Transistor with internal matching circuit

Details Transistor with internal matching circuit Transistor with internal matching circuit

2000-01-04

2001-08-28

Mottola, Steven J. (Department: 2817)

Amplifiers

With semiconductor amplifying device

Including frequency-responsive means in the signal...

C330S295000

Reexamination Certificate

active

06281756

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transistor with an internally impedance matched circuit for use in the microwave band and, more particularly, to such an internal matching transistor incorporated in the same package with a stabilizing circuit for preventing unwanted oscillation.
2. Description of Related Art
High output transistors operable in the microwave band used in satellites and mobile communications stations typically comprise semiconductor components and a matching circuit in the same package.
FIG. 8
shows the internal design of such a high output transistor, and
FIG. 9
is an equivalent circuit diagram for the high output transistor shown in FIG.
8
.
In the high output transistor
100
shown in
FIGS. 8 and 9
there are a plurality of semiconductor elements
101
, which are field effect transistors. An input impedance matching circuit
102
is disposed toward the microwave signal input side, and an output impedance matching circuit
103
is disposed toward the output side, of each semiconductor element
101
.
Bonding wires connect the semiconductor elements
101
to the input impedance