(12) United States Patent
`Sakuno
`
`USOO6433641B1
`US 6,433,641 B1
`(10) Patent No.:
`Aug. 13, 2002
`(45) Date of Patent:
`
`5.241284 A 8/1993 Nyqvist et al. ............. 330/297
`5,363,058 A 11/1994 Sasaki ........................ 330/136
`5,675.290 A 10/1997 Tsukahara et al. .......... 330/296
`1/1998 Kobayashi .................. 330/300
`5,710,523 A *
`5,760,651 A 6/1998 Wong ......................... 330/296
`5,814,038 A 9/1998 Ogura et al. ................ 330/149
`6,262,631 B1
`7/2001 Li .............................. 330/149
`
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`(54) POWER AMPLIFIER AND
`COMMUNICATION DEVICE INCLUDING
`POWER AMPLIFIER
`
`(75) Inventor: Keiichi Sakuno, Nara (JP)
`(73) Assignee: Sharp Kabushiki Kaisha, Osaka (JP)
`(*) Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/618,448
`(22) Filed:
`Jul. 18, 2000
`(30)
`Foreign Application Priority Data
`Jul. 19, 1999
`(JP) ........................................... 11-204484
`Jul. 5, 2000
`(JP) ....................................... 2000-203516
`(51) Int. Cl. .................................................. HO3F 3/04
`(52) U.S. Cl. ........................................ 330/296; 330/149
`(58) Field of Search ................................. 330/149, 296,
`330/285
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,984,783 A * 10/1976 Bickley ...................... 330/296
`
`
`
`FOREIGN PATENT DOCUMENTS
`
`JP
`
`A9260964
`
`10/1997
`
`* cited by examiner
`
`Primary Examiner Robert Pascal
`Assistant Examiner Khanh Van Nguyen
`(57)
`ABSTRACT
`A resistor and a capacitor are provided for a variable
`impedance element which performs distortion compensation
`of a power amplifier. Thus, compensation of amplitude
`amplitude distortion and amplitude-phase distortion can be
`Separately adjusted. As a result, distortion of the power
`amplifier can be reduced effectively and a highly efficient
`operation is made possible.
`
`19 Claims, 13 Drawing Sheets
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`RX
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`Vb
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`100
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`HD
`OUTPUT
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`N-te
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`GOOGLE EXHIBIT 1012
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`U.S. Patent
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`Aug. 13, 2002
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`Sheet 1 of 13
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`US 6,433,641 B1
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`F.G. 1
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`HD
`OUTPUT
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`N-te
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`U.S. Patent
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`Aug. 13, 2002
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`Sheet 2 of 13
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`US 6,433,641 B1
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`OUTPUT
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`N-te
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`U.S. Patent
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`Aug. 13, 2002
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`Sheet 3 of 13
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`US 6,433,641 B1
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`OUTPUT
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`Tr1
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`Page 4 of 24
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`U.S. Patent
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`Aug. 13, 2002
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`Sheet 4 of 13
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`US 6,433,641 B1
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`INESEHd
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`N0||NEAN |
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`W O
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`W O
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`(BERJ930)
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`G8
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`
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`08
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`GZ
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`0€.
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`G |
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`0 ||
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`Aug. 13, 2002
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`Sheet 5 of 13
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`US 6,433,641 B1
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`9 L. NOILHO ISIQ
`(Ep)
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`Aug. 13, 2002
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`Sheet 6 of 13
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`US 6,433,641 B1
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`9 10 | -!
