Title: Predistortion type distortion compensation apparatus
Abstract: To update the control value to a value of higher precision in a predistortion type distortion compensation apparatus for compensating the distortion occurring in an amplifier for amplifying an input signal by the control using a control value corresponding to the level of the input signal.Distortion generating means (1) generates distortion in an input signal, input signal level detecting means (3) detects the level of the input signal, distortion control means (4) controls the distortion generated by the distortion generating means 1 by using a control value corresponding to the level of the detected input signal, distortion component level detecting means (7) detects the level of distortion component contained in the amplified signal issued from the amplifier (2), integrating means K1 to KN integrate the level of the distortion component detected at every level of the detected input signal, and control value updating means (10) updates the control value corresponding to the level so that the integration result at every level of the input signal may be small.
Patent Number: 6,925,106 Issued on 08/02/2005 to Horaguchi, et al.
| Inventors:
|
Horaguchi; Masato (Tokyo, JP);
Hongo; Naoki (Tokyo, JP);
Uchida; Takashi (Tokyo, JP);
Suto; Masaki (Tokyo, JP);
Takada; Toshio (Tokyo, JP)
|
| Assignee:
|
Hitachi Kokusai Electric Inc. (Tokyo, JP)
|
| Appl. No.:
|
880958 |
| Filed:
|
June 15, 2001 |
Foreign Application Priority Data
| Feb 01, 2001[JP] | 2001-025419 |
| Current U.S. Class: |
375/146; 375/285; 375/296; 330/260; 330/271; 330/284; 455/115; 455/126 |
| Intern'l Class: |
H04L 027/30 |
| Field of Search: |
375/130,146,285,295,296,297,299
330/254,260,271,278,284,294
455/115,123,126
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Ha; Dac V.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack, L.L.P.
Claims
1. A predistortion type distortion compensation apparatus for compensating distortion
occurring in an amplifier for amplifying an input signal, comprising:
distortion generating means for generating distortion in an input signal,
input signal level detecting means for detecting a level of the input signal,
distortion control means for controlling the distortion generated by the distortion
generating means by using a control value corresponding to the level of the input
signal detected by the input signal level detecting means,
distortion component level detecting means for detecting a level of distortion
component contained in the amplified signal issued from the amplifier,
integrating means for integrating the level of the distortion component detected
by the distortion component detecting means in every level of the input signal
detected by the input signal level detecting means, and
control value updating means for updating the control value corresponding to
the level used by the distortion control means so that the integration result of
every level of the input signal obtained from the integrating means may be small.
2. A predistortion type distortion compensation apparatus according to claim
1, wherein the distortion control means is composed by using a memory for, storing
the level of input signal and the control value in correspondence to each other.
3. A predistortion type distortion compensation apparatus according to claim 1,
wherein the distortion generating means comprises a predistortion unit including
a variable attenuator and a variable phase shifter, the input signal level detecting
means comprises an envelope detector, the distortion control means comprises a
compensation table including an attenuator table and a phase shifter table, the
amplifier comprises a power amplifier, the distortion component level detecting
means comprises a side band power measuring unit, the integrating means comprises
a quantizing circuit, a first selection circuit, and plural integrating circuits,
and the control value updating means comprises a control circuit and a second selection
circuit,
the input signal coming in from an input end of the predistortion type distortion
compensation apparatus is divided into two signals, and an amplitude of one distribution
signal is compensated of distortion by the variable attenuator in the predistortion
unit according to the control from the attenuator table of the compensation table,
a phase of this distribution signal is compensated of distortion by the variable
phase shifter in the predistortion unit according to the control from the phase
shifter table of the compensation table, and this distribution signal of which
amplitude and phase are compensated of distortion is amplified by the power amplifier,
and issued from an output end of the predistortion type distortion compensation
apparatus,
an envelope information of the other distribution signal is detected by the envelope
detector, the control value for amplitude control corresponding to this detection
result is read out by referring to the attenuator table of the compensation table
and issued to a control terminal of the variable attenuator of the predistortion
unit, and the control value for phase shift control corresponding to the detection
result is read out by referring to the phase shifter table of the compensation
table, and is issued to a control terminal of the variable phase shifter of the
predistortion unit, and
adjacent channel leak power contained in part of the amplified signal issued
from the power amplifier is measured by the side band power measuring unit, the
detection result of the envelope detector is converted into a digital value by
the quantizing circuit, one integrating circuit is selected and changed over out
of plural integrating circuits as the output destination of the adjacent channel
leak power issued from the side band power measuring unit by the first selection
circuit depending on the digital value entered from the quantizing circuit, the
adjacent channel leak power issued from the first selection circuit is integrated
by each integrating circuit, one integrating circuit is selected from these plural
integrating circuits by the second selection circuit according to control from
the control circuit, and control values to be stored in the attenuator table and
phase shifter table of the compensation table are updated by the control circuit
according to the integration result obtained from the selected integrating circuit.
4. A predistortion type distortion compensation apparatus for compensating distortion
occuring in an amplifier for amplifying an input signal, comprising:
distortion generating means for generating distortion in an input signal,
input signal level detecting means for detecting a level of the input signal,
distortion control means for controlling the distortion generated by the distortion
generating means by using a control value corresponding to the level of the input
signal detected by the input signal level detecting means,
distortion component level detecting means for detecting a level of distortion
component contained in the amplified signal issued from the amplifier,
counting means for counting inputs at specified level of the level of input signal
detected by the input signal level detecting means,
integrating means for integrating the level of the distortion component detected
by the distortion component detecting means when the level of the input signal
detected by the input signal level detecting means is the specified level for a
period until a specified value is counted by the counting means, and
control value updating means for updating the control value corresponding to
the specified level used by the distortion control means so that the integration
result of the integrating means may be small.
