Amplifiers – With semiconductor amplifying device – Including frequency-responsive means in the signal...
Reexamination Certificate
2002-10-28
2004-04-20
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including frequency-responsive means in the signal...
C330S303000, C333S032000
Reexamination Certificate
active
06724263
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-254226, filed on Aug. 30, 2002, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-frequency power amplifier.
2. Related Background Art
The high-frequency power amplifier is used for supplying electric power to the antenna of a communication gear such as a portable terminal. The high-frequency power amplifier is required to have a high power gain and a high power efficiency and be as small as possible because it is used for the portable terminals and the like.
Recently, a high-frequency power amplifier incorporating a matching circuit has been designed. The matching circuit is used to match the impedance (normally 50&OHgr;) of input/output between the high-frequency power amplifier and an antenna. Therefore, a small high-frequency power amplifier, which incorporates such an external circuit as the matching circuit as a module, is in demand.
To reduce the size of the high-frequency power amplifier, various kinds of methods are available, such as miniaturization of a semiconductor chip, intensification of the precision of mounting technology, refining the pattern of a module substrate. Particularly, because an output-matching circuit requires a large space, the miniaturization of the output-matching circuit provides a significant effect upon reduction of the size of the entire high-frequency power amplifier.
FIG. 10
shows the circuit diagram of a conventional high-frequency power amplifier
600
. Its input-matching circuit is omitted from this diagram. A fundamental signal is outputted from a transistor Tr produced on a semiconductor chip
10
. The fundamental signal is matched by a fundamental-signal matching circuit
20
having an inductor L
1
and a capacitor C
1
formed on a substrate. Ordinarily, the fundamental-signal matching circuit
20
matches the impedance of the fundamental signal to 50 &OHgr; and outputs the fundamental signal through the capacitor C
4
for DC current block.
A power supplying circuit
30
comprises a capacitor C
2
, an inductor L
2
and a direct current (DC) power supply
32
so as to supply power to the transistor Tr. The capacitor C
2
is a decoupling capacitor provided for grounding the high-frequency signal. The inductor L
2
is a so-called &lgr;/4 line which is set to &lgr;/4 with respect to the wavelength &lgr; of the fundamental signal. Consequently, the inductor L
2
turns to a large impedance for the fundamental signal propagated from the transistor Tr to the fundamental-signal matching circuit
20
. In other wards, the inductor L
2
turns to open state to the fundamental signal at a node
50
in which the power supplying circuit
30
is connected to the fundamental-signal matching circuit
20
. Therefore, the power supplying circuit
30
never affects the fundamental-signal matching circuit
20
. The secondary harmonic signal of an output signal from the transistor Tr is short-circuited by the inductor L
2
.
The high-frequency power amplifier
600
further comprises a harmonic matching circuit
40
having an inductor L
3
and a capacitor C
3
. The tertiary harmonic signal of the output signals from the transistor Tr is short-circuited by the harmonic matching circuit
40
.
If the inductor L
2
(&lgr;/4 line) is formed of a 50 &OHgr; line and the frequency of the fundamental signal is 900 MHz, the inductor L
2
needs to be about 30 mm long. Due to a demand for reduction of the size of the high-frequency power amplifier in recent years, the high-frequency power amplifier
600
including the output-matching circuit
60
is formed in the form of a square module 4 mm to 6 mm in one side. Therefore, it is very difficult to accommodate the output-matching circuit
60
having the inductor L
2
about 30 mm long in the module.
When the length of the inductor L
2
is shorter than 30 mm (for example, shortened to 20 mm) in order to solve this problem, the power supply circuit
30
is not in the open state to the fundamental signal because the inductor L
2
is shorter than the ideal &lgr;/4 line. Consequently, the electric loss of the output-matching circuit
60
is increased and the output impedance of the transistor Tr is changed.
When the inductor L
2
is formed of a transmission line having a higher impedance than the 50 &OHgr; line, for example, when the width of the transmission line of the inductor L
2
is reduced, the influence on the fundamental signal by the power supplying circuit
30
can be reduced. However, when the width of the transmission line is decreased, the resistance component possessed by the inductor L
2
is increased, and thereby the power from the DC power supply
32
is lost. As a result, the power efficiency of the high-frequency power amplifier
600
drops. Further, because the voltage drop by the inductor L
2
is increased, the voltage amplitude at the operating time of the transistor Tr is limited, and thereby the linear motion of the high-frequency power amplifier
600
is disturbed, and distortion component is increased in the output signal. The linear motion is important in digital modulation system. If the high-frequency power amplifier
600
is based on the digital modulation system, the increase in the distortion component leads to a large drop in the performance of the high-frequency power amplifier
600
.
To solve such a problem, the high-frequency power amplifier
700
shown in
FIG. 11
has been proposed. The output-matching circuit
60
possessed by the high-frequency power amplifier
700
comprises a parallel-resonant circuit
70
composed of a capacitor C
5
and an inductor L
4
. If the resonant frequency of the parallel-resonant circuit
70
is set to the frequency (for example, assumed to be f
0
) of the fundamental signal, the impedance of the power supplying circuit
32
as viewed from the node
50
is increased. The relation between the capacity C
5
of the capacitor C
5
, the inductance L
4
of the inductor L
4
and the angular frequency &ohgr;
0
(=2&tgr;f
0
) of the fundamental signal is expressed in the expression 1.
L
4
=1/(&ohgr;
0
2
*C
5
) (expression 1)
Because the value L
4
can be set smaller by increasing the value C
5
, a small inductor can be used as the inductor L
4
. The inductor L
2
does not have to be provided with a large inductance due to the effect of the resonant circuit. Consequently, the length of the inductor L
2
can be shorter than the &lgr;/4 line under the condition in which the power supplying circuit
32
gives no influence upon the fundamental-signal matching circuit
20
. Further, because the size of the inductor L
4
is small, and because the length of the inductor L
2
is shorter than the &lgr;/4 line, the high-frequency power amplifier
700
is smaller than the high-frequency power amplifier
600
and loss in DC current can be reduced.
However, in the high-frequency power amplifier
700
, the power supplying circuit
30
is incapable of short-circuiting the secondary harmonic. The harmonic matching circuit
40
needs to be formed as a secondary harmonic matching circuit in order to remove the secondary harmonic from the output signal. As a result, the high-frequency power amplifier
700
is incapable of matching harmonic higher than secondary harmonic. Thus, in case of adjusting up to the tertiary harmonic like the high-frequency power amplifier
600
shown in
FIG. 10
, it is necessary to add other harmonic matching circuit to the high-frequency power amplifier
700
. This increases the number of necessary components, which is contrary to the demand for reduction of the size. Adding another high-frequency matching circuit may cause a loss in the fundamental signal.
For the reason, there is demand for a high-frequency power amplifier having a high power efficiency and capable of matching secondary harmonic or higher order harmonic while the size thereof is smaller than the convent
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