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`(Uu?BP) HEM OCH LÍldNI
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`08 OZ 0 ||0 0 ! – OZ– 08–
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`Page 7 of 24
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`Aug. 13, 2002
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`Sheet 7 of 13
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`US 6,433,641 B1
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`FIG. 7 A
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`Vb
`
`OUTPUT
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`N-Tr1
`(60 UNIT TRANSISTOR CELLS)
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`OUTPUT
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`N-Tr90
`(60 UNIT TRANSISTOR CELLS)
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`Page 8 of 24
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`U.S. Patent
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`Aug. 13, 2002
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`Sheet 8 of 13
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`US 6,433,641 B1
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`FG. 8
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`RX
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`Wb
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`N COLLECTOR
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`FG. 9
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`300
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`HD
`OUTPUT
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`400
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`e-D
`OUTPUT
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`Sheet 9 of 13
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`US 6,433,641 B1
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`F.G. 10
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`500
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`F.G. 11
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`-D
`OUTPUT
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`600
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`-D
`OUTPUT
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`U.S. Patent
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`Aug. 13, 2002
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`Sheet 10 Of 13
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`US 6,433,641 B1
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`F.G. 12
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`700
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`HD
`OUTPUT
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`FG. 15 PRIOR ART
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`Vb
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`900
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`C90
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`N
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`-O-
`OUTPUT
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`N-Trg0
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`U.S. Patent
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`Aug. 13, 2002
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`Sheet 11 of 13
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`US 6,433,641 B1
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`F.G. 13
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`1013 - 1012
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`1003
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`DUPLEXER
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`2.
`A HZN
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`1002
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`1014
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`1007
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`1001
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`1024
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`1010
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`CONTROL
`DETECTION
`IRCUIT CIRCUIT
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`CIRCUIT
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`Aug. 13, 2002
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`Sheet 12 of 13
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`US 6,433,641 B1
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`F.G. 14
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`WOLTAGE
`SUPPLY
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`CIRCUIT Fl SE LEVEL
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`CONTROL
`CIRCUIT
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`DETECTION
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`|F/BASEBAND PORTION
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`Page 13 of 24
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`U.S. Patent
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`Aug. 13, 2002
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`Sheet 13 of 13
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`US 6,433,641 B1
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`F.G. 16A
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`1
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`Tr1
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`1 OO
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`FIG. 16B
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`Tr2
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`Tr1
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`-
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`1OO
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`1
`POWER AMPLIFER AND
`COMMUNICATION DEVICE INCLUDING
`POWER AMPLIFER
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to power amplifiers and
`communication devices. More particularly, the present
`invention relates to a power amplifier for transmission which
`is used in a radio communication device or the like requiring
`amplification with low distortion, and a communication
`device which includes the power amplifier.
`2. Description of the Background Art
`AS in mobile communication Systems for mobile phones
`or the like, radio communication Systems using quasi
`microwave and microwave bands have rapidly spread in
`recent years. That greatly contributes to attaining portable
`terminals of lighter weight and lower power consumption.
`In order to achieve lighter weight of portable terminals, it
`is effective to use lighter batteries of a Small capacity type.
`However, employment of the Small capacity type generally
`shortens the time till the battery runs out. Therefore, lower
`power consumption, that is, improvement in the power
`efficiency is strongly required for power amplifiers for
`transmission which lead to most power consumption of
`terminals at the time of transmission.
`In constant amplitude analog modulation/demodulation
`Systems using conventional FM modulation/demodulation
`methods, power amplifiers can operate in a Saturated State
`and thus they can be made more efficient relatively easily.
`Recently, however, communication Systems which employ
`digital modulation/demodulation using QPSK (quadrature
`phase shift keying) modulation or the like with high fre
`quency utilization efficiency have become the mainstream.
`In the digital modulation/demodulation methods, infor
`mation is transmitted by both the amplitudes and phases of
`Signals, and thus power amplifiers are required to linearly
`amplify input Signals. Generally, as an increase in output
`power due to the increased input power approaches
`Saturation, the power amplifiers come to have higher dis
`tortion and power efficiency. Therefore, high power effi
`ciency and low distortion are in a tradeoff relationship.
`Attempts to improve the power efficiency are often made by
`adding a distortion compensation circuit So that the opera
`tion is performed with low distortion even at high input
`power. One example is described in Japanese Patent Laying
`Open No. 9-260964 entitled “High Frequency Amplification
`Circuit” (hereinafter, referred to as Document 1).
`FIG. 15 shows a circuit configuration of a power amplifier
`disclosed in Document 1. Referring to FIG. 15, a power
`amplifier 900 includes a bipolar transistor Tr90 for power
`amplification, a diode D90, a capacitor C90, and bias
`resistors R91, R92. Diode D90 and capacitor C90 form a
`distortion compensation circuit. When a bias voltage Vb is
`supplied, the base bias condition of bipolar transistor Tr'90 is
`determined by the direct current characteristics of bias
`resistors R91, R92 and diode D90.
