Pulse or digital communications – Spread spectrum
Reexamination Certificate
1999-07-12
2004-04-20
Chin, Stephen (Department: 2634)
Pulse or digital communications
Spread spectrum
C375S153000, C375S213000, C375S295000, C375S315000, C375S316000, C375S352000, C455S073000, C455S090300
Reexamination Certificate
active
06724804
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to frequency converters and radio communications systems employing the frequency converter and, more particularly, to a frequency converter and a radio communication, in which a received radio frequency signal is converted into an intermediate frequency signal and an intermediate frequency signal to be transmitted is converted into a radio frequency signal.
2. Description of the Related Art
There is a growing demand for a high-speed network as data communications rapidly gain widespread use. High-speed communications provided by wired networks are still very expensive for individual users, and local radio communications networks providing a low-cost service are now actively studied and developed. Such a local radio network uses radio frequency bands, such as quasi millimeter waves (20 GHz-30 GHz) or millimeter waves (30 GHz-300 GHz), capable giving a high antenna gain with a small antenna. In the local radio network, a hub station, for example, installed in a telephone exchange station, provides high-speed two-way data communications service or local TV phone service to a plurality of (user) subscriber stations within a predetermined coverage area.
When radio communications are performed using radio frequency signals in the quasi millimeter band or the millimeter band, an intermediate frequency signal of several tens to several hundreds of megahertz, rather than radio frequency signals, is subjected to a receiving process including an isolation decoding step, a transmitting process including coding and synthesis steps, and an amplification of signals. The cost of a circuit arrangement required for the receiving and transmitting processes and the signal amplification is thus reduced.
FIG. 16
shows a frequency converter, which converts a radio frequency signal into an intermediate frequency signal or an intermediate frequency signal into a radio frequency signal.
The frequency converter is installed in a subscriber station, for example, and receives radio waves, transmitted from a hub station, through its receiving antenna
1001
. Out of the radio waves received by the receiving antenna
1001
, radio frequency RF(RX) signals of interest for reception in a plurality of frequency channels in a range of 22.6 GHz-23.0 GHz are extracted by a bandpass filter
1002
.
The radio frequency RF(RX) signal extracted through the bandpass filter
1002
is amplified to an appropriate level by a low noise amplifier
1003
, and is then mixed with a TX/RX local oscillation frequency signal LO
1
, for example, a 21 GHz signal, by a mixer
1004
.
The local oscillation frequency signal LO
1
is generated by a phase-locked oscillator
1100
.
The phase-locked oscillator
1100
includes a phase-locked loop including a counter circuit
1102
, a frequency comparator
1103
, a loop filter
1105
, and a voltage-controlled oscillator
1106
, and frequency multipliers
1107
and
1109
.
In the phase-locked oscillator
1100
, a signal output by the voltage-controlled oscillator
1106
is frequency-divided, for example, by
175
, by the counter circuit
1102
. The frequency comparator
1103
compares a signal output by the counter circuit
1102
to a reference signal, for example, a 10 MHz reference signal supplied by a reference oscillator
1204
employing a highly stable crystal oscillator. A voltage, corresponding to the difference between the two signals, is then amplified by the loop filter
1105
in appropriate frequency characteristics. The voltage output from the loop filter
1105
is fed back to a control input of the voltage-controlled oscillator
1106
.
A 1.75 GHz signal output by the voltage-controlled oscillator
1106
is frequency-multiplied by four times by the frequency multiplier
1107
, becoming a 7.0 GHz signal. The remaining signals contained in the output of the frequency multiplier
1107
are filtered out by a bandpass filter
1108
.
The signal output by the bandpass filter
1108
is further frequency-multiplied by three times by the frequency multiplier
1109
, becoming a 21.0 GHz signal. The remaining signals contained in the output of the frequency multiplier
1109
are filtered out by a bandpass filter
1110
.
