Modulators – Phase shift keying modulator or quadrature amplitude modulator
Reexamination Certificate
2002-03-18
2004-10-26
Kinkead, Arnold (Department: 2817)
Modulators
Phase shift keying modulator or quadrature amplitude modulator
C332S107000, C330S149000, C330S136000, C330S256000, C330S294000, C375S296000
Reexamination Certificate
active
06809607
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “Circuit and Method for Compensating for Non-linear Distortion” filed in the Japanese Patent Office on Mar. 19, 2001 and assigned Serial No. 2001-79534, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a quadrature modulation circuit used in a radio transmitter, and in particular, to an apparatus and method for compensating for non-linear distortion generated during high-power amplification after quadrature modulation of a baseband signal.
2. Description of the Related Art
A conventional quadrature (or orthogonal) modulation circuit quadrature-modulates a baseband signal and then high-power amplifies the modulated signal. The high-power amplified modulated signal is subject to non-linear amplification in order to improve power efficiency. This is because an amplification region of an amplifier is divided into a linear region and a non-linear region and the high-power amplification is performed in the non-linear region. When amplified in the non-linear region, the amplified modulated signal suffers non-linear distortion. Thus, in order to linearize an input/output characteristic, it is necessary to compensate for distortion of the non-linearly distorted signal. A typical, conventional non-linear distortion compensation circuit includes a predistortion-type non-linear distortion compensation circuit shown in FIG.
4
.
A predistortion-type non-linear distortion compensation circuit will be described with reference to FIG.
4
. Referring to
FIG. 4
, complex baseband signals I and Q are applied to a first D/A (Digital-to-Analog) converter
2
and a second D/A converter
3
through a distortion compensation operator
1
. The first and second D/A converters
2
and
3
convert received digital signals to analog signals, and provide the converted analog signals to a quadrature modulator
4
. The quadrature modulator
4
quadrature-modulates received baseband signals I and Q, and provides the quadrature-modulated signals to a high-power amplifier (HPA)
5
. The high-power amplifier
5
then high-power amplifies the quadrature-modulated analog signals.
A compensation data table
7
stores compensation data in the form of a table. The compensation data stored in the compensation data table
7
is determined by previously measuring a non-linear characteristic of the high-power amplifier
5
during amplification. A power calculator
6
calculates power of the baseband signals I and Q, and provides the calculated power information to the compensation data table
7
. The compensation data table
7
reads compensation data corresponding to the calculated power by consulting the table according to the power of the baseband signals I and Q, and then provides the read compensation data to the distortion compensation operator
1
.
In this way, the distortion compensation operator
1
previously applies an inverse distortion component for canceling the non-linear distortion generated in the high-power amplifier
4
to the received baseband signals I and Q before quadrature modulation. The signals including the inverse distortion component for removing the non-linear distortion are provided to the first and second D/A converters
2
and
3
. As a result, the modulated signals high-power amplified by the high-power amplifier
5
have reduced the non-linear distortion.
As stated above, the conventional predistortion-type non-linear distortion compensation circuit compensates for non-linear distortion through the use of the data table based on the power of the baseband signals, without considering a characteristic deviation of the high-power amplifier
5
and a variation of temperature. Therefore, overall performance of the circuit may be deteriorated due to the characteristic deviation of the high-power amplifier
5
and the temperature variation.
To solve this problem, a directional combiner
8
, as illustrated in
FIG. 5
, divides an output of the high-power amplifier
5
into two signals, and applies one of the divided signals to a quadrature demodulator
9
. The quadrature demodulator
9
quadraturede-modulates the divided signal and feeds the demodulated divided signal to a compensation data operator
10
. The compensation data operator
10
multiplies a coefficient, based on the feedback information, by data read from an internal compensation data table (though not shown, it is equal to the compensation data table
7
of FIG.
4
). As a result, the compensation data operator
10
provides the distortion compensation operator
1
with compensated data having a high accuracy regardless of the characteristic deviation of the high-power amplifier
5
and the temperature variation.
However, since the elements
8
-
10
generate pseudo non-linear distortion, it is not possible to completely resolve the problem. In addition, all the elements perform a complicated digital operation, resulting in an increase in the circuit size and cast Further, the increase in the circuit size may increase power consumption, causing a reduction in a batter-run time of a mobile communication terminal using a battery as a power source.
To solve this problem, the applicant has proposed a non-linear distortion compensation circuit of
FIG. 3
, disclosed in Japanese patent application No. 2000-233631, the contents of which are hereby incorporated by reference. The non-linear distortion compensation circuit includes directional combiners/dividers
19
and
21
, a delay circuit/phase shifter
20
, an attenuator
13
, a subtracter
14
, a quadrature demodulator
15
, a phase adjuster
22
, amplitude adjusters
23
and
24
, and subtracters
16
and
17
. Further, the non-linear distortion compensation circuit includes a quadrature modulator
11
, a carrier generator
18
and a transmission frequency control circuit
30
. The transmission frequency control circuit
30
changes the frequency of a carrier signal output from the carrier generator
18
when a transmission channel is changed according to a carrier frequency setting signal.
The non-linear distortion compensation circuit interposes the directional combiner/divider
19
between the quadrature modulator
11
and a high-power amplifier
12
. The directional combiner/divider
19
divides a modulated signal provided from the quadrature modulator
11
into two signals, and provides one of the divided modulated signals to the delay circuit/phase shifter
20
and provides the other divided modulated signal to the high-power amplifier
12
. The delay circuit/phase shifter
20
then shifts the phase of the received signal to match it to the phase of an output signal of the attenuator
13
, and then provides the phase-shifted signal to the subtracter
14
.
Also, an output of the high-power amplifier
12
is divided into two signals by the directional combiner/divider
21
: one of the two signals becomes an output signal and the other signal is provided to the attenuator
13
. The subtracter
14
calculates a difference between the signal from the delay circuit/phase shifter
20
and the signal from the attenuator
13
, and provides the calculated difference to the phase adjuster
22
. That is, a non-linear distortion component calculated by the subtracter
14
is phase-adjusted through the phase adjuster
22
, and then provided to the quadrature demodulator
15
. Baseband non-linear distortion components output from the quadrature demodulator
15
are amplitude-adjusted to a proper level through the amplitude adjusters
23
and
24
, and then provided to the subtracters
16
and
17
. A non-linear distortion extractor
1
A for extracting a non-linear distortion component from the non-linearly high-power amplified modulated signal includes the directional combiners/dividers
19
and
21
, the delay circuit/phase shifter
20
, the attenuator
13
and the subtracter
14
.
The non-linear distortion compensation circuit of
FIG. 3
can solve the above-stated problem, but it has the following problem. Each tim
Dilworth & Barrese LLP
Kinkead Arnold
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