Telecommunications – Transmitter – With feedback of modulated output signal
Reexamination Certificate
2000-07-05
2002-11-12
Chin, Vivian (Department: 2745)
Telecommunications
Transmitter
With feedback of modulated output signal
C455S234100, C455S114100, C455S127500, C330S136000, C330S149000
Reexamination Certificate
active
06480705
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of compensating for a nonlinear distortion of a power amplifier of a transmission section of a wireless communication apparatus, and a wireless communication apparatus which compensates for a nonlinear distortion of a power amplifier of a transmission section.
In a digital wireless communication apparatus at present, the demand for linearity of a power amplifier for transmission becomes severe as increase of the speed and capacity of communication proceeds. However, if the demand for linearity of a power amplifier becomes severe, then the power efficiency of the power amplifier decreases, and this prevents, for example, elongation of the time within which a terminal telephone set of a digital portable telephone system can enjoy a continuous service. Therefore, it has been proposed to compensate for a nonlinear distortion of a power amplifier to augment the power efficiency of the power amplifier.
FIG. 14
illustrates a conventional distortion compensation method disclosed in Japanese Patent No. 2,689,011, “Linear Transmission Apparatus”. Referring to
FIG. 14
, an input signal Si of a modulated wave from an input terminal
101
is inputted to a power amplifier
91
through a directional coupler
92
and a power control circuit
93
. An output signal of the power amplifier
91
is led out as an output signal So to an output terminal
102
through another directional coupler
94
.
Then, the input signal Si is branched by the directional coupler
92
and supplied to an envelope detection circuit
95
, by which an envelope of the input signal Si is detected. The envelope detection signal of the envelope detection circuit
95
is supplied to a dc voltage conversion circuit
96
, by which a dc voltage from a power supply terminal
103
is converted in accordance with the envelope of the input signal Si. A dc voltage after the conversion of the dc voltage conversion circuit
96
is supplied as a power supply voltage to the power amplifier
91
.
Further, the output signal So is branched by the directional coupler
94
and supplied to another envelope detection circuit
97
, by which an envelope of the output signal So is detected. The envelope detection signal of the envelope detection circuit
97
is supplied together with the envelope detection signal from the envelope detection circuit
95
to a difference signal production circuit
98
. The difference signal production circuit
98
produces a signal of a difference between the envelope of the input signal Si and the envelope of the output signal So. The difference signal of the difference signal production circuit
98
is supplied through a dc amplifier
99
to the power control circuit
93
. The power control circuit
93
controls the input power of the power amplifier
91
in accordance with the difference between the envelope of the input signal Si and the envelope of the output signal So.
According to this method, the power supply voltage of the power amplifier
91
is controlled in accordance with the envelope of the input signal Si to decrease a nonlinear distortion of the input signal Si, and the input power of the power amplifier
91
is controlled in accordance with the difference between the envelope of the input signal Si and the envelope of the output signal So to absorb a gain variation of the power amplifier
91
which is caused by a temperature variation or the like.
With the conventional distortion compensation method described above, however, since the power supply voltage of the power amplifier
91
is modulated by the dc voltage conversion circuit
96
to amplitude modulate the signal to be amplified by the power amplifier
91
, there is a drawback that a distortion by the modulation is produced. Besides, since the power supply voltage of the power amplifier
91
is modulated in accordance with the envelope of the input signal Si, there is another drawback that a nonlinear distortion which cannot be detected from the envelope of the input signal Si and does not rely upon the power supply voltage of the power amplifier
91
, for example, a distortion which originates from a nonlinear parameter such as a parasitic capacitance Cgs between the gate and the source of a GaAs FET which forms the power amplifier
91
, cannot be reduced.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a distortion compensation method and a wireless communication apparatus which can reduce a nonlinear distortion of a power amplifier without producing a distortion by modulation and reduce a nonlinear distortion, which cannot be detected from an envelope of an input signal and does not rely upon the power supply voltage of the power amplifier, with certainty.
In order to attain the object described above, according to the present invention, there is provided a distortion compensation method for compensating for a nonlinear distortion of a power amplifier, comprising a detection step of detecting envelopes of an input signal and an output signal of the power amplifier individually, and an addition step of adding a signal corresponding to a finite difference between the detection signals of the envelopes obtained by the detection step to the input signal of the power amplifier.
In the distortion compensation method, not a signal obtained by modulating a power supply voltage of the power amplifier and amplifying the modulated power supply voltage by the power amplifier is amplitude modulated, but a signal for compensation is added to an input signal of the power amplifier. Consequently, a nonlinear distortion of the power amplifier can be reduced without production of a distortion by modulation. Besides, since a signal corresponding to a finite difference between an envelope of the input signal and an envelope of an output signal of the power amplifier is added as the signal for compensation, also a nonlinear distortion which cannot be detected from the envelope of the input signal and does not rely upon the power supply voltage of the power amplifier can be reduced with certainty.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.
REFERENCES:
patent: 3486128 (1969-12-01), Lohrmann
patent: 3789236 (1974-01-01), Lacroix
patent: 3900823 (1975-08-01), Sokai et al.
patent: 4276514 (1981-06-01), Huang
patent: 5121081 (1992-06-01), Hori
patent: 5376895 (1994-12-01), Aihara
patent: 5606285 (1997-02-01), Wang et al.
patent: 5697074 (1997-12-01), Makikallio et al.
patent: 5712593 (1998-01-01), Buer et al.
Chin Vivian
Maioli Jay H.
Nguyen Duc
Sony Corporation
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