U.S. patent application number 10/802850 was filed with the patent office on 2004-09-09 for mobile telecommunication apparatus having a power amplifier which operates stably during changes in control voltage and temperature.
Invention is credited to Yamashita, Kiichi.
Application Number | 20040176053 10/802850 |
Document ID | / |
Family ID | 18937297 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040176053 |
Kind Code |
A1 |
Yamashita, Kiichi |
September 9, 2004 |
Mobile telecommunication apparatus having a power amplifier which
operates stably during changes in control voltage and
temperature
Abstract
A mobile telecommunication apparatus includes an antenna, a
receiving front end having an input end coupled to the antenna, a
baseband-signal processing circuit coupled to an output end of the
receiving front end, and a power amplifier module coupled at an
output end to the antenna and coupled at an input end to the
baseband-signal processing circuit. The power amplifier module
includes a bias circuit to produce an idling current, and a power
amplifier which has its gain controlled by the idling current. With
this arrangement, effects of changes of control voltage and ambient
temperature of the power amplifier module can be removed by a first
detector in the bias circuit to detect changes of the control
voltage and a second detector in said bias circuit to detect
changes of the ambient temperature.
Inventors: |
Yamashita, Kiichi;
(Shiroyama, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
18937297 |
Appl. No.: |
10/802850 |
Filed: |
March 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10802850 |
Mar 18, 2004 |
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10080558 |
Feb 25, 2002 |
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6731171 |
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Current U.S.
Class: |
455/127.1 |
Current CPC
Class: |
H03F 3/3435 20130101;
H03F 3/345 20130101; H03F 1/301 20130101; H03F 1/302 20130101; H03F
3/189 20130101 |
Class at
Publication: |
455/127.1 |
International
Class: |
H03F 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 21, 2001 |
JP |
2001-081143 |
Claims
What is claimed is:
1. A mobile telecommunication apparatus comprising: an antenna; a
receiving front end coupled at an input end to said antenna; a
baseband-signal processing circuit coupled to an output end of said
receiving front end; and a power amplifier module coupled at an
output end to said antenna and coupled at an input end to said
baseband-signal processing circuit, wherein said power amplifier
module comprises: a bias circuit to produce an idling current; and
a power amplifier of which gain is controlled by said idling
current produced by said bias circuit, and wherein effects of
changes of control voltage and ambient temperature of said power
amplifier module can be removed by a first detector in said bias
circuit to detect changes of the control voltage and a second
detector in said bias circuit to detect changes of the ambient
temperature.
2. The mobile telecommunication apparatus according to claim 1,
wherein said bias circuit further comprises a differential circuit
to make error amplification with said first detector provided to
perform as a standard voltage source for ambient-temperature
detection by said second detector and said second detector provided
to perform as a standard voltage source for control-voltage
detection by said first detector.
3. The mobile telecommunication apparatus according to claim 1,
wherein said power amplifier module further comprises: a first
matching circuit to apply an input signal to said power amplifier;
and a second matching circuit to apply an output signal of said
power amplifier to an output terminal of said power amplifier
module.
4. The mobile telecommunication apparatus according to claim 2,
wherein said power amplifier module further comprises: a first
matching circuit to apply an input signal to said power amplifier;
and a second matching circuit to apply an output signal of said
power amplifier to an output terminal of said power amplifier
module.
5. The mobile telecommunication apparatus according to claim 3,
wherein said bias circuit, said power amplifier, said first
matching circuit and said second matching circuit are
monolithically mounted on a circuit board.
6. The mobile telecommunication apparatus according to claim 4,
wherein said bias circuit, said power amplifier, said first
matching circuit and said second matching circuit are
monolithically mounted on a circuit board.
7. A mobile telecommunication apparatus comprising: an antenna; a
receiving front end coupled at an input end to said antenna; a
baseband-signal processing circuit coupled to an output end of said
receiving front end; and a power amplifier module coupled at an
output end to said antenna and coupled at an input end to said
baseband-signal processing circuit, wherein said power amplifier
module comprises: a bias circuit to produce an idling current; and
a power amplifier of which gain is controlled by said idling
current produced by said bias circuit, wherein said bias circuit
further includes an ambient temperature detector to detect changes
of ambient temperature so that effects of changes of ambient
temperature of said power amplifier module can be removed by the
ambient temperature detector without using Schottky diodes.
8. The mobile telecommunication apparatus according to claim 7,
wherein said bias circuit further includes a control voltage
detector to detect changes of the control voltage so that effects
of changes of control voltage of said power amplifier module can be
removed by the control voltage detector.