5. A predistortion type distortion compensation apparatus according to claim
4, wherein the distortion control means is composed by using a memory for storing
the level of input signal and the control value in correspondence to each other.
6. A predistortion type distortion compensation apparatus according to claim 4,
wherein the distortion generating means comprises a predistortion unit including
a variable attenuator and a variable phase shifter, the input signal level detecting
means comprises an envelope detector, the distortion control means comprises a
compensation table including an attenuator table and a phase shifter table, the
amplifier comprises a power amplifier, the distortion component level detector
comprises a side band power measuring unit, the counting means comprises a quantizing
circuit, comparator and a counter, the integrating means comprises a changeover
circuit and integrating circuit, and the control value updating means comprises
a control circuit,
the input signal coming in from an input end of the predistortion type distortion
compensation apparatus is divided into two signals, and an amplitude of one distribution
signal is compensated of distortion by the variable attenuator in the predistortion
unit according to the control from the attenuator table of the compensation table,
a phase of this distribution signal is compensated of distortion by the variable
phase shifter in the predistortion unit according to the control from the phase
shifter table of the compensation table, and this distribution signal of which
amplitude and phase are compensated of distortion is amplified by the power amplifier,
and issued from an output end of the predistortion type distortion compensation
apparatus,
an envelope information of the other distribution signal is detected by the envelope
detector, the control value for amplitude control corresponding to this detection
result is read out by referring to the attenuator table of the compensation table
and issued to a control terminal of the variable attenuator of the predistortion
unit, and the control value for phase shift control corresponding to the detection
result is read out by referring to the phase shifter table of the compensation
table, and is issued to a control terminal of the variable phase shifter of the
predistortion unit, and
adjacent channel leak power contained in part of the amplified signal issued
from the power amplifier is measured by the side band power measuring unit, the
detection result of the envelope detector is converted into a digital value by
the quantizing circuit, a specified ON signal is issued to the control terminal
of the changeover circuit and counter from the comparator when the level of the
input signal corresponding to this digital value is included in a level range on
the basis of the threshold information from the control circuit, the count value
is increased by the counter every time the ON signal is entered in the counter
from the comparator, the adjacent channel leak power issued from the side band
power measuring unit is issued to the integrating circuit by the changeover circuit
when the ON signal is entered in the changeover circuit from the comparator, the
adjacent channel leak power is integrated by the integrating circuit, and control
values to be stored in the attenuator table and phase shifter table of the compensation
table are updated by the control circuit according to the integration result.
7. A CDMA radio base station apparatus for compensating the distortion occurring
in an amplifier for amplifying a transmission signal by a predistortion type distortion
compensation apparatus, said predistortion type distortion compensation apparatus comprising:
distortion generating means for generating distortion in an input signal, input
signal level detecting means for detecting a level of the input signal, distortion
control means for controlling the distortion generated by the distortion generating
means by using a control value corresponding to the level of the input signal detected
by the input signal level detecting means, distortion component level detecting
means for detecting a level of distortion component contained in the amplified
signal issued from the amplifier, integrating means for integrating the level of
the distortion component detected by the distortion component detecting means in
every level of the input signal detected by the input signal level detecting means,
and control value updating means for updating the control value corresponding to
the level used by the distortion control means so that the integration result of
every level of the input signal obtained from the integrating means may be small.
8. A CDMA radio base station apparatus according to claim 7, wherein the distortion
control means of the predistortion type distortion compensation apparatus is composed
by using a memory for storing the level of input signal and the control value in
correspondence to each other.
9. A CDMA radio base station apparatus for compensating the distortion occurring
in an amplifier for amplifying a transmission signal by a predistortion type distortion
compensation apparatus, said predistortion type distortion compensation apparatus comprising:
distortion generating means for generating distortion in an input signal, input
signal level detecting means for detecting a level of the input signal, distortion
control means for controlling the distortion generated by the distortion generating
means by using a control value corresponding to the level of the input signal detected
by the input signal level detecting means, distortion component level detecting
means for detecting a level of distortion component contained in the amplified
signal issued from the amplifier, counting means for counting inputs at specified
level of the level of input signal detected by the input signal level detecting
means, integrating means for integrating the level of the distortion component
detected by the distortion component detecting means when the level of the input
signal detected by the input signal level detecting means is the specified level
for a period until a specified value is counted by the counting means, and control
value updating means for updating the control value corresponding to the specified
level used by the distortion control means so that the integration result of the
integrating means may be small.
10. A CDMA radio base station apparatus according to claim 9, wherein the distortion
control means of the predistortion type distortion compensation apparatus is composed
by using a memory for storing the level of input signal and the control value in
correspondence to each other.
