U.S. patent application number 09/899987 was filed with the patent office on 2002-01-24 for transmission power amplification method and apparatus.
This patent application is currently assigned to NEC CORPORATION. Invention is credited to Nakajima, Toshikazu.
Application Number | 20020008576 09/899987 |
Document ID | / |
Family ID | 18706889 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020008576 |
Kind Code |
A1 |
Nakajima, Toshikazu |
January 24, 2002 |
Transmission power amplification method and apparatus
Abstract
A transmission power amplification apparatus includes a first
automatic gain control section, second automatic gain control
section, power amplifier, and control section. The first automatic
gain control section amplifies an input signal. The second
automatic gain control section amplifies an output from the first
automatic gain control section. The power amplifier nonlinearly
amplifies an output from the second automatic gain control section
and outputs a transmission signal. The control section controls
amplification of the input signal by using the synthetic gain of
the first and second automatic gain control sections and the power
amplifier in the transmission power range from a maximum value to
an intermediate value, and controls amplification of the input
signal by using only the gain of the first automatic gain control
section in the transmission power range from the intermediate value
to a minimum value. The second automatic gain control section has a
gain characteristic that corrects nonlinearity of the power
amplifier 102. A transmission power amplification method is also
disclosed.
Inventors: |
Nakajima, Toshikazu; (Tokyo,
JP) |
Correspondence
Address: |
SUGHRUE MION ZINN MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, NW
Washington
DC
20037-3213
US
|
Assignee: |
NEC CORPORATION
|
Family ID: |
18706889 |
Appl. No.: |
09/899987 |
Filed: |
July 9, 2001 |
Current U.S.
Class: |
330/51 ;
330/285 |
Current CPC
Class: |
H03F 1/0261 20130101;
H03F 1/32 20130101; H03G 1/0088 20130101; H03F 1/0277 20130101 |
Class at
Publication: |
330/51 ;
330/285 |
International
Class: |
H03G 003/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 12, 2000 |
JP |
210655/2000 |
Claims
What is claimed is:
1. A transmission power amplification apparatus comprising: first
variable gain amplification means for amplifying an input signal;
second variable gain amplification means for amplifying an output
from said first variable gain amplification means; nonlinear gain
amplification means for nonlinearly amplifying an output from said
second variable gain amplification means and outputting a
transmission signal; and control means for controlling
amplification of the input signal by using the synthetic gain of
said first and second variable gain amplification means and said
nonlinear gain amplification means in a transmission power range
from a maximum value to an intermediate value, and controlling
amplification of the input signal by using only the gain of said
first variable gain amplification means in a transmission power
range from the intermediate value to a minimum value, wherein said
second variable gain amplification means has a gain characteristic
that corrects nonlinearity of said nonlinear gain amplification
means.
2. An apparatus according to claim 1, wherein a total gain of said
second variable gain amplification means and said nonlinear gain
amplification means is set to substantially 0 at the intermediate
value of transmission signal power after correction.
3. An apparatus according to claim 1, wherein said apparatus
further comprises switch means for connecting said first variable
gain amplification means to a transmission output terminal upon
selectively switching between a first route in which said second
variable gain amplification means and said nonlinear gain
amplification means are connected in series and a second route
which bypasses the first route, and said control means controls
said first switch means such that an amplified signal from said
first variable gain amplification means is output to the
transmission output terminal through the first route in the
transmission power range from the maximum value to the intermediate
value, and an amplified signal from said first variable gain
amplification means is output to the transmission output terminal
through the second route in the transmission power range from the
intermediate value to the minimum value.
4. An apparatus according to claim 1, wherein when the second route
is selected by said switch means, supply of power to said second
variable gain amplification means and said nonlinear gain
amplification means constituting the first route is stopped.
5. An apparatus according to claim 1, wherein said nonlinear gain
amplification means comprises a field-effect transistor as an
amplification element, and a gain of said field-effect transistor
is controlled by controlling a drain voltage.
