Title: Power amplification circuit for communication device
Abstract: The power amplification circuit for a communication device includes an initial-stage amplifier for amplifying a modulation signal of a predetermined frequency band, a first amplification system having a subsequent-stage amplifier and a final-stage amplifier for amplifying power of an amplified output of the initial-stage amplifier without modification and outputting the amplified output as a first transmission signal, and a second amplification system having a frequency conversion circuit composed of a local oscillation circuit and a mixing circuit for converting an amplified output of the initial-stage amplifier into a signal of a frequency band different from that of the first transmission signal and a subsequent-stage amplifier and a final-stage amplifier for amplifying power of an output signal of the frequency conversion circuit and outputting the amplified output as a second transmission signal.
Patent Number: 7,006,803 Issued on 02/28/2006 to Ishii
| Inventors:
|
Ishii; Katsuhiro (Tokyo, JP)
|
| Assignee:
|
NEC Corporation (Tokyo, JP)
|
| Appl. No.:
|
875819 |
| Filed:
|
June 6, 2001 |
Foreign Application Priority Data
| Jun 19, 2000[JP] | 2000-183626 |
| Current U.S. Class: |
455/93; 455/75; 455/76 |
| Current Intern'l Class: |
H04B 1/02 (20060101) |
| Field of Search: |
455/75,76,77,78,93
|
References Cited [Referenced By]
U.S. Patent Documents
| 5406615 | Apr., 1995 | Miller, II et al.
| |
| 5732330 | Mar., 1998 | Anderson et al.
| |
| 5966666 | Oct., 1999 | Yamaguchi et al.
| |
| 5974302 | Oct., 1999 | Adamiecki et al.
| |
| 6064665 | May., 2000 | Leuck et al.
| |
| Foreign Patent Documents |
| 0 851 598 | Jul., 1998 | EP.
| |
| 0 926 838 | Jun., 1999 | EP.
| |
| 10-178375 | Jun., 1998 | JP.
| |
| 2000-40969 | Feb., 2000 | JP.
| |
| 3063346 | May., 2000 | JP.
| |
| 2002/-517121 | Jun., 2002 | JP.
| |
| WO 98/0092/7 | Jan., 1998 | WO.
| |
Other References
UK Examination Report dated Jul. 24, 2003.
|
Primary Examiner: Bui; Bing Q.
Attorney, Agent or Firm: Scully, Scott, Murphy & Presser
Claims
What is claimed is:
1. A power amplification circuit for a communication device having a plurality
of transmission frequency bands, comprising:
a first amplification system for amplifying power of a modulation signal of a
predetermined frequency band output from a single signal source without modification
and outputting the amplified signal as a first transmission signal; and
a second amplification system for converting the modulation signal of a predetermined
frequency band output from said single signal source into a signal of a frequency
band different from that of said first transmission signal, amplifying power of
the converted signal and outputting the amplified output as a second transmission signal,
wherein said second amplification system including a single local oscillation
circuit for outputting a signal of a frequency band for the conversion into a frequency
band different from a predetermined frequency band of the modulation signal output
from said single signal source, and
a single mixing circuit for mixing a signal whose frequency band is the same
as that of the modulation signal output from said single signal source and an oscillation
output of said local oscillation circuit.
2. The power amplification circuit for a communication device as set forth in
claim 1, further comprising:
an initial-stage amplifier for amplifying power of the modulation signal of a
predetermined frequency band output from the single signal source without modification.
3. The power amplification circuit for a communication device as set forth in
claim 1, wherein
a plurality of said second amplification systems are provided to output transmission
signals of a plurality of frequency bands not less than three kinds.
4. The power amplification circuit for a communication device as set forth in
claim 1, further comprising:
an initial-stage amplifier for amplifying power of the modulation signal of a
predetermined frequency band output from the single signal source without modification, wherein
said first amplification system including
an amplifier for amplifying power of an output of said initial-stage amplifier
without modification and outputting the amplified output as the first transmission
signal, and
said single local oscillation circuit of said second amplification system outputs
a signal of a frequency band for converting an output signal of said initial-stage
amplifier to have a frequency band different from a predetermined band,
said second amplification system further comprising an amplifier for amplifying
power of an output of said mixing circuit and outputting the amplified output as
the second transmission signal.
