Amplifiers – With amplifier bypass means
Reexamination Certificate
2001-12-26
2004-06-01
Tokar, Michael J. (Department: 2819)
Amplifiers
With amplifier bypass means
C330S149000
Reexamination Certificate
active
06744317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a feedforward linearizer, and more particularly to a digital linearizer of a power amplifier and a digital linearizing method thereof.
2. Background of the Related Art
In general, a high power amplifier (HPA) is used to increase the power of an input radio frequency (RF) signal. An ideal HPA does not distort the input RF signal while it amplifies the magnitude of the input RF signal. However, since the HPA generally consists of active elements having non-linear characteristics, an output signal from the HPA inevitably includes distortion components. Therefore, various linearizing technologies and algorithms for improving the non-linear characteristics of the HPA are provided in the related art. Representative linearizing methods include a predistortion method, an envelope feedback method, and a feedforward method.
FIG. 1
is a block diagram of a related art feedforward linearizer. As shown therein, the feedforward linearizer includes a divider
101
for dividing an input signal a main amplifying unit
102
for amplifying the divided input signal, and a directional coupler
105
for adding the input signal delayed by a delay
103
to the output signal of the main amplifying unit
102
, which is divided by a divider
104
. The distortion components included in the output signal of the main amplifying unit
102
are thus detected. The feedforward linearizer further includes an error amplifying unit
106
for amplifying the detected distortion components, and a directional coupler
108
for coupling the amplified distortion components to thus remove the distortion components.
The main amplifying unit
102
includes a variable attenuator
11
for attenuating an input signal, a variable phase shifter
12
for shifting the phase of the attenuated input signal, and a HPA
13
for amplifying the phase shifted input signal.
The error-amplifying unit
106
includes a variable attenuator
14
for attenuating the distortion components, a variable phase shifter
15
for shifting the phases of the attenuated distortion components, and an error amplifier
16
for amplifying the phase shifted distortion components.
In operation, an input signal is divided by the divider
101
and the divided signals pass through paths
17
and
18
, respectively. The input signal that passes through the path
17
is amplified by the main amplifying unit
102
. At this time, multiple harmonics components, that is, distortion components other than the input signal, exist in the output signal of the main amplifying unit
102
due to the non-linear characteristics of the HPA
13
. The input signal that passes through the path
18
is delayed by the delay
103
and is inputted to the directional coupler
105
. The time of delay
103
is set equal to the amount of time required for the operation of amplifying unit
102
.
The first directional coupler
105
couples the output signal of the main amplifying unit
102
input through the divider
104
with the input signal delayed by the delay
103
, to detect the distortion components included in the output signal of the main amplifying unit
102
.
The input signal of the path
17
sequentially passes through the variable attenuator
11
, the variable phase shifter
12
, and the HPA
13
of the main amplifying unit
102
, and is converted into a signal having a magnitude that is identical to the magnitude of the input signal of the path
17
and a phase that is opposite of the phase of the input signal of the path
17
. That is, the phase is different from the phase of the input signal by 180°. Therefore, when the input signal of the path
17
is added to the input signal of the path
18
by the directional coupler
105
, the original input signal disappears and only the distortion components exist.
The detected distortion components sequentially pass through the variable attenuator
14
, the variable phase shifter
15
, and the error amplifier
16
of the error amplifying unit
106
. The distortion components are thus converted into signals having magnitudes that are identical to the magnitudes of the detected distortion components, and phases that are opposite to the phases of the detected distortion components. That is, phases are different from the phases of the detected distortion components by 180°. The converted signals are then inputted to the directional coupler
108
. For the above process, the error amplifier
16
is designed to increase only the magnitude of the signal and not to generate the harmonics components.
The output signal of the main amplifying unit
102
, which is divided by the divider
104
, is delayed by the delay
107
by the time delay of the error-amplifying unit
106
and is input to the directional coupler
108
. Therefore, when the output signal of the main amplifying unit
102
is coupled with the output signal of the error-amplifying unit
106
by the directional coupler
108
, the distortion components, whose phases are 180° out of phase, offset each other. Accordingly, only the amplified input signal exists in the output signal of the directional coupler
108
.
As mentioned above, the related art feedforward linearizer compensates for the non-linearity of the HPA by detecting the distortion components included in the output signal of the HPA and offsetting the distortion components included in the output signal of the HPA by the detected distortion components.
The feedforward linearizer of the related art has many problems and disadvantages. For example, if the time delay of the delay units
103
and
107
do not coincide with the time delay of the main amplifying unit and the time delay of the error amplifying unit, respectively, then the conventional feedforward linearizer can not effectively remove the distortion components.
In addition, if the related art feedforward linearizer does not correctly control the variable attenuator and the variable phase shifter, it cannot generate the output signal and the distortion signal of the main amplifying unit, whose phases are shifted by 180°.
Moreover, since the related art feedforward linearizer processes all of the signals in an analog way and, in particular, all of the signals are processed in a high frequency band, it is very difficult to correctly control the variable attenuator and the variable phase shifter. Additional circuits must inevitably be used in order to correctly control the variable attenuator and the variable phase shifter.
Furthermore, the non-linear characteristics of the HPA change according to time or external circumstances such as a temperature or bias. The related art feedforward linearizer cannot effectively compensate for such changes.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
SUMMARY OF THE INVENTION
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Another object of the present invention is to provide a digital linearizer of a HPA, which is capable of accurately detecting the distortion components included in the output signal of the HPA by a digital processing method, and a digital linearizing method.
Another object of the present invention is to provide a digital linearizer of a HPA, which is capable of adaptively coping with changes in the non-linear characteristics of the HPA, caused by time or external circumstances such as a temperature or bias, and a digital linearizing method.
In order to achieve at least the above objects in whole or in part, and in accordance with the purposes of the present invention, as embodied and broadly described herein, there is provided a digital linearizer including a main amplifying unit configured to amplify a digital input signal on a first path, a distortion component detecting unit coupled to receive the digital input signal on a second path and an output signal of the main amplifying unit and detect dis
Kim Dae Weon
Kim Woo Sik
Fleshner & Kim LLP
LG Electronics Inc.
Nguyen Linh V
Tokar Michael J.
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