6. A transmission power amplification method comprising the steps
of: amplifying an input signal by using a first variable gain
amplifier; amplifying an output from the first variable gain
amplifier by using a second variable gain amplifier and nonlinear
gain amplifier connected in series; setting a gain characteristic
for the second variable gain amplifier to correct nonlinearity of
the nonlinear gain amplifier; amplifying the input signal by using
the first and second variable gain amplifiers and the nonlinear
gain amplifier in a transmission power range from a maximum value
to an intermediate value; and amplifying an input signal upon
bypassing the second variable gain amplifier and the nonlinear gain
amplifier in a transmission power range from an intermediate value
to a minimum value.
7. A method according to claim 6, further comprising the step of
setting a total gain of the second variable gain amplifier and the
nonlinear gain amplifier to substantially 0 at the intermediate
value of transmission power after correction.
8. A method according to claim 6, further comprising the step of
controlling a gain of an amplification element by controlling a
drain voltage of a field-effect transistor constituting the
nonlinear gain amplifier.
9. A method according to claim 6, further comprising the step of
stopping supply of power to the second variable gain amplifier and
the nonlinear gain amplifier in bypassing operation.
10. A transmission power amplification apparatus comprising: first
variable gain amplifier for amplifying an input signal; second
variable gain amplifer for amplifying an output from said first
variable gain amplifier; nonlinear gain amplifier for nonlinearly
amplifying an output from said second variable gain amplifier and
outputting a transmission signal; and controller for controlling
amplification of the input signal by using the synthetic gain of
said first and second variable gain amplifier and said nonlinear
gain amplifier in a transmission power range from a maximum value
to an intermediate value, and controlling amplification of the
input signal by using only the gain of said first variable gain
amplifier in a transmission power range from the intermediate value
to a minimum value, wherein said second variable gain amplifier has
a gain characteristic that corrects nonlinearity of said nonlinear
gain amplifier.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a transmission power
amplification method and apparatus which realize transmission power
control suitable for a case where a transmission power
amplification section includes a nonlinear gain amplifier.
[0002] In a recent digital mobile communication system, a
next-generation portable telephone scheme based on a W-CDMA
(Wideband-Code Division Multiple Access) scheme using a spread
spectrum scheme has proceeded toward commercialization in order to
further improve the frequency usage efficiency. According to the
W-CDMA scheme, to solve the so-called near-far problem, a dynamic
range of 70-odd dB or more needs to be quickly changed with high
precision in transmission power control.
[0003] Even if the use of a Class-A or Class-B power amplifier used
in a transmission power amplification section is limited to an
operating point at which the amplifier exhibits excellent
linearity, transmission is not frequency performed at the maximum
output in practice, and power is always consumed even in the
low-transmission output mode owing to DC bias currents. Demands
have therefore arisen for improvements in the power conversion
efficiency of these nonlinear gain amplifiers.
[0004] As means for improving the power conversion efficiency of a
nonlinear gain amplifier using an FET (Field Effect Transistor)
element, a bias control method, a method of bypassing a nonlinear
gain amplifier by using a switch, and the like are available. FIG.
5 shows the relationship between the transmission output of a
nonlinear gain amplifier and the power conversion efficiency in a
case where the drain voltage is so controlled as to optimize the
power conversion efficiency in consideration of the operation
stability of the nonlinear gain amplifier. As shown in FIG. 5, the
power conversion efficiency greatly improves when the drain voltage
is controlled as compared with a case where the drain voltage is
not controlled.
[0005] If, however, the drain voltage is low, the linearity of the
nonlinear gain amplifier deteriorates, and its operation becomes
unstable. When a nonlinear gain amplifier is to be bypassed by
using a switch, the power consumption of the nonlinear gain
amplifier can be reduced to zero by turning off the power supply of
the nonlinear gain amplifier. However, the transmission output
level becomes discontinuous in switching operation.
