Field effect transistor including stabilizing circuit

Details Field effect transistor including stabilizing circuit Field effect transistor including stabilizing circuit

2000-02-23

2001-10-16

Ngô ;, Ngâ ;n V. (Department: 2814)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Junction field effect transistor

C257S275000, C257S277000, C257S379000, C257S401000

Reexamination Certificate

active

06303950

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a field effect transistor (FET) used for a power amplifier and, more particularly, to an FET comprising a stabilization circuit between a connecting portion of a gate electrode and a source electrode.
A power amplifier with an FET is required the FET to be stabilized, without oscillating in a frequency range in which the power amplifier is used. Therefore, the typical power amplifier includes a stabilization circuit in order to stabilize the FET.
FIG. 9
shows a circuit diagram of a conventional power amplifier comprising an external stabilization circuit
34
. As shown in the drawing, an input matching circuit
32
is connected to an input terminal of the FET
31
, and an output matching circuit
33
is connected to its output terminal. An external stabilization circuit
34
is connected between a gate electrode and the input matching circuit
32
of the FET
31
, so that the power amplifier is stabilized. The external stabilization circuit
34
is designed according to a measurement of S parameters of the FET
31
.
In this arrangement, an input matching circuit
32
as well as the external stabilization circuit
34
are formed in the circuit of the power amplifier. In this instance, the external stabilization circuit
34
can be arranged close to other circuit elements. This results in an interaction between the external stabilization circuit
34
designed according to the S parameters interact with other circuit elements to dissatisfy the stabilization requirements, which disadvantageously causes oscillation the FET
31
.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an FET having a stabilization circuit whose stabilization condition will not be affected by an other circuit element, for example, a matching circuit.
To this end, the inventors of the present invention have made intensive researches on this subject. As a result, the inventors have found that, by forming a stabilization circuit in an FET and thereby pre-stabilizing the FET in a frequency range in which a power amplifier is used, no variation will occur in a stabilization requirement for the FET, which would otherwise be caused by arranging another circuit in the vicinity of the FET.
That is, present invention provides a field effect transistor for use in a power amplifier, comprising: at least one unit including gate, source, and drain electrodes; and wherein said gate electrode includes a finger portion extending between said source and drain electrode; a connecting portion electrically connecting said finger electrode to a common electrode; and a stabilizing circuit electrically connecting said connecting portion to said source electrode in the same unit.
The stabilization circuit is pre-formed to connect between the gate electrode and the connecting portion, so that no external stabilization circuit for the field effect transistor is needed on the designing process of the power amplifier. This means that, only the impedance matching to the FET at the input and output terminals is considered in the designing of the power amplifier.
Also, this prevents an interaction between microwaves passing through the stabilization circuit and the matching circuit or the like. Thereby, a predetermined microwave characteristic can be provided to the power amplifier.
Also, the present invention provide the field effect transistor, wherein said connecting portion extends vertically from said common electrode in a comb-like fashion.
By providing the stabilization circuits between each of the connecting portions and the electrode portion respectively, the interaction between microwaves passing through the stabilization circuit and a matching circuit or the like can be prevented.
The stabilization circuit preferably includes a resistor and a capacitor, the resistor and capacitor being connected in series.
The capacitor is preferably an MIM capacitor.
The finger portion preferably has a first and second layers positioned one on top the other, said first layer being made of tungsten silicide and said second layer being made of gold, and said resistance has a third layer made of tungsten silicide and also formed in the formation of said first layer.
It is because a producing process can be simplified by using such a resistor.
It is preferable that the field effect transistor further comprises a substrate having first and second surfaces, said first surface supporting said source electrode and said second surface supporting another electrode, said substrate being formed with a via-hole extending between said first and second surfaces for electrically connecting said source and another electrodes.
It is because the source electrodes of the field effect transistor have the same electric potential.
Also, the present invention provides a monolithic microwave integrated circuit, which comprises the field effect transistor mentioned above.
It is because the use of the field effect transistor allows the monolithic microwave integrated circuit to eliminate the stabilization circuit as the external circuit of the field effect transistor.
Also, the present invention provide a method for designing a power amplifier having a field effect transistor, comprising the steps of: (a) providing said field effect transistor having a stabilizing circuit which stabilizes said field effect transistor in a frequency range in which said power amplifier operates; and (b) designing an input matching circuit so that an input impedance of said field effect transistor matches with an impedance of a circuit connected to a input terminal of said field effect transistor, and an output matching circuit so that an output impedance of said field effect transistor matches with an impedance of a circuit connected to an output terminal of said field effect transistor in a frequency range in which said power amplifier operates.
By using the designing method of the present invention, no consideration should be made to stabilize the field effect transistor, except for the matching of the impedance at input and output terminals of the field effect transistor. This simplifies the designing process and increases the design efficiency.
The step (a) preferably comprises preparing a plurality of said field effect transistors having respective gates each of which having different widths; and said step (b) is preferably performed for each of said plural field effect transistors.
As can be seen from the above description, the FET of the present invention comprises the stabilization circuit in the FET. Therefore, in the process of designing the power amplifier, no need should be made to design the stabilization circuit, which considerably simplifies the design process of the power amplifier.
Also, an interaction between microwaves passing through a matching circuit or the like formed outside of the FET and the stabilization circuit can be prevented, which ensures a required high frequency characteristic to the FET.


REFERENCES:
patent: 6177834 (2001-01-01), Blair et al.
patent: 6120414 (1994-04-01), None
patent: 9283710 (1997-10-01), None
patent: 1083998 (1998-03-01), None

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