5. The power amplification circuit for a communication device as set forth in
claim 1, further comprising:
an initial-stage amplifier for amplifying power of the modulation signal of a
predetermined frequency band output from the single signal source without modification, wherein
said single local oscillation circuit of said second amplification system outputs
a signal of a frequency band for converting an output signal of said initial-stage
amplifier to have a frequency band different from a predetermined frequency band,
said second amplification system further comprising a subsequent-stage amplifier
and a final-stage amplifier for amplifying power of an output of said mixing circuit
and outputting the amplified output as the second transmission signal.
6. The power amplification circuit for a communication device as set forth in
claim 1, further comprising:
an initial-stage amplifier for amplifying power of the modulation signal of a
predetermined frequency band output from the single signal source without modification, wherein
said first amplification system includes
a subsequent-stage amplifier and a final-stage amplifier for amplifying power
of an output of said initial-stage amplifier without modification and outputting
the amplified output as the first transmission signal.
7. The power amplification circuit for a communication device as set forth in
claim 1, further comprising:
an initial-stage amplifier for amplifying power of the modulation signal of a
predetermined frequency band and output from the single signal source without modification, wherein
said first amplification system including
a subsequent-stage amplifier and final-stage amplifier for amplifying power of
an output of said initial-stage amplifier without modification and outputting the
amplified output as the first transmission signal, and
said single local oscillation circuit of said second amplification system outputs
a signal of a frequency band for converting an output signal of said initial-stage
amplifier to have a frequency band different from a predetermined frequency band,
said second amplification system further comprising a subsequent-stage amplifier
and a final-stage amplifier for amplifying power of an output of said mixing circuit
and outputting the amplified output as the second transmission signal.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power amplification circuit for a communication
device, and more particularly, to a power amplification circuit for a communication
device suitable for use in mobile communication.
2. Description of the Related Art
In the field of mobile communication in recent years, there is a sharp increase
in traffic because portable terminals have been widely used and therefore a plurality
of communication systems exist whose frequency bands are largely apart from each other.
In order to improve users' convenience, it is demanded by the market that these
plurality of communication systems should be realized by one terminal device.
Under these circumstances, for the transmission and reception of signals at
a plurality of communication systems, it is desirable in terms of costs and mounting
areas, rather than that one terminal device is mounted with a plurality of circuits
for transmitting and receiving signals whose frequencies for use are largely apart
from each other as many as the number of communication systems, that a part of
the circuit is shared. This is obvious because the market demand trends toward
terminal down-sizing.
Presented as a conventional example of a power amplification circuit for
a communication device capable of transmitting signals of a plurality of frequency
bands is an example of a power amplification circuit structure shown in FIG. 4
or
5.
A power amplification circuit
400 shown in FIG. 4 is structured such that
an initial-stage amplifier
401 for amplifying power of a modulation signal
output from a signal source
470 is used in common by two frequency bands
and at the subsequent stages, a transmission signal of one frequency band has its
power amplified by amplifiers
402 and
403 and a transmission signal
of the other frequency band has its power amplified by amplifiers
404 and
405 and the amplified signals are output as external signals.
On the other hand, a conventional power amplification circuit
500 shown
in FIG. 5 is structured such that two amplification systems completely independent
of each other, that is, an amplification system composed of amplifiers
501,
502 and
503 for amplifying an output signal of a signal source
580
and an amplification system composed of amplifiers
511,
512 and
513
for amplifying an output signal of a signal source
590, respectively amplify
power of the output signals of the signal sources
580 and
590 which
output signals whose frequency bands are apart from each other and respectively
output these amplified outputs as independent transmission signals.