[0006] Japanese Patent Laid-Open No. 10-294626 (reference 1)
discloses a gain controller for reducing discontinuous portions of
the transmission output level by bypassing the nonlinear gain
amplifier using a switch. FIG. 6 shows a gain controller disclosed
in reference 1. Referring to FIG. 6, a signal input from an input
terminal 501 is branched into two paths by a distributor 510 and
respectively input to first and second variable gain amplifiers
516. An output from the first variable gain amplifier 511 is
amplified by a linear power amplifier 514 through a filter 512 and
driver amplifier 513. The resultant signal is output to a
synthesizer 515.
[0007] The synthesizer 515 synthesizes the output from the second
variable gain amplifier 516 with the output from the linear power
amplifier 514. The resultant signal is output from an output
terminal 502. A voltage from a power supply 503 is applied to the
linear power amplifier 514, driver amplifier 513, and first
variable gain amplifier 511 through a switch circuit 518. A control
circuit 517 controls the first variable gain amplifier 511, second
variable gain amplifier 516, and switch circuit 518.
[0008] The operation of the gain controller having the above
arrangement will be briefly described next. If a desired
transmission output is high, the gains of the first and second
variable gain amplifiers 516 are set to be large and small,
respectively. In this case, a main signal is transmitted through a
first path formed by the first variable gain amplifier 511. If a
desired transmission output low, a main signal is transmitted
through a second path formed by the second variable gain amplifier
516.
[0009] When the gain level of the first variable gain amplifier 511
becomes sufficiently lower than that of the second path, the switch
circuit 518 is switched to turn off the power supply for the first
variable gain amplifier 511, driver amplifier 513, and linear power
amplifier 514, thereby suppressing their current consumption to
0.
[0010] That is, two parallel paths are independently
gain-controlled such that a route exhibiting an optimal power
efficiency is selected in accordance with a required transmission
output level, and the gains of the respective paths are
continuously switched/controlled to reduce discontinuity.
[0011] In the above conventional gain controller, however, when
outputs from the first and second paths are to be synthesized,
since the first and second paths are connected in parallel, the
gain values of the respective paths which are required to obtain a
desired transmission output level cannot be obtained by simply
adding the gain of the first path to the gain of the second path.
That is, the levels of the respective paths must be inversely
calculated such that the level after synthesis becomes the desired
transmission output level, and the necessary gains of the
respective paths must be calculated from the inversely calculated
levels.
[0012] In a digital mobile communication system in which
transmission power must be variably controlled with high precision
at high speed with respect to an ambient radio environment that
changes incessantly in order to cover a wide dynamic range, a
complicated algorithm is required for transmission power control,
and much time is required for processing.
SUMMARY OF THE INVENTION
[0013] It is an object of the present invention to provide a
transmission power amplification method and apparatus which can
ensure an optimal power conversion efficiency and linearity in
obtaining a desired transmission power.
[0014] In order to achieve the above object, according to the
present invention, there is provided an transmission power
amplification apparatus comprising first variable gain
amplification means for amplifying an input signal, second variable
gain amplification means for amplifying an output from the first
variable gain amplification means, nonlinear gain amplification
means for nonlinearly amplifying an output from the second variable
gain amplification means and outputting a transmission signal, and
control means for controlling amplification of the input signal by
using the synthetic gain of the first and second variable gain
amplification means and the nonlinear gain amplification means in a
transmission power range from a maximum value to an intermediate
value, and controlling amplification of the input signal by using
only the gain of the first variable gain amplification means in a
transmission power range from the intermediate value to a minimum
value, wherein the second variable gain amplification means has a
gain characteristic that corrects nonlinearity of the nonlinear
gain amplification means.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a block diagram showing a transmission power
amplification apparatus according to an embodiment of the present
invention;
[0016] FIG. 2 is a level diagram of each block of the transmission
power amplification apparatus in FIG. 1;
[0017] FIG. 3 is a graph showing the relationship between the gain
of a power amplifier and the gain of a second AGC section in FIG.
