Television – Receiver circuitry – Automatic frequency control
Reexamination Certificate
1999-11-05
2002-05-28
Kostak, Victor R. (Department: 2714)
Television
Receiver circuitry
Automatic frequency control
C348S731000
Reexamination Certificate
active
06396550
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a television, and in particular, to a method and device for precision tuning and a method and device for matching a vestigial sideband (VSB) signal in a television.
2. Description of the Related Art
VSB modulation is used in an 8-level HDTV (High Definition Television) based on the U.S. standard. Carrier recovery will be described referring to
FIG. 1
which is a block diagram of a carrier recovery device in an American 8-level HDTV and
FIG. 2
which shows the operational signal waveform in each component. Here, carrier recovery is a process of shifting a VSB signal of a channel to be tuned to a base band. A tuner receives a plurality of VSB signals in a radio frequency (RF) band through an antenna
100
. The tuner
102
multiplies the plurality of VSB signals by a local frequency, first LO received from a synthesizer
104
which outputs a different first LO according to channel tuning, so that a VSB signal of a channel to be tuned among the plurality of VSB signals is shifted to an intermediate frequency (IF) band. Here, the frequency multiplied by the VSB signals of the RF band is called a tuning frequency.
For example, (a) of
FIG. 2
shows a VSB signal of a channel among the plurality of VSB signals in the RF band. The VSB signal is between 174 and 180 MHz. The central frequency and bandwidth of the VSB signal are 177 MHz and 6 MHz, respectively. The VSB signal includes a pilot signal P at a location decreased from its maximum amplitude by 3 dB, that is, at 174.31 MHz. Here, the tuner
102
shifts the VSB signal to the IF band ranging from 41 to 47 MHz by multiplying the VSB signal by the tuning frequency, that is, the local frequency, the first LO. The IF band-shifted VSB signal is between 41 and 47 MHz and has a central frequency of 44 MHz, as shown in (b) of FIG.
2
. The IF band-shifted VSB signal includes the pilot signal P at a location dropped from the maximum amplitude by
3
dB, that is, at 46.69 MHz. The pilot signal P can be at 46.69 or 41.31 MHz according to the tuning frequency.
The above VSB signal is applied to a surface acoustic waveform (SAW) filter
106
. The SAW filter band of the SAW filter
106
ranges from 41 to 47 MHz, where the IF band-shifted VSB signal is located. The SAW filter
106
passes only a signal within the SAW filter band, that is, the IF band-shifted VSB signal from the output of the tuner
102
. The SAW filter
106
also drops the IF band-shifted VSB signal between ±0.31 MHz with respect to the pilot signal location by 3 dB. The SAW filter
106
drops the IF band-shifted VSB signal between ±0.31 MHz with respect to a location opposite to the pilot signal location by 3 dB. The opposite location is 41.31 MHz if the pilot signal is at 41.39 MHz, and vice versa. The SAW filter
106
drops the IF band-shifted VSB signal between ±0.31 MHz with respect to the pilot signal location and the opposite location by 3 dB in order to obtain entire flat frequency characteristics when the VSB signal is shifted to a base band. Here, as the VSB signal between ±0.31 MHz with respect to the pilot signal location drops by 3 dB, the pilot signal location in the VSB signal also falls by 3 dB. Therefore, the pilot signal is at a location dropped from the maximum amplitude by 6 dB in the output signal of the SAW filter
106
.
Here, when the IF band-shifted VSB signal as shown in (b) of
FIG. 2
is applied to the SAW filter
106
, the SAW filter
106
passes only a signal within the SAW filter band and blocks the other signals (not shown). The SAW filter
106
drops the IF band-shifted VSB signal between ±0.31 MHz with respect to the pilot signal location and the opposite location by 3 dB, respectively. Thus, the output signal of the SAW filter
106
is in a frequency area ranging from 41 to 47 MHz and the pilot signal P is at the location dropped from the maximum amplitude by 6 dB in the output signal, as shown in (c) of FIG.