Although the conventional power amplification circuit shown in FIG. 4 has
a less number of components than that of a power amplification circuit according
to an embodiment of the present invention which will be described later, when two
frequency bands are apart from each other as described above, it is extremely difficult
with respect to the two frequency bands to ensure high efficiency of power amplification
at the initial-stage amplifier
401, whereby frequency characteristics (amplification
characteristics) of one of the frequency band is largely limited.
The conventional power amplification circuit shown in FIG. 5, unlike the power
amplification circuit shown in FIG. 4, enables optimization of the frequency characteristics
of the initial-stage amplifiers
501 and
511 in the respective frequency bands.
However, as much space for a semiconductor die of the initial-stage amplifier
and a matching circuit and the like to be formed preceding thereto is as a matter
of course needed as a space equivalent to the number of frequency bands. This is
not desirable in terms of costs and size.
As described in the foregoing, a power amplification circuit for use in a conventional
communication device, in a case where the communication device has a plurality
of transmission frequency bands, is provided with a plurality of the same circuits
even though a circuit size is increased or has the circuit partly shared while
sacrificing amplification efficiency in a certain frequency band.
SUMMARY OF THE INVENTION
An object of the present invention, in consideration of such circumstances, is
to provide a power amplification circuit for a communication device which enables
power amplification in all transmission frequency bands with high efficiency without
increasing a circuit scale.
According to one aspect of the invention, a power amplification circuit
for a communication device having a plurality of transmission frequency bands, wherein
a modulation signal of a predetermined frequency band output from a single signal
source is converted into transmission signals of a plurality of frequency bands
and the transmission signals are output.
In the preferred construction, when outputting the transmission signal of the
same frequency as that of the signal of the signal source, the signal of the signal
source has power amplified without modification and output as a transmission signal, and
when outputting the transmission signal of a frequency different from that of
the signal of the signal source, the signal of the signal source is frequency-converted
and has power amplified and output as a transmission signal.
In another preferred construction, the power amplification circuit for a communication
device further comprises a first amplification system for amplifying power of the
modulation signal of a predetermined frequency band output from the single signal
source without modification and outputting the amplified signal as a first transmission
signal, and a second amplification system for converting the modulation signal
of a predetermined frequency band output from the single signal source into a signal
of a frequency band different from that of the first transmission signal, amplifying
power of the converted signal and outputting the amplified output as a second transmission signal.
In another preferred construction, a plurality of the second amplification systems
are provided to output transmission signals of a plurality of frequency bands not
less than three kinds.
According to another aspect of the invention, a power amplification circuit
for a communication device having a plurality of transmission frequency bands, comprises
a first amplification system for amplifying power of a modulation signal of a
predetermined
frequency band output from a single signal source without modification and outputting
the amplified signal as a first transmission signal, and
a second amplification system for converting the modulation signal of a predetermined
frequency band output from the single signal source into a signal of a frequency
band different from that of the first transmission signal, amplifying power of
the converted signal and outputting the amplified output as a second transmission signal.
In the preferred construction, the second amplification system includes a local
oscillation circuit for outputting a signal of a frequency band for the conversion
into a frequency band different from a predetermined frequency band of the modulation
signal output from the single signal source, and a mixing circuit for mixing a
signal whose frequency band is the same as that of the modulation signal output
from the single signal source and an oscillation output of the local oscillation circuit.
In another preferred construction, the power amplification circuit for a communication
device further comprises an initial-stage amplifier for amplifying power of the
modulation signal of a predetermined frequency band output from the single signal
source without modification.
In another preferred construction, a plurality of the second amplification systems
are provided to output transmission signals of a plurality of frequency bands not
less than three kinds.
In another preferred construction, the power amplification circuit for a communication
device further comprises an initial-stage amplifier for amplifying power of the
modulation signal of a predetermined frequency band output from the single signal
source without modification, wherein
the first amplification system includes an amplifier for amplifying power of
an output of the initial-stage amplifier without modification and outputting the
amplified output as the first transmission signal, and
the second amplification system includes a local oscillation circuit for outputting
a signal of a frequency band for converting an output signal of the initial-stage
amplifier to have a frequency band different from a predetermined frequency band,
a mixing circuit for mixing a signal whose frequency band is the same as that of
the modulation signal output from the single signal source and an oscillation output
of the local oscillation circuit, and an amplifier for amplifying power of an output
of the mixing circuit and outputting the amplified output as the second transmission signal.