1;
[0018] FIGS. 4A to 4E are graphs respectively showing the
relationships between the gain of the power amplifier in FIG. 1 and
the transmission output power, between the gain of the second AGC
section and the transmission output power, between the total gain
of the power amplifier and second AGC section and the transmission
output power, between the gain of the first AGC section and the
transmission output power, and between the total gain of the power
amplifier and the first and second AGC sections and the
transmission output power;
[0019] FIG. 5 is a graph showing the relationship between an output
from a nonlinear gain amplifier and power conversion efficiency;
and
[0020] FIG. 6 is a block diagram showing a conventional
transmission power amplification apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] The present invention will be described in detail below with
reference to the accompanying drawings.
[0022] FIG. 1 shows a transmission power amplification apparatus
according to an embodiment of the present invention. Referring to
FIG. 1, the level of a signal input from an input terminal 112 is
adjusted by a first automatic gain control (AGC) section 107. The
resultant signal is amplified by a driver amplifier 106. A
band-pass filter (BPF) 105 removes unnecessary spurious components
such as harmonic components produced by the driver amplifier 106
from the output from the driver amplifier 106. The level of this
signal is then adjusted by a second AGC section 103. The output
from the second AGC section 103 is amplified to a desired
transmission output level by a nonlinear gain amplifier 102. The
resultant signal is output to an antenna terminal 100. The gain
amplifier 102 is formed by a power amplifier 102 including FETs
112.
[0023] Path switches 101 and 104 are respectively connected to the
output stage of the power amplifier 102 and the input stage of the
second AGC section 103. By interlocking and switching the path
switches 101 and 104, the first route in which the second AGC
section 103 and power amplifier 102 are cascaded is bypassed, and
the output from the BPF 105 is directly output to the antenna
terminal 100 through a second route as a bypass route.
[0024] The transmission power amplification apparatus of this
embodiment further includes a drain voltage control section 108 to
improve the power conversion efficiency of the power amplifier 102.
The drain voltage control section 108 is mainly formed by a DC/DC
(Direction Current/Direction Current) converter and controls the
drain voltages of the FETs 112 forming the power amplifier 102 on
the basis of the drain voltage code generated by a code generating
section 110.
[0025] A control voltage control section 109 for controlling the
gains of the first and second AGC sections 107 and 103 is comprised
of a DSP (Digital Signal Processor), D/A (Digital to Analog)
converter, and the like. The control voltage control section 109
converts the control voltage code output from the code generating
section 110 into control voltage values for the first and second
AGC sections 107 and 103.
[0026] The path switches 101 and 104 are interlocked/controlled by
switching signals output from the code generating section 110 to
perform path switching for transmission signals. The code
generating section 110 is controlled by a transmission power code
from a CPU (Central Processing Unit) 111 to output a switching
signal.
[0027] The operation of the transmission power amplification
apparatus having the above arrangement will be described next with
reference to FIGS. 2 to 4.
[0028] FIG. 2 shows the level diagrams of transmission outputs from
the respective blocks from the input terminal 112 to the antenna
terminal 100 in FIG. 1. Referring to FIG. 2, a characteristic 11
represents the level diagram obtained when the transmission output
power from the antenna terminal 100 is a maximum value (Xdbm); a
characteristic 12, the level diagram obtained when the transmission
output power ranges from the maximum value to an intermediate value
(Xdbm to Ydbm); and a characteristic 13, the level diagram obtained
when the transmission output power is a minimum value (Zdbm).
[0029] Referring to FIG. 3, a characteristic 14 represents the
relationship between the gain of the power amplifier 102 and the
drain voltage code output from the code generating section 110 on
the basis of a transmission power code from the CPU 111; a
characteristic 15, the relationship between the control voltage
code output from the code generating section 110 and the gain of
the second AGC section 103; and 16, the sum of these two
relationships, i.e., a transmission output from the first route
passing through the second AGC section 103 and power amplifier
102.
[0030] The drain voltage code output from the code generating
section 110 is a value set in advance in accordance with the drain
voltage value of the power amplifier 102. The control voltage code
output from the code generating section 110 is a value set in
advance in accordance with the gain of the second AGC section 103.
As the values represented by these codes decrease, the voltage
value and gain also decrease.
