Amplifiers – With amplifier bypass means
Reexamination Certificate
2001-03-09
2003-06-10
Pascal, Robert (Department: 2817)
Amplifiers
With amplifier bypass means
C330S149000
Reexamination Certificate
active
06577193
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a linear power amplifying apparatus, and more particularly, to a linear power amplifying apparatus in base station for a mobile communication.
2. Description of the Background Art
Generally, a radio frequency band amplifier using active elements creates undesired distorted components according to power level variation. Especially, when an amplifier is operated in the vicinity of a saturation area, a non-linear phenomenon remarkably occurs, distorting an amplitude and a phase of an output. In case that more than two signals are inputted, inter-modulation distortion (IMD) components are generated between the inputted signals, having a big influence on an adjacent channel. Such IMD components work as a noise source, degrading a transfer quality of a communication system.
Accordingly, in case of an amplifier in use for a radio frequency transmission terminal of the base station for mobile communication, an operating point of the amplifier is positioned at a few decibel (dB) back-off position from the saturation area, so that the amplifier can be operated at the linear area.
In this case, however, since the input level of the amplifier needs to be low, so that its output level becomes too low.
In an effort to solve the problem, a research has been conducted for a method to add a linear circuit which minimizes an IMD component among outputs of the amplifier, to the amplifier. This method is advantageous in that even though the amplifier is operated in the non-linear area in the vicinity of the saturation area, an output signal of a desired amplitude having less IMD component is obtained.
FIG. 1
is a schematic block diagram of a linear power amplifying apparatus including a linear circuit in accordance with a conventional art.
As shown in the drawing, a linear power amplifying apparatus includes a pre-amplifier
1
, a first distributor
2
, a main amplification circuit
6
, a second distributor
7
, a second delay unit
8
, a second coupler
9
, a first delay unit
10
, a first coupler
11
and an error amplification circuit
15
.
The pre-amplifier
1
amplifies an infinitesimal input signal to a predetermined amplitude with which main amplification circuit
6
is operable. The first distributor
2
distributes the output signal of the pre-amplifier
1
.
The main amplification circuit
6
amplifies one signal distributed by the first distributor
2
to an amplitude suitable to a mobile communication radio interface. The second distributor
7
distributes the amplified signal outputted from the main amplification circuit
6
.
The first delay unit
10
delays the other signal distributed by the first distributor
2
as long as the time taken for one signal to pass the main amplification circuit
6
. The first coupler
11
couples one signal distributed by the second distributor
7
and the other signal delayed by the first delay unit
10
.
The error amplification circuit
15
amplifies an error signal outputted from the first coupler
11
as large as the amplification of the main amplification circuit
6
. The second delay unit
8
delays the other signal distributed by the second distributor
7
as long as the time taken for one signal to pass the error amplification circuit
15
.
The second coupler
9
couples the signal delayed by the second delay unit
8
and the signal outputted from the error amplification circuit
15
and outputs it.
The main amplification circuit
6
and the error amplification circuit
15
includes variable attenuators
3
and
12
for variably attenuating an inputted signal, variable phase shifters
4
and
13
for varying a phase of a signal outputted from the variable attenuators
3
and
12
, and a main amplifier
5
and an error amplifier
14
each for amplifying the signal outputted from the variable phase shifters
4
and
13
to a predetermined amplitude, respectively.
The operation of the conventional linear power amplifying apparatus constructed as described will now be explained.
First, when an infinitesimal input signal is inputted, the pre-amplifier
1
amplifies the input signal to a predetermined amplitude with which the main amplification circuit
6
is operable.
The first distributor
2
distributes the output signal of the pre-amplifier
1
and outputs one signal to the main amplification circuit
6
and the other signal to the first delay unit
10
.
The signal outputted to the main amplification circuit
6
passes the variable attenuator
3
, the variable phase shifter
4
and the main amplifier
5
, and then is amplified to an amplitude suitable to the mobile communication radio interface. At this time, a large amount of harmonics are generated.
The second distributor
7
distributes the output signal including the harmonics component from the main amplification circuit
6
, and outputs one signal to the second delay unit
8
and the other signal to the first coupler
11
.
Meanwhile, the first delay unit
10
the signal distributed by the first distributor
2
as long as the passing time of the main amplification circuit
6
and outputs it to the first coupler
11
.
The first coupler
11
couples the signal including the harmonic component distributed by the second distributor
7
and the signal delayed by the first delay unit
10
and outputs a carrier-cancelled error signal.
The error amplification circuit
15
amplifies the error signal outputted from the first coupler
11
, passing through the variable attenuator
12
, the variable phase shifter
13
and the error amplifier
14
, and amplifies the amplitude of amplification of the main amplification circuit
6
. At this time, the error amplifier
14
amplifies only the amplitude without generating harmonics.
The second delay unit
8
delays the signal including the harmonics outputted from the second distributor
7
as long as the passing time of the error amplification circuit
15
and outputs it to the second coupler
9
.
The second coupler
9
couples the carrier signal including the harmonics received from the second delay unit
8
and the error signal of which only the harmonics has been amplified received from the error amplification circuit.
At this time, the carrier signal including the harmonics and the error signal of which only the harmonics has been amplified have the same amplitude to each other and are adjusted to have a phase difference of 180°. Thus, when the two signals are coupled by the second coupler
9
, the high frequency component are mutually canceled, so that an amplified carrier signal having an amplitude suitable to the mobile communication radio interface, which is similar to the original input signal, is outputted.
However, the conventional linear power amplifying apparatus has a problem that the variable attenuator which variably attenuates the amplitude of the input signal and the variable phase shifter which variably shifts the phase of the input signal are not accurately controlled, resulting in that it is difficult to obtain a signal having the opposite phase, and thus, the harmonic component cancellation effect is degraded.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a linear power amplifying apparatus suitable to cancellation of harmonics in a mobile communication.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a linear power amplifying apparatus including: a first distributor for distributing an input signal; a variable attenuator for receiving one signal distributed by the first distributor and variably attenuating the amplitude of the signal according to an amplitude control signal; a variable phase shifter for shifting a phase of the signal outputted from the variable attenuator according to a phase control signal; a main amplifier for amplifying the signal shifted by the variable phase shifter to a predetermined level; a second distributor for distributing the signal outputted from the main amplifier; a delay
Fleshner & Kim LLP
Nguyen Khanh Van
Pascal Robert
LandOfFree
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