Pulse or digital communications – Receivers – Angle modulation
Reexamination Certificate
1998-05-19
2002-01-15
Pham, Chi (Department: 2734)
Pulse or digital communications
Receivers
Angle modulation
Reexamination Certificate
active
06339623
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a reference carrier generator device for use in a demodulator system which outputs quadrature demodulated signals by synchronous detection and demodulation of a quadrature modulated wave.
A demodulator system outputs quadrature demodulated signals by synchronous detection and demodulation of a quadrature modulated wave when the modulated wave is received. Generally, the demodulator system is provided with a reference carrier generator device which outputs a reference carrier synchronous with a carrier of the modulated wave.
There are several existing demodulator systems having various configurations. It is desired that a reference carrier generator device be configured to output a reference carrier that quickly responds to a change of the carrier of the quadrature modulated wave. It is desired that the reference carrier generator device provide a broad capability to pull the reference carrier into synchronism while avoiding a false stabilized point of synchronism.
(2) Description of the Related Art
FIG. 6
shows a conventional analog demodulator system.
As shown in
FIG. 6
, in the conventional analog demodulator system, a synchronous detection unit
51
, a roll-off filter
52
, a roll-off filter
53
, an analog-to-digital (A/D) converter
54
, an analog-to-digital (A/D) converter
55
, and a transversal equalizer
56
are provided. Further, a voltage-controlled oscillator
57
, a voltage-controlled clock generator
58
, a reference carrier generator device
59
, a control unit
63
, and a low-pass filter
64
are provided.
In the conventional analog demodulator system of
FIG. 6
, the voltage-controlled oscillator
57
outputs a reference carrier to the synchronous detection unit
51
. The voltage-controlled clock generator
58
outputs a sampling clock to both the A/D converter
54
and the A/D converter
55
.
A quadrature modulated wave is produced based on, for example, quadrature amplitude modulation (QAM). In the conventional analog demodulator system of
FIG. 6
, an intermediate-frequency quadrature modulated wave (IN) is input to the synchronous detection unit
51
when the modulated wave is received.
In the synchronous detection unit
51
, synchronous detection of an I-channel signal and a Q-channel signal from the quadrature modulated wave IN is performed based on the reference carrier from the voltage-controlled oscillator
57
. The I-channel signal and the Q-channel signal, output by the synchronous detection unit
51
, are passed through the roll-off filter
52
and the roll-off filter
53
, and input to the A/D converter
54
and the A/D converter
55
, respectively.
The I-channel signal and the Q-channel signal are converted into digital signals by the A/D converter
54
and the A/D converter
55
based on the sampling clock from the voltage-controlled clock generator
58
, and the digital signals are input to the equalizer
56
. The equalizer
56
outputs an I-channel demodulated signal (Iout) and a Q-channel demodulated signal (Qout). The demodulated signals Iout and Qout are further supplied to a next circuit (not shown) connected to an output of the conventional analog demodulator system.
In the reference carrier generator device
59
, as shown in
FIG. 6
, a phase error detection unit
60
, a loop filter
61
, and a sweep unit
62
are provided. However, a modification may be made such that the reference carrier generator device
59
further includes the voltage-controlled oscillator
57
. See Japanese Laid-Open Patent Application No.1-78058(Japanese Patent No. 2,553,103) for a background technology of the reference carrier generator device of the present invention.
In the reference carrier generator device
59
of
FIG. 6
, the phase error detection unit
60
detects a phase error between a reference carrier and the carrier of the quadrature modulated wave IN based on the demodulated signals Iout and Qout from the equalizer
56
. Suppose that “Pe ” indicates a reference carrier phase error signal, “Id ” indicates an I-channel identifying signal, “Qd ” indicates a Q-channel identifying signal, “Ie ” indicates an I-channel phase error signal, and “Qe ” indicates a Q-channel phase error signal. The phase error detection unit
60
outputs the phase error signal Pe indicating the phase error between the reference carrier and the carrier of the quadrature modulated wave IN, which is represented by the formula:
Pe=Id×Qe−Ie×Qd (1)
See Japanese Laid-Open Patent Application No. 6-54014 for a background technology of the reference carrier generator device of the present invention.
In the reference carrier generator device
59
of
FIG. 6
, the phase error signal Pe from the phase error detection unit
60
is passed through the loop filter
61
and converted into a control voltage by the loop filter
61
. The sweep unit
62
supplies the control voltage, output by the loop filter
61
, to the voltage-controlled oscillator
57
. The voltage-controlled oscillator
57
outputs the reference carrier to the synchronous detection unit
51
based on the control voltage from the sweep unit
62
, the reference carrier being synchronous with the carrier of the quadrature modulated wave IN.
The sweep unit
62
changes the control voltage output to the voltage-controlled oscillator
57
, in order to provide a broad capability to pull the reference carrier into synchronism. An error detection unit (not shown) is provided on the output side of the conventional analog demodulator system. The error detection unit detects whether an out-of-sync error of the reference carrier is increasing. When the out-of-sync error of the reference carrier is detected as increasing, it is determined that the reference carrier is going out of synchronism. The error detection unit in such a case outputs an out-of-sync alarm signal to the sweep unit
62
, and the sweep unit
62
changes the control voltage upon receiving the out-of-sync alarm signal. When the out-of-sync error of the reference carrier is detected as decreasing, it is determined that the reference carrier is being pulled into synchronism. The error detection unit in such a case outputs no alarm signal to the sweep unit
62
, and the sweep unit
62
stops changing the control voltage.
The control unit
63
detects a clock component based on the demodulated signals Iout and Qout from the equalizer
56
, and supplies a control voltage to the voltage-controlled clock generator
58
through the low-pass filter
64
. The voltage-controlled clock generator
58
outputs the sampling clock to both the A/D converter
54
and the A/D converter
55
in accordance with the control voltage from the control unit
63
.
FIG. 7
shows a conventional digital demodulator system.
As shown in
FIG. 7
, in the conventional digital demodulator system, a quasi synchronous detection unit
71
, a roll-off filter
72
, a roll-off filter
73
, an analog-to-digital (A/D) converter
74
, an analog-to-digital (A/D) converter
75
, an equalizer
76
, and a phase rotation unit
77
are provided. Further, a voltage-controlled phase signal generator
78
, a reference carrier generator device
79
, a control unit
83
, a low-pass filter
84
, a voltage-controlled clock generator
85
, and a local oscillator
86
are provided.
In the conventional digital demodulator system of
FIG. 7
, an intermediate-frequency quadrature modulated wave (IN) is input to the quasi synchronous detection unit
71
when the modulated wave is received. The local oscillator
86
outputs a fixed-frequency signal to the quasi synchronous detection unit
71
. The fixed-frequency signal from the local oscillator
86
is preset such that a fixed frequency of the signal from the local oscillator
86
matches with a frequency of the carrier of the quadrature modulated wave IN.
In the quasi synchronous detection unit
71
, synchronous detection of an I-channel signal and a Q-channel signal from the quadrature modulated wave IN is performed based on the fixed-frequency signal from th
Burd Kevin M
Fujitsu Limited
Pham Chi
Roseman & Colin LLP
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