2
.
The output of the SAW filter
106
is amplified in an IF amplifier
108
and then applied to first and second mixers
112
and
116
. A reference oscillator
110
outputs a
10
local frequency, a third LO to be used for shifting the output signal of the SAW filter
106
to a base band. The third LO is fed to the first mixer
112
. The phase of the third LO is shifted by 90° in a 90° phase shifter
114
and then the phase-shifted third LO is applied to the second mixer
116
. The first mixer
112
shifts the output signal of the IF amplifier
108
to a base band by multiplying the output signal of the IF amplifier
108
by the third LO and outputs a quadrature phase signal Q. The second mixer
116
shifts the output signal of the IF amplifier
108
to the base band by multiplying the output signal of the IF amplifier
108
by the 90° phase-shifted third LO and outputs an in-phase signal I. The VSB signals I and Q shifted to the base band are illustrated in (d) of FIG.
2
. The baseband-shifted VSB signals experience spectral overlapping between ±0.3 MHz with respect to 0 MHz, so that frequency characteristics are flat as shown in (d) of FIG.
2
. Here, a pilot signal in the baseband-shifted VSB signal is at 0 MHz.
As described above, the conventional carrier recovery device uses the SAW filter
106
which passes a signal in the frequency band of an IF signal, that is, between 41 and 47 MHz. However, the frequency band of a VSB signal in a channel can be shifted according to a frequency offset. Thus, the frequency band of a VSB signal which shifts the VSB signal to the IF band may be shifted according to the frequency offset. Therefore, the frequency band of the IF band-shifted VSB signal shifts due to he frequency offset and beyond the SAW filter band between 41 and 47 MHz. The IF and-shifted VSB signal exceeding the SAW filter band is lost in the SAW filter
10
, making it impossible to entirely shift the VSB signal to a base band.
Therefore, the carrier recovery device of
FIG. 1
employs a frequency and phase looked loop (FPLL)
108
to thereby control the tuning frequency of the tuner
102
and compensate for the above frequency offset. The FPLL
118
is comprised of an AFC (Automatic Frequency Control) low pass filter
120
, a limiter
122
, a third mixer
124
. an APC (Automatic Phase Control) low pass filter
126
, and a VCO (Voltage Controlled Oscillator)
128
. The baseband signal I is applied to the third mixer
124
through the AFC low pass filter
120
and the limiter
122
. The third mixer
124
generates a direct current signal by multiplying the output signal of the limiter
122
by the baseband signal Q. The direct current signal is applied to the APC low pass filter
126
to control the VCO
128
such that the frequency offset is compensated for. The VCO
128
feeds a local frequency, a second LO for compensating for the frequency offset to the tuner
102
. The tuner
102
controls the tuning frequency according to the second LO, thereby compensating for the frequency offset.
The above conventional carrier recovery device is configured in a long loop structure where the FPLL controls the tuning frequency of the tuner to prevent the decrease of carrier recovery performance due to the frequency offset. As a result, a long time is required to compensate for the frequency offset. In addition, the conventional carrier recovery device performs matching filtering by dropping the IF band-shifted VSB signal between ±0.31 MHz by 3 dB with respect to a pilot signal location and its opposite location by use of the SAW filter. Hence, the characteristics of the SAW filter seriously affects the performance of a receiver. Furthermore, the carrier recovery device operated in an analog scheme varies in performance with an analog device used and it is difficult to configure the entire receiver in ASICs (Application Specific Integrated Circuits). Therefore, many advanced appliance manufacturers employ a DFPLL (Digital Frequency and Phase Locked Loop) based on digital signal processing for a ca
Kostak Victor R.
Samsung Electronics Co,. Ltd.
LandOfFree
Method and device for precision tuning, and method and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for precision tuning, and method and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for precision tuning, and method and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2886858