Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
2002-05-28
2004-01-13
Shingleton, Michael B (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
C330S136000, C330S107000
Reexamination Certificate
active
06677821
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a power amplifying circuit to be used for a transmitting section of a base station or a terminal station of a radio communication system and a radio communication apparatus such as a mobile phone, and more particularly, to a distortion compensating device which compensates for non-linear distortion of an output signal of the power amplifying circuit.
BACKGROUND ART
In a transmission high-frequency power amplifying circuit (hereinafter referred to as power amplifying circuit) of a mobile phone or the like, if it is intended to increase power availability, non-linearity is intensified so that a distortion is generated in the output signal. As a distortion compensating device for compensating such a distortion, predistortion technology employing a compensating means having a characteristic inverse to the distortion of the power amplifying circuit has been well known.
Prior to description of the above described predistortion technology, principle about compensation of amplitude distortion will be described. The high-frequency signal which is an input signal to be considered now is a signal for use in the mobile phone, which is an orthogonal phase modulation signal such as &pgr;/4 shift QPSK (Quad Phase Shift Keying), 0-degree QPSK and the like subject to a band restriction. These signals can be expressed by a waveform obtained by amplitude-modulating high-frequency carrier components with envelope components changing slowly with the passage of time. This is expressed in an equation (1).
V=Vi
(
t
)·cos(&ohgr;
t
) (1)
where V is a general expression of high-frequency signal voltage, Vi is the aforementioned envelope component, &ohgr; is an angular frequency of the high-frequency component. The signal expressed by the equation (1) is subjected to distortion when it is amplified by the power amplifying circuit
12
(see FIG.
11
).
Although in the general power amplifying circuit
12
, as shown in
FIG. 4
, the output power increases as the input power increases, its amplification factor decreases gradually. That is, gain suppression is generated, so that distortion is generated by this characteristic. When in an amplitude characteristic curve
21
of
FIG. 4
, the input power is a value indicated by A in
FIG. 4
, the output power is a value indicated by B. In this case, if the amplitude characteristic
22
of the power amplifying circuit
12
is linear, its output power must become B′. Then, if the input power A′ is used instead of the input power A, its output power is B′, so that by providing the input voltage with the non-linear distortion preliminarily, no distortion is generated in the output power. By converting input voltage A to input voltage A′ like this, the distortion becomes to be improved.
The technology of predistortion is an art for having the base band portion carry out an operation for converting this input voltage A to input voltage A′. Here, it should be noted that converting the input power A having no distortion originally to the input power A′ leads to adding the distortion to the input power A. This added distortion is killed by a distortion generated in the power amplifying circuit
12
, so that it is considered that the distortion is improved. This added distortion acts like an inverted distortion with respect to a distortion generated in the power amplifying circuit
12
.
FIG. 11
shows a block diagram about a typical predistortion well known since before.
FIG. 11
will be described simply.
FIG. 11
shows a transmitting portion of a mobile phone. Analog in-phase component I and orthogonal component Q generated in a signal processing portion
30
are digitalized by I and Q analog-digital converters (ADC)
31
,
32
and then, the aforementioned operation for converting the input power A to the input power A′ is carried out by I- and Q-signal predistorters
33
,
34
. After that, the signals are converted to analog signals by I- and Q-signal digital-analog converters (DAC)
35
,
36
and modulated by an orthogonal transformer
37
. Then, it is converted to a high-frequency signal by an up-converter
38
, amplified by a power amplifying circuit
12
and transmitted. If the predistortion is not carried out, the aforementioned ADCs
31
,
32
, the predistorters
33
,
34
and the DACs
35
,
36
in the base band portion
39
in the block shown in
FIG. 11
are not necessary. That is, the predistortion conducts a signal conversion operation with respect to the original I, Q signals.
If the aforementioned predistortion is carried out, a signal provided with the inverted distortion component is outputted from the base band portion
39
. However, in a general mobile phone, it is indispensable to provide a filter for removing digital noise contained in the base band output and a band-pass filter may be provided for an intermediate frequency portion also depending on the case. These filters cannot be removed in consideration of the purpose for which they are installed. It turns out that the inverted distortion component is removed together with the digital noise by this filter. As a result, the distortion in the power amplifying circuit
12
is not killed, so that the distortion compensation is not carried out.
DISCLOSURE OF THE INVENTION
A first distortion compensating device of the present invention is a distortion compensating device for carrying out predistortion with respect to a power amplifying means
12
whose distortion should be compensated, comprising: an envelope detecting means
1
to which a high-frequency signal S
1
generating an envelope change is supplied for detecting an envelope signal of the high-frequency signal S
1
; an amplitude correction memory means
3
for storing an inverted distortion amplitude value of a distortion generated in the power amplifying means
12
with digital data S
3
obtained by digitalizing the envelope signal S
2
of the envelope detecting means
1
as an address; and a gain variable means
10
disposed in a prestage of the power amplifying means
12
to which the high-frequency signal S
1
generating the envelope change is supplied, capable of controlling a passage gain of the high-frequency signal, characterized in that the inverted distortion data of the amplitude correction memory means
3
is converted to analog data and supplied to the gain variable means
10
so as to compensate a distortion of the amplitude of a gain of the power amplifying means
12
.
A second distortion compensating device of the present invention is a distortion compensating device for carrying out predistortion on a power amplifying means
12
whose distortion should be compensated, comprising: an envelope detecting means
1
to which a high-frequency signal S
1
generating an envelope change is supplied for detecting an envelope signal S
2
of the high-frequency signal S
1
; a phase correction memory means
6
for storing an inverted distortion phase value of a distortion generated in the power amplifying means
12
with digital data S
3
obtained by digitalizing the envelope signal S
2
of the envelope detecting means
1
as an address; and a phase-shifting means
11
disposed in a prestage of the power amplifying means
12
to which the high-frequency signal S
1
generating the envelope change is supplied, capable of controlling a passage phase of the high-frequency signal, characterized in that the inverted distortion data of the phase correction memory means
6
is converted to analog data and supplied to the phase-shifting means
11
so as to compensate a distortion of the phase of the power amplifying means
12
.
A third distortion compensating device of the present invention is a distortion compensating device according to the first invention, further including; a phase correction memory means
6
, parallel located with the amplitude correction memory means
3
, which stores an inverted distortion phase value of distortion to be generated in the power amplifying means
12
, with digital data S
3
obtained by digitalizing the
Kusunoki Shigeo
Yamamoto Katsuya
Maioli Jay H.
Shingleton Michael B
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