`Capacitor C90 has capacitance which is regarded as a
`grounded State regarding a high frequency at the operating
`frequency of power amplifier 900. Impedance measured
`from the base end of bipolar transistor Tr90 toward diode 90
`is only the resistance and capacitance components of diode
`D90 with regard to a high frequency. The impedance is
`equivalent to parallel connection between the base and
`emitter of bipolar transistor Tr'90 with regard to a high
`frequency.
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`US 6,433,641 B1
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`An input Signal causes the instantaneous Voltage between
`the base and emitter of bipolar transistor Tr'90 to fluctuate
`with time. However, Since a diode characteristic is observed
`between the base and the emitter, higher Voltage fluctuation
`and lower Voltage fluctuation of the instantaneous Voltage
`are asymmetrical, with the center being a Voltage when a
`Signal is not applied. Thus, the average Voltage varies with
`input power. Specifically, because of the diode
`characteristics, when the Voltage acroSS the diode increases
`and the current increases, then the impedance is lowered.
`Since the Voltage amplitude at the higher Voltage Side is
`Small, the average Voltage is shifted toward the lower
`Voltage Side because of the input signal. The shift amount
`increases with an increase in the input power.
`The capacitance component of a diode depends on a
`voltage across the both ends of the diode (both end Voltage
`dependence). Therefore, the Voltage shift due to an increase
`in input power changes the capacitance between the base
`and emitter of bipolar transistor Tr'90. Thus, the reactance
`component of bipolar transistor Tr90 from the base end is
`changed, which changes the transmit of a signal. This is
`“amplitude-phase distortion' as a cause of distortion for a
`power amplifier.
`In power amplifier 900 shown in FIG. 15, phase distortion
`caused by the non-linearity of capacitance between the base
`and emitter of bipolar transistor Tr90 is compensated for by
`adding a distortion compensation circuit formed of diode
`D90 and capacitor C90.
`In other words, an increase in input power decreases the
`average Voltage of the diode portion (between the base and
`emitter) of bipolar transistor Tr90 and, at the same time,
`increases the average Voltage acroSS the both ends of diode
`D90 which is connected in parallel, with regard to a high
`frequency, with the base and emitter of bipolar transistor
`Tr'90. Therefore, the change in the diode capacitance value
`between the base and emitter of bipolar transistor Tr90 and
`the change in the capacitance value of diode D90, which are
`caused by an increased or decreased input power, offset each
`other, mitigating the dependence of the transmit on the input
`power in the power amplifier. Thus, bipolar transistor Tr90
`can effectively maintain linearity even at input power closer
`to Saturation. As a result, the power efficiency is improved.
`If bias power supply Vb and the base of bipolar transistor
`Tr'90 are connected only through fixed resistance, the higher
`the base power caused by an increase in input power, the
`higher the effect of Suppressing an increase in the base
`current becomes, which is caused by a reduction in the
`Voltage at the fixed resistance portion. Therefore, the col
`lector current is prevented from increasing, which reduces a
`gain due to an increase in the input power, that is, causes
`amplitude-amplitude distortion. In power amplifier 900, as
`the base current flowing in diode D90 is larger, the resistance
`component of diode D90 is lowered and the voltage drop is
`mitigated. It is therefore possible to reduce amplitude
`amplitude distortion.
`AS described above, the amplitude-phase distortion char
`acteristic and the amplitude-amplitude distortion character
`istic have to be compensated for to lower distortion of the
`power amplifier. In the above described distortion compen
`sation method in power amplifier 900, however, only the
`non-linearity of the resistance and capacitance components
`of diode D90 is used to provide compensation. Thus, once
`diode 90 to be used is determined, the non-linearity of the
`resistance and capacitance components are fixed at the same
`time. The non-linearity of them cannot be set to an optimum
`value Separately.
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`Page 15 of 24
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`Consequently, in Some cases, only one of amplitude-phase
`distortion and amplitude-amplitude distortion can be com
`pensated for or distortion compensation of one of them can
`exacerbate the other distortion. When the amplitude-phase
`distortion and amplitude-amplitude distortion are to be com
`pensated for at the same time, compensation for both may be
`insufficient.
`Such a power amplifier has to be operated at a higher bias
`current to maintain low distortion. If low distortion is
`realized, the power efficiency decreases, that is, the power
`consumption increases. Therefore, when the power amplifier
`is used for a battery-driven communication terminal, the
`communication time till the battery runs out is shortened.