9. The mobile telecommunication apparatus according to claim 8,
wherein said bias circuit further comprises a differential circuit
to make error amplification with said control voltage detector
provided to perform as a standard voltage source for
ambient-temperature detection of said ambient temperature detector
and said ambient temperature detector provided to perform as a
standard voltage source for control-voltage detection of said
control voltage detector.
10. The mobile telecommunication apparatus according to claim 7,
wherein said power amplifier module further comprises: a first
matching circuit to apply an input signal to said power amplifier;
and a second matching circuit to apply an output signal of said
power amplifier to an output terminal of said power amplifier
module.
11. The mobile telecommunication apparatus according to claim 4,
wherein said power amplifier module has a plurality of
power-amplifying transistors provided in series, wherein said first
matching circuit is connected to an input transistor of the
plurality of said power-amplifying transistors in series, and
wherein said second matching circuit is connected to an output
transistor of the plurality of said power-amplifying transistors in
series.
12. The mobile telecommunication apparatus according to claim 11,
wherein said bias circuit is coupled to each of said
power-amplifying transistors.
13. The mobile telecommunication apparatus according to claim 4,
further comprising a power-amplifying transistor, wherein said
first detector further comprises a voltage-dividing-resistor
circuit to divide the control voltage, wherein said second detector
further comprises transistors in diode connection, the transistors
in diode connection having substantially the same structure as said
power-amplifying transistor, the power-amplifying transistor and
the transistors in diode connection constituting a current mirror,
wherein said idling current of said bias circuit is generated from
a first resistive element provided in said bias circuit, between an
input terminal of the control voltage and of said power-amplifying
transistor, and wherein said differential circuit of said bias
circuit stabilizes the current passing through said resistive
element by the error-amplifying performance of said differential
circuit to stabilize the idling current.
14. The mobile telecommunication apparatus according to claim 13,
wherein said transistors in diode connection of said second
detector are in a configuration of a first transistor and a second
transistor, wherein a pair of said power-amplifying transistors are
provided in a configuration of a third transistor and a fourth
transistor in a Darlington connection, and wherein at least a
second resistive element is provided between the emitter of said
third transistor and the base of said fourth transistor, and the
input signal is fed through a coupling capacitance to the base of
said fourth transistor.
15. The mobile telecommunication apparatus according to claim 14,
wherein said differential circuit further comprises transistors
which have substantially the same structure as said
power-amplifying transistors, wherein said bias circuit and said
power-amplifying transistors are integrated into a single
semiconductor integrated circuit, and wherein said first and second
matching circuits are mounted, as parts external of the
semiconductor integrated circuit, on said printed circuit
board.
16. The mobile telecommunication apparatus according to claim 15,
wherein said transistors used in said bias circuit and said
power-amplifying transistors are heterojunction bipolar
transistors.
17. The mobile telecommunication apparatus according to claim 15,
wherein said transistors used in said bias circuit and said
power-amplifying transistors are metal-oxide-semiconductor field
effect transistors.
18. The mobile telecommunication apparatus according to claim 13,
wherein said voltage dividing circuit of said first detector has an
external terminal through which the control voltage is input into
said voltage dividing circuit.
19. The mobile telecommunication apparatus according to claim 4,
wherein said power amplifier comprises a power-amplifying
transistor and said bias circuit includes transistors in diode
connection, which generate a base-emitter bias voltage of said
power-amplifying transistor and which are formed with said power
amplifying transistor on a first semiconductor chip, wherein said
bias circuits, except said transistors in diode connection for
generating the bias voltage, are formed on a second semiconductor
chip, wherein said first semiconductor chip is constituted by one
of GaAs- and SiGe-heterojunction bipolar transistors, and wherein
said second semiconductor chip is constituted by one of Si bipolar
transistors and metal-oxide-semiconductor field effect
transistors.
20. A mobile telecommunication apparatus comprising: an antenna; a
receiving front end coupled at an input end to said antenna; a
baseband-signal processing circuit coupled to an output end of said
receiving front end; and a power amplifier module coupled at an
output end to said antenna and coupled at an input end to said
baseband-signal processing circuit, wherein said power amplifier
module comprises: a bias circuit for producing an idling current so
that effects of changes of control voltage and ambient temperature
can be removed; a power-amplifying transistor of which gain is
controlled by the idling current produced by said bias circuit; a
first matching circuit for feeding an input signal to the
power-amplifying transistor; and a second matching circuit for
feeding an output signal of the power amplifier circuit to a load
circuit, wherein said bias circuit comprises: a first means for
detecting changes of control voltage of the module; a second means
for detecting changes of ambient temperature of the module; and a
differential circuit for making error amplification with the first
means serving as a standard voltage source for ambient-temperature
detection and the second means serving as a standard voltage source
for control-voltage detection, and wherein said bias circuit, said
power-amplifying transistor, and said first and second matching
circuits are mounted on a printed circuit board.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a power amplifier module.
