Pulse or digital communications – Receivers – Angle modulation
Reexamination Certificate
2000-08-18
2004-06-08
Chin, Stephen (Department: 2634)
Pulse or digital communications
Receivers
Angle modulation
Reexamination Certificate
active
06748029
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for restoring carrier waves and a method therefor in receiving a VSB signal, and more particularly, to an apparatus for restoring carrier waves by selectively controlling an operation of a matching filter which inputs broadcast signals and a method therefor.
2. Description of the Background Art
FIG. 1
is a schematic block diagram of a carrier wave restoring apparatus using an analog signal in accordance with a conventional art.
As shown in the drawing, the carrier wave restoring apparatus using an analog signal processing method includes: a frequency synthesizer
1
for generating a first local oscillating frequency to tune a channel frequency desired by a user; a tuner
2
for receiving a broadcasting signal received by an antenna, turning a frequency of the received broadcasting signal according to the first local oscillating frequency outputted from the frequency synthesizer
1
and outputting a tuned signal of which gain has been controlled by an auto gain control (AGC); a SAW filter for receiving the signal outputted from the tuner
2
and band-pass filtering it; an intermediate frequency amplifier
4
for amplifying the band-pass filtered signal to an intermediate frequency(IF), controlling its gain, and outputting the IF signal as gain-controlled and amplified; a reference frequency oscillator
5
for generating a local oscillation frequency signal having a certain frequency, to generate an ‘I (In-phase)’ signal and a ‘Q (Quadrature)’ signal from the amplified IF signal outputted from the IF amplifier
4
; a 90° shifter
5
-
1
for shifting a phase of the local oscillation frequency signal outputted from the reference frequency oscillator
5
; a multiplier
4
-
1
for multiplying the IF signal outputted from the IF amplifier
4
and the signal outputted from the 90° shifter
5
-
1
, to output an ‘I’ signal; a multiplier
4
-
2
for multiplying the IF signal and the local oscillation frequency signal outputted from the reference frequency oscillator
5
, to output a ‘Q’ signal; an automatic frequency control(AFC) filter
6
for detecting an error component of a carrier wave from the ‘I’ signal outputted from the multiplier
4
-
1
; a limiter
7
for receiving and processing the signal outputted from the AFC filter
6
and outputting pulse signals; a multiplier
7
-
1
for multiplying the pulse signals outputted from the limiter
7
and the ‘Q’ signal outputted from the multiplier
4
-
2
; an automatic phase control (APC) filter
8
for detecting a frequency and a phase component from the signal outputted from the multiplier
7
-
1
and compensating the phase component; and a voltage control oscillator (VCO)
9
for receiving the phase compensated signal outputted from the APC filter
8
and outputting a second local oscillation frequency signal to compensate the carrier wave into the tuner
2
.
The carrier wave restoring apparatus using an analog signal processing method as shown in
FIG. 1
, however, is disadvantageous in that when the carrier waves is demodulated in a baseband by using an analog signal processing method, it is difficult to control the phase difference between the ‘I’ and ‘Q’ channels precisely by 90°, analog circuit elements are easily degraded as they are susceptible to temperature characteristics, and the analog circuit elements are hardly integrated either.
Meanwhile, a quadruple orthogonal amplitude modulation(QOAM) method according to a conventional art, since the gains of the ‘I’ signal and the ‘Q’ signal and the phase difference therebetween should be controlled equivalently, does not perform to restore a carrier wave easily, but includes many steps to do.
Thus, in an effort to solve the problem, a method for demodulating carrier waves in a digital region has been proposed.
FIG. 2
is a schematic block diagram of a carrier wave restoring apparatus using digital signal processing method in accordance with another conventional art.
As shown in the drawing, the carrier wave restoring apparatus includes: a tuner
11
for tuning a frequency corresponding to a channel desired by a user; a SAW filter
12
for receiving a turning signal from the tuner
11
and passing a certain band; a multiplier
12
-
1
for multiplying the signal outputted from the SAW filter
12
by a local oscillation frequency signal, and outputting an analog signal having a certain frequency; an A/D converter
13
for converting the analog signal outputted from the multiplier
12
-
1
to a digital signal; an SRC filter
14
for detecting and outputting only a signal existing in a certain band of the digital signal, which matches the frequency of the inputted signal thereinto; a Hilbert
16
for receiving the signal from the SRC filter
14
, delaying a phase of 90° and outputting a ‘Q’ signal; a delay
15
for delaying the signal outputted from the SRC filter
14
until the ‘Q’ signal is outputted from the Hilbert
16
, and then outputting an ‘I’ signal; a complex multiplier
17
for receiving the ‘I’ and ‘Q’ signals, multiplying them by a carrier wave, and outputting an ‘I’ and ‘Q’ signal of baseband; an infinitive impulse response (IIR) filters
18
and
20
for filtering the ‘I’ and ‘Q’ signals outputted from the complex multiplier
17
, respectively; a delay/limiter
19
for delaying the signal outputted from the IIR filter
18
and outputting pulse signals; a multiplier
19
-
1
for multiplying the pulse signals outputted from the delay/limiter
19
by the signal outputted from the IIR filter
20
, and outputting an error component of a frequency and a phase; a loop filter
21
for accumulating the error component outputted from the multiplier
19
-
1
; and a numerically controlled oscillator
22
for receiving the accumulated error component outputted from the loop filter
21
, and outputting 0° and 90° phase signals to the complex multiplier
17
, so as for the complex multiplier
17
to compensate the error in the carrier wave.
The differences between the carrier wave restoring apparatus using the analog signal processing method and the carrier wave restoring apparatus using the digital signal processing method are in that, the former compensates the tuning frequency to restore the carrier wave by the voltage control oscillator
9
as used in the latter of FIG.
1
and the latter compensates the frequency by the NCO
22
of FIG.
2
.
Of the apparatuses, in the aspect of integrated circuit, the carrier wave restoring apparatus using the digital signal processing method is considered to be better than the carrier wave restoring apparatus using the analog signal processing method.
FIG. 3
is a schematic block diagram of a carrier wave restoring apparatus using a digital signal in accordance with another conventional art, which additionally includes A/D converters for converting signals outputted from the multipliers
4
-
1
and
4
-
2
to digital signals and outputting an ‘I’ signal and ‘Q’ signal, respectively, in the carrier wave restoring apparatus using the analog signal processing method of FIG.
1
.
The carrier wave restoring apparatus using the digital signal processing method of
FIG. 3
separates an IF signal into an ‘I’ channel and a ‘Q’ channel in the analog region, converts them to digital signals by using the two A/D converters
31
and
32
, so that the carrier wave is restored by the signals from the VCO
9
after processing the converted signals.
However, the carrier wave restoring apparatuses using the analog and digital signals processing methods still have problems that, in case that the a channel of a frequency is being received is changed or in case that power is supplied to the system at an initial stage (initial mode), a carrier wave deviation occurs, and when the thusly occurred carrier wave passes the matching filter, the carrier wave component is attenuated, which is hardly restored. In addition, the same problem also arises in the case that a carrier wave deviation occurs due to the aging of the analog circuit elements. Especially, the conventional c
Chin Stephen
Kim Kevin
LG Electronics Inc.
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