Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
2002-04-23
2004-06-29
Nguyen, Khanh Van (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
C330S151000
Reexamination Certificate
active
06756844
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an amplification apparatus; and, more particularly, to a distortion compensation amplification apparatus capable of reducing power consumption by way of employing an automatic bias control scheme.
BACKGROUND OF THE INVENTION
In a mobile communications system, a base station transmits an amplified high frequency multi-carrier signal having a plurality of carriers separated from each other by different frequency bands and respectively modulated in a proper way,
Required in a radio amplification apparatus used in such base station of the mobile communications system are low power consumption and a high linearity as well as a high efficiency of a radio transmission circuit incorporated therein. Since an amplification apparatus with a poor linearity produces large distortion, e.g., inter-modulation distortion, which hampers the realization of a normal and a high quality communication, the amplification apparatus for use in the amplification of the multi-carrier signal is required to exhibit good linearity characteristics across the whole frequency band the multi-carrier signal belongs to.
One among various methods for satisfying such a linearity requirement of the amplification apparatus is a feed forward distortion compensation technique. First, referred to as the term ‘main line’ in the following description is a signal path from an input terminal to an output terminal via a main amplifier, i.e., a signal path for transferring a to-be-amplified signal and an amplified signal.
In the feed forward distortion compensation technique, a distortion detection loop is arranged in such a manner as to couple a signal branched from a position at the back end of the main amplifier to a signal sampled from somewhere in front of the main amplifier on the main line. If the two signals have same amplitudes but with inverse phases, the carrier signals are cancelled out by the above-described signal coupling operation of the distortion detection loop and, then, an error signal corresponding distortion components introduced by the main amplifier and its neighboring circuits can be outputted.
The feed forward distortion compensation technique further employs a distortion compensation loop for re-coupling the error signal outputted from the distortion detection loop to the signal on the main line. The distortion components produced by the main amplifier can be compensated by compensating on the main line a signal delay in the distortion compensating loop and, further by appropriately performing an adjustment on the amplitude and the phase of the signal on the distortion compensation loop or the main line, in such a manner that the distortion components in the signal on the main line and the signal obtained from the distortion compensation loop are controlled to have identical amplitudes but with inverse phases.
The feed forward distortion compensation technique will now be described hereinafter in further detail with reference to FIG.
15
.
Referring to
FIG. 15
, there is provided a conventional distortion compensation amplification apparatus having a feed forward configuration. The feed forward distortion compensation amplification apparatus includes two blocks: one is a distortion detection loop block including a directional coupler
1
, a phase shifter
2
, an amplitude adjuster
3
, a pilot signal generator
4
, a coupler
5
and a main amplifier
6
; and the other is a distortion compensation loop block including a coupler
8
, a detector
9
, a phase shifter
10
, an amplitude adjuster
11
and an error amplifier
12
. The feed forward distortion compensation apparatus further includes dividers
7
and
13
, a termination device
14
, a coupler
15
and a control unit
18
for controlling each element of the feed forward distortion compensation amplification apparatus.
Within the distortion detection loop block there exist two routes: one is a distortion-free route of a→c→e→g; and the other is a distortion route through a→b→d→f. At the point of “g”, only the distortion component is extracted by way of, e.g., inverting the signs of the transfer functions. At this time, the control unit
18
performs an automatic control on the phase shifter
2
and the amplitude adjuster
3
such that a received signal level of the distortion component measured by the detector
9
is minimized.
Another widely employed technique for achieving a good linearity in an amplification apparatus is an adaptive pre-distortion compensation technique (hereinafter referred to as an ADP technique) using a digital signal processing scheme. The ADP technique in general can be classified as a radio signal input type and a base band signal input type. Referring to
FIGS. 16A and 16B
, there are provided distortion compensation amplification apparatuses of such types.
FIG. 16A
shows a distortion compensation amplification apparatus of the radio signal input type. A radio signal is inputted to an input terminal
21
and is successively subjected to a delay circuit
22
, a gain control circuit
23
and a phase control circuit
24
and then, amplified at a power amplifier
34
. The amplified radio signal is outputted through a coupler
38
. Meanwhile, the input radio signal is also converted to a digital data signal by passing through a logarithmic amplifier (LOG AMP)
27
and an A/D converter
28
-
1
, both of which are incorporated in a power meter
29
. Afterwards, the digital data signal is provided to a data processing unit
30
-
1
.
Then, the amplified radio data signal outputted from the power amplifier
34
is delivered to a multiplier circuit
33
-
1
through the directional coupler
38
and combined with the local frequency
32
-
1
thereat. The coupled signal from the multiplier circuit
33
-
1
is then subjected to a band-pass filter
31
to have a limited frequency band. Next, the signal with the limited frequency band is inputted to the data processing unit
30
-
1
through an A/D converter
28
-
2
. The data processing unit
30
-
1
operates by an algorithm for minimizing a level of the signal passing through the band-pass filter
31
, i.e., off-band spectrum components generated by non-linear distortion characteristics of the power amplifier
34
.
The data processing unit
30
-
1
refers to addresses of memory circuits
26
-
1
and
26
-
2
based on the digital data signal provided from the power meter
29
to thereby control the gain control circuit
23
and the phase control circuit
24
through D/A converters
25
-
1
and
25
-
2
, respectively. The contents of the memory circuits
26
-
1
and
26
-
2
are determined on a trial and error basis such that the non-linear distortion of the power amplifier
34
becomes minimized.
Referring to
FIG. 16B
, there is provided a conventional distortion compensation amplification apparatus of the base band signal input type.
Carrier offset circuits
35
-
1
to
35
-
4
serve to offset carrier frequencies against respective input digital channel data based on carrier information for each input channel. The carrier offset circuit may be implemented, for example, by a complex multiplier. The outputs from the carrier offset circuits
35
-
1
to
35
-
4
are provided to an adder
39
, which generates, in response thereto, a combined base band signal to the complex multiplier
36
and a power meter
29
.
The complex multiplier
36
controls the phase and the amplitude of the combined base band signal. Thereafter, the thus processed base band signal is subjected to a D/A converter
25
-
4
and a quadrature amplitude modulation unit (hereinafter, a QAM-MOD)
37
, successively, and, then, combined with a signal from a local oscillator
32
-
2
at a multiplier circuit
33
-
2
. Subsequently, the combined signal is transferred as a radio signal to the power amplifier
34
to be amplified thereat and finally outputted through a directional coupler
38
. An algorithm for minimizing non-linear distortion of the power amplifier
34
controls, as in the earlier-described radio signal input type, the com
Matsuda Masahiro
Nanao Yoshinari
Satoh Matsuo
Hitachi Kokusai Electric Inc.
Nguyen Khanh Van
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