More specifically, the present invention relates to technology
effectively applicable to power amplifier modules for, e.g.,
cellular phones which need to keep high linearity under
environmental changes such as changes of ambient temperature and
control voltage.
[0003] 2. Description of the Related Art
[0004] Portable telephones used in CDMA (Code Division Multiple
Access), PDC (Personal Digital Cellular), TDMA (Time Division
Multiple Access), and other systems are required to have high
linearity and efficiency under environmental changes such as
changes of ambient temperature and control voltage. To meet this
requirement without allowing the performance of the telephone to
drop, it is essential to maintain a stable operating point (idling
current) of the power amplifier, which, among other components of
the telephone has the greatest influence on the linearity and
efficiency of the telephone, under environmental changes such as
changes of ambient temperature and control voltage.
[0005] FIGS. 11A and 11B show examples of power amplifiers using
GaAs-HBTs (Heterojunction Bipolar Transistors) presented in the
C-10-7 of the 2000 General Conference of the Institute of
Electronics, Information and Communication Engineers. FIG. 11A
shows one of the unit amplifiers of a power amplifier. Reference
numeral 1 is a power terminal; 14, a grounding terminal; 2, a
control terminal; 8, an input terminal; 11, an output terminal; 22
to 24 and 28, GaAs-HBTs (hereinafter simply referred to gas
"transistors"); 21, 25, and 26, resistors; 27, a coupling
capacitance; 29, an RF choke inductor; and 15, a bias circuit
comprised of some of the above parts.
[0006] In the circuit of FIG. 11A, the transistors 24 and 28
connected by a Darlington connection and the transistors 22 and 23
connected by a diode connection constitute a current mirror
circuit. If the ratio of the current mirror is set to "n" by
setting the emitter area of the transistor 28 "n" times as large as
the emitter area of the transistors 22 and 23, a current Iq, which
is "n" times as large as a current Ib passing through the
transistors 22 and 23 in the diode configuration, passes through
the amplifying transistor 28 as an idling current. Keeping the
current Ib constant is, therefore, important to stabilize the
idling current Iq.
[0007] An input signal is input through the input terminal 8,
amplified by the amplifying transistor 28, and output through the
output terminal 11. A matching circuit (not shown) is connected to
the input terminal 8; another matching circuit (not shown), to the
output terminal 11. The resistor 26 and the RF choke inductor 29
are used to isolate signal components from the bias circuit 15 and
the power line of low impedance.
[0008] In the circuit of FIG. 11B, an idling current Iq is
stabilized by offsetting the temperature characteristics of
base-emitter voltage of transistors 24 and 28 by the temperature
characteristics of Schottky diodes 30 to 33 connected in series in
bias circuit 15. Although the threshold voltage of the Schottky
diode is about a half of that of the GaAs-HBT, the former's
temperature characteristics are almost the same as the temperature
characteristics of base-emitter voltage of the latter. It is
therefore possible to connect in series twice as many Schottky
diodes as GaAs-HBTs, and any desired temperature compensation
effect can be accomplished by changing the ratio of the resistance
of resistor 21 to the resistance of resistor 36. In this unit
amplifier, four Schottky diodes are connected in series to obtain
temperature characteristics of the idling current Iq of a practical
level. Reference numerals 34 and 35 also indicate Schottky diodes,
which are dispensable from the point of view of the basic function
of the unit amplifier.
SUMMARY OF THE INVENTION
[0009] The power amplifier of FIG. 11A is simple in configuration
and has an advantage that all active elements can be formed by a
transistor process. However, because a current Ireg passing through
the resistor 21 is governed by: (i) the difference between the
voltage at the control terminal 2 and the sum of the base-emitter
voltage of the transistor 22 and that of the transistor 23; and
(ii) the resistance of the resistor 21, the current Ireg varies in
accordance with changes of ambient temperature and control voltage.
The current Ib changes in proportion to the current Ireg. In other
words, no means is provided for stabilizing the idling current Iq
when changes of ambient temperature and control voltage occur.
Therefore, the dependency of the idling current Iq on the ambient
temperature and the control voltage is large. In addition, it is
difficult to achieve a high yield because the performance of the
unit amplifier is liable to be affected by the deviation in
manufacture of resistors 21. When the control voltage is 2.8 V and
the ambient temperature varies within a range of 30.+-.60.degree.
