Amplifiers – With semiconductor amplifying device – Including frequency-responsive means in the signal...
Reexamination Certificate
1999-12-29
2002-05-21
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including frequency-responsive means in the signal...
C330S149000, C330S286000, C330S302000
Reexamination Certificate
active
06392491
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-frequency amplifier for amplifying a multicarrier signal generated by combining plural carrier waves modulated independently.
2. Description of the Related Art
CDMA (Code Division Multiple Access) system inherently has confidentiality and interference-resistibility and is the multiple access system capable of making efficient use of radio frequencies. Therefore, CDMA system is applied to various communication systems.
Furthermore, CDMA system is being actively applied to mobile communication system since the transmitting power control technology with high response and high accuracy has been established so that the near-far problem is solvable in recent years.
The transmitting section of a radio base station of a mobile communication system to which CDMA system described above is applied is composed of high-frequency amplifiers
101
-
1
to
101
-N which amplify the power of plural N of RF signals that have different frequencies of carrier waves respectively and whose frequencies are assigned based on a given frequency allocation and on the zone configuration and a combiner
102
which generates multicarrier signals to be fed to an antenna system by combining RF signals given respectively by the output of high-frequency amplifiers
101
-
1
to
101
N as shown in FIG.
13
.
It is now assumed that the number N of the RF signals described above is 2, for simplicity. The frequencies of the carrier waves of these RF signals are indicated by f
1
and f
2
, respectively.
In the transmitting section configured as described above, the high-frequency amplifiers
101
-
1
and
101
-
2
amplify the electric powers of first and second RF signals, respectively, which contain the frequencies f
1
and f
2
, in the occupied bands.
Since these high-frequency amplifiers
101
-
1
and
101
-
2
amplify the first and second RF signals, respectively, even if nonlinear regions are contained in the characteristics of amplification elements provided in the high-frequency amplifiers
101
-
1
and
101
-
2
, noises are not generated due to cross modulation (intermodulation) of these RF signals. Furthermore, such noises will be hereinafter referred to simply as cross modulation distortion.
In the prior art described above, as the number N of the frequencies of carrier waves assigned to the radio base station increases, the number N of the amplifiers
101
-
1
to
101
-N increases, thus increasing the size of the hardware.
As for the configuration of the hardware of the radio base station, it is generally required to be adaptable to the maximum value Nmax of the number of carrier waves that can be assigned.
However, as for the radio base station, as the size of the hardware increases, constraints on the office establishment, such as floor space and volume needed for installation and power consumption, may become more stringent and the reliability may deteriorate.
The increases of constraints and deterioration of the reliability may be alleviated by a combiniation of a combiner for combining the plural N of RF signals and a single common amplifier for amplifying the multicarrier signals gained from the output of the combiner. However, the common amplifier is required to have high linearity enough to suppress the level of the cross modulation distortion of the plural N of RF signals below a desired upper level.
Furthermore, the dynamic range of the common amplifier is required to become wider with increasing the number N of the RF signals described above and with increasing the area of the wireless zone formed by the radio base station.
Accordingly, even though the common amplifier is technically realizable, it is rarely put into practical use because of costs and other constraints.
The cross modulation distortion described above, as shown in ((
4
) in FIG.
14
), is generally generated as a component of frequencies of summation and subtraction between the frequencies f
1
, to f
N
((
1
) and (
2
) in
FIG. 14
) of plural N of carrier waves assigned to the radio base station and the cross modulation distortion ((
3
) in
FIG. 13
) of frequencies equal to the frequency difference &Dgr;f among the frequencies f
1
to f
N
on the frequency axis, as for that distortion, it is referred to hereinafter as the basic modulation product.
For simplicity, the frequency difference &Dgr;f is assumed hereinafter that it is the frequency difference between the frequencies of adjacent carrier waves as given by
&Dgr;f=f
k+1
−f
k
where k is an arbitrary integer (k=1 to (N−1)).
However, the impedance or inductance of a line to be grounded inside the common amplifier generally increases with increasing the frequency &Dgr;f of the basic modulation product described above. Similarly, the level of the basic modulation product increases.
That is, as the frequency difference &Dgr;f between the frequencies of the plural N of RF signals contained in the multicarrier signals to be amplified increases, the level of the generated cross modulation distortion increases.
Accordingly, it has been necessary that the conventional common amplifier described above be made of a circuit having an impedance that is low enough to tolerate the level of the cross modulation distortion.
In a mobile communication system to which wideband CDMA system is applied, the frequency &Dgr;f of the basic modulation product generally assumes large values of more than 10 MHz to tens of MHz.
Therefore, it has been difficult to use a common amplifier including the circuit of low impedance as described above unless the following conditions hold:
(1) Increase of the power consumption is tolerable under other constraints including running costs.
(2) It is possible to cope with the technical constraints on mechanical dimensions and thermal design of amplifier elements and other elements.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a high-frequency amplifier which includes small-scale hardware but is capable of flexibly adapting itself to various frequency allocations.
It is another object of the invention to provide a high-frequency amplifier including a small-scale circuit that can accomplish high power efficiency and a high SN ratio.
It is a further object of the invention to provide a high-frequency amplifier that can stably maintain SN ratio even if there are a large number of carrier waves used for the generation of multicarrier signals to be amplified or even if the frequencies of these carrier waves are allocated in a various or variable manner.
It is yet another object of the invention to provide a high-frequency amplifier applied in electronic appliances, equipments, or systems, which can reduce them in price and size, and improve them in reliability. It is also to provide the high-frequency amplifier applied in electronic appliances and such which can also allow the maintenance and operation to be more efficient and be done at reduced costs.
The above objects are achieved by a high-frequency amplifier comprising an amplification means for amplifying a multicarrier signal generated by combining plural carrier waves modulated independently and a filtering means connected to the output terminal of the amplification means, having a passband lying within the range of the band occupied by the multicarrier signal,such transfer characteristics as to suppress the level of noise below a predetermined upper limit, the noise being generated as a modulation product between the multicarrier signal and modulation product having a frequency equal to the frequency difference &Dgr;f in the frequency axis as a resulting product between said carrier waves, and a rejection band including the frequency difference &Dgr;f in its range.
In this high-frequency amplifier, the noise described above mainly includes nonlinear distortion generated due to the nonlinearity of the amplification means.
Accordingly, as long as filtering characteristics adaptive to the characteristics of the amplification means and desired frequency allocati
Ohkawa Shigeru
Takahashi Kiyotaka
Takayashiki Takumi
Fujitsu Limited
Nguyen Patricia T.
Rosenman & Colin LLP
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