Telecommunications – Transmitter – Measuring – testing – or monitoring of transmitter
Reexamination Certificate
1997-02-04
2001-06-12
Tsang, Fan (Department: 2746)
Telecommunications
Transmitter
Measuring, testing, or monitoring of transmitter
C332S107000, C375S296000, C455S126000
Reexamination Certificate
active
06246865
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmitter of a radio communication system and, specifically, to a device for controlling distortion characteristic of a predistorter which compensates the distortion of a transmitting signal by using ready-only memory (ROM) data, and to a method therefor.
2. Description of the Related Art
A non-linear characteristic generated in a high output transmitter of a radio transmitting system brings about the distortion of a transmitting signal, thereby causing the deterioration of the transmitting characteristic. For the sake of compensating the above deterioration, a non-linear distortion characteristic in opposition to the non-linear distortion characteristic caused in a high output amplifier of the above transmitter is beforehand generated in an input terminal of the above transmitter. The non-linear distortion characteristic generated in the predistorter reciprocally cancels the distortion characteristic caused in the high output amplifier disposed at a rear terminal of the predistorter. The output level of the high output amplifier for use in the radio transmitting system is adjusted by the input level of a counterpart's receiver, that is, the transmitting system has an automatic power control function. At this time, the distortion characteristic of the high output amplifier is varied according to the variation of the output level and, accordingly, the distortion characteristic of the predistorter is varied.
FIG. 1
is a detailed block diagram showing the construction of a general predistorter
1
, and
FIG. 2
is a diagram showing a transmitter for outputting a linear radio signal by using the predistorter of FIG.
1
. In this instance, the predistorter
1
varies its distortion characteristic depending on the output level thereof. Here, it is a distortion control voltage Vc that varies the distortion characteristic of the predistorter
1
.
An explanation on the operation of the predistorter
1
will be given briefly with reference to FIG.
1
. The predistorter
1
receives a modulation signal a as an input signal thereof. Then, the received modulation signal a is amplified in a first amplifier
2
to have enough distortion in a distortion generator
12
. Then, a power divider
4
divides the power in a delay compensator
6
and the distortion generator
12
. The distortion generator
12
has its third distortion characteristic and then performs the distortion. Thereafter, an output signal of the distortion generator
12
is applied to a distortion adjuster
14
to adjust the size and the phase of the distortion, so that the adjusted size and phase can be combined with a delay compensated signal in the delay compensator
6
through a power coupler
8
. At this moment, the distortion signal regarding the delay compensated signal has a phase difference of 180° relative to the distortion characteristic of an output amplifier to be compensated. After the output of the power coupler
8
is amplified in a second amplifier
10
as much as that of the first amplifier
2
, the amplified output is outputted as a distorted modulation signal B. The frequency spectrum of both the modulation signal A as the input signal of the power coupler
8
and the distorted modulation signal B as the output signal thereof is illustrated in FIG.
1
.
The predistortion process performed in the predistorter
1
of
FIG. 1
is naturally achieved in an intermediate frequency band.
With reference to
FIG. 2
, the distorted signal B outputted from the predistorter
1
of
FIG. 1
, for example, an intermediate frequency band, is inputted to an up-converter
20
, the output C of which is provided to an output amplifier
22
of the radio frequency band, and is canceled with the non-linear distortion characteristic of the output amplifier
22
, so that a linear radio signal can be outputted to a directional coupler
24
.
At this moment, the distortion control voltage Vc is provided to the predistorter
1
in
FIG. 2
to thereby vary the distortion characteristic depending on the output level of the predistorter
1
. The processes of generating the distortion control voltage Vc are as follows. The directional coupler
24
divides the output of the output amplifier
22
and applies the divided output to the local down-converter
30
. The radio signal outputted from the directional coupler
24
is converted into the intermediate frequency bandpass by the local down-converter
30
and the result is outputted through a bandpass filter
32
as an inter-modulation signal (hereinafter, referred to as IMD). The bandpass filter
32
performs bandpass filtering to minimize the power of the IMD. The IMD signal as the output of the bandpass filter
32
has its power level detected in the power level detector
34
. A controller
36
provides the distortion control voltage Vc to the predistorter
1
in response to the detected power.
In the meantime, as depicted in
FIG. 2
, a local oscillator
28
provides a local oscillation signal and the power divider
26
divides the local oscillation signal of the local oscillator
28
to provide a divide signal to the up-converter
20
and the local down-converter
30
.
However, it is a disadvantage that the transmitter as illustrated in
FIG. 2
, should be indispensably constructed with an additional circuit such as the local down-converter
30
, the bandpass filter
32
, the power level detector
34
and the controller
36
for the sake of providing to predistorter the distortion control voltage Vc for changing the distortion characteristic in accordance with the output level. Also, it is impossible to softly meeting the distortion characteristics of the predistorter
1
depending on the distortion characteristic of the output amplifier
22
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a device and a method for softly meeting the distortion characteristic of the predistorter in accordance with the distortion characteristic of an output amplifier in a transmitter.
It is another object of the present invention to provide a device and a method for converting an IMD signal component into digital data in accordance with the variation of the output level of the transmitter, storing the digital data, and controlling the distortion characteristic to generate the distortion control voltage so as to have the distortion in conformity with the variation of the output level.
In order to achieve the above objects, the present invention is provided with a device for controlling the non-linear distortion characteristic of a predistorter in a radio communication transmitter which includes the predistorter for beforehand generating the non linear distortion characteristic in opposition to non-linear distortion characteristic arising in an output amplifier, and an up-converter for converting the output frequency of the predistorter into a radio frequency bandpass and outputting the converted frequency to the output amplifier, the device comprising: a monitoring unit for monitoring the output level of the output amplifier; a storing unit for beforehand storing the non-linear distortion characteristics of the predistorter as digital data; a distortion controller for outputting and controlling given non-linear distortion characteristic digital data stored in the storing unit in correspondence with the output level of the monitoring unit; and a digital analog converter for converting the non-linear distortion characteristic digital data outputted by the distortion controller into an analog signal and providing the converted data to the predistorter.
REFERENCES:
patent: 4412185 (1983-10-01), Gerard
patent: 5142240 (1992-08-01), Isota et al.
patent: 5262734 (1993-11-01), Dent et al.
patent: 5524285 (1996-06-01), Wray et al.
patent: 5678198 (1997-10-01), Lemson
patent: 5867065 (1999-02-01), Leyendecker et al.
patent: 5913172 (1999-06-01), Mc Cabe et al.
patent: 5923712 (1999-07-01), Leyendecker et al.
Bushnell , Esq. Robert E.
Samsung Electronics Co,. Ltd.
Smith Sheila
Tsang Fan
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