11. A CDMA radio repeater amplifying apparatus for compensating the distortion
occurring in an amplifier for amplifying a transmission signal by a predistortion
type distortion compensation apparatus, said predistortion type distortion compensation
apparatus comprising:
distortion generating means for generating distortion in an input signal, input
signal level detecting means for detecting a level of the input signal, distortion
control means for controlling the distortion generated by the distortion generating
means by using a control value corresponding to the level of the input signal detected
by the input signal level detecting means, distortion component level detecting
means for detecting a level of distortion component contained in the amplified
signal issued from the amplifier, integrating means for integrating the level of
the distortion component detected by the distortion component detecting means in
every level of the input signal detected by the input signal level detecting means,
and control value updating means for updating the control value corresponding to
the level used by the distortion control means so that the integration result of
every level of the input signal obtained from the integration means may be small.
12. A CDMA radio repeater amplifying apparatus according to claim 11, wherein
the distortion control means of the predistortion type distortion compensation
apparatus is composed by using a memory for storing the level of input signal and
the control value in correspondence to each other.
13. A CDMA radio repeater amplifying apparatus for compensating the distortion
occurring in an amplifier for amplifying a transmission signal by a predistortion
type distortion compensation apparatus, said predistortion type distortion compensation
apparatus comprising:
distortion generating means for generating distortion in an input signal, input
signal level detecting means for detecting a level of the input signal, distortion
control means for controlling the distortion generated by the distortion generating
means by using a control value corresponding to the level of the input signal detected
by the input signal level detecting means, distortion component level detecting
means for detecting a level of distortion component contained in the amplified
signal issued from the amplifier, counting means for counting inputs at specified
level of the level of input signal detected by the input signal level detecting
means, integrating means for integrating the level of the distortion component
detected by the distortion component detecting means when the level of the input
signal detected by the input signal level detecting means is the specified level
for the period until a specified value is counted by the counting means, and control
value updating means for updating the control value corresponding to the specified
level used by the distortion control means so that the integration result of the
integrating means may be small.
14. A CDMA radio repeater amplifying apparatus according to claim 13, wherein
the distortion control means of the predistortion type distortion compensation
apparatus is composed by using a memory for storing the level of input signal and
the control value in correspondence to each other.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a predistortion type distortion compensation
apparatus for compensating the distortion occurring in an amplifier for amplifying
an input signal by the control using a control value corresponding to the level
of the input signal, and more particularly to a technique of updating the control
value to a more precise value.
2. Description of the Related Art
For example, in a base station apparatus (CDMA base station apparatus) of a mobile
communication system conforming to a W-CDMA (wide-band code division multiple access)
mobile communication method, the radio signal must be sent to a mobile station
apparatus (CDMA mobile station apparatus) physically at a long distance, and the
transmission signal must be sent out by largely amplifying by an amplifier.
However, the amplifier is an analog device, and there is limitation in amplification.
This limitation in amplification is also known as a saturation point, and after
the saturation point, the output power is unchanged if the power entered in the
amplifier is increased, and the output is nonlinear. This nonlinear output causes
a nonlinear distortion.
FIG. 7 shows an example of spectrum of transmission signal before input into
the amplifier, and FIG. 8 shows an example of spectrum of the transmission signal
amplified and issued by the amplifier when distortion is not compensated. In FIG.
7 and FIG. 8, the axis of abscissas of the graph indicates the frequency
(in kHz) and the axis of ordinates denotes the power ratio (in dB).
As shown in FIG. 7, in the transmission signal before amplification, the signal
component out of desired signal band is suppressed to a low level by the band limiting
filter, but in the signal after passing through the amplifier, as shown in FIG.
8, the signal is distorted, and signal component has leaked to outside of the desired
signal band (adjacent channel).
For example, in the base station apparatus, since the transmission power is high
as mentioned above, the magnitude of leak power to adjacent channel is strictly
regulated, and it is an important problem how to curtail such adjacent channel
leak power (ACP).
As means for curtailing the adjacent channel leak power, an example of a transmission
power amplifier with distortion compensation used in a conventional base station
apparatus is explained.
FIG. 9 is a structural example of such transmission power amplifier with distortion
compensation, and its operation is explained.
In the transmission power amplifier with distortion compensation, a transmission
signal (including I component and Q component) generated in a base band signal
generator
61 is put into a vector adjusting unit (predistortion unit)
62
and a power measuring unit
69, and the transmission signal entering the
vector adjusting unit
62 is compensated of distortion by this vector adjusting
unit
62. The vector adjusting unit
62 is generally composed of a
complex multiplier, and is designed to compensate the distortion of the transmission
signal, according to the control from a controller
68 described below, by
setting the amplitude-phase plane characteristic so as to be a reverse characteristic
of the nonlinear characteristic of an amplifier
64 described below, and
giving this characteristic (that is, the reverse characteristic) to the transmission
signal as the distortion compensation characteristic.
The transmission signal compensated of distortion by the vector adjusting unit
62 is up-converted from the base band to the carrier frequency band by a
transmission modulator
63, and is amplified by the amplifier
64,
and is supplied into the antenna not shown.
In the amplifier
64, distortion occurs when amplifying the transmission
signal, and the amplifying apparatus with distortion compensation is provided with
a feedback system for detecting the residue of distortion for observing whether
the distortion is compensated properly or not.
This feedback system comprises a local frequency generator
65, a demodulator
66, and an A/D converter
67, and part of the output signal (amplified
signal) of the amplifier
64 supplied into the antenna is, for example, taken
out by a directional coupler, and put into the demodulator
66.