`SUMMARY OF THE INVENTION
`Therefore, the present invention provides a power ampli
`fier of low distortion and high power efficiency, and a low
`power consumption communication device including the
`power amplifier.
`A power amplifier according to one aspect of the present
`invention includes a power amplification element including
`a first bipolar transistor of a common-emitter type, a Voltage
`Supply circuit for Supplying the base of the first bipolar
`transistor with a bias Voltage, and a distortion compensation
`circuit for compensating for distortion of the power ampli
`fication element. The distortion compensation circuit
`includes a variable impedance element provided between the
`Voltage Supply circuit and the base of the first bipolar
`transistor, and an adjustment circuit for adjusting at least one
`of a reactance component and a resistance component from
`the first transistor toward the variable impedance element.
`Therefore, according to the power amplifier, the reactance
`component and the resistance component from the base end
`of the bipolar transistor for amplification toward the variable
`impedance element can be separately adjusted. Thus,
`amplitude-amplitude distortion and amplitudephase distor
`tion can be separately compensated for. As a result, lower
`distortion of the power amplifier can be realized.
`Preferably, the power amplifier includes a resistor having
`one terminal connected to the power Supply circuit, and a
`capacitor connected between the other terminal of the resis
`tor and a ground potential.
`Therefore, according to the power amplifier, the reactance
`component and the resistance component from the base end
`of the bipolar transistor for amplification toward the variable
`impedance element can be separately adjusted by the resistor
`and the capacitor. Particularly, the Smaller the resistance
`component is, the Smaller the gain of the power amplifier
`becomes because of Signal power consumption with the
`resistance component. For example, when adjustment of the
`reactance component is more effective than adjustment of
`the resistance component for distortion compensation,
`however, addition of the resistor can increase the resistance
`component and improve the gain of the power amplifier.
`More preferably, the variable impedance element is
`formed of a diode element having an anode connected to the
`Voltage Supply circuit and a cathode connected to the base of
`the first bipolar transistor.
`Therefore, according to the power amplifier, a diode is
`particularly used as the variable impedance element, and
`therefore the both end voltage dependence of the variable
`impedance element comes to have the same type as the both
`end Voltage dependence of impedance at a diode portion
`between the base and emitter of the bipolar transistor used
`for amplification. It can be especially effective for distortion
`compensation in the case of a wide-ranging input power.
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`More preferably, the variable impedance element includes
`a Second bipolar transistor configured to form a PN junction
`between the Voltage Supply circuit and the base of the first
`bipolar transistor.
`Therefore, according to the power amplifier, employment
`of the diode portion of the bipolar transistor as the variable
`impedance element enables the variable impedance element
`to be manufactured in the same process as the bipolar
`transistor for amplification. Since a Semiconductor element
`used for the power amplifier can be limited to one type of
`bipolar transistors, it simplifies the device parameter extrac
`tion proceSS for circuit design of circuit elements used for
`the power amplifier. Since a power amplifier circuit includ
`ing the variable impedance element can be formed in a
`monolithic manner on a Semiconductor Substrate, the power
`amplifier can be miniaturized.
`More preferably, the variable impedance element is
`formed of a Second bipolar transistor having an emitter
`connected to the base of the first bipolar transistor, a base
`connected to the Voltage Supply circuit, and a collector
`connected to a node for connecting the resistor and the
`capacitor.
`Therefore, according to the power amplifier, the emitter
`current of the Second bipolar transistor is a Sum of the base
`current and the collector current. Since the collector current
`is almost proportional to the base current, the emitter current
`also has a diode-like current-voltage characteristic.
`Therefore, the Second bipolar transistor functions as a vari
`able impedance element.
`Since the collector current is made variable by the resistor
`as a result, the emitter current is also made variable by the
`resistor. Therefore, even after a bipolar transistor, which also
`Serves as a variable impedance element to be used, is
`Selected, the variable resistance characteristic of the bipolar
`transistor can be adjusted by the resistor. As a result, the
`freedom of adjusting distortion compensation is increased.
