Television – Image signal processing circuitry specific to television – Noise or undesired signal reduction
Reexamination Certificate
2000-07-18
2003-02-04
Miller, John (Department: 2614)
Television
Image signal processing circuitry specific to television
Noise or undesired signal reduction
C348S723000, C348S724000, C375S296000
Reexamination Certificate
active
06515712
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal distortion compensating apparatus and method, and more particularly to a signal distortion compensating apparatus and method in a digital TV translator.
2. Background of the Related Art
A variety of linearizing techniques have been proposed to compensate for non-linear behaviors of radio frequency (RF) high-power amplifiers (HPAs) to allow those RFHPAs to meet a standard associated with digital communication systems. Representative related art linearizing methods include a pre-distortion scheme, a feed-forward scheme, and a look-up table (LUT) scheme using a vector signal analyzer.
First, a linearizing method based on the related art pre-distortion scheme will be described. In accordance with this linearizing method, a pre-distorter is arranged upstream from the main amplifier in an amplifying system. The pre-distorter has characteristics opposite to those of the main amplifier. Thus, the upstream pre-distorter compensates for a signal distortion occurring in a particular direction in terms of gain and phase characteristics when an input signal passes through the main amplifier, thereby maintaining the output signal from the amplifying system to be the same as the input signal in terms of characteristics. The related art pre-distortion linearizing method makes it possible to obtain outputs improved in non-linearity.
In accordance with a linearizing method based on the related art feed-forward scheme, a delay line and an error amplifier are used. When an output signal from a main amplifier amplifying an input signal contains distorted intermodulation components, a 180° phase adjustment is conducted for those distorted intermodulation components by the delay line and the error amplifier to offset phase distortions of the intermodulation components. As a result, only the signal components similar to the components of the original input signal are outputted.
However, both of the above described related art pre-distortion and feed-forward linearizing methods can be implemented only with hardware configurations. Further, they are limited and problenmatic in that only the linear distortion can be compensated.
For this reason, a related art linearizing method based on a look-up table scheme using a vector signal analyzer has been mainly used.
FIG. 1
is a block diagram schematically illustrating a related art signal distortion compensating apparatus applied to digital TV translators.
Referring to
FIG. 1
, the related art signal distortion compensating apparatus includes a transmitting unit
100
and a linear
on-linear correction receiving unit
200
. The transmitting unit
100
includes a modulator
110
consisting of a vestigial sideband (VSB) processor
111
, a linear filter
112
, and a non-linear pre-corrector
113
. The transmitting unit
100
also includes an intermediate frequency (IF) modulator
120
, an up-converter
130
, an intermediate power amplifier (IPA)
140
, an HPA
150
, a directional coupler
160
, and an antenna
170
. The linear
on-linear correction receiving unit
200
includes a vector signal analyzer
210
consisting of a down-converter
211
and a demodulator
212
, and a computer
220
.
FIG. 2
is a block diagram schematically illustrating an internal software configuration of the computer
220
for producing a reference signal associated with a distorted signal in the related art signal distortion compensating apparatus shown in FIG.
1
. Referring to
FIG. 2
, the internal software configuration of the computer
220
includes a termination slice unit
221
a linear filter unit
222
, a non-linear pre-corrector
223
, a root raised cosine (RRC) filter unit
224
, a scaling unit
225
, a pilot signal recovering unit
228
, a complex division unit
226
, and a look-up table (LUT) storing memory
227
. The related art signal distortion compensating apparatus will now be described in additional detail, in conjunction with
FIGS. 1 and 2
.
Input data is first applied to the VSB processor
111
, which in turn conducts a channel coding for the input signal, thereby producing symbols. The produced symbols are applied to the linear filter
112
, which in turn produces an in-phase (I) signal and a quadrature (Q) signal, based on the symbols.
The I and Q signals from the linear filter
112
are transmitted to the IF modulator
120
, and then to the up-converter
130
. The I and Q signals are subjected to a frequency up-conversion while passing through the up-converter
130
. The resultant signals pass through the IPA
140
and HPA
150
. The resultant output signal from the HPA
150
is transmitted as a TV signal for general subscribers over the antenna
170
after passing through the directional coupler
160
.
However, the TV signal, which is transmitted to general subscribers from the antenna
170
, may involve a distortion because the VSB signal outputted from the baseband modulator
110
may be distorted because of non-linear factors of temperature, degradation, and noise while passing through the IF modulator
120
, IPA
140
, and HPA
150
. To correct such a signal distortion, distortion components are extracted from the output signal of the HPA
150
through the directional coupler
160
. Based on the extracted distorted signal, a reference signal is also produced in accordance with a termination slice scheme. The reference signal is then compared with the distorted signal. Based on the result of the comparison, the signal distortion of the transmitting unit
100
is measured.
That is, the extracted distorted signal from the directional coupler
160
is applied to the down-converter
211
of the vector signal analyzer
210
that down-converts the up-converted frequency signal into an IF signal of 44 MHz. The resultant signal outputted from the clown-converter
211
passes through the demodulator
212
, which in turn extracts I and Q digital data.
Based on the extracted I and Q digital signals from the demodulator
212
, a reference signal is produced using the internal software of the computer
220
to correct a distortion in the transmission signal outputted from the transmitting unit. The software producing the reference signal consists of a routine for producing a reference signal for distortion correction based on a distorted signal, which is illustrated in FIG.
2
.
Referring to
FIG. 2
, a source reference signal is produced in the termination slice unit
221
based on the distorted signal. The source reference signal is then sequentially processed by the linear filter unit
222
and the non-linear pre-corrector
223
, so that it has the same signal as that of the output from the modulator shown in FIG.
1
.
Since the distorted signal has been subjected to a root raised cosine filtering process, a pilot removal process, and a scaling process while passing through the vector signal analyzer, the reference signal should also be subjected to those processes so that it can be compared with the distorted signal. To this end, those processes are implemented in a software fashion by the RRC unit
224
and the scaling unit
225
.
The resultant reference signal is then applied to the complex division unit
226
at which the distorted signal emerging from the pilot signal recovering unit
228
is also received. Based on the distorted signal and the reference signal extracted using the distorted signal, the complex division unit
226
produces an LUT coefficient for error calculation and non-lineaarity correction.
The produced LUT coefficient is temporarily stored in the LUT storing memory
227
, and then inputted to the linear filter
112
and the non-linear pre-corrector
113
via a standard serial cable such as an RS-232C. The linear distortion may be corrected using an adaptive complex equalizer included in the vector signal analyzer.
As described above, the related art signal distortion compensating apparatus and method applied to digital TV translators have various problems. First, it is necessary to use additional devices such as the vector signal analyzer and
Fleshner & Kim LLP
LG Information & Communications Ltd.
Miller John
Tran Trang U.
LandOfFree
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