In another preferred construction, the power amplification circuit for a communication
device further comprises an initial-stage amplifier for amplifying power of the
modulation signal of a predetermined frequency band output from the single signal
source without modification, wherein
the second amplification system includes a local oscillation circuit for outputting
a signal of a frequency band for converting an output signal of the initial-stage
amplifier to have a frequency band different from a predetermined frequency band,
a mixing circuit for mixing a signal whose frequency band is the same as that of
the modulation signal output from the single signal source and an oscillation output
of the local oscillation circuit, and a subsequent-stage amplifier and a final-stage
amplifier for amplifying power of an output of the mixing circuit and outputting
the amplified output as the second transmission signal.
In another preferred construction, the power amplification circuit for a communication
device further comprises an initial-stage amplifier for amplifying power of the
modulation signal of a predetermined frequency band output from the single signal
source without modification, wherein
the first amplification system includes a subsequent-stage amplifier and a final-stage
amplifier for amplifying power of an output of the initial-stage amplifier without
modification and outputting the amplified output as the first transmission signal.
In another preferred construction, the power amplification circuit for a communication
device further comprises an initial-stage amplifier for amplifying power of the
modulation signal of a predetermined frequency band output from the single signal
source without modification, wherein
the first amplification system includes a subsequent-stage amplifier and a final-stage
amplifier for amplifying power of an output of the initial-stage amplifier without
modification and outputting the amplified output as the first transmission signal, and
the second amplification system includes a local oscillation circuit for outputting
a signal of a frequency band for converting an output signal of the initial-stage
amplifier to have a frequency band different from a predetermined frequency band,
a mixing circuit for mixing a signal whose frequency band is the same as that of
the modulation signal output from the single signal source and an oscillation output
of the local oscillation circuit, and a subsequent-stage amplifier and a final-stage
amplifier for amplifying power of an output of the mixing circuit and outputting
the amplified output as the second transmission signal.
According to a power amplification circuit for a communication device of
the present invention, since a power amplification circuit for a communication
device having a plurality of transmission frequency bands is structured to convert
a modulation signal of a predetermined frequency band output from a single signal
source into transmission signals of a plurality of frequency bands and output the
transmission signals, amplification characteristics of an initial-stage amplifier
can be optimized to some extent in a narrow band, thereby preventing extreme deterioration
of amplification efficiency in any of the plurality of transmission frequency bands
to reduce current consumption of the communication device.
Other objects, features and advantages of the present invention will become
clear from the detailed description given herebelow.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood more fully from the detailed description
given herebelow and from the accompanying drawings of the preferred embodiment
of the invention, which, however, should not be taken to be limitative to the invention,
but are for explanation and understanding only.
In the drawings:
FIG. 1 is a block diagram showing a basic structure of a power amplification
circuit for a communication device according to the present invention;
FIG. 2 is a block diagram showing a structure of a power amplification circuit
according to an embodiment of the present invention;
FIG. 3 is an explanatory diagram showing a frequency scheme of the power amplification
circuit shown in FIG. 2;
FIG. 4 is a block diagram showing one example of a structure of a power amplification
circuit in a conventional communication device;
FIG. 5 is a block diagram showing another example of a structure of a power
amplification circuit in a conventional communication device.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the present invention will be discussed hereinafter
in detail with reference to the accompanying drawings. In the following description,
numerous specific details are set forth in order to provide a thorough understanding
of the present invention. It will be obvious, however, to those skilled in the
art that the present invention may be practiced without these specific details.
In other instance, well-known structures are not shown in detail in order to unnecessary
obscure the present invention.
Basic structure of a power amplification circuit for a communication device
according to the present invention is shown in FIG. 1.
