Composite transistor device

Details Composite transistor device Composite transistor device

1999-11-12

2001-06-05

Pascal, Robert (Department: 2817)

Amplifiers

With semiconductor amplifying device

Including plural amplifier channels

C330S307000

Reexamination Certificate

active

06242985

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a semiconductor device for a high-frequency power amplifier, and more particularly, to a semiconductor device which forms a high-frequency power amplifier accommodated in a transmitter of a mobile communication equipment such as a portable telephone.
2. Related Art
A mobile communication system has been widely utilized for radio-frequency communication between a number of pieces of mobile communication equipment and base stations located at distance in a service area. Such communication system is realized as a portable telephone or the like. A typical portable telephone comprises a transmitter section including a sonic-electric converter, modulator, frequency converter, and radio-frequency (RF) power amplifier.
The high-frequency (RF) power amplifier of a transmitter section of a portable telephone is required to carry out high-quality power-amplification of digitally modulated high-frequency signals of 2 GHz band. Most of conventional high-frequency power amplifiers are formed by single-ended circuits which have a proven track record in hybrid ICs. Recently, various attempts have been made to configure a high-frequency power amplifier by a balanced amplifier circuit such as a differential amplifier circuit comprised of a pair of high-frequency transistors of a common emitter type.
As schematically shown in
FIG. 1
, a high-frequency power amplifier
200
of transmitter section of a portable telephone is configured to amplify a high-frequency signal Sp, Sn which is balanced-input through bases of a pair of high-frequency transistors
1
and
2
, and output the amplified high-frequency signal to inductive load
4
and
5
connected to collectors of these transistors
1
and
2
. A transistor
3
connected to emitters of the transistors
1
and
2
serves as a constant current source for determining the bias current for these transistors.
As shown in
FIG. 2
, each of the transistors
1
,
2
and
3
is formed in actual by a transistor cell
12
comprised of parallel-connected high-frequency transistors (hereinafter referred to as transistor elements)
11
each having a desire high-frequency characteristic. More specifically, the transistor elements
11
forming each transistor cell
12
are formed in array on a semiconductor substrate. For instance, each transistor element has a device configuration (not shown) having emitter and collector regions between which a base region is provided. The transistor elements
11
have their emitter electrodes E, base electrodes B and collector electrodes C which are formed as exemplarily shown in FIG.
3
and connected to electrode wiring patterns
13
,
14
and
15
, respectively. Ordinarily, each transistor cell
12
composed of transistor elements
11
serves as a single transistor having a desired high-frequency characteristic and a required current capacity (rated current).
In the case of a high-frequency power amplifier for use in a portable telephone, each of the transistors
1
,
2
and
3
is formed by a group of transistors (hereinafter referred to as a composite transistor)
16
so as to attain a power handling capacity (rated power) corresponding to a maximum transmitting power output, each composite transistor
16
being composed of a required number of parallel-connected transistor cells
12
, as exemplarily shown in
FIG. 4. A
high-frequency signal is power-amplified by the transistors
1
and
2
, and the bias current level for the transistors
1
,
2
is adjusted by the transistor
3
.
The high-frequency power amplifier having the transistors
1
and
2
composed of the composite transistors
16
may produce a low-quality power-amplified high-frequency signal, due to the difference between operation characteristics of the two composite transistors
16
. Even if the two groups of the transistor cells forming the two composite transistors
16
are formed monolithically on the semiconductor substrate with the intention of equalizing their operation characteristics, the operation characteristics may vary, in a strict sense, among individual transistor cells
12
due to the differences between positions on the substrate where these transistor cells
12
are formed. In the power amplifier shown in
FIG. 4
, one group of transistor cells
12
forming one composite transistor
16
serving as the transistor
1
are formed on one end of the semiconductor substrate, whereas another group of transistor cells
12
forming another composite transistor
16
serving as the transistor
2
are formed on another end of the substrate. Due to such a positional difference between these two transistor cell groups, a certain difference appears between their operation characteristics, resulting in low-quality power amplification of a high-frequency signal.
It is preferable for the power-amplified high-frequency signal to satisfy such a requirement on the balance characteristic that “high-frequency signal currents appearing at two output lines of a power amplifier be the same in magnitude and opposite in phase.” Depending on a layout of electrode wiring patterns through which associated electrodes of the transistor cells
12
are connected, the power-amplified high-frequency signal can have unsatisfactory balance characteristic.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device suited to configure a power amplifier for performing stable, high-quality power amplification of a high-frequency signal, while guaranteeing the balance characteristic of the high-frequency signal.
According to the present invention, there is provided a semiconductor device for a high-frequency power amplification. This semiconductor device comprises: a first composite transistor comprised of parallel-connected first transistor cells comprised of parallel-connected transistor elements; a second composite transistor comprised of parallel-connected second transistor cells comprised of parallel-connected transistor elements; first and second input wiring patterns connected to input ends of said first and second composite transistors, respectively; first and second output wiring patterns connected to output ends of said first and second composite transistors, respectively; and a semiconductor substrate formed with said first and second composite transistors, said first and second input wiring patterns, and said first and second output wiring patterns. The first and second transistor cells are alternately arranged one another to form a transistor cell array in which adjacent ones of the first and second transistor cells are close to each other. The first and second input wiring patterns and said first and second output wiring patterns extend in an arraying direction of the first and second transistor cells in the transistor cell array. The first and second composite transistors operate to balanced-input a high-frequency signal through said first and second input wiring patterns, perform power-amplification of the high-frequency signal, and output the power-amplified high-frequency signal from said first and second output wiring patterns.
In the semiconductor device of this invention, the power handling capacity of each composite transistor can be appropriately determined by selecting the number of the transistor cells forming the composite transistor and/or the number of transistor elements forming each transistor cell. Thus, the present invention can provide various types of power amplifier including a power amplifier for a transmitter section of a portable telephone required to produce a relatively large maximum transmitting output. In addition, the power amplifier of this invention is capable of performing stable, high-quality power amplification of high-frequency signals.
In the semiconductor device of this invention, the first and second transistor cells are alternately arranged, whereby transistor-cell pairs are formed. The first and second transistor cells forming each transistor-cell pair are formed in the semiconductor substrate so as to be adjac

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