`More preferably, the variable impedance element is
`formed of a Second bipolar transistor having a collector
`connected to the base of the first bipolar transistor, a base
`connected to the Voltage Supply circuit, and an emitter
`connected to a node for connecting the resistor and the
`capacitor.
`Therefore, according to the power amplifier, the collector
`current of the Second bipolar transistor has a diode-like
`current-Voltage characteristic for the bias Voltage and func
`tions as a variable impedance element. In this case, Since the
`emitter current is made variable by the resistor, the collector
`current is also made variable by the resistor. Therefore, even
`after a Second bipolar transistor to be used is Selected, the
`variable resistance characteristic of the Second bipolar tran
`Sistor can be adjusted by the resistor, and the freedom of
`adjusting distortion compensation is increased.
`Preferably, the adjustment circuit includes a resistor hav
`ing one terminal connected to the Voltage Supply circuit and
`the other terminal connected to the variable impedance
`element, and a capacitor connected between the Voltage
`Supply circuit and a ground potential.
`Therefore, according to the power amplifier, the reactance
`component and the resistance component from the base end
`of the bipolar transistor for amplification toward the variable
`impedance element can be separately adjusted by the resistor
`and the capacitor. Thus, both amplitude-amplitude distortion
`and amplitude-phase distortion can be compensated for and
`the amplifier can have lower distortion.
`More preferably, the variable impedance elements is
`formed of a Second bipolar transistor having an emitter
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`Page 16 of 24
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`S
`connected to the base of the first bipolar transistor, a
`collector connected to the Voltage Supply circuit, and a base
`connected to the other terminal of the resistor.
`Therefore, according to the power amplifier, the emitter
`current of the Second bipolar transistor is a Sum of the base
`current and the collector current. Since the collector current
`is almost proportional to the base current, the emitter current
`also has a diode-like current-Voltage characteristic for the
`bias Voltage. Therefore, the Second bipolar transistor func
`tions as a variable impedance element. Since the base
`current is made variable by the resistor as a result, the
`collector current and the emitter current are also made
`variable by the resistor. Thus, even after a second bipolar
`transistor to be used is Selected, the variable resistance
`characteristic of the Second bipolar transistor portion can be
`adjusted by the resistor, and the freedom of adjusting dis
`tortion compensation is increased.
`More preferably, the variable impedance element is
`formed of a Second bipolar transistor having a collector
`connected to the base of the first bipolar transistor, an emitter
`connected to the Voltage Supply circuit, and a base connected
`to the other terminal of the resistor.
`Therefore, according to the power amplifier, the collector
`current in the Second bipolar transistor has a diode-like
`current-Voltage characteristic for the bias Voltage. Therefore,
`the Second bipolar transistor functions as a variable imped
`ance element. Since the base current is made variable by the
`resistor in this case, the emitter current and the collector
`current are also made variable by the resistor. Thus, even
`after a Second bipolar transistor to be used is Selected, the
`variable resistance characteristic of the Second bipolar tran
`Sistor portion can be adjusted by the resistor, and the
`freedom of adjusting distortion compensation is increased.
`More preferably, the first bipolar transistor and the vari
`able impedance element are formed on one Semiconductor
`Substrate.
`Therefore, according to the power amplifier, the bipolar
`transistor for amplification and the variable impedance ele
`ment which are formed on one SubStrate can be configured
`in a monolithic manner. Therefore, the power amplifier itself
`can be miniaturized.
`Furthermore, the variable impedance element can be
`manufactured in the same process as the bipolar transistor
`for amplification. Since a Semiconductor element used for
`the power amplifier can be limited to one type of bipolar
`transistors, it is possible to Simplify the device parameter
`extraction process for circuit design of circuit elements used
`for the power amplifier.
`Preferably, the first bipolar transistor operates in a Class
`B or Class AB mode.
`Therefore, according to the power amplifier, employment
`of the variable impedance element and the adjustment circuit
`enables compensation of amplitude-amplitude distortion and
`amplitude-phase distortion. Thus, the bipolar transistor for
`amplification can be operated at a bias current in about the
`Class B or Class AB operating mode. As a result, the
`efficiency of the linear amplifier can be improved.
`Preferably, the gain of the power amplifier can be con
`trolled by controlling an output Voltage of the Voltage Supply
`circuit.
