Amplifiers – With semiconductor amplifying device – Including particular power supply circuitry
Reexamination Certificate
1999-12-28
2002-05-14
Shingleton, Michael B (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including particular power supply circuitry
C330S296000, C330S277000, C330S286000
Reexamination Certificate
active
06388530
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a microwave circuit and, more particularly, to a microwave amplifier implemented by field effect transistors.
DESCRIPTION OF THE RELATED ART
A typical application of the microwave amplifier is a power control for a transmitter incorporated in a wireless telephone. The output power of the wireless telephone is controlled by using the microwave amplifier, and a field effect transistor is the essential circuit component of the prior art microwave amplifier circuit. The gate voltage or the drain voltage is varied for controlling the output power as described hereinbelow.
FIG. 1
shows a typical example of the amplifier circuit. An input terminal
601
and an output terminal
602
are connected to the gate electrode of a field effect transistor
611
and the drain node of the field effect transistor
611
, respectively. The field effect transistor
611
serves as a main amplifier. A power source
641
is connected through a choking coil
613
to the drain node of the field effect transistor
611
, and the controller
612
is connected through a resistor
663
to the gate electrode of the field effect transistor
611
. The power source
641
supplies electric current through the choking coil
613
to the drain node of the field effect transistor
611
at all times. The field effect transistor
611
discharges part of the electric current through the source node thereof, and remaining electric current flows into the output terminal
602
. The controller
612
varies the potential level at the gate electrode of the field effect transistor
611
, and, accordingly, controls the gain of the field effect transistor
611
. As a result, the field effect transistor
611
varies the electric power at the output terminal
602
.
FIG. 2
shows another example of the amplifier circuit. The second prior art amplifier circuit also includes a field effect transistor
711
. An input terminal
701
and an output terminal
702
are connected to the gate electrode of the field effect transistor
711
and the drain node of the field effect transistor
711
, respectively. A power source
741
is connected through a dc-to-dc converter
739
and a choking coil
713
to the drain node of the field effect transistor
711
, and a gate bias terminal
712
is connected through a resistor
763
to the gate electrode of the field effect transistor
711
. The dc-to-dc converter
739
varies the potential level at the drain node of the field effect transistor
711
so that the field effect transistor
711
controls the electric power at the output terminal
702
. The dc-to-dc converter
739
is implemented by MOS (Metal-Oxide-Semiconductor) field effect transistors, which are fabricated on a silicon substrate. On the other hand, the field effect transistor
711
is usually fabricated on a compound semiconductor. A field effect transistor with a channel region of silicon is hereinbelow referred to as “field effect silicon transistor”, and a field effect transistor with a channel region of compound semiconductor is hereinbelow referred to as “field effect compound semiconductor transistor”.
Yet another example of the prior art amplifier circuit is disclosed in Japanese Patent Publication of unexamined Application No. 9-64757. The third prior art amplifier circuit detects an output electric power, and changes the drain voltage at drain nodes of field effect transistors incorporated in a power amplifier between two potential levels depending upon the output electric power. The drain node is connected to a variable dc voltage circuit or a dc-to-dc converter, and the two potential levels are selectively supplied to the drain node of the field effect transistor. With the two potential levels selectively supplied to the drain node, the power amplifier is expected to offer linear input-to-output characteristics. A pulse width modulation converter is usually used for the dc-to-dc converter, and MOS field effect silicon transistors form the pulse width modulation converter. MES (Metal-Semiconductor) field effect compound semiconductor transistors form the power amplifier. However, bipolar transistors, MOS field effect silicon transistors and heterobipolar transistors are available for the power amplifier.
Following problems are encountered in the above-described prior art amplifier circuits. The problems inherent in the first prior art amplifier circuit are a low efficiency and a distortion. This is because of the fact that the controller
612
varies the biasing voltage at the gate electrode of the field effect transistor
611
.
The problem inherent in the second prior art amplifier circuit is a low power efficiency, a difficulty in integration on a single semiconductor chip and poor response characteristics. The low efficiency, the difficulty and the poor response characteristics are derived from the dc-to-dc converter
739
. As described hereinbefore, the dc-to-dc converter
739
is implemented by the field effect silicon transistors, and are low in switching speed. The second prior art amplifier circuit is expected to control the output power at a highspeed. However, the dc-to-dc converter can not respond to the high-speed power control due to the low switching speed of the field effect silicon transistors. This results in the poor response. The efficiency of the dc-to-dc converter
739
is of the order of 85 to 90 percent, and the field effect silicon transistors incorporated therein decrease the efficiency together with decrease of the power voltage. As a result, the second prior art amplifier circuit can not achieve a high power efficiency. It is difficult to integrate the field effect compound semiconductor transistor
711
and the field effect silicon transistors of the dc-to-dc converter on a single semiconductor chip. If the field effect compound semiconductor transistor is replaced with a field effect silicon transistor, a silicon substrate is shared between the field effect silicon transistor and the field effect silicon transistors of the dc-to-dc converter
739
. However, the field effect silicon transistors are designed to have a wide channel in order to decrease the series resistance. This means that the field effect silicon transistors and the dc-to-dc converter
739
occupy wide real estate on the silicon substrate. For this reason, the second prior art amplifier circuit requires a large-sized silicon chip. The large-size silicon chip makes the integration difficult from the viewpoint of production cost.
A problem inherent in the third prior art amplifier circuit is high production cost. The third prior art amplifier circuit changes the drain voltage between two potential levels depending upon the detected output power. The change of the drain voltage aims at a constant power gain and, accordingly, good linearity over a wide output power range. The set drain current is made constant in a lower power operation mode for the good linearity. The output power is detected by using an output power envelope detecting circuit. The output power envelope detecting circuit is a large electric circuit, and is expensive. This results in the high production cost of the third prior art amplifier circuit.
SUMMARY OF THE INVENTION
It is therefore an important object of the present invention to provide a microwave amplifier circuit, which is high in efficiency in a low output power operation, small in distortion and easy for integration on a single semiconductor chip.
In accordance with one aspect of the present invention, there is provided a microwave amplifier circuit comprising a field effect transistor serving as a main amplifier and a drain bias controlling circuit including a power source for generating an electric power and first heterojunction field effect transistors formed of compound semiconductor and serving as switching units electrically connected between the power source and a drain node of the field effect transistor and selectively changed between on-state and off-state so as to vary a drain voltage applied to the drain node.
REFERENCES:
patent: 5081511 (1992
Iwata Naotaka
Nishimura Takeshi
Rosenman & Colin LLP
Shingleton Michael B
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