Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
2001-05-29
2003-07-08
Choe, Henry (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
C330S280000, C375S297000
Reexamination Certificate
active
06590449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to linearization of a power amplifier used in a cellular phone and base station, for example, as well as to a low-distortion power amplifier and the like.
2. Description of the Related Art
FIG. 17
shows a conventional predistortion circuit. As shown in
FIG. 17
, a signal that is input to an input terminal
1701
is divided to two routes by a divider circuit
1703
. In the first route, the signal is input to a combiner
1707
via a delay circuit
1704
. On the other hand, in the second route, a distortion is generated by a distortion generation circuit
1705
and the signal is input to the combiner
1707
via a vector adjustment circuit
1706
. The two signals are combined with each other by the combiner
1707
and a resulting signal is output from an output terminal
1702
and supplied to a power amplifier (not shown). The predistortion circuit generates a signal for suppressing a distortion of the downstream power amplifier by varying the amplitude and phase of a distortion with the vector adjustment circuit
1706
, whereby a distortion at the output of the power amplifier is suppressed. The delay time of the delay circuit
1704
is so set as to equalize the delay times of the first and second routes.
However, in particular, where a transmission signal has a wide bandwidth and the power amplifier performs a class-AB operation, the amplitude and phase characteristics of a intermodulation distortion generated by the amplifier lose balance and hence the effect of linearization (for example, suppressing distortion) degrades.
A more detailed description will be made below. It is assumed that the power amplifier is matched in a wide band and that the gain and the pass phase have no deviations in a transmission band. When two signals having different frequencies and the same amplitude are input, the output voltage V
O
is given by
V
O
=A
O
(cos &ohgr;
1
t
+cos &ohgr;
2
t
)+
B
OL
cos [(2&ohgr;
1
−&ohgr;
2
)
t+&phgr;
3L
]+B
OU
cos[(2&ohgr;
2
−&ohgr;
1
)
t+&phgr;
3U
] [Equation 1]
where &ohgr;
1
and &ohgr;
2
are the angular frequencies of the input signals, A
O
is the amplitude component of voltages having angular frequencies &ohgr;
1
and &ohgr;
2
(among the output voltages), B
OL
and B
OU
are the amplitude components of third-order intermodulation distortion voltages occurring on the low-frequency side and the high-frequency side, and &phgr;
3L
and &phgr;
3U
are the phase components of the third-order intermodulation distortion voltages occurring on the low-frequency side and the high-frequency side.
In this case, both intermodulation distortions occurring on the low-frequency side and the high-frequency side can be suppressed for by generating a voltage VI given by the following equation with the lonearizer (for example, predistortion circuit) and inputting it to the power amplifier:
V
I
=A
I
(cos &ohgr;
1
t
+cos &ohgr;
2
t
)−
B
IL
cos[(2&ohgr;
1
−&ohgr;
2
)
t+&phgr;
3L
]−B
IU
cos[(2&ohgr;
2
−&ohgr;
1
)
t+&phgr;
3U
] [Equation 2]
where A
I
is the amplitude component of voltages having angular frequencies &ohgr;
1
and &ohgr;
2
and B
IL
and B
IU
are the amplitude components of third-order intermodulation distortion voltages occurring on the low-frequency side and the high-frequency side in the predistortion circuit. There are relationships A
O
=A
I
·G, B
OL
=B
IL
·G, and B
OU
=B
IU
·G, where G is the voltage gain of the power amplifier.
According to the conventional technique, the amplitudes and the phases of third-order intermodulation distortion occurring in the predistortion circuit cannot be controlled independently on the low-frequency side and the high-frequency side. That is, B
IL
, B
IU
, &phgr;
3L
, and &phgr;
3U
cannot be controlled independently.
No particular problems occur with the above conventional linealizer if the amplitude components of third-order intermodulation distortion voltages on the low-frequency side and the high-frequency side are the same and their phase components are also the same.
However, if the amplitude components and/or the phase components of third-order intermodulation distortion voltages on the low-frequency side and the high-frequency side are different from each other as in the case that a transmission signal has a wide bandwidth and the power amplifier performs a class-AB operation, a problem arises that a sufficient linearization (for example, sufficient suppressing distortion) cannot be obtained.
BRIEF SUMMARY OF THE INVENTION
Object of the Invention
The present invention has been made in view of the above problems in the art, and an object of the invention is therefore to provide a predistortion circuit, a low-distortion power amplifier, control methods therefor, etc. in which at least one of the amplitudes and the phases of a distortion on the high-frequency side and the low-frequency side are controlled independently and that are therefore effectively used for a power amplifier having such an unbalanced distortion characteristic.
The 1st invention of the present invention (corresponding to claim 1) is a predistortion circuit comprising:
a divider for branching an input signal into plural branched signals;
a delay circuit for delaying one of the branched signals by a predetermined delay time;
a distortion generating circuit for receiving the other branched signal and for generating a distortion signal;
a vector adjustment circuit for varying an amplitude and a phase of the distortion signal; and
a combining circuit for combining an output signal of the delay circuit and an output signal of the vector adjustment circuit and for outputting a combined signal to circuit means as a subject of linearization to be provided downstream of and connected directly or indirectly to the combining circuit,
wherein the delay time of the delay circuit is set based on a phase difference of a distortion that would be generated by the circuit means if the vector adjustment circuit did not produce the output signal.
The 2nd invention of the present invention (corresponding to claim 2) is a predistortion circuit comprising:
a divider for branching an input signal into plural branched signals;
a delay circuit for delaying one of the branched signals by a predetermined delay time;
a distortion generating circuit for receiving the other branched signal and for generating a distortion signal;
an amplitude frequency characteristic adjustment circuit for varying an amplitude frequency characteristic of the distortion signal;
a vector adjustment circuit for varying an amplitude and a phase of the distortion signal that is output from the amplitude frequency characteristic adjustment circuit; and
a combining circuit for combining an output signal of the delay circuit and an output signal of the vector adjustment circuit.
The 3rd invention of the present invention (corresponding to claim 3) is the predistortion circuit according to 2nd invention, wherein the delay time of the delay circuit is set based on a phase difference of a distortion that would be generated by circuit means as a subject of linearization to receive an output signal of the combining circuit if the vector adjustment circuit did not produce the output signal.
The 4th invention of the present invention (corresponding to claim 4) is the predistortion circuit according to 1st or 3rd inventions, wherein the delay time of the delay circuit is set based on the phase difference in such a manner that a first delay time is so set that a difference between the first delay time and a second delay time substantially equivalent to or corresponding to the phase difference, where the first delay time is the delay time itself and the second delay time is a delay time of a signal that is input to the combining circuit via the distortion generation circuit and the vector adjustment circuit.
The 5th invention of the present inv
Fujiwara Seiji
Ishida Kaoru
Matsuura Toru
Sakakura Makoto
Choe Henry
Matsushita Electric - Industrial Co., Ltd.
Smith , Gambrell & Russell, LLP
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