C., the idling current varies within a range larger than .+-.40%.
When the ambient temperature is 30.degree. C. and the control
voltage lowers from 2.8 V to 2.7 V, the idling current Iq is
reduced by 30% or so.
[0010] The idling current of the unit amplifier of FIG. 11B is
stabilized by using Schottky diodes. This method, however, requires
a Schottky diode process which is different from the GaAs-HBT
process. Because it is difficult to stably control Schottky
barriers and electrode contact in a Schottky diode process, it is
difficult to manufacture power amplifiers at high repeatability and
a high yield. As in the case of the unit amplifier of FIG. 11A, the
unit amplifier of FIG. 11B has no means for stabilizing the idling
current when a variation of the control voltage occurs.
Accordingly, the idling current is reduced by 50% or so when the
control voltage lowers from 2.8 V to 2.7V.
[0011] In accordance with the above, an object of the present
invention is to provide a power amplifier module with a bias
circuit capable of feeding stable idling currents to power
amplifier units. Another object of the present invention is to
provide a power amplifier module which can be manufactured at low
cost and a high yield by forming a bias circuit and power amplifier
units in a stable transistor process.
[0012] A representative example of the invention disclosed in this
application is as follows. A differential circuit provides error
amplification with a first arrangement to detect changes of the
control voltage and a second arrangement to detect changes of
ambient temperature as mutual standard voltage inputs to produce an
idling current. As a result, the effects of the changes of the
control voltage and the ambient temperature are removed. The idling
current controls the gain of a power-amplifying transistor. Input
signals are fed to the power-amplifying transistor through a first
matching circuit, and output signals from the power-amplifying
transistor are fed to a load circuit through a second matching
circuit.
[0013] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] A preferred form of the present invention is illustrated in
the accompanying drawings in which:
[0015] FIG. 1 is a circuit diagram showing a basic configuration of
a power amplifier module embodying the present invention;
[0016] FIG. 2 is a specific circuit diagram of an embodiment of the
unit amplifier of FIG. 1;
[0017] FIG. 3 shows the ambient temperature-idling current
characteristic curves of the unit amplifier of FIG. 2;
[0018] FIG. 4 is a specific circuit diagram of another embodiment
of the unit amplifier of FIG. 1;
[0019] FIG. 5 is a specific circuit diagram of yet another
embodiment of the unit amplifier of FIG. 1;
[0020] FIG. 6 is a specific circuit diagram of still another
embodiment of the unit amplifier of FIG. 1;
[0021] FIG. 7 is a block diagram of an embodiment of the power
amplifier module of the present invention;
[0022] FIG. 8 is a circuit diagram of an embodiment of the power
amplifier module of the present invention;
[0023] FIG. 9 is a general block diagram of an embodiment of a
portable telephone for CDMA mobile telecommunication, noting the
power amplifier module of the present invention can be applied to
such portable telephones;
[0024] FIG. 10 is a schematic sectional view of an embodiment of a
heterojunction bipolar transistor suitable to use in the power
amplifier module of the present invention; and
[0025] FIGS. 11A and 11B are a circuit diagrams showing examples of
the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Preferred embodiments of the present invention will now be
described with reference to the accompanying drawings.
[0027] FIG. 1 is a circuit diagram showing a basic configuration of
a power amplifier module embodying the present invention. In
general, a power amplifier module for portable telephones described
earlier consists of two or three unit amplifiers. This embodiment
of the present invention presents such a unit amplifier. The unit
amplifier of this embodiment comprises: (i) a power amplifier unit
16 including an amplifying transistor 10 which is, for example, a
GaAs-HBT, coupling capacitance 7, resistors 6 and 9, and an RF
choke inductor 12; and (ii) a bias circuit 15 including an error
amplifier circuit 4, a temperature detection circuit/standard
voltage source for control voltage detection 5, a control voltage
detection circuit/standard voltage source for temperature detection
17, and a resistor 3. Reference numerals 13 and 14 are a power
terminal and a grounding terminal, respectively.
[0028] The working principle of the unit amplifier of FIG. 1 will
now be described. A high-frequency signal, which is input through a
terminal 8, is sent through the coupling capacitance 7 to the
amplifying transistor 10 to be amplified thereby and output through
a terminal 11. An input matching circuit (not shown) is connected
to the terminal 8; an output matching circuit (not shown), to the
terminal 11. Accordingly input signals are sent through the input
matching circuit to the terminal 8, and output signals, which are
output through the terminal 11, drive a load (antenna), etc.
through the output matching circuit. The resistor 9 stabilizes the
working of the amplifying transistor 10. Even if the resistor 9 is
short-circuited, the basic working of the amplifying transistor 10
remains the same. The resistor 6 and the inductor 12 are used to
shut out high-frequency signals. In other words, they are used to
isolate signal components from the bias circuit 15 and the power
line of low impedance.
