Amplifiers – With semiconductor amplifying device – Including frequency-responsive means in the signal...
Reexamination Certificate
2001-09-07
2004-08-03
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including frequency-responsive means in the signal...
C330S310000
Reexamination Certificate
active
06771130
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a power amplifier which is used, for example, in a transmission circuit of a radio communication apparatus and is required particularly to perform a low-distortion amplification, and also relates to a radio communication apparatus using the power amplifier.
In recent years, radio communication systems using a microwave band or a submicrowave band, including mobile communication systems such as a mobile phone, have rapidly come into wide use. This is greatly attributed to the reduction in weight and power consumption of the portable terminals. To make the portable terminal lightweight, it is effective to reduce the weight and capacity of a battery. But the battery having a small capacity is exhausted in a short time. Thus there has been strong demand for the reduction of electric power consumed by a signal transmission power amplifier in the portable terminal, because the power amplifier consumes most of the electric power of the portable terminal. That is, improvement of electric power efficiency has been strongly demanded for. In the recent digital modulation and demodulation using QPSK (Quadrature Phase Shift Keying) modulation technique, the power amplifier is required to amplify an inputted signal linearly because information is represented by amplitude and phase of the signal.
Generally, in the power amplifier, as an output electric power becomes closer to saturation owing to increase of an inputted electric power, distortion and power efficiency become increasingly high. Thus a high power efficiency and a low distortion are in a reciprocal relationship.
A power amplifier developed to realize a low distortion operation is disclosed in Japanese Patent Application Laid-Open No.10-135750
FIG. 13
is a circuit diagram showing the construction of the power amplifier. The power amplifier includes a front-stage signal-amplifying bipolar transistor
101
; a rear-stage signal-amplifying bipolar transistor
102
, an input terminal
103
, an output terminal
104
, an input matching circuit
105
, a interstage matching circuit
106
, an output matching circuit
107
, a supply voltage terminal
108
, a supply voltage terminal
109
for the base of the front-stage signal-amplifying bipolar transistor
101
, and a supply voltage terminal
110
for the base of the rear-stage signal-amplifying bipolar transistor
102
.
The operation of the power amplifier having the construction will be described below.
In the power amplifier, the low distortion operation and the high efficiency operation are in the reciprocal relationship, as descried above. To realize both the low distortion operation and the high efficiency operation, a front-stage base-biasing point is set to class A or class AB close to class A, and a rear-stage base-biasing point is set to class B or class AB close to class B.
The operation of the power amplifier will be described below from the viewpoint of a gain distortion of the power amplifier. Because the front stage is set to class A or class AB close to class A, if an input power increases and approaches a saturated power, the gain decreases. On the other hand, because the rear stage is set to class B or class AB close to class B, if the level of the input power increases, the gain also increases. As described above, the amplitude distortion characteristic at the front amplification stage is reverse to that at the rear amplification stage. By controlling the front- and rear-stage amplitude distortion characteristics appropriately, it is possible to adjust the distortion characteristic of the entire power amplifier while not affecting the power efficiency. The distortion characteristic of each of the front and rear stages of the power amplifier can be finely adjusted by changing the base-biasing point of each stage. In particular, because the rear stage is set to class B or class AB close to class B, there is a large change in the distortion characteristic with respect to the change of the base-biasing point. Accordingly, the distortion characteristic of the entire power amplifier is adjusted by utilizing the rear stage mainly.
However, the power amplifier has a problem that because the distortion characteristic is adjusted by changing the base-biasing point, the gain changes simultaneously with the adjustment of the distortion.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a high-efficiency and low-distortion power amplifier capable of accomplishing a distortion adjustment with a simple construction, without changing the gain, and also to provide a radio communication apparatus using the power amplifier.
In order to accomplish the above object, a power amplifier according to an aspect of the present invention includes:
a plurality of amplification stages in each of which a transistor is used as an amplification element; and
a distortion compensation circuit for compensating a distortion in at least one of the plurality of amplification stages,
wherein the amplification stage that undergoes distortion compensation by the distortion compensation circuit and the remaining amplification stage or stages that dos not undergo the distortion compensation by the distortion compensation circuit have opposite dependencies of an amplitude and/or a phase on an input power level.
In the power amplifier having the construction, the base-biasing point may be set to, for example, class A or class AB close to class A in the amplification stage that does not undergo the distortion compensation by the distortion compensation circuit, whereas the base-biasing point may be set to, for example, class B or class AB close to class B in the at least one amplification stage that undergoes the distortion compensation by the distortion compensation. The distortion characteristic of the power amplifier will be described below from the viewpoint of the amplitude distortion. The amplification stage not having the distortion compensation circuit has a characteristic that as the input power level increases toward a saturated power, a gain decreases, since its operation is set to class A or class AB close to class A. On the other hand, the amplification stage having the distortion compensation circuit has a characteristic that as the input power level increases toward the a saturated power, the gain increases, since its operation is set to class B or class AB close to class B. That is, the amplification stage having the distortion compensation circuit and the amplification stage not having the distortion compensation circuit have opposite dependencies of the amplitude on the input power level. Accordingly, by optimally adjusting the amplitude distortion characteristic of the amplification stage having the distortion compensation circuit, it is possible to offset the amplitude distortion of the amplification stage not having the distortion compensation circuit. If the amplification stage having the distortion compensation circuit and the amplification stage not having the distortion compensation circuit have opposite dependencies of the phase on the input power level, it is possible to adjust the phase distortion characteristic of the amplification stage having the distortion compensation circuit in such a way as to offset the phase distortion of the amplification stage not having the distortion compensation circuit. The transistor in each amplification stage may be a bipolar transistor or a field effect transistor.
There is also provided a power amplifier, according to another aspect of the present invention, which includes:
a plurality of amplification stages in each of which a bipolar transistor is used as an amplification element; and
a distortion compensation circuit for compensating a distortion in at least one of the plurality of amplification stages,
the distortion compensation circuit functioning also as a biasing circuit for the bipolar transistor in the amplification stage that undergoes distortion compensation by the distortion compensation circuit.
In the power amplifier having the above constru
Hasegawa Takao
Sakuno Keiichi
Birch & Stewart Kolasch & Birch, LLP
Choe Henry
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