In the feedback system, the amplified signal entered from the directional coupler
into the demodulator
66 is demodulated by using a local signal entered from
the local frequency generator
65 into the demodulator
66, and the
demodulated signal is converted from analog signal into digital signal by the A/D
converter
67, and the digital signal is put into the controller
68.
In the power measuring unit
69, the power of transmission signal (transmission
power) entered from the base band signal generator
61 is detected, and the
detection result is sent to the controller
68.
The controller
68 is composed of, for example, DSP (digital signal processor),
and it detects the residual distortion amount from the digital signal entered from
the A/D converter
67, and controls the vector adjusting unit
62 so
that the distortion may be compensated properly by the vector adjusting unit
62
on the basis of the detection result. In this control, it is controlled so that
the distortion compensation characteristic corresponding to the transmission power
noticed from the power measuring unit
69 may be used in the distortion compensation.
As described herein, according to the transmission power amplifier with distortion
compensation shown in FIG. 9, appropriate distortion compensation is done for the
distortion occurring in the amplifier
64, and an efficient transmission
power amplification process is realized.
FIG. 10 shows an example of spectrum of the transmission signal amplified and
issued by the amplifier
64 when distortion is thus compensated, and in this
signal spectrum, the adjacent channel leak power is curtailed substantially. The
axis of abscissas of the graph indicates the frequency (in kHz) and the axis of
ordinates denotes the power ratio (in dB).
Several prior arts relating to such distortion compensation are presented below.
For example, in the digital wireless apparatus disclosed in Japanese Laid-open
Patent No. 9-294144, distortion is compensated by using a feedback system similar
to the one shown in FIG. 9, and in this feedback system, same as in FIG. 9, the
required signal to be transmitted (the original transmission signal) is down-converted
together with undesired signal generated in adjacent channel (that is, the distortion
generated in the amplifier), and all signals are processed by orthogonal demodulation
or the like.
In the automatic follower type predistorter disclosed in Japanese Patent Publication
No. 63-10613, distortion occurring in the amplifier is compensated by using the
feedback system similar to the one shown in FIG. 9, and this feedback system, similarly,
demodulates the amplified signal including the transmission signal band (that is,
reproduces the base band signal before modulation), and processes by A/D conversion
or the like.
Although not intended to compensate distortion, in the measuring apparatus
and measuring method of adjacent channel leak power disclosed in Japanese Laid-open
Patent No. 9-138251, same as above, the carrier signal (corresponding to the required
signal) is taken out together with the adjacent channel signal (corresponding to
undesired signal), and they are processed by fast Fourier transform (FFT), and
the adjacent channel leak power ratio (power ratio of required signal and undesired signal).
As in distortion compensation of the transmission power amplifier with distortion
compensation shown in FIG. 9, the predistortion system is known as one of the methods
of compensating distortion occurring in the amplifier. In the predistortion system,
the reverse characteristic of the nonlinear characteristic of the amplifier is
preliminary given to the signal to be entered in the amplifier, and distortion
occurring in the amplifier is compensated. The nonlinear characteristic of the
amplifier includes the AM-AM characteristic changing the level of output signal
nonlinearly depending on the level of input signal, and AM-PM characteristic changing
the phase of output signal nonlinearly depending on the level of input signal.
FIG. 11 shows other circuit example of the apparatus employing such predistortion
system (predistortion type distortion compensation amplifying apparatus), and this
predistortion type distortion compensation amplifying apparatus comprises a predistortion
unit
71 including a variable attenuator (ATT)
81 and a variable phase
shifter
82, a power amplifier (PA)
72 composed of one or plural power
amplifiers, an envelope detector
73, a compensation table
74 including
a table for amplitude control (ATT table)
83 corresponding to the variable
attenuator
81 and a table for phase shift control (phase shifter table)
84 corresponding to the variable phase shifter
82, a side band power
measuring unit
75, a specific time integrating circuit
76, and a
control circuit
77.
An example of operation of the shown predistortion type distortion compensation
amplifying apparatus is shown.
The signal entering from the input end of the predistortion type distortion compensation
amplifying apparatus is distributed into two signals, and one distribution signal
is put into the variable attenuator
81 of the predistortion unit
71,
and other distribution signal is put into the envelope detector
73.
The envelope detector
73 detects the envelope information of the input
signal (momentary power level), and issues the result of detection to the compensation
table
74.
The compensation table
74, referring to the ATT table
83, reads
out the control value for amplitude control corresponding to the envelope information
entered from the envelope detector
73, and issues the control value to the
control terminal of the variable attenuator
81 of the predistortion unit
71 as a control signal for amplitude compensation.
Further, the compensation table
74, referring to the phase shifter
table
84, reads out the control value for phase shift control corresponding
to the envelope information entered from the envelope detector
73, and issues
the control value to the control terminal of the variable phase shifter
82
of the predistortion unit
71 as a control signal for phase shift compensation.
The ATT table
83 and phase shifter table
84 are composed of memories
for storing, for example, the envelope information as reference address, and control
value corresponding to the reference address. The compensation table
74
reads out the control value corresponding to the address, the address being the
envelope information entered from the envelope detector
73, from the ATT
table
83 and phase shifter table
84, and issues to the variable attenuator
81 and variable phase shifter
82 of the predistortion unit
71.
The variable attenuator
81 in the predistortion unit
71 attenuates
the amplitude of the input signal by the attenuation amount controlled by the control
signal entered from the compensation table
74, and issues to the variable
phase shifter
82.