[0029] An idling current is fed to the amplifying transistor 10 as
follows. A positive-pole terminal and a negative-pole terminal of
the error amplifier circuit 4 are connected to the control-voltage
detection circuit/standard voltage source for temperature detection
17 and the temperature detection circuit/standard voltage source
for control-voltage detection 5, respectively. The voltage at the
positive- and negative-pole terminals and circuit parameters are
set so as to render a current Ireg passing through the resistor 3
and currents Ib and Icp equal to their respective prescribed
values. When the ambient temperature rises, the electric potential
at an "a" point and the negative pole terminal lowers. When the
electric potential at the "a" point lowers, the current Ireg
increases; accordingly, the current Ib and the idling current Iq
passing through the amplifying transistor 10 increase.
[0030] When the negative pole's electric potential of the error
amplifier circuit 4 lowers, the current Icp into the error
amplifier circuit 4 increases because the positive pole's electric
potential is constant. Therefore, the increase of the current Ib
can be held down by designing the error amplifier circuit 4 so as
to render the increments of the currents Ireg and Icp equal to each
other.
[0031] Considered next is a case where the control voltage rises
while the ambient temperature is constant. In this case, the
current Ib is kept constant to stabilize the idling current Iq by
offsetting the increment of the current Ireg by increasing the
current Icp into the error amplifier circuit 4.
[0032] According to the present invention, a bias circuit is
provided with detection circuits for detecting the changes of
ambient temperature and control voltage and an error amplifier
circuit for amplifying the changes of ambient temperature and
control voltage detected by the detection circuits. Because the
current Ireg varies as the ambient temperature and the control
voltage vary, the variation of the current Ireg is offset by
feeding a current Ii corresponding to the variation to the error
amplifier circuit so as to keep the current Ib constant and feed a
stable idling current to a power amplifier unit. The above
embodiment is characterized by a temperature detection circuit
which not only detects the ambient temperature but also serves as a
standard voltage source for control-voltage detection and a
control-voltage detection circuit which not only detects the
control voltage but also serves as a standard voltage source for
temperature detection. Thus, they serve as detection circuits and
standard voltage sources mutually.
[0033] FIG. 2 is a specific circuit diagram of an embodiment of the
unit amplifier of FIG. 1. The control-voltage detection
circuit/standard voltage source for temperature detection 17
comprises resistors 42 and 43 connected in series. The connection
between the resistor 42 and the terminal 2 is the point for
control-voltage detection, and the connection between the resistors
42 and 43 is the reference point for temperature detection. The
temperature detection circuit/standard voltage source for
control-voltage detection 5 comprises GaAs-HBTs 50 and 51
(hereinafter referred to as "transistors") in a series diode
configuration. The connection between the collector and the base of
the transistor 50 is the point for temperature detection or the
reference point for control-voltage detection. Capacitance 48 is
used to smooth the high-frequency components of a current passing
through the base during the high-frequency operation of the
amplifying transistor 10 and thereby stabilize the workings of the
amplifying transistor 10. The capacitance 48, however, is
dispensable.
[0034] The error amplifier circuit 4 is a differential circuit
including GaAs-HBTs 46 and 47 (hereinafter referred to as
"transistors"). Emitter resistors 44 and 45 are provided to expand
the dynamic range of the differential circuit. Reference numeral 49
is a current source, which can be made of a resistor or a resistor
and a transistor. Fed to the base of the differential transistor 46
is the divided voltage of voltage dividing resistors 42 and 43
constituting the control-voltage detection circuit/standard voltage
source for temperature detection 17. Fed to the base of the
differential transistor 47 is the voltage of the connection between
the base and the collector of the transistor 50, the connection
being the detection point of the temperature detection
circuit/standard voltage source for control-voltage detection 5. In
other words, fed to the base of the differential transistor 47 is
the voltage drop at the resistor 41 which causes the current
Ireg.
[0035] A transistor 52 is connected to the amplifying transistor 10
by a Darlington connection. The transistors 50 and 51 in the diode
configuration and the transistors 52 and 10 constitute a current
mirror; accordingly, if the resistor 53 is short-circuited, the
basic workings remain the same. The configuration of the other part
of the unit amplifier is the same as the counter part of the unit
amplifier of FIG. 1, accordingly, its description is omitted.
[0036] If the unit amplifier is not provided with an error
amplifier circuit 4, and the ambient temperature rises, the
base-emitter voltage of the transistors 50 and 51 lowers.
