the band can be done without having to pause overlong at each channel to determine whether it carries programming and what the nature of the programming is. In prior digital TV receiver designs carrier synchronization and symbol synchronization are necessary before data line and field synchronization can be undertaken. The problem of carrier synchronization is considerably more difficult when receiving QAM transmissions, in which there is no accompanying pilot carrier, than it is when receiving VSB transmissions, in which there is an accompanying pilot carrier. In any case carrier synchronization takes some time to complete, and symbol synchronization carried out after synchronous detection takes additional time to complete. The time required for these procedures to be completed can make tuning from channel to channel sluggish. This is particularly so if an automatic successive-channel scan is being conducted by the HDTV receiver, looking for a desired program identification code.
As described in U.S. Pat. No. 5,511,099 data line and field synchronization can be accomplished independently of the data slicing procedures used for symbol decoding. Match filtering responsive to data line synchronization codes (or data segment synchronization codes) can be used to identify the start of each data line and to supplying pulses for counting by a data line counter, as described and claimed by J. Yang in U.S. Pat. No. 5,594,506 issued 14 Jan. 1977. Match filtering responsive to data field synchronization codes can be used to identify the start of each data line and to supplying pulses for counting by a data line counter, as claimed hereinafter.
In U.S. Pat. No. 5,511,099 J. W. Ko et alii describe the use of match filters for detecting prescribed digital sequences having high auto-correlation properties that modulate a radio-frequency carrier. The invention is described with particular regard to a digital VCR using a modulated radio-frequency carrier with upper- and lower-frequency sidebands (e.g., a 16-state QAM radio-frequency carrier), though U.S. Pat. No. 5,511,099 indicates the invention may also have application in other fields. The invention is described in terms of each sync block in the recorded information including a short prescribed digital sequence having high auto-correlation properties such as a Barker code or a pseudo-random (PR) sequence (also referred to as a “pseudo-random noise sequence” or “PN sequence”) inserted as a sync signal into a predetermined time portion (in usual designs, the beginning) of the sync sub-block, or used repeatedly in selected polarities for coding at least a portion of the synchronizing information. The prescribed sequence for the sync information is constructed so as to have a zero-valued direct component, but also to have a high-valued auto-correlation property. A seven-bit Barker Code is indicated in U.S. Pat. No. 5,511,099 to be preferred, because it is shorter than most PR sequences that might be used. The development of the digital tape recording art for digital TV signals has strongly tended to favor the direct recording of NRZI digital codes on electromagnetic video tape using
24-
to
-25
modulation, rather than the use of modulated radio-frequency carriers for recording, however.
In the digital TV signals proposed for broadcasting, each data field contains 313 data segments or data lines, and the fields are consecutively numbered modulo-two in order of their occurrence. Each data segment or data line starts with a segment synchronization code group of four symbols having successive values of +S, −S, −S and +S. The value +S is one level below the maximum positive data excursio
Limberg Allen LeRoy
Patel Chandrakant B.
Bushnell , Esq. Robert E.
Harvey David E.
Samsung Electronics Co,. Ltd.
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