The variable phase shifter
82 in the predistortion unit
71 changes
(shifts) the phase of the signal entered from the variable attenuator
81
by the phase shift amount controlled by the control signal entered from the compensation
table
74, and issues to the power amplifier
72.
Thus, in the predistortion unit
71, the input signal is corrected (compensated)
of amplitude or corrected (compensated) of phase depending on the envelope information
of the input signal, and the input signal after correction is issued to the power
amplifier
72.
The power amplifier
72 amplifies the input signal after predistortion
entered from the variable phase shifter
82 of the predistortion unit
71,
and issues the amplified signal from the output end of the predistortion type distortion
compensation amplifying apparatus.
The side band power measuring unit
75, specific time integrating circuit
76, and control circuit
77 process to optimize the control value
to be stored in the ATT table
83 and phase shifter table
84 of the
compensation table
74.
Specifically, the side band power measuring unit
75 couples
and receives a part of the amplified signal issued from the power amplifier
72
from, for example, the directional coupler, measures the adjacent channel leak
power (side band component power) included in the received amplified signal, and
issues the measured power to the specific time integrating circuit
76. The
component of the adjacent channel leak power includes the distortion component
generated in the power amplifier
72.
The specific time integrating circuit
76 integrates the adjacent channel
leak power entered from the side band power measuring unit
75 for a predetermined
specific time, and issues the integration result to the control circuit
77.
Herein, the integration result of the adjacent channel leak power is issued to
the control circuit
77, but it may be also designed, for example, to average
the adjacent channel leak power issued from the side band power measuring unit
75 for a predetermined specific time, and issue the averaged result to the
control circuit
77, and in this case the averaged result corresponds to
the average of the integration result in the specific time.
The control circuit
77 updates the control values stored in the ATT table
83 and phase shifter table
84 of the compensation table
74,
for example, by the following updating method on the basis of the integration result
of the adjacent channel integration result entered from the specific time integrating
circuit
76.
The ATT table
83 compares the integration result obtained from the specific
time integrating circuit
76 when, for example, part of the control value
stored in the ATT table
83 is changed and the distortion is compensated
by using the changed control value of the ATT table
83, and the integration
result obtained from the specific time integrating circuit
76 when the distortion
is compensated by using the control value of the ATT table
83 before the
change. The control value of the ATT table
83 in the case of obtaining the
smaller integration result of the two integration results compared is used as a
more appropriate table value. By repeating such operation, the control value stored
in the ATT table
83 is brought closer to an optimum value.
In the phase shifter table
84, by similar operation, the control value
stored in the phase shifter table
84 is brought gradually to an optimum value.
Preferably, the control values stored in the ATT table
83 and
phase shifter table
84 should be updated so that the integration result
obtained in the specific time integrating circuit
76 may be minimum.
Referring now to FIGS.
12(
a)-
12(
e), the principle
of compensating the distortion occurring in the amplifier is explained.
FIG.
12(
a) shows an example of gain characteristic P
1 corresponding
to the input signal level (input level) and an example of characteristic Q
1
of phase change corresponding to the input level, as the characteristic of the
amplifier, in which the axis of abscissas denotes the input level, and the axis
of ordinates represents the gain and phase changes. As shown in FIG.
12(
a),
the gain and phase changes of the amplifier are constant in the linear region of
a relatively small input level, but the changes are nonlinear depending on the
input level in the nonlinear region where the input level is relatively large.
FIG.
12(
b) shows, as the input and output characteristic of the
amplifier, an example of characteristic P
2 of level (output level) of the
output signal corresponding to the input level, and an example of characteristic
Q
2 of phase (output phase) of the output signal corresponding to the input
level. As shown in FIG.
12(
b), in the above linear region, the input
level and output level are proportional, and the output phase is constant, but
in the nonlinear region, the output level and output phase vary nonlinearly depending
on the input level. In such amplifier, an amplitude distortion is generated by
the nonlinear change of the output level, and a phase distortion is generated by
the nonlinear change of the output phase.
On the other hand, FIG.
12(
c) shows an example of characteristic
P
3 of compensation gain corresponding to the input level and an example
of characteristic Q
3 of compensation phase change corresponding to the input
level, as the compensation characteristic for compensating the amplitude distortion
and phase distortion occurring in such amplifier, in which the axis of abscissas
denotes the input level and the axis of ordinates represents the compensation gain
and compensation phase changes. The characteristic P
3 of compensation gain
and characteristic Q
3 of compensation phase change shown in FIG.
12(
c)
have the characteristic (reverse characteristic) for canceling the gain P
1
and phase change Q
1 of the amplifier shown in FIG.
12(
a),
and by applying the compensation gain P
3 and compensation phase change Q
3
having such reverse characteristic to the signal to be amplified by the amplifier,
generally, the amplitude distortion and phase distortion generated in the amplifier
can be compensated.
FIG.
12(
d) shows an example of characteristic P
4 of gain
to input level and an example of characteristic Q
4 of phase change to input
level, as the characteristic in the case of such compensation of amplitude distortion
and phase distortion occurring in the amplifier, in which the axis of abscissas
denotes the input level and the axis of ordinates represents the gain and compensation
phase changes. As shown in FIG. 12 (
d), in the characteristic after distortion
compensation, if the input level is relatively large, the gain and phase changes
are constant.
