Amplifiers – With semiconductor amplifying device – Including frequency-responsive means in the signal...
Reexamination Certificate
2002-04-16
2003-10-28
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including frequency-responsive means in the signal...
C330S285000, C330S297000
Reexamination Certificate
active
06639471
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high efficiecy power amplifier circuit with a wide dynamic range, a control method for the power amplifier circuit, and a portable terminal apparatus for mobile communication.
2. Description of the Related Art
For example, CDMA portable terminals are seldom operated at maximum power, but are often operated at 10 to 20 dB lower power. Thus, in order to extend battery life of terminals, it is important to reduce power consumption during such low power operation.
FIG. 11
shows a conventional power amplifier which can reduce power consumption during such low power operation.
In
FIG. 11
, the power amplifier consists of an input terminal
1101
, output terminal
1102
, matching circuit
1103
, transistor
1104
, matching circuit
1105
, bias circuit
1106
, bias circuit
1107
, step-down DC/DC converter
1108
, and control means
1109
.
The conventional power amplifier impedance-matches an input signal entered from the input terminal
1101
using the matching circuit
1103
, amplifies the signal using the transistor
1104
, impedance-matches the signal using the matching circuit
1105
, and outputs the signal from the output terminal
1102
.
The step-down DC/DC converter
1108
adjusts the supply voltage fed from a power supply terminal
1111
by lowering an output voltage to be delivered to the bias circuit
1107
, under the control of the control means
1109
.
Specifically, the conventional power amplifier achieves high efficiency with a wide dynamic range by using the step-down DC/DC converter
1108
, which sets the collector or drain voltage of the transistor
1104
to a value equal to or slightly lower than the supply voltage from the voltage supply terminal
1111
when the output power from the output terminal
1102
is high and sets the collector or drain voltage of the transistor
1104
to a value much lower than the supply voltage from the voltage supply terminal
1111
when the output power from the output terminal
1102
is low. Thus, conventionally, the collector or drain voltage of the transistor has never been used at a level higher than the supply voltage.
Besides, with the power amplifier used for CDMA or other portable terminals, an isolator is placed between the power amplifier and an antenna to reduce load variations in the power amplifier.
FIG. 13
shows such a conventional power amplifier
1302
.
During reception, an antenna switch (or antenna duplexer)
1304
outputs signals received by an antenna
1306
to an output terminal
1305
for received signals.
During transmission, the power amplifier
1302
amplifies transmitted signals entered from an input terminal
1301
for transmitted signals and outputs them to an isolator
1303
, which in turn sends the output of the power amplifier
1302
to the antenna switch (or antenna duplexer)
1304
, which then routes the output of the isolator
1303
to the antenna
1306
.
Antenna
1306
load will change during transmission, for example, due to causes such as a human body approaching the antenna
1306
. However, even if the antenna load changes in this way, the isolator
1303
placed between the power amplifier
1302
and antenna switch (or antenna duplexer)
1304
keeps the load on the output side of the power amplifier
1302
virtually almost constant.
FIG. 12B
shows characteristics of the step-down DC/DC converter
1108
used in the power amplifier shown in FIG.
11
.
FIG. 12A
shows the step-down DC/DC converter
1108
, where reference character Vin denotes an input voltage fed to the step-down DC/DC converter
1108
from a power supply connected to the power supply terminal
1111
while reference character Vout denotes an output voltage produced by the step-down DC/DC converter
1108
.
Specifically, in
FIG. 12B
, on the condition that the input voltage Vin is constant, the horizontal axis represents the output voltage Vout and the vertical axis represents efficiency (%) of the step-down DC/DC converter
1108
. The efficiency here is the percent ratio of output power Pout to input power Pin when the input voltage Vin is applied to the power supply terminal
1111
and the output voltage Vout is produced. In short, the efficiency is given by Pout/Pin×100.
It can be seen from
FIG. 12B
that the efficiency lowers with decreases in the output voltage Vout of the step-down DC/DC converter
1108
.
During the operation of the power amplifier shown in
FIG. 11
, actually the output power from the output terminal
1102
is relatively low in most cases. When the output power is low, so is the output voltage of the step-down DC/DC converter
1108
. Therefore, as can be seen from
FIG. 12B
, when the power amplifier produces low output power, the voltage conversion ratio of the step-down DC/DC converter
1108
is high. In such cases, the conversion efficiency of the step-down DC/DC converter
1108
lowers. Since the conversion efficiency of the step-down DC/DC converter
1108
lowers under low power conditions in which the power amplifier is used frequently, there is not much reduction in power consumption.
That is, a problem with the conventional power amplifier is that its power consumption cannot be reduced due to the lowered conversion efficiency of the step-down DC/DC converter.
On the other hand, the isolator
1303
placed between the power amplifier
1302
and antenna switch (or antenna duplexer)
1304
, described with reference to
FIG. 13
, poses a problem of increased circuit scale.
Also, the isolator
1303
causes a power loss of approximately 0.2 to 0.8 dB, for example. Thus, although load variations of the power amplifier
1302
can be reduced, the output power of the power amplifier
1302
must be increased to make up for the power loss caused by the isolator
1303
. This results in increased power consumption.
That is, a problem with conventional power amplifier is that the isolator causes power loss, which when compensated for, results in increased power consumption.
SUMMARY OF THE INVENTION
In view of the problems with the conventional power amplifier described above, an object of the present invention is to provide a power amplifier circuit with a smaller circuit scale and with good characteristics over a wide range of load impedance, a control method for the power amplifier circuit, and a portable terminal apparatus using the power amplifier circuit. Another object of the present invention is to provide a highly efficient power amplifier circuit with a wide dynamic range, a control method for the power amplifier circuit, and a portable terminal apparatus using the power amplifier circuit.
The 1st invention of the present invention is a power amplifier circuit, comprising:
a first matching circuit which impedance-matches incoming input signals before outputting them;
a first bias circuit connected to an output of said first matching circuit;
a transistor connected to the output of said first matching circuit;
a second bias circuit one end of which is connected to the output of said transistor;
a second matching circuit which is connected to the output of said transistor and impedance-matches output signals of said transistor before outputting them;
voltage transformation means whose output is connected to the other end of said second bias circuit and whose input is connected with a power supply; and
control means of controlling operation of said voltage transformation means,
wherein said power amplifier circuit further comprises load impedance detecting means of detecting the load impedance on the output side of said power amplifier circuit,
said control means changes output voltage of said voltage transformation means based at least on the results of said detection by said load impedance detecting means, and
said output voltage is applied to said transistor as a supply voltage.
The 2nd invention of the present invention is the power amplifier circuit according to 1st invention, further comprising an isolator disposed between said load impedance detecting means and an antenna.
The 3rd invention of the present
Adachi Hisashi
Handa Hiroyuki
Matsuura Toru
Obara Toshio
Sakakura Makoto
Choe Henry
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
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