Amplifiers – With pilot frequency control means
Reexamination Certificate
2002-08-21
2004-05-11
Le, Dinh Thanh (Department: 2816)
Amplifiers
With pilot frequency control means
C330S151000
Reexamination Certificate
active
06734727
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a feedforward amplifier and a feedforward amplification method used for a base station apparatus of mobile communication equipment and so on.
2. Related Art of the Invention
In recent years, a power amplifier of high efficiency and high linearity is required for a transmitter of a base station of mobile communication equipment in order to amplify a large number of signaling channels by one operation, and improvement in the linearity is implemented by performing distortion compensation by a feedforward method.
A feedforward amplifier will not be described in detail here since it is also described in John L. B. Walker, “High-Power GaAs FET Amplifiers,” Artech House, 1993, pp. 332 to 333, for instance. Moreover, the entire disclosure of this literature are incorporated herein by reference in its entity.
And in recent years, a CDMA (Code Division Multiple Access) method of a broad band is adopted as a modulation method of a portable telephone, so that the base station also requires broad-band transmission, and broad-band distortion compensation control is also required for feedforward distortion compensation. Moreover, the CDMA method will not be described in detail here since it is also described in Nick Pothecary, “Feedforward Linear Power Amplifiers,” Artech House, 1999, pp. 73 to 76, for instance. Moreover, the entire disclosure of this literature are incorporated herein by reference in its entity.
The feedforward amplifier of implementing such broad-band control is exemplified by Japanese Patent Laid-Open No. 8-56126 “Distortion Compensation Amplifier Circuit,” which will be described by referring to FIG.
3
. In
FIG. 3
, reference numeral
1
denotes a first directional coupler,
2
denotes a first vector adjustor,
3
denotes a main amplifier,
4
denotes a second directional coupler,
5
denotes a first delay element,
6
denotes a second delay element,
7
denotes a second vector adjustor,
8
denotes an auxiliary amplifier,
9
denotes a third directional coupler,
10
denotes an amplifier,
11
a
denotes a pilot signal generator,
11
b
denotes a modulation signal generator,
12
denotes a detector,
14
denotes a digital-type control circuit comprised of an A/D converter, a D/A converter, a CPU and a memory,
21
denotes a DSB signal generator comprised of the pilot signal generator
11
a
and modulation signal generator
11
b
, and
22
denotes a DSB orthogonal detection circuit comprised of a reference signal generator, an orthogonal mixer, a filter and the A/D converter.
In this configuration, a removal control circuit uses at least two oscillators of the pilot signal generator
11
a
and modulation signal generator
11
b
and mixes signals from these two oscillators while rendering the signal from the pilot signal generator
11
a
as a carrier signal and the signal from the modulation signal generator
11
b
as a modulation signal so as to generate a pilot signal to be injected into the feedforward amplifier.
In addition, a reference signal generator
22
a
of receiving the carrier signal directly outputted from the pilot signal generator
11
a
to the DSB orthogonal detection circuit
22
is used to down-convert an output signal taken out of a coupler connected between the directional coupler
9
and the output side so as to have a transmission carrier removed by a filter, and results of sampling with the A/D converter are used to output a voltage of controlling the second vector adjustor
7
so that the control circuit
14
surpresses a distortion signal of the feedforward amplifier, that is, the level of the pilot signal becomes the lowest.
While the feedforward amplifier is originally an apparatus of controlling the vector adjustor mainly based on the output signal including the pilot signal and the pilot signal taken out thereof, it is necessary to set a frequency of the pilot signal outside a frequency band of the output signal and so the distortion signal cannot be sufficiently suppressed.
The feedforward amplifier of the above past example generates the pilot signal from the signals of the two oscillators of the pilot signal generator
11
a
and modulation signal generator
11
b
, and detects the output signal with the signal of the pilot signal generator
11
a
. Thus, it is possible to set the frequency of the pilot signal within the frequency band of the output signal so as to suppress the distortion signal under an optimum condition.
In the above configuration, however, there are a large number of the oscillators used to detect generation of the pilot signals, and at least the DSB signal generator
21
needs the pilot signal generator
11
a
and modulation signal generator
11
b
. As the oscillators are not small enough to be integrated on an integrated circuit together with other components, they need to have a separate configuration from other circuit components that can be integraded on an intergrade circuit, and this has hindered miniaturization of the feedforward amplifier.
Furthermore, a plurality of oscillators need to be mutually placed with certain spacing in order to secure isolation, and this has further hindered the miniaturization of the feedforward amplifier.
SUMMARY OF THE INVENTION
The present invention has been implemented in consideration of the above problems, and an object thereof is to obtain the feedforward amplifier and so on capable of further being miniaturized by reducing the number of the oscillators while suppressing the distortion signal under the optimum condition.
One aspect of the present invention is a feedforward amplifier having:
amplifying means of amplifying an input signal to obtain an amplified signal;
pilot signal generating means, having one local oscillator and a frequency divider for dividing output of said local oscillator, of generating a predetermined pilot signal based on the output of said local oscillator and the output of said frequency divider;
combining means of combining said input signal or said amplification signal with said pilot signal to generate a combined signal;
extracting means of extracting any distortion component from said combined signal;
output signal generating means of removing said extracted distortion component from said combined signal to generate an output signal; and
adjusting means of using any one of the output of said local oscillator, the output of said frequency divider, said pilot signal and said output signal from said output signal generating means to make an adjustment for removing said distortion component.
Another aspect of the present invention is the feedforward amplifier, wherein said pilot signal generating means has modulating means of having the output of said local oscillator modulated by the output of said frequency divider, a frequency of the output of said local oscillator is within a frequency band of the output signal from said output signal generating means, and a frequency of the output of said frequency divider is outside the frequency band of the output signal from said output signal generating means.
Still another aspect of the present invention is the feedforward amplifier, wherein said pilot signal generating means has a first mixer of mixing the output of said local oscillator and the output of said frequency divider, and the frequency of the output of said local oscillator is within a frequency band of the output signal from said output signal generating means, and the frequency of the output of said frequency divider is outside the frequency band of the output signal from said output signal generating means.
Yet still another aspect of the present invention is the feedforward amplifier, wherein said adjusting means performs said adjustment by using said pilot signal and said output signal.
Still yet another aspect of the present invention is the feedforward amplifier, wherein said adjusting means has a first converting means of converting said output signal into a low frequency band which is lower than the original frequency band and a second converting means of
Ishida Kaoru
Saito Yuji
Takachi Naoki
Le Dinh Thanh
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
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