FIG.
12(
e) shows an example of characteristic P
5 of output
level to input level and an example of characteristic Q
5 of output phase
to input level, as the input and output characteristic in the case of compensation
of amplitude distortion and phase distortion occurring in the amplifier, in which
the axis of abscissas denotes the input level and the axis of ordinates represents
the output level and output phase. As shown in FIG.
12(
e), in the
input and output characteristic after distortion compensation, if the input level
is relatively large, the output level is proportional to the input level, and the
output phase remains invariable.
In this way, to the signal amplified by an amplifier having characteristic g,
by giving compensation characteristic f of reverse characteristic of the characteristic
g, the distortion of this signal can be compensated.
In the ATT table
83 and phase shifter table
84 of the compensation
table
74, control values for realizing such compensation characteristic
f are stored.
An example of prior art relating to predistortion is given below.
For example, in the predistortion of the amplifier and the amplifying device
disclosed in Japanese Laid-open Patent No. 2000-78037, as a manner of predistorting
by preliminarily deforming the input signal of the amplifier, the input signal
is deformed by the compensation coefficient corresponding to differential or integral
or both values of the input signal, and the adjacent channel leak power is reduced
by broadening the signal band, and the frequency characteristic in the base band
is improved.
In the predistortion device and its method disclosed in Japanese Laid-open Patent
No. 2000-201099, by predistorting by using a predistortion function obtained from
the inverse function of the input and output characteristic holding the inclination
of small power portion of favorable linearity to the input and output characteristic
of the power amplifier, a precise distortion is realized. Specifically, an arbitrary
straight line (for example, function y=x) is set as the reference, the predistortion
unit is roughly controlled by using table values of two stages and then controlled
finely, and the error from the reference is minimized. This publication includes
an embodiment in the base band and an embodiment in radio frequency (RF) band.
However, in the predistortion type distortion compensation amplifying apparatus
as shown in FIG. 11, since the control value of the compensation table
74
is updated on the basis of the integration result of the adjacent channel leak
power observed for a specific time regardless of the level of input signal, when
processing a signal, such as CDMA signal, which is large in peak factor of input
signal and low in frequency of occurrence of specific input level, the ratio of
components corresponding to the input level of such low frequency of occurrence
contained in the integration result of adjacent channel leak power is small.
Accordingly, when updating the control value corresponding to the input
level of low frequency of occurrence, the density of the adjacent channel leak
power component corresponding to such input level is low in the integration result,
and the control value of the compensation table
74 cannot be updated to
a proper value, or it takes much in convergence into optimum control value, or
the control value does not converge.
The invention is devised to solve such problems of the prior arts, and it is
hence an object thereof to present a predistortion type distortion compensation
apparatus capable of updating the control value to a precise value, when compensating
the distortion occurring in an amplifier for amplifying an input signal by controlling
by using a control value corresponding to the level of the input signal.
SUMMARY OF THE INVENTION
To achieve the object, in the predistortion type distortion compensation apparatus
of the invention, distortion generating means generates distortion in an input
signal, input signal level detecting means detects the level of the input signal,
and distortion control means controls the distortion generated by the distortion
generating means by using a control value corresponding to the level of the input
signal detected by the input signal level detecting means, thereby compensating
the distortion occurring in the amplifier for amplifying the input signal, in which
the control value is updated in the following procedure.
That is, distortion component level detecting means detects the level of distortion
component contained in the amplified signal issued from the amplifier, integrating
means integrates the level of the distortion component detected by the distortion
component detecting means in every level of the input signal detected by the input
signal level detecting means, and control value updating means updates the control
value corresponding to the level used by the distortion control means so that the
integration result of every level of input signal obtained from the integrating
means may be small.
Therefore, since the level of the distortion component contained in the
amplified signal is integrated at every level of the input signal, and the control
value is updated at every level of input signal on the basis of the integration
result, the control value for controlling the distortion compensation can be updated
to a precise value, so that distortion -compensation of high precision is realized
when processing a signal, for example, low in frequency of occurrence of specific
input level.
Various signals may be used as the input signal.
Various amplifiers may be used, and either a single amplifier may be used,
or plural amplifiers may be combined.
The distortion generating means is preferred to generate both amplitude distortion
and phase distortion, but may be designed to generate either.
The level of input signal to be detected by the input signal level detecting
means, and the level of distortion component to be detected by the distortion component
detecting means are not particularly limited, and, for example, power level and
amplitude level may be used.
As the level of distortion component, for example, when transmission signal is
used as input signal, the level of adjacent channel leak power may be used.
As the control value for controlling the distortion generated by the distortion
generating means, for example, the control value for controlling the amplitude
distortion to be generated, or the control value for controlling the phase distortion
to be generated may bemused.
As the manner of controlling the amplitude distortion to be generated or the
phase
distortion to be generated, for example, the quantity of the amplitude distortion
to be generated or the quantity of the phase distortion to be generated may be controlled.
As the manner of integrating the level of distortion component at every level
of input signal, for example, the level of the distortion component may be integrated
by a different integrating circuit at every level of input signal by using plural
integrating circuits, or the level of distortion component may be integrated when
the input level of a specified level is amplified by using one integrating circuit
corresponding to input signal of specific level.
