Television – Synchronization
Reexamination Certificate
2001-10-19
2004-10-12
Lee, Michael H. (Department: 2614)
Television
Synchronization
C348S521000, C348S537000, C375S321000, C375S316000
Reexamination Certificate
active
06803966
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital TV receiver that receives a vestigial side band (VSB) signal and demodulates it, and more particularly, to a digital TV receiver and a method for receiving a digital TV signal, in which a symbol clock and a synchronizing signal are recovered from received data.
2. Background of the Related Art
Generally, a VSB transmission system of a Grand Alliance adopted as a standard of a digital TV transmission mode in USA and Korea modulates one side band signal of two side bands generated up and down around a carrier wave when the other side band signal is attenuated. That is, the VSB transmission system transmits one side band spectrum of a base band to a pass band to efficiently use a band region.
The VSB transmission system is more remarkable than other digital TV transmission systems in that it includes a pilot signal, a data segment synchronizing signal, and a field synchronizing signal. These signals can be used to improve carrier recovery characteristic and timing recovery characteristic. The recovery characteristic of the synchronizing signals greatly act on performance of the overall VSB system.
A transmitting party such as a broadcasting station transmits a signal through a mapper that acts to convert the signal to a desired power level. As an example, in case of 8 VSB for terrestrial broadcasting, an output level of the mapper is one of eight symbol values (amplitude level), −168, −120, −72, −24, 24, 72, 120, and 168. The mapper forcibly inserts a segment synchronizing signal of four symbols for each unit of 828 symbols by a protocol and forcibly inserts a field synchronizing signal into a 313rd data segment location.
At this time, the protocol of the segment synchronizing signal has a logic format of 1, 0, 0, and 1. The output level of the mapper is 120 when the synchronizing signal is 1 while the output level is −120 when the synchronizing signal is 0. That is, the segment synchronizing signal is repeated with two levels per data segment.
FIG. 1
shows a VSB data frame format including the data and the synchronizing signal. Referring to
FIG. 1
, one frame includes two fields while one filed includes 313 data segments. One data segment includes 832 symbols. In this case, first four symbols in one data segment correspond to a segment synchronizing portion, and the first data segment in one field corresponds to a field synchronizing portion.
FIG. 2
shows a configuration of the field synchronizing portion.
Referring to
FIG. 2
, a data segment synchronization of four symbols, a PN511 sequence which is a pseudo random sequence, three PN63 sequences, and VSB mode information of 24 symbols are provided, while other 014 symbols are reserved. In other words, the PN511 sequence includes 511 pseudo random symbols. The second PN63 sequence of the PN63 sequences has an inverted symbol configuration per field, wherein ‘1’ is inverted to ‘0’ while ‘0’ is inverted to ‘1’. Accordingly, one field may be divided into an even field and an odd field depending on polarity of the second PN63 sequence.
FIG. 3
is a block diagram illustrating a general digital TV receiver that receives and recovers the synchronizing signal. Referring to
FIG. 3
, if a radio frequency (RF) signal modulated in a VSB mode is received through an antenna
101
, a tuner
102
selects a user's desired special channel frequency. Then, the tuner
102
acts to transit a VSB signal of an RF band loaded in the channel frequency to a primary fixed intermediate frequency (IF) band of 44 MHz or 43.75 MHz and to filter other channel signals.
An output signal of the tuner
102
that acts to transit an arbitrary channel spectrum to the primary fixed IF band passes through a surface acoustic wave (SAW) filter
103
adapted to remove an adjacent channel signal and a noise signal.
At this time, since all information exist in a band of 6 MHz from the IF of 44 MHz, the SAW filter
103
removes all periods except for the band of 6 MHz with information from the output of the tuner
102
and then outputs a digital broadcasting signal to the down converter
104
.
The down converter
104
performs down conversion of the signal filtered by the SAW filter
103
with an oscillation frequency for generating a second IF signal and outputs the converted second IF signal to a demodulator
105
.
The demodulator
105
demodulates a VSB modulated signal in an analog mode and outputs the demodulated signal to an A/D converter
106
.
The A/D converter
106
converts the VSB demodulated signal to a digital signal in accordance with an A/D clock provided from a timing recovery unit
107
and outputs the digital signal to the timing recovery unit
107
, a synchronizing signal recovery unit
108
, and an equalizer
109
.
In this case, a VSB transmission system of an advanced television systems committee (ATSC) suggested by a US digital TV mode transmits a transmitting signal which includes data only.
Therefore, to recover the data in a receiving party shown in
FIG. 3
, the same clock as that used during transmission should be generated. The timing recovery unit
107
acts to generate the clock. In the currently suggested ATSC standard, the receiving party performs timing recovery using a data segment synchronizing signal regularly inserted from the transmission party.
Namely, the timing recovery unit
107
obtains a symbol timing error, which will be used as an A/D clock (A/D clk) of the A/D converter
106
, using the segment synchronizing signal detected by the synchronizing detector
108
.
The segment synchronizing signal is used to determine a start position of a segment and at the same time to recover timing of the system. Accordingly, the synchronizing recovery unit
108
detects a segment synchronizing signal and outputs the detected segment synchronizing signal to the timing recovery unit
107
and the equalizer
109
. The timing recovery unit
107
performs timing recovery using the segment synchronizing signal. The synchronizing recovery unit
108
recovers the field synchronizing signal using the detected segment synchronizing signal and outputs the recovered field synchronizing signal to the equalizer
109
.
However, since the segment synchronizing signal consists of four symbols
1001
, it may be difficult to be detected due to a damaged channel having a large sized ghost even if it is repeated per segment. Particularly, under a ghost channel environment in which a serious null is generated around the segment synchronizing signal, it is more difficult to detect the segment synchronizing signal. Generally, in a downtown area where big buildings are located, or in an area where a VSB terrestrial broadcasting is received through an indoor antenna, it is well known that a serious near-by ghost signal is generated.
Therefore, if the segment synchronizing signal is not detected for the above reasons, timing recovery and field synchronizing signal detection are not implemented. In this case, data recovery may be delayed or may not be implemented as the overall systems as well as a channel equalizer do not work.
In other words, if the synchronizing detecting unit
108
does not detect the segment synchronizing signal, the timing recovery unit
107
cannot recover timing data. Since the timing data is provided to the A/D clock of the A/D converter
106
, the segment synchronizing signal cannot be detected unless the timing data is recovered. Moreover, since the structure of
FIG. 3
has many analog components, it is difficult to control the components.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a digital TV receiver and a method for receiving a digital TV signal that substantially obviate one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a digital TV receiver and a method for receiving a digital TV signal, in which timing recovery and segment synchronizing signal recovery are independently implemented.
Another obje
Lee Michael H.
Lee Hong Degerman Kang & Schmadeka
Natnael Paulos
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