In FIG. 1, a power amplification circuit
10 serves to amplify power of
transmission signals of a plurality of frequency bands different from each other
and output the amplified signals and includes an initial-stage amplifier
20
for amplifying power of a modulation signal of a predetermined frequency band output
from a signal source
70, an amplifier
30 for amplifying power of
an amplified output of the initial-stage amplifier
20 without modification
and outputting the amplified output as a first transmission signal, a local oscillation
circuit
40 and a mixing circuit
50 for frequency-converting an output
signal of the initial-stage amplifier
20 into a signal of a frequency band
different from the predetermined frequency band, and an amplifier
60 for
amplifying power of an output signal of the mixing circuit
50 and outputting
the amplified output as a second transmission signal.
Since the above-described power amplification circuit is thus structured such
that a modulation signal of a predetermined frequency band output from the single
signal source
70 is converted into and output as transmission signals of
a plurality of frequency bands, highly efficient power amplification in a plurality
of frequency bands largely apart from each other is possible even though it has
a single input structure.
Although shown in FIG. 1 is a case where the number of transmission signals
of a plurality frequency bands different from each other is two for the convenience
of explanation, the number is not limited thereto. By connecting a plurality of
amplification systems including a frequency conversion means composed of a local
oscillation circuit and a mixing circuit to the output side of the initial-stage
amplifier
20, highly efficient power amplification of transmission signals
of a plurality of frequency bands not less than three and output of the amplified
signals can be realized without increasing a circuit scale.
Next, shown in FIG. 2 is a structure of a power amplification circuit for a
communication device according to an embodiment of the present invention. In FIG.
2, a power amplification circuit
100 is a power amplification circuit for
a communication device having a plurality of transmission frequency bands and includes
an initial-stage amplifier
110 for amplifying power of a modulation signal
of a predetermined frequency band output from a single signal source
70,
a first amplification system composed of a subsequent-stage amplifier
120
and a final-stage amplifier
130 for amplifying power of an amplified output
of the initial-stage amplifier
110 without modification and outputting the
amplified output as a first transmission signal, and a second amplification system
composed of a frequency conversion circuit having a local oscillation circuit
140
and a mixing circuit
150 for converting an amplified output of the initial-stage
amplifier
110 into a signal of a frequency band different from that of the
first transmission signal, a subsequent-stage amplifier
160 and a final-stage
amplifier
170 for amplifying power of an output signal of the frequency
conversion circuit and outputting the amplified output as a second transmission signal.
In response to applied two signals, an output signal of the initial-stage amplifier
110 and an output signal of the local oscillation circuit
140, the
mixing circuit
150 outputs a signal having a frequency equivalent to a difference
between the two signals.
The signal source
70 has a function of generating a transmission signal
and is mainly composed of a frequency synthesizer and a modulator to generate a
modulation signal to be sent out in practice to the outside of the device through
an aerial wire.
The local oscillation circuit
140 has a frequency set in advance such
that when a frequency of an output signal of the signal source
70 and output
frequencies of the subsequent-stage amplifier
160 and the final-stage-amplifier
170 are different from each other, a signal of a frequency equivalent to
a different between them is generated.
In the above-described structure, a signal (modulation signal) output from the
signal source
70 has its power amplified by the initial-stage amplifier
110. Here, when the signal source
70 and the final output signal
(transmission signal) have the same frequency, the output of the initial-stage
amplifier
110 is amplified by the subsequent-stage amplifier
120
and the final-stage amplifier
130 and then externally sent out as an output
of the power amplification circuit
100 itself.
On the other hand, when the signal source
70 and the final output signal
have different frequencies, the output signal of the initial-stage amplifier
110
is frequency-converted by the local oscillation circuit
140 and the mixing
circuit
150 to have a frequency band different from that of the frequency
of the signal source
70 and the output signal of the mixing circuit
150
has its power amplified by the subsequent-stage amplifier
160 and the final-stage
amplifier
170, so that the amplified signal is externally sent out as an
output signal of the power amplification circuit
100 itself.