In this way, the phase-locked oscillator
1100
results in the signal having the local-oscillation frequency LO
1
(21 GHz) at the same frequency accuracy level as that provided by the highly stable reference oscillator
1204
.
The local-oscillation frequency signal LO
1
is output by the bandpass filter
1110
, and is amplified by an amplifier
1112
, and is then received by the RX mixer
1004
.
An output of the mixer
1004
contains the frequency components of the sum of, and the difference between, the radio frequency RF(RX) signal and the local-oscillation frequency LO
1
signal. The difference between the two signals, i.e., a signal in an intermediate frequency band IF
1
(RX) of 1.6 GHz-2.0 GHz, is extracted by the bandpass filter
1005
, is amplified by an amplifier
1006
, and is fed to an RX mixer
1007
.
The RX mixer
1007
mixes the signal in the intermediate frequency band IF
1
(RX) and a local-oscillation frequency LO
2
signal, for example, a 1.1 GHz signal supplied by a phase-locked oscillator
1200
.
The local-oscillation frequency LO
2
signal is generated by the phase-locked oscillator
1200
.
The phase-locked oscillator
1200
includes a phase-locked loop including a counter circuit
1202
, a frequency comparator
1203
, a loop filter
1205
, and a voltage-controlled oscillator
1206
, and the high-accuracy reference oscillator
1204
employing a crystal oscillator.
In the phase-locked oscillator
1200
, a signal output by the voltage-controlled oscillator
1206
is frequency divided, for example, by
110
, by the counter circuit
1102
. The frequency comparator
1203
compares a signal output by the counter circuit
1202
to a reference signal, for example, a 10 MHz reference signal supplied by the reference oscillator
1204
. A voltage, corresponding to the difference between the two signals, is then amplified by the loop filter
1205
in appropriate frequency characteristics. The voltage output from the loop filter
1205
is fed back to a control input of the voltage-controlled oscillator
1206
.
In this way, the phase-locked oscillator
1200
results in the signal having the local-oscillation frequency LO
2
(1100 MHz) at the same frequency accuracy level as that provided by the highly stable reference oscillator
1204
.
The output of the RX mixer
1007
contains frequency components of the sum of, and the difference between, the signal in the intermediate frequency band IF
1
(RX) and the local-oscillation frequency LO
2
signal. The difference between the two signals, i.e., a signal in an intermediate frequency band IF
2
(RX) of 500 MHz-900 MHz, is extracted through the bandpass filter
1008
.
The signal in the intermediate frequency band IF
2
(RX), picked up by the bandpass filter
1008
, is amplified by an amplifier
1009
, is fed to a diplexer
1010
, and is then fed to a demodulator (not shown) via an IF cable.
The signal in the radio frequency band RF(RX) thus received is converted into a signal in an appropriate intermediate frequency band IF
2
(RX).
The signal in the intermediate frequency band IF
2
(TX), for example, 10 MHz-60 MHz, supplied by a modulator (not shown), is received from the diplexer
1010
via the IF cable, is amplified by an amplifier
1012
, and fed to a TX mixer
1013
. The RX intermediate frequency IF
2
(RX) and the TX intermediate frequency IF
2
(TX) are assigned in separate frequency ranges.
The TX mixer
1013
mixes the signal in the intermediate frequency band IF
2
(TX) with the signal having the local-oscillation frequency LO
2
output by the phase-locked oscillator
1200
.
The output of the TX mixer
1013
contains the signals of the sum of, and the difference between, the signal in the intermediate frequency band IF
2
(TX) and the local-oscillation frequency LO
2
signal. The signal of the sum of the two signals, i.e., a signal in an int
Goto Yuichiro
Inoue Koji
Kegasa Koyo
Kusaka Takuya
Manabe Chitaka
A. Marquez, Esq. Juan Carlos
Chin Stephen
Fisher Esq. Stanley P.
Kabushiki Kaisha Kobe Seiko Sho
Munoz Guillermo
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