`Therefore, according to the power amplifier, the distortion
`compensation circuit is also used as the bias circuit of the
`first bipolar transistor. By controlling the output voltage of
`the Voltage Supply circuit, therefore, the bias current of the
`first bipolar transistor can be controlled. Thus, the gain of the
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`6
`power amplifier can be controlled while the function of
`distortion compensation is maintained. It is therefore pos
`Sible to improve the power efficiency of a power amplifier
`used especially in a communication System which requires
`low distortion of the power amplifier and gain control in a
`wide dynamic range such as W-CDMA (Wide Band-Code
`Division Multiple Access) and IS-95 (interim standard 95).
`Preferably, the power amplifier controls the distortion
`compensation amount of the distortion compensation circuit
`by controlling the output Voltage from the Voltage Supply
`circuit.
`Therefore, according to the power amplifier, a DC voltage
`acroSS the variable impedance element included in the
`distortion compensation circuit can be controlled by con
`trolling the output Voltage of the Voltage Supply circuit.
`Thus, the impedance of the variable impedance element can
`be controlled. Since the distortion compensation amount of
`the distortion compensation circuit can be adjusted as a
`result, it is possible to provide distortion compensation
`corresponding to the degree of distortion caused in the first
`bipolar transistor. As a result, the freedom of distortion
`compensation is increased as compared with a case where
`the output Voltage of the Voltage Supply circuit is fixed.
`A communication device according to a further aspect of
`the present invention includes a power amplifier having a
`power amplification element including a first bipolar tran
`Sistor of a common-emitter type for Signal amplification and
`a distortion compensation circuit for compensating for dis
`tortion of the power amplification element, and a Voltage
`Supply circuit for Supplying the base of the first bipolar
`transistor with a bias Voltage. The distortion compensation
`circuit includes a variable impedance element provided
`between the voltage supply circuit and the base of the first
`bipolar transistor, and an adjustment circuit for adjusting at
`least one of a reactance component and a resistance com
`ponent from the first bipolar transistor toward the variable
`impedance element.
`Preferably, the adjustment circuit includes a resistor hav
`ing one terminal connected to the Voltage Supply circuit, and
`a capacitor connected between the other terminal of the
`resistor and a ground potential.
`More preferably, the variable impedance element is
`formed of a diode element having an anode connected to the
`Voltage Supply circuit and a cathode connected to the base of
`the first bipolar transistor.
`More preferably, the variable impedance element includes
`a Second bipolar transistor configured to form a PN junction
`between the Voltage Supply circuit and the base of the first
`bipolar transistor.
`More preferably, the variable impedance element is
`formed of a Second bipolar transistor having an emitter
`connected to the base of the first bipolar transistor, a base
`connected to the Voltage Supply circuit, and a collector
`connected to a node for connecting the resistor and the
`capacitor.
`More preferably, the variable impedance element is
`formed of a Second bipolar transistor having a collector
`connected to the base of the first bipolar transistor, a base
`connected to the Voltage Supply circuit, and an emitter
`connected to a node for connecting the resistor and the
`capacitor.
`Preferably, the adjustment circuit includes a resistor hav
`ing one terminal connected to the Voltage Supply circuit and
`the other terminal connected to the variable impedance
`element, and a capacitor connected between the Voltage
`Supply circuit and a ground potential.
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`More preferably, the variable impedance element is
`formed of a Second bipolar transistor having an emitter
`connected to the base of the first bipolar transistor, a
`collector connected to the Voltage Supply circuit, and a base
`connected to the other terminal of the resistor.
`More preferably, the variable impedance element is
`formed of a Second bipolar transistor having a collector
`connected to the base of the first bipolar transistor, an emitter
`connected to the Voltage Supply circuit, and a base connected
`to the other terminal of the resistor.
`More preferably, the first bipolar transistor and the vari
`able impedance element are formed on one Semiconductor
`Substrate.
`Preferably, the first bipolar transistor operates in a Class
`B or Class AB mode.
`Preferably, the gain of the power amplifier is controlled by
`controlling an output Voltage of the Voltage Supply circuit.
`Preferably, the distortion compensation amount of the
`distortion compensation circuit is controlled by controlling
`the output Voltage of the Voltage Supply circuit.