[0031] FIGS. 4A to 4E show the gain values that the respective
blocks can take when the transmission output power at the antenna
terminal 100 changes to Xdbm, Ydbm, and Zdbm.
[0032] When the desired transmission output at the antenna terminal
100 is the maximum value, the code generating section 110 sends a
switching signal to the path switches 101 and 104 on the basis of a
transmission power code from the CPU 111. With this operation, the
path switches 101 and 104 are switched to set the first route
passing through the second AGC section 103 and power amplifier
102.
[0033] At the same time, the code generating section 110 outputs a
drain voltage code to the drain voltage control section 108 on the
basis of a transmission power code from the CPU 111, and also
outputs a control voltage code to the control voltage control
section 109. The drain voltage control section 108 controls the
drain voltage value to maximize the power conversion efficiency of
the power amplifier 102. The control voltage control section 109
sets a control voltage value to maximize the gains of the second
AGC section 103 and first AGC section 107 in accordance with the
control voltage code. As a consequence, a level diagram like that
indicated by the characteristic 11 in FIG. 2 is obtained.
[0034] This state will be described with reference to FIGS. 4A to
4E. As shown in FIGS. 4A, 4B, and 4D, when the transmission output
power at the antenna terminal 100 is XdBm, the gains of the power
amplifier 102, second AGC section 103, and first AGC section 107
are respectively set to maximum values AdB, CdB, and FdB. As shown
in FIG. 4E, therefore, the transmission output power XdBm is
obtained in accordance with the total gain (A+C+F) dB.
[0035] If the desired transmission output at the antenna terminal
100 falls with the range from the maximum value to the intermediate
value, the path switches 101a and 104 maintain the state where the
first route passing through the second AGC section 103 and power
amplifier 102 is selected with the switching signal output from the
code generating section 110 on the basis of a transmission power
code from the CPU 111.
[0036] At the same time, the code generating section 110 outputs a
drain voltage code and control voltage code to the drain voltage
control section 108 and control voltage control section 109,
respectively, on the basis of a transmission power code from the
CPU 111. At this time, the gain of the first AGC section 107 is
maintained maximum owing to the setting of a control voltage value.
For this reason, as indicated by the characteristic 11 in FIG. 2,
the same level diagram as that obtained when the transmission
output is the maximum value appears until a signal is output from
the path switch 104.
[0037] To obtain a desired transmission output at the antenna
terminal 100, therefore, the gains of the second AGC section 103
and power amplifier 102 must be adjusted respectively. The gain of
the power amplifier 102 is adjusted while the power conversion
efficiency is maintained. As indicated by the characteristic 14 in
FIG. 3, however, if the drain voltage code is decreased, the
linearity of the gain of the power amplifier 102 is impaired.
[0038] Control voltage values for the control voltage control
section 109 and second AGC section 103 are set to maintain the
linearity of a transmission output from the first route passing
through the second AGC section 103 and power amplifier 102. That
is, as indicated by the characteristic 14 in FIG. 3, the
nonlinearity of the gain of the power amplifier 102 is compensated
by the gain of the second AGC section 103 as indicated by the
characteristic 15 in FIG. 3 to correct the transmission output
characteristic so as to obtain linearity as indicated by the
characteristic 16 in FIG. 3.
[0039] This relationship will be described with reference to FIGS.
4A to 4E. When the transmission output power changes from XdBm to
YdBm, the set gain of the power amplifier 102 changes nonlinearly,
as shown in FIG. 4A. The gain of the second AGC section 103 is
therefore changed in the direction to decrease the set gain of the
power amplifier 102, as shown in FIG. 4B. With this operation, the
transmission output at the first route passing through the power
amplifier 102 and second AGC section 103 changes linearly, as shown
FIG. 4C. That is, the nonlinearity of the gain of the power
amplifier 102 is corrected by the set gain of the second AGC
section 103.
