Amplifiers – With plural amplifier channels – Redundant amplifier circuits
Reexamination Certificate
2002-02-06
2004-06-15
Nguyen, Khanh Van (Department: 2817)
Amplifiers
With plural amplifier channels
Redundant amplifier circuits
C330S126000, C330S295000
Reexamination Certificate
active
06750707
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a RF amplifier used in a mobile communication system wherein a plurality of terminals are connected to each of base stations, and particularly to a RF amplifier suitable for use in a mobile communication system which simultaneously uses a plurality of carriers different in frequency between each base station and one terminal.
A current mobile communication system, which performs communications through the use of radio waves, adopts a cellular system capable of using limited frequencies with satisfactory efficiency with a view toward increasing subscriber capacity to be held therein. As shown in
FIG. 14
, the cellular system is one wherein a range of a radio wave (frequency f
1
) emitted from one base station
60
a
is localized by sharpening the directivity of an antenna
61
a
to thereby narrow a service area like
62
a
, whereby a plurality of base stations (corresponding to a base station
60
b
in
FIG. 14
, whose antenna and service area are designated at
61
b
and
62
b
respectively) spaced one base station or more away from the base station
60
a
can utilize the same frequency f
1
.
In the current cellular mobile communication system from the viewpoint of a demand for downsizing of a terminal, the amount of information transfer required by a system, and attenuation characteristics of an electro-magnetic wave in free space, the range of the radio wave emitted from the base station is set from a few km to about 20 km, the frequency to be used ranges from several hundreds of MHz to a few GHz, and radiation power of one terminal ranges from a few hundreds of mW to about 2 W.
The number of subscribers to be accommodated, which is required for one base station, reaches from several tens to several hundreds of subscribers under such conditions. To this end, average transmitting power of from several tens of W to several hundreds of W is required as the output of a transmitting power amplifier of the base station.
Digital mobile communications are mainstream at present to realize a variety of communication services. Since a modulation system takes phase/amplitude modulation in this case, a transmitting power amplifier needs to have high linearity. While a high-power RF semiconductor is used in the transmitting power amplifier, the efficiency of the same power amplifier is inevitably reduced in the existing circumstances to compensate for its non-linearity. Incidentally, the required transmitting power ranges from several hundreds of W to a few KW as a saturated output.
Assuming now that RF power is transmitted from a transmitting power amplifier placed adjacent to a base station for indoor use, having a ground height of several tens of m to an antenna installed at a height of 100 m, for example, the loss of a RF cable for connection cannot be neglected. Namely, since a loss of about 5 dB to 6 dB is normally generated when the length of the cable is about 100 m, it is necessary to increase the output of the transmitting power amplifier to about five times as the loss-free case. Accordingly, the transmitting power amplifier of the base station is installed as close to the antenna as possible.
Various services for providing more amounts of information have been proposed to obtain many subscribers and improve the utility of the system. With a view toward implementing such services, a method has been discussed which simultaneously uses a plurality of carriers (multi-carrier) different in frequency between a base station and one terminal, thereby increases the capacity of a radio communication network equivalently, and performing the transfer of larger amounts of data. A configuration of the base station used in the current multi-carrier mobile communication system for providing such services is shown in FIG.
15
.
A modem
63
for modulating and demodulating plural carriers is placed inside an office or building for a base station
60
. A plurality of output lines of the modem
63
are connected to an amplifier of a transmitting signal and amplifier of a receiving signal
64
installed near an array antenna
61
placed in the rooftop of the building. The amplifier of transmitting signal and amplifier of receiving signal
64
is connected to the array antenna
61
through a RF cable
65
.
Upon use of the plural carriers, an increase in the number of antennas for the base station with an increase in frequency and the placement of a RF (Radio Frequency) unit comprising the modem
63
in the base station
60
and the amplifier of transmitting signal and amplifier of receiving signal
64
, etc. in plural form will cause problems such as ensuring of a construction place, an increase in the number of in-office devices, etc. Even in the case of a terminal for receiving signals sent from the base station
60
, the provision of a transmitting circuit and a high-output power amplifier every different frequencies to transmit the plural carriers will lead to an increase in circuit scale, an increase in the volume of the terminal and a rise in the cost of each part, thus causing a problem.
Therefore, a system for amplifying a plurality of frequencies of carriers by the same RF unit has been discussed. Circuit configurations of a general base station and a terminal having adopted such a system are respectively shown in
FIGS. 16 and 17
. An amplifier of transmitting signal and amplifier of receiving signal
64
of the base station has a multi-carrier power amplifier (RF amplifier)
66
for simultaneously amplifying plural carriers and a low noise amplifier
67
for amplifying the received plural carriers.
A circuitry of terminal
68
included in the terminal has a baseband LSI (BB LSI)
69
for processing data to be transmitted and received, an analog front end
70
for modulating and demodulating the data to thereby generate a plurality of carriers, a RF/IF transmitting circuit
71
for amplifying the plural carriers outputted from the analog front end
70
and effecting frequency conversion thereon, a multi-carrier power amplifier (RF amplifier)
72
for amplifying a plurality of radio frequency carriers, and a duplexer
74
for sending a transmitting signal outputted from the RF amplifier
72
to an antenna
73
and simultaneously sending a receiving signal inputted from the antenna
73
to a RF/IF receiving circuit
75
. The receiving signal outputted from the RF/IF receiving circuit
75
is brought to receive data by the analog front end
70
, followed by supply to the baseband LSI
69
.
A circuit configuration for reducing distortion by feedforward type feedback, which has been described in the specification of U.S. Pat. No. 4,580,105, for example, has been adopted for the multi-carrier power amplifiers
66
and
72
to amplify a plurality of carrier signals.
SUMMARY OF THE INVENTION
When signals having a plurality of frequencies are simultaneously inputted, RF amplifiers, i.e., multi-carrier power amplifiers for the current base station and terminal will produce unnecessary spurious signals called inter modulation spurious in the vicinity of the plural frequencies within a frequency band of a wireless system due to non-linearity of an amplification characteristic of a semiconductor. It is difficult to eliminate the spurious signals by an external filter because they appear within the frequency band of the system. Further, since the spurious correspond to spurious emissions, the spurious must be reduced to an allowable value or less by any means according to strict law's control.
A limitation is imposed on the method of reducing distortion by the single amplifier like the above-described conventional circuit. It is thus difficult to sufficiently suppress the generation of the spurious signals. In order to realize services by the multi-carrier mobile communication system using the plural carriers, the development of a method for reducing spurious signals caused by a multi-carrier becomes an important problem in terms of the development of a cellular base station and terminal.
An object of the present invention is to provid
Sekine Kenji
Takei Ken
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