Every level of input signal may be, for example, every level in a specified
range, or every level of value of one point. In the invention, therefore, the level
of distortion component may be integrated in every specified level range concerning
the input signal, or the level of distortion component may be integrated at every
level value of one point concerning the input signal.
In the invention, integration of level of distortion component by integrating
means includes averaging of the level of distortion component, for example, by
integration time or integration counts, and the averaged result substantially corresponds
to the quotient of the integration result divided by the integration time or integration counts.
To update the control value corresponding to the level so that the integration
result at every level of input signal may be small means specifically to update
the control value corresponding to the level range so that the integration result
obtained corresponding to the input signal in a certain level range may be small.
The degree of the integration result of distortion component level to be small
is preferably minimum, but as far as the distortion is compensated effectively,
it may not be always minimum.
Similarly, the degree of compensating the distortion is preferably zero
distortion, but as far as the distortion can be decrease effective, it may not
be always zero.
Further, in the predistortion type distortion compensation apparatus of
the invention, distortion generating means generates distortion in an input signal,
input signal level detecting means detects the level of the input signal, and distortion
control means controls the distortion generated by the distortion generating means
by using a control value corresponding to the level of the input signal detected
by the input signal level detecting means, thereby compensating the distortion
occurring in the amplifier for amplifying the input signal, in which the control
value is updated in the following procedure.
That is, distortion component level detecting means detects the level of distortion
component contained in the amplified signal issued from the amplifier, counting
means counts inputs at specified level of the level of input signal detected by
the input signal level detecting means, integrating means integrates the level
of the distortion component detected by the distortion component detecting means
when the level of the input signal detected by the input signal level detecting
means is the specified level for the period until a specified value is counted
by the counting means, and control value updating means updates the control value
corresponding to the specified level used by the distortion control means so that
the integration result of the integrating means may be small.
Therefore, since the level of the distortion component when the input
signal of specified level is amplified is integrated for a period corresponding
to the specified count value, and the control value is updated corresponding to
the specified level on the basis of the integration result, the control value for
controlling the distortion compensation can be updated to a precise value, so that
distortion compensation of high precision is realized when processing a signal,
for example, low in frequency of occurrence of specific input level.
Herein, various levels may be used as the specified level of input signal,
and, for example, a level range may be used or a level value of a point may be used.
As the manner of counting inputs when the input signal level is a specified level,
the input times may be counted, for example, by adding +1 to the count value of
input of input signals of the specified level, or the input times may be counted
by adding +1 to the count value when the input signal of the specified level continues
for a predetermined duration, or the input duration may be counted by counting
the duration of input of input signal of the specified level.
The specified value to be counted by the counting means may be any value as far
as the control value can be updated properly.
Thus, according to the invention, during the period of counting of such specified
value by the counting means, the level of the distortion component when the level
of the input signal is the specified level is integrated, and the integration result
is used in updating of the control value.
In the predistortion type distortion compensation apparatus of the invention,
preferably, the distortion control means is composed by using a memory for storing
the input signal level and control value in correspondence to each other.
Various memories may be used for this purpose.
This predistortion type distortion compensation apparatus is preferably applied
in the radio base station apparatus or radio repeater amplifying device of CDMA
system such as W-CDMA system.
Specifically, the CDMA radio base station apparatus in the invention
comprises the predistortion type distortion compensation apparatus as described
above, and compensates the distortion occurring in the amplifier for amplifying
the transmission signal by the predistortion type distortion compensation apparatus.
Further, the CDMA radio repeater amplifying device in the invention comprises
the predistortion type distortion compensation apparatus as described above, and
compensates the distortion occurring in the amplifier for amplifying the transmission
signal by the predistortion type distortion compensation apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing a circuit configuration of predistortion type distortion
compensation amplifying apparatus in a first embodiment of the invention;
FIG. 2 is a diagram showing an example of correspondence of reference address
and compensation value;
FIG. 3 is a diagram showing a circuit configuration of predistortion type distortion
compensation amplifying apparatus in a second embodiment of the invention;
FIG. 4 is a schematic block diagram of a base station apparatus in a third embodiment
of the invention;
FIG. 5 is a diagram showing a structural example of an amplifier for amplifying individually;
FIG. 6 is a diagram showing a structural example of an amplifier for amplifying commonly;
FIG. 7 is a diagram showing an example of spectrum of transmission signal before
input into an amplifier;
FIG. 8 is a diagram showing an example of spectrum of transmission signal amplified
and issued from an amplifier without distortion compensation;
FIG. 9 is a block diagram of transmission power amplifier with distortion compensation
in a prior art;
FIG. 10 is a diagram showing an example of spectrum of transmission signal amplified
and issued from an amplifier by distortion compensation;
FIG. 11 is a diagram showing a circuit configuration of predistortion type distortion
compensation amplifying apparatus; and
FIGS. 12(
a)-12(
e) are diagrams for explaining the
principle of distortion compensation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A predistortion type distortion compensation apparatus in a first embodiment
of
the invention is described below while referring to the accompanying drawings.
FIG. 1 shows a circuit configuration of the predistortion type distortion compensation
amplifying apparatus of the embodiment according to the predistortion type distortion
compensation apparatus of the invention, and this predistortion type distortion
compensation amplifying apparatus comprises distortion compensation amplifying
circuit parts for amplifying the signal by compensating distortion by predistortion
system, that is, a predistortion unit
1 including a variable attenuator
(ATT)
11 and a variable phase shifter
12, a power amplifying unit
(PA)
2 composed of one or plural power amplifiers, an envelope detector
3, and a compensation table
4 including an amplitude control table
(ATT table)
13 corresponding to the variable attenuator
11, and a
phase control table (phase shifter table)
14 corresponding to the variable
phase shifter
12.