`Therefore, according to the communication device, the
`power amplifier for transmission has low distortion and high
`efficiency and thus the power consumption of the commu
`nication device is reduced. Especially for a battery-run
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`communication device, the communication time till the
`battery runs out can be increased. For attaining the same
`communication time as conventional products, a much
`Smaller battery can be employed, resulting in a Smaller or
`lighter communication terminal.
`Preferably, the communication device is used in a com
`munication System in which a Signal includes an amplitude
`modulation component. If a transmitted signal includes an
`amplitude modulation component, distortion of the wave
`form of the transmitted Signal at an amplification Stage for
`amplifying the transmitted Signal to a predetermined antenna
`output level makes it impossible to correctly demodulate the
`transmitted information at the receiver side. Therefore, the
`communication System requires a low distortion power
`amplifier which faithfully amplifies and outputs an input
`Signal waveform as the power amplifier for transmission
`power. Such a communication System is, for example,
`W-CDMA, IS-95, PDC (Personal Digital Cellular), PHS
`(Personal Handy-Phone System), IMT-2000 (International
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`Mobile Telecommunication 2000) and a wireless LAN
`(Local Area Network) at 5 GHz band.
`Therefore, according to the communication device, the
`low distortion power amplifier is included for transmission
`and thus correct information can be transmitted to the
`receiver side without distortion of the waveform of the
`transmitted Signal.
`If the above-described communication device is used for
`the communication system such as W-CDMA, IS-95, PDC,
`PHS and IMT-2000 which requires a severe low distortion
`characteristic represented by adjacent channel leakage
`power Standard for a power amplifier for transmission, it is
`possible to attain both low distortion and high efficiency.
`Since the power consumption of the communication device
`can be reduced, the communication time till the battery runs
`out can be increased if the communication device runs on a
`battery. For attaining the same communication time as
`conventional product, a much Smaller battery can be used,
`resulting in a Smaller or lighter communication terminal.
`Preferably, the communication device further includes a
`detection circuit for detecting a signal power level input to
`the power amplifier or a signal power level output from the
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`power amplifier, and a control circuit for controlling an
`output Voltage of the Voltage Supply circuit according to the
`Signal power level detected by the detection circuit.
`Therefore, according to the communication device, even
`in a communication System which requires Signal amplifi
`cation with low distortion, the gain or the distortion com
`pensation amount of the power amplifier can be controlled
`by controlling the output Voltage of the Voltage Supply
`circuit according to the detected input signal level or output
`Signal level So that power consumption is minimized with a
`prescribed gain or with distortion within a determined value.
`Therefore, the power consumption of the communication
`device is reduced and, in the case of a battery-driven
`communication device, the communication time till the
`battery runs out can be increased. For attaining the same
`communication time as conventional products, a much
`Smaller battery can be used, resulting in a Smaller or lighter
`communication terminal.
`The foregoing and other objects, features, aspects and
`advantages of the present invention will become more
`apparent from the following detailed description of the
`present invention when taken in conjunction with the
`accompanying drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 shows a configuration of a power amplifier 100 in
`a first embodiment of the present invention.
`FIG. 2 shows one example of another configuration of the
`power amplifier in the first embodiment of the present
`invention.
`FIG. 3 shows a configuration of a power amplifier 200 in
`a Second embodiment of the present invention.
`FIG. 4 shows the result of a test comparing operating
`characteristics of the power amplifier according to the
`present invention and a conventional power amplifier.
`FIG. 5 shows the result of a test examining relations
`between a capacitor and an operating characteristic of the
`power amplifier according to the present invention.
`FIG. 6 shows the result of a test examining relations
`between a resistance value and an operating characteristic of
`a resistor in the power amplifier according to the present
`invention.
`FIGS. 7A and 7B are conceptual diagrams for describing
`test conditions.
`FIG. 8 shows a configuration of a power amplifier 300 in
`a third embodiment of the present invention.
`FIG. 9 shows a configuration of a power amplifier 400 in
`a fourth embodiment of the present invention.
`FIG. 10 shows a configuration of a power amplifier 500
`in a fifth embodiment of the present invention.
`FIG. 11 shows a configuration of a power amplifier 600 in
`a sixth embodiment of the present invention.
`FIG. 12 shows a configuration of a power amplifier 700
`in a Seventh embodiment of the present invention.
`FIG. 13 shows a configuration of a main