[0040] When the desired transmission output at the antenna terminal
100 becomes YdBm, the code generating section 110 outputs a
switching signal to the path switches 101 and 104 on the basis of a
transmission power code from the CPU 111. With this operation, the
path switches 101 and 104 switch the transmission path from the
first route to the second route that bypasses the first route. At
this time, the gain of the power amplifier 102 cannot be set to a
given level or lower as indicated by the characteristic 14 in FIG.
13. By decreasing the gain of the second AGC section 103 therefore,
the total gain of the first route passing through the second AGC
section 103 and power amplifier 102 is set to 0. That is, as the
transmission output Ydbm at the antenna terminal 100, the gain
value of the first AGC section 107 is output without any change
before and after path switching.
[0041] This state will be described further in detail with
reference to FIGS. 4A to 4E. To obtain the transmission output
power YdBm, as shown in FIG. 4A, the gain of the power amplifier
102 cannot be set to BdB or less. For this reason, as shown in FIG.
4B, the gain of the second AGC section 103 is changed to cancel out
the gain BdB of the power amplifier 102 from DdB to EdB, thus
performing correction to obtain the linearity of a transmission
output from the first route passing through the power amplifier 102
and second AGC section 103, as shown in FIG. 4C.
[0042] When the transmission output power at the antenna terminal
100 is YdBm, a gain EdB set in the second AGC section 103 is set to
EdB=-BdB so as to set the total gain of the first route passing
through the power amplifier 102a and second AGC section 103 to 0
dB.
[0043] When, therefore, the transmission output power is YdBm,
i.e., path switching is to be performed, the set gain FdBm of the
second AGC section 103 appears as the transmission output power
(B+E+F=B+(-B)+F=FdBm) shown in FIG. 4E, as shown in FIG. 4D. As a
consequence, no discontinuous portion occurs in the transmission
output power before and after path switching.
[0044] When the first route passing through the power amplifier 102
is to be bypassed, the drain voltage value is set to 0 by the drain
voltage control section 108, i.e., the power supply for the power
amplifier 102 is turned off. When the transmission output shifts
near YdBm, a hysteresis characteristic is set for the transmission
output in advance to prevent variations in transmission output in
path switching operation.
[0045] If the desired transmission output at the antenna terminal
100 falls within the range from the intermediate value to the
minimum value, the code generating section 110 generate a control
voltage code to the control voltage control section 109 to change
the control voltage value of the first AGC section 107. At this
time, a switching signal output from the code generating section
110 makes the path switches 101 and 104 maintain the state where
the transmission path is switched to the second route that bypasses
the first route. With this operation, a desired transmission output
can be obtained by only the set gain of the first AGC section
107.
[0046] FIG. 4D to 4E show this state. More specifically, when the
transmission output power falls within the range from YdBm to ZdBm,
the transmission output power shown in FIG. 4E is determined by the
set gains FdB to GdB of the first AGC section 107 shown in FIG. 4D.
In other words, in the above transmission power range, the set
gains FdB to GdB of the first AGC section 107 become transmission
output powers.
[0047] In the above embodiment, the respective blocks of the
transmission power amplification apparatus are independent of each
other. However, the driver amplifier 106, path switch 104, and
second AGC section 103 may be integrated into a 1-chip LSI (Large
Scale Integrated circuit).
[0048] As has been described above, according to the present
invention, if the transmission output power is high, the variable
gain amplifier compensates for the nonlinearity of the nonlinear
gain amplifier to obtain the linearity of the transmission power.
If the transmission power is low, path switching is performed after
the gain of the nonlinear gain amplifier is canceled out by the
variable gain amplifier. This can prevent the transmission output
power from becoming discontinuous at the time of switching
operation. In addition, a reduction in current consumption can be
attained by turning off the power supply of the nonlinear gain
amplifier after path switching.
[0049] In addition, when the nonlinearity of the nonlinear gain
amplifier is to be corrected, only the gain of the variable gain
amplifier may be controlled in switching the paths for the
nonlinear gain amplifier and variable gain amplifier. This makes it
possible to simplify the algorithm for transmission power control
and hence increase the processing speed.
* * * * *