FIG. 3 shows an example of a transmission frequency of the communication device
according to the embodiment of the present invention, which is conforming to the
GSM transmission frequency standard used in portable telephones in Europe and the
like. This standard has two transmission frequency bands, GSM900 in the vicinity
of 900 MHz and DCS1800 in the vicinity of 1800 MHz. Market demands one portable
telephone to conduct transmission in the two frequency bands.
In the embodiment of the present invention, the initial-stage amplifier
110
is adjusted so as to conduct amplification most efficiently in the frequency band
of DCS1800, and transmission using the frequency band of GSM900 is conducted through
the mixing circuit
150.
According to the above arrangement, frequency characteristics (amplification
characteristics) of the subsequent-stage amplifier
120 and the final-stage
amplifier
130 are optimized in the frequency band of DCS1800, while frequency
characteristics of the subsequent-stage amplifier
160 and the final-stage
amplifier
170 are optimized in the frequency band of GSM 900.
When such a power amplification circuit is structured mainly using GaAs devices,
it is extremely difficult to conduct power amplification of frequency characteristics
of the initial-stage amplifier
110 in a broad band with high efficiency.
Therefore, both in a case where a frequency band of GSM900 is used and
in a case where a frequency band of DCS1800 is used, arranging the initial-stage
amplifier
110 to use the frequency band of DCS1800 enables the amplifier
to realize optimization in a narrow band to a certain extent, so that deterioration
of power amplification efficiency is reduced. This is the reason why such a frequency
scheme as shown in FIG. 3 is selected in the embodiment of the present invention.
Expressions "frequency band of GSM900" and "frequency band of DCS1800"
in the present embodiment represent frequency bands in the vicinity of 900 MHz
and 1800 MHz, respectively, and place no limitations on the system of the present invention.
In addition, although in the present embodiment, a part of the transmission circuits
of the two communication systems is shared, the number of bands of the transmission
circuit is arbitrary.
Furthermore, in a case where transmission is conducted using the local
oscillation circuit
140 and the mixing circuit
150 in the present
embodiment, although a transmission frequency is converted with an output frequency
of the signal source
70 fixed and an output frequency of the local oscillation
circuit
140 set to be variable, a relation between a fixed frequency and
a variable frequency may be reversed.
In the present embodiment, at the initial-stage amplifier
110, frequency
characteristics, that is, amplification characteristics, are optimized in a frequency
band of the DCS1800. This arrangement is made in consideration of the fact that
when a frequency is high, an output level of the mixing circuit
150 lowers
relatively. Without such a problem, a frequency band common to an initial-stage
amplifier is not limited.
In addition, although the present embodiment is on the premise that a power amplification
circuit is manufactured by a GaAs process, manufacturing process and the like of
the semiconductor is not limited thereto.
As described in the foregoing, according to the power amplification circuit for
a communication device of the present invention, since a power amplification circuit
for a communication device having a plurality of transmission frequency bands is
structured to convert a modulation signal of a predetermined frequency band output
from a single signal source into transmission signals of a plurality of frequency
bands and output the transmission signals, amplification characteristics of an
initial-stage amplifier can be optimized to some extent in a narrow band, thereby
preventing extreme deterioration of amplification efficiency in any of the plurality
of transmission frequency bands to reduce current consumption of the communication
device. More specifically, while the mixing circuit
150 and the local oscillation
circuit
140 consume current to a certain extent, the amount of consumed
current is much smaller than the amount of increase in current consumption caused
by deterioration of amplification efficiency of the power amplification circuit.
Although the invention has been illustrated and described with respect to
exemplary embodiment thereof, it should be understood by those skilled in the art
that the foregoing and various other changes, omissions and additions may be made
therein and thereto, without departing from the spirit and scope of the present
invention. Therefore, the present invention should not be understood as limited
to the specific embodiment set out above but to include all possible embodiments
which can be embodies within a scope encompassed and equivalents thereof with respect
to the feature set out in the appended claims.
*