Accordingly, the electric potential of the base of the differential
transistor 47 lowers, the voltage across the resistor 41 rises, the
currents Ireg and Ib increase, and, hence, the idling current Iq
increases due to the current mirror effect between the transistors
50 and 51 and the transistors 52 and 10. On the other hand, if the
unit amplifier is provided with an error amplifier circuit as shown
in FIG. 2, and the electric potential of the base of the
differential transistor 47 lowers below that of the differential
transistor 46, more electricity fed from the current source 49
passes through the differential transistor 46, increasing the
current Icp. Because circuit parameters are determined so as to
render the increments of the currents Icp and Ireg equal to each
other, the current Ib is kept constant, and, thereby, the idling
current Iq is kept stable.
[0037] If the unit amplifier is not provided with an error
amplifier circuit 4, and the control voltage rises while the
ambient temperature is stable, the voltage across the resistor 41
rises, increasing the currents Ireg and Ib and the idling current
Iq because the base-emitter voltage of the transistors 50 and 51
does not change, and, hence, the electric potential of the base of
the transistor 47 is kept constant. On the other hand, if the unit
amplifier is provided with an error amplifier circuit, as shown in
FIG. 2, the electric potential of the base of the differential
transistor 46 rises over that of the other differential transistor
47; accordingly, more electricity fed from the current source 49
passes through the differential transistor 46, increasing the
current Icp. Because circuit parameters are determined so as to
render the increments of the currents Icp and Ireg equal to each
other, the current Ib is kept constant, and, thereby, the idling
current Iq is kept stable.
[0038] In actual circuit design, the circuit parameters are
determined from the viewpoint of both ambient temperature and
control voltage variations. FIG. 3 shows the ambient
temperature-idling current characteristic curves of the unit
amplifier of FIG. 2. The curves represent simulation results and
actual measurements based on the following conditions: resistance
of resistor 41, 400 .OMEGA.; base-emitter voltage of transistors 50
and 51, 2.5 V (two-stage connection); its change, -2.4 mV/.degree.
C.; temperature range, 30.+-.60.degree. C.; control voltage, 2.8 V;
its range .+-.0.1 V; current Ib, 0.25 mA; and current mirror ratio
(n), 116.
[0039] According to the simulation, the idling current Iq is stable
in the temperature range of .+-.60.degree. C. under the control
voltage of 2.8 V. This simulation result was supported by actual
measurement wherein the idling current Iq changed about 5% in the
range from 30.degree. C. to 90.degree. C. It is apparent that if
the GaAs-HBTs in FIG. 2 are replaced with SiGe-HBTs' or Si bipolar
transistors, the same compensation effect can be accomplished.
[0040] As described above, if the ambient temperature rises, the
sum of the base-emitter voltage of the transistor 50 and that of
the transistor 51 lowers, and, hence, the current Ireg increases.
If a current equivalent to the increment of the current Ireg is
passed through the error amplifier circuit 4, the current Ib
passing through the transistors 50 and 51 is kept constant. During
the temperature compensation, a control-voltage detection circuit
17 serves as a standard voltage source for temperature detection
too. If the control voltage rises, the current Ireg increases
because the sum of the base-emitter voltage of the transistor 50
and that of the transistor 51 is constant. If a current equivalent
to the increment of the current Ireg is passed through the error
amplifier circuit 4, the current Ib passing through the transistors
50 and 51 is kept constant. During the control-voltage
compensation, a temperature detection circuit 5 serves as a
standard voltage source for control-voltage detection as well.
Thus, from a functional point of view, the control-voltage
detection circuit 17 becomes a control-voltage detection
circuit/standard voltage source for temperature detection 17 and
the temperature detection circuit 5 becomes a temperature detection
circuit/standard voltage source for control-voltage detection
5.
[0041] FIG. 4 is a specific circuit diagram of another embodiment
of the unit amplifier of FIG. 1. The configuration shown in FIG. 4
is for the integration of the bias system on a chip and the
integration of the power amplification system on another chip.
Paired transistors 10 and 51 in a power amplifier IC 202 are
GaAs-HBTs, and paired transistors 50-1 and 52-1 in a bias IC 201
are SiGe-HBTs or Si bipolar transistors, both pairs constituting a
current mirror.
[0042] It is desirable to build resistors 6 and 9 and capacitance 7
into the power amplifier IC 202 and transistors 46-1 and 47-1
constituting an error amplifier, resistors 41 to 45, 53, and 54,
and a current source 49 into the bias IC 201. The transistors 46-1
and 47-1 constituting the error amplifier are SiGe-HBTs or Si
bipolar transistors. The resistor 54 may be built into the power
amplifier IC 202.
[0043] FIG. 5 is a specific circuit diagram of yet another
embodiment of the unit amplifier of FIG. 1. As compared with the
unit amplifier of FIG. 4, the difference is that the resistor 42 is
not connected to the terminal 2, but to an additional terminal 2-1.
With this configuration, the current Ireg can be adjusted by
connecting an external resistor to the terminal 2 in series;
therefore, the idling current Iq can be set to any value. The unit
amplifier of FIG. 5 functions in the same way as that of the FIG. 4
if the terminal 2-1 is externally connected to the terminal 2.
[0044] If the terminal 2-1 is left open, the base of the transistor
46 of the error amplifier is grounded, and, hence, the error
amplifier circuit 4 does not function. Thus, a power amplifier
module applicable to portable telephones for cellular systems such
as the GSM (Global System for Mobile Communication), the PCN
(Personal Communications Network), etc. where the output power is
controlled by O-V, control signals to burst signals of any
amplitude can be accomplished. In other words, a single power
amplifier module can be used for portable telephones of different
systems.
[0045] FIG. 6 is a specific circuit diagram of still another
embodiment of the unit amplifier of FIG. 1. Instead of GaAs-HBTs,
SiGe-HBTs, etc. used in the unit amplifiers of FIGS. 2, 4, and 5,
MOSFETs are used in this embodiment. In FIG. 6, reference numerals
75, 76, 79 to 81, and 86 are MOSFETs; 70 to 74 and 82 to 83,
resistors; 77, a current source; 85, coupling capacitance; and 87,
an RF choke inductor.
[0046] The workings of this unit amplifier are the same as those of
the unit amplifier of FIG. 2. Accordingly, the detailed description
of its workings is omitted. Because the transfer conductance of the
differential circuit can be adjusted by the gate width of the
MOSFETS, the resistors 73 and 74 are dispensable. Besides, because
the input current (gate current) of the MOSFET is zero, unlike
GaAs-HBTs or the SiGe-HBTs, the resistor 84 can be of a k.OMEGA.
order; therefore the resistor 82 is dispensable.
[0047] FIG. 7 is a block diagram of an embodiment of the power
amplifier module of the present invention. In general, a power
amplifier module consists of two or three unit amplifies connected
in series. Shown in FIG. 7 is an example of a two-stage power
amplifier module, wherein a bias circuit 91 is applied to power
amplifier units 92 and 93. One more power amplifier unit may be
added to the module to make it three-stage.
[0048] In FIG. 7, a signal input through the terminal 8 is
amplified by the power amplifier unit 92 and the power amplifier
unit 93 and output through the terminal 11. Idling currents for the
power amplifier units 92 and 93 are fed from the bias circuit 91
with a current mirror circuit such as shown in FIG. 2 or FIG. 4.
Each power amplifier unit may be provided with a bias circuit, or
the output of a bias circuit may be divided and fed to the two
power amplifier units. The power amplifier units 92 and 93 and the
bias circuit 91 may be integrated onto a single chip, or the power
amplifier units 92 and 93 may be integrated onto one chip and the
bias circuit 91 may be integrated onto another.
[0049] FIG. 8 is a circuit diagram of an embodiment of the power
amplifier module of the present invention. In FIG. 8, a
representative amplifying stage and a representative bias circuit
alone are illustrated. By adding more of the same type of
amplifying stage(s) and the same type of bias circuit(s), two-stage
or three-stage module can be accomplished. In such two- or
three-stage modules, coupling capacitance is provided between
amplifying stages to allow high-frequency components alone to
pass.
[0050] Mounted externally on the PCB of the power amplifier module
are an integrated circuit IC comprising a bias circuit and an
amplifying transistor, a matching circuit which sends input signals
input through an RF input terminal of the module to an input
terminal 8 of the integrated circuit IC, a matching circuit which
sends output signals output from an output terminal 11 of the
integrated circuit IC to an RF output terminal of the module, and
an inductor 12 to be connected to the collector of the amplifying
transistor 10. A control input terminal of the module is connected
to a control voltage terminal of the bias circuit. These circuits
elements are mounted on a PCB and sealed to constitute a power
amplifier module, which is built into portable telephones as
described later.
[0051] FIG. 9 is a general block diagram of an embodiment of a
portable telephone for CDMA mobile telecommunication using the
power amplifier module of the present invention, which is
particularly useful for such portable telephones. Signals received
by an antenna 101 are amplified by a receiving front end comprising
a common unit 102, an amplifier 103, a filter 104, and a mixer 105.
