Amplifiers – With semiconductor amplifying device – Including protection means
Reexamination Certificate
2001-11-14
2003-10-21
Nguyen, Patricia (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including protection means
C330S20700P, C330S307000, C327S314000, C327S325000
Reexamination Certificate
active
06636118
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a high frequency power amplifier module for obtaining a predetermined amplification factor by cascade connecting a plurality of heterojunction bipolar transistors, and a wireless communication apparatus in which the high frequency power amplifier module is assembled. More particularly, the invention relates to a technique effective for improving destruction resistance of a heterojunction bipolar transistor to fluctuations in load impedance.
BACKGROUND ART
At an input stage of a transmitter of a wireless communication apparatus (mobile communication apparatus) such as an automobile telephone or portable telephone, an amplifier (high frequency power amplifier module, or RF power module) in which MOSFETs (Metal Oxide Semiconductor Field-Effect-Transistors), GaAs-MES (Metal-Semiconductor) FETs, HEMTs (High Electron Mobility Transistors), or HBTs (Heterojunction Bipolar Transistors) are formed at multiple stages is assembled.
The heterojunction bipolar transistor (HBT) is described in, for example, “A robust 3W high efficiency 8-14 Ghz GaAs/AlGaAs heterojunction bipolar transistor power amplifier”, IEEE-MTTS, p581-584. This literature discloses a multi-finger HBT structure using cascade connection to improve destruction resistance of the HBT. Specifically, by using cascaded HBTs for each finger, a hot spot caused by concentration of currents can be suppressed, a breakdown voltage is increased, and destruction resistance is improved.
“Hitachi power MOSFET databook” issued by Semiconductor Division of Hitachi, Ltd., p47-48 describes that a diode (parasitic diode) is equivalently provided between the source and the drain of a power MOSFET and the parasitic diode has characteristics which are not inferior to those of a normal diode. It also describes that the parasitic diode can be used for a bridge circuit, an output stage of a PWM amplifier, and the like, so that an external commutation diode can be omitted. Therefore, the number of parts can be reduced.
Since the HBT has excellent characteristics such as high processing speed and low power consumption, it is being used as a semiconductor amplifying device of an RF power amplifier module or the like.
FIG. 20
is a diagram showing the basic structure of a power amplifying circuit of the HBT.
As shown in
FIG. 20
, a heterojunction bipolar transistor (HBT)
1
employs a multi-finger structure in which a plurality of small HBT fingers
5
each having an emitter finger
2
, a base finger
3
, and a collector finger
4
are arranged in parallel. The fingers
2
,
3
, and
4
are connected in parallel with each other and connected to an emitter terminal
6
, a base terminal
7
, and a collector terminal
8
, respectively.
In an operating mode, a power supplied from the base terminal
7
is distributed to the HBT fingers
5
and amplified. An amplified power is output to the collector fingers
4
and is further added, and a super power is output to the collector terminal
8
.
In the power amplification circuit, to effectively supply the power to the load side, a load impedance
10
as a signal source is conjugate matched with an optimum impedance of the HBT via a matching circuit
11
, thereby realizing characteristics of high gain and high efficiency.
Conventionally, destruction resistance of an output power amplifying device (semiconductor amplifying device) in a normal operation mode of the RF power amplifier is assured. Consequently, the output power amplifying device is not destroyed in the normal operation mode. Except for a specific example that the parasitic diode between the source and drain of an Si-MOSFET has the possibility that it operates as an equivalent protective device, a protective device is not intentionally provided for the output power amplifying device.
In the normal operation mode of a power amplifier in a mobile communication terminal such as a portable telephone, the output power amplifying device is not destroyed. It was, however, found that in the case such that the user touches the antenna of a mobile communication terminal, or a source voltage is applied in a state where an output terminal of a power amplifier is not properly terminated due to an erroneous work of an operator at the time of assembling a mobile communication terminal, the output power amplifying device of the power amplifier in the mobile communication terminal is destroyed.
FIG. 21
is a diagram schematically showing the relation between a static characteristic
15
of the power HBT and a matched load line
16
. Under the matched condition, a current and a voltage on the load line are output to the load side. Under the matched condition, only a voltage lower than the breakdown voltage (BV
ceo
) is applied to the collector terminal
8
of the HBT, so that a problem does not occur.
It was, however, found that in a practical state, when the HBT power amplifier is used for a transmitting unit of a portable telephone, the case that the matching condition particularly on the load side fluctuates from the optimal state often occurs. Specifically, as shown in
FIG. 21
, a load line
17
,
18
,or
19
that the load impedance is in an unmatched state is obtained, a voltage having an amplitude higher than that of a source voltage is applied to the collector terminal
8
in the HBT. When the voltage exceeds a device breakdown voltage, a device breakdown occurs, and it becomes a problem in practical use.
Also in an assembling work of manufacturing an RF power amplifier module by mounting an HBT on a module substrate, there is a case such that a device breakdown similarly occurs when the operator inadvertently touches a terminal or a line in the HBT. It can deteriorate the manufacturing yield of the RF power amplifier module and a wireless communication apparatus.
In order to prevent the device breakdown due to fluctuations in load, a method of setting the breakdown voltage of the HBT to a higher value can be generally considered but has a problem such that the method is not a sufficient countermeasure due to limitations of characteristics and structure.
On the other hand, in the conventional structure proposed to improve the destruction resistance of the HBT, it is difficult to perform a low voltage operation (of 2.7 to 4.2V) as the characteristic of GaAs. Since two HBTs are formed for each finger, there is a problem such that the device size (chip size) enlarges.
An object of the invention is to provide a high frequency power amplifier module and a wireless communication apparatus having a high destruction resistance to a load fluctuation.
Another object of the invention is to provide a technique capable of preventing destruction of a transistor such as a heterojunction bipolar transistor caused by fluctuations in potential due to a contact of the operator or the like at the time of manufacture of the high frequency power amplifier module and a wireless communication apparatus.
Further another object of the invention is to provide a high frequency power amplifier module and a wireless communication apparatus which operate excellently even in a state where a source voltage is lower than 5V.
Further another object of the invention is to provide a technique of realizing a smaller high frequency power amplifier module and a smaller wireless communication apparatus.
The above and other objects and novel features of the invention will become apparent from the description of the specification and the appended drawings.
Disclosure of Invention
Representative ones of inventions disclosed in the application will be briefly described as follows.
(1) A high frequency power amplifier module has:
an input terminal;
an output terminal;
a first voltage terminal;
a second voltage terminal;
a bias supply terminal;
a first semiconductor amplifying device having a control terminal connected to the input terminal and the bias supply terminal, a first terminal connected to the first voltage terminal, and a second terminal connected to the second voltage terminal, for supplying a signal according to a signal supplied to the inpu
Fujita Takahiro
Hase Eiichi
Kagaya Osamu
Kusano Cyushiro
Ono Hideyuki
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Nguyen Patricia
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