Television – Image signal processing circuitry specific to television – Gray scale transformation
Reexamination Certificate
2001-01-25
2004-01-13
Kostak, Victor R. (Department: 2611)
Television
Image signal processing circuitry specific to television
Gray scale transformation
C375S345000
Reexamination Certificate
active
06678010
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device and method for generating an auto gain control (AGC) signal in a digital TV receiver using a vestigial sideband (VSB) method.
2. Description of the Related Art
A digital TV makes users feel as if they were in theaters. That is, as compared with a general analog TV, the digital TV has a high resolution (for example, 1080×1920) and a wide screen in a lateral direction (16:9, to maximally apply an aspect ratio of movies such as 4:3, 5:3, 1.85:1, 2.4:1, etc.), and provides a CD level sound through a multi channel (maximally 5.1 channel).
The countries worldwide including the USA, Europe and Japan have been standardizing the digital TV by preparing their own broadcasting methods and standards. For example, the USA has introduced a vestigial sideband (VSB) method suggested by Zenith as a transmission format, an MPEG as a video compression format, a Dolby AC-3 as an audio compression format, and a display method compatible with a general display method as a display format.
On the other hand, a gain magnitude of a signal from a transmitter is constant, but may be varied by a distance from the transmitter to the receiver and various kinds of channels. Accordingly, the signal with a varied gain is inputted to the receiver. However, most of the digital sections of the receiver are designed, presuming that the signal having a constant gain is inputted. Therefore, it is required to convert an analog signal inputted to the receiver into a digital signal, after controlling a gain of the analog signal to have a constant magnitude. Here, a signal level of a transmission terminal may be smaller or greater than a signal level of a reception terminal according to a transmission or reception power, and thus it is necessary to control the gain.
The gain control operation is performed by an auto gain control (AGC) device. The AGC device judges a gain of the current input signal on the basis of an average or power of the input signals. Thereafter, the AGC device controls an analog amplifier between an RF terminal and an IF terminal according to the resultant gain, so that the signal can have a wanted magnitude.
A delayed AGC method as shown in
FIG. 1
has been widely employed as a transmission method.
Firstly, when a VSB modulated RF signal is inputted through an antenna
101
, a tuner
102
selects a frequency of a wanted channel by tuning, and converts the frequency into an IF signal. A demodulator
103
is used to exactly restore a base band signal from the IF signal.
The analog base band signal restored in the demodulator
103
is inputted to an A/D converter
104
. The A/D converter
104
converts the analog signal into a digital signal, and outputs the digital signal to a digital processor
105
and an AGC signal generator
106
. In addition, the demodulator
103
increases or decreases the gain according to gain control signals GainUp, GainDn fed back from the AGC signal generator
106
.
The digital processor
105
equalizes the digital signal from the A/D converter
104
in order to correct linear distortion of an amplitude causing interference between symbols and ghost generated due to reflection to buildings or mountains. Thereafter, the digital processor
105
corrects errors of the digital signal generated through a transmission channel, and outputs the digital signal to a video decoder
107
. The video decoder
107
decodes the error-corrected signal by the MPEG algorithm, converts the decoded signal into a visible signal, and outputs it to a display device
108
.
On the other hand, the AGC signal generator
106
judges the gain magnitude of the currently inputted digital signal, and feeds back the gain up control signal GainUp for increasing the gain of the input signal or the gain down control signal GainDn for decreasing the gain of the input signal to the demodulator
103
, thereby adjusting the gain of the analog signal inputted to the A/D converter
104
to have a wanted magnitude. In order to control the actual gain, the receiver is set to have a maximum gain in a power on or channel change operation, and the demodulator
103
firstly controls the gain according to the gain magnitude of the input signal.
When the demodulator
103
is not able to control the gain, if an output signal from the A/D converter
104
does not have a wanted magnitude, the demodulator
103
transmits the delayed AGC signal to the tuner
102
, controls the gain of the tuner
102
, and thus constantly maintains the gain of the input signal.
Here, the AGC signal generator
106
which is the most important unit of the AGC device judges whether to increase or decrease the gain of the input signal.
FIG. 2
is a detailed block diagram illustrating a conventional AGC signal generator. The AGC signal generator judges the gain of the input signal on the basis of an average of the input signals to an absolute value, and generates the gain up/down signal GainUp/Dn to control the gain of the input signal.
That is, an absolute value calculator
201
calculates an absolute value of the inputted digital signal, and transmits the absolute value to an integrator
202
. So as to compute an average of the output signals from the absolute value calculator
201
, the integrator
202
performs integration in predetermined units, and outputs a resultant value to an average calculator
203
. At this time, the absolute value of the input signal is calculated, instead of squaring the input signal. As a result, the output bit from the absolute value calculator
201
is reduced more than the input bit by one bit.
The average calculator
203
calculates the average of the input signals to the absolute value according to the output from the integrator
202
, and generates the gain control signal GainUp/Dn to adjust the average to a wanted value. The gain control signal GainUp/Dn is transmitted to the demodulator
103
, and controls the gain magnitude of the signal inputted to the A/D converter
104
.
FIG. 3
is a detailed block diagram illustrating the integrator
202
. A subtracter
301
outputs a difference between the input signal and a presumed average. An adder
302
adds the difference signal to an output from a buffer
303
, outputs the resultant value to the average calculator
203
, and feeds back it to the buffer
303
. Here, the receiver is designed, presuming that the gain magnitude of the input signal is always constant. Accordingly, the receiver can presume the average by the gain magnitude.
At this time, the buffer
303
is reset once in an initial stage of the operation. An integral value for the gain is increased to infinity by repeated integration. It is thus impossible to embody the integrator
202
as an actual hardware.
Therefore, the subtracter
301
is positioned before the adder
302
to subtract a wanted average from the input signal, and then the integration is performed, thereby remarkably reducing the integral value. Accordingly, it considerably reduces a load in hardware constitution of the integrator
202
.
However, in the case of the integrator shown in
FIG. 3
, the buffer
303
is reset once in the initial stage of the operation, and thus the integral value is increased when the gain of the input signal is very different from the wanted gain.
SUMMARY OF THE INVENTION
The present invention is proposed to solve the foregoing problems, and it is therefore an object of the invention to provide a device and method for generating an auto gain control (AGC) signal which can obtain a signal having a constant magnitude, by repeatedly resetting an integrator.
Another object of the present invention is to provide a device and method for generating an AGC signal which can facilitate reception of the AGC signal when a fast moving substance exists on a channel, by improving a speed of the AGC signal.
In order to achieve the above-described objects of the present invention, there is provided a device for generating an AGC signal, including: an A/D converter for converting an inputted analog signal into a digital sig
Kostak Victor R.
LG Electronics Inc.
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