The amplified signals are converted into intermediate-frequency
signals by the mixer 105 and converted further into baseband
signals by an intermediate signal processing unit comprising a
filter 106, a gain controller/amplifier 107, and a down-converter
108. The converted signals are sent to a baseband-signal processing
circuit 118. Audio signals are processed by the baseband-signal
processing circuit 118 and reproduced by a speaker 120.
[0052] On the sending side, signals are processed in reverse order.
Sounds and voices are converted by a microphone 119 into electric
signals and sent to a mixer 112 through the baseband-signal
processing circuit 118, an up-converter 117, a signal attenuator
115, and a filter 114. The signals are converted into
sending-frequency band signals by a frequency synthesizer 113 and a
mixer 112, unnecessary frequency components are removed from the
signals by a filter 111, and the signals are power-amplified by a
power amplifier module 109. The signals output from the power
amplifier module 109 are sent through an isolator 110 and the
common unit 102 to the antenna 101 to be transmitted into air.
[0053] The baseband-signal processing circuit 118 generates a
control signal to control the workings of the power amplifier
module 109. The control signal is set to 0 V while signals are not
transmitted so as to stop the workings of the bias circuit of the
power amplifier module 109. Because the control signal generated by
the baseband-signal processing circuit 118 corresponds to a binary
signal generated by a digital circuit of the circuit 118, and,
hence, the voltage change of the control signal is relatively
large, the stabilization of the idling current at the bias circuit
is important for the elongation of battery life and stable
telecommunication.
[0054] FIG. 10 is a schematic sectional view of an embodiment of
the heterojunction bipolar transistor suitable to use in the power
amplifier module of the present invention. A semiconductor of a
wide band gap is used for the emitter of the heterojunction bipolar
transistor. Because the reverse injection of minority carriers from
the base to the emitter is held down by the wide-band-gap emitter,
the injection efficiency of the emitter, and, hence, the current
gain are high. Even if the carrier density of the base is raised, a
high current gain can be maintained and the resistance of the base
can be lowered. Therefore, very-high-speed operation with a high
current gain and a high driving capacity of the transistor is
possible.
[0055] In this embodiment, the carrier density of the collector Nc
is lowered to reduce the capacitance between the base and the
collector Cbc. The necessary collector field is the area for the
emitter-base junction, and, hence, the external base-collector
capacitance Cbc under the base electrode B is a parasitic extra
capacitance. To reduce the capacitance Cbc, oxygen 02 is injected
into the n.sup.- field for insulation.
[0056] As described above, the bias circuit of the present
invention enables feeding stable idling currents to power amplifier
units under environmental changes such as changes of ambient
temperature and control voltage. Therefore, a power amplifier
module with high linearity and efficiency can be accomplished.
Besides, all the active elements of the power amplifier module
including diodes for temperature compensation can be formed
collectively by a GaAs-HBT, SiGe-HBT, or MOSFET process.
Accordingly, the yield can be raised and the production cost can be
reduced.
[0057] While particular embodiments of the present invention have
been shown, the invention is not restricted to such embodiments,
and it is apparent that changes and modifications may be made
without departing from the spirit of the invention. For example,
when providing a plurality of amplifying stages as in the
embodiment of FIG. 7, a GaAs-HBT showing a high driving capacity
and a SiGe-HBTs are used as an element to amplify signals. Further,
among bias circuits, since fast operation is not required in an
error amplification circuit, a circuit comprising conventional
bipolar transistors or MOSFETs is used. Thus, in the case where a
plurality of ICs and external parts are mounted on a PCB, a
resistor producing the previously described current Ireg may be
comprised of an external element. In such a case, process
variations in a semiconductor integrated circuit device can be
reduced, and the idling current can be set to any value. This
invention can be applied to various portable telephones, etc. as a
power amplification module, as well as other types of devices.
[0058] The advantages offered by the representative examples of the
invention disclosed in this application are as follows. A
differential circuit makes error amplification with a first means
for detecting changes of control voltage and a second means for
detecting changes of ambient temperature as mutual standard voltage
source inputs to produce an idling current wherein the effects of
the changes of the control voltage and the ambient temperature are
removed. The idling current controls the gain of a power-amplifying
transistor. Input signals are fed to the power-amplifying
transistor through a first matching circuit, and output signals
from the power-amplifying transistor are fed to a load circuit
through a second matching circuit. Thus, stable idling currents are
fed to power amplifier units under environmental changes such as
changes of ambient temperature and control voltage. Therefore, a
power amplification module with high linearity and efficiency can
be accomplished.
* * * * *