The predistortion type distortion compensation amplifying apparatus further comprises
control value updating circuit parts for updating the control values stored in
the ATT table
13 and phase shifter table
14 of the compensation table
4 by feedback, that is, a side band power measuring unit
5, a quantizing
circuit
6, a first selection circuit
7 of one input to multiple outputs,
an integrating circuit group
8 composed of N integrating circuits K
1
to KN, a second selection circuit
9 of multiple inputs to one output, and
a control circuit
10. Herein, N is an arbitrary plural number.
Examples of structure and operation of the distortion compensation amplifying
circuit parts are explained below.
The structure and operation of the distortion compensation amplifying circuit
parts of the embodiment are nearly same as shown in FIG.
11.
Specifically, the signal entered from the input end of the predistortion
type distortion compensation amplifying apparatus of the embodiment is distributed
into two signals, and one distribution signal is put into the variable attenuator
11 of the predistortion unit
1, and other distribution signal is
put into the envelope detector
3.
The envelope detector
3 detects the envelope information of input signal
(level of momentary power), and issues the detection result into the compensation
table
4 and quantizing circuit
6.
The compensation table
4, referring to the ATT table
13, reads
out the control value for amplitude control corresponding to the envelope information
entered from the envelope detector
3, and issues the control value to the
control terminal of the variable attenuator
11 of the predistortion unit
1 as a control signal for amplitude compensation.
Further, the compensation table
4, referring to the phase shifter
table
14, reads out the control value for phase shift control corresponding
to the envelope information entered from the envelope detector
3, and issues
the control value to the control terminal of the variable phase shifter
12
of the predistortion unit
1 as a control signal for phase shift compensation.
The ATT table
13 and phase shifter table
14 are composed of memories
for storing, for example, the envelope information as reference address, and control
value corresponding to the reference address. The compensation table
4 reads
out the control value corresponding to the address, the address being the envelope
information entered from the envelope detector
13, from the ATT table
13
and phase shifter table
14, and issues to the variable attenuator
11
and variable phase shifter
12 of the predistortion unit
1.
The variable attenuator
11 in the predistortion unit
1 attenuates
the amplitude of the input signal by the attenuation amount controlled by the control
signal entered from the compensation table
4, and issues to the variable
phase shifter
12.
The variable phase shifter
12 in the predistortion unit
1 changes
(shifts) the phase of the signal entered from the variable attenuator
11
by the phase shift amount controlled by the control signal entered from the compensation
table
4, and issues to the power amplifier
2.
Thus, in the predistortion unit
1, the input signal is corrected (compensated)
of amplitude or corrected (compensated) of phase depending on the envelope information
of the input signal, and the input signal after correction is issued to the power
amplifier
2.
The power amplifier
2 amplifies the input signal after predistortion entered
from the variable phase shifter
12 of the predistortion unit
1, and
issues the amplified signal from the output end of the predistortion type distortion
compensation amplifying apparatus of the embodiment.
Examples of structure and operation of the control value updating circuit
parts are explained.
In the embodiment, the control value updating circuit parts include a plurality
of integrating circuits K
1 to KN for integrating the measured adjacent channel
leak power, and the first selection circuit
7 of one input to multiple outputs
is disposed at the input side of the integrating circuit group
8 composed
of these N integrating circuits K
1 to KN, and the second selection circuit
9 of multiple inputs to one output is disposed at the output side of the
integrating circuit group
8. The first selection circuit
7 receives
a digital value issued from the quantizing circuit
6 at its control terminal,
and controls it, and the second selection circuit
9 receives a selection
signal issued from the control circuit
10 at its control terminal, and controls it.
Specifically, the side band power measuring unit
5 couples and
receives a part of the amplified signal issued from the power amplifier
2
from, for example, a directional coupler, measures the adjacent channel leak power
(side band component power) included in the received amplified signal, and issues
the measured power to the first selection circuit
7. The component of the
adjacent channel leak power includes the distortion component generated in the
power amplifier
2.
The quantizing circuit
6 converts the envelope information entered from
the envelope detector
3 into a digital value, and sends the converted digital
value into the control terminal of the first selection circuit
7.
The first selection circuit
7 receives the adjacent channel leak power
entered from the side band power measuring unit
5, and selects and changes
over one integrating circuit from the N integrating circuits K
1 to KN as
the output destination of the adjacent channel leak power depending on the digital
value entered from the quantizing circuit
6.
In this embodiment, corresponding to N integrating circuits K
1 to KN,
different
level ranges of input signals are predetermined. The first selection signal
7
selects the integrating circuit set in the level range including the level of the
input signal corresponding to the digital value, depending on the digital value
entered from the quantizing circuit
6, and changes over the output destination
of the adjacent channel leak power to this integrating circuit.
Each one of the integrating circuits K
1 to KN integrates the adjacent
channel leak power entered from the first selection circuit
7, and issues
the integration result to the second selection circuit
9. Herein, the integration
result of the adjacent channel leak power is issued to the control circuit
10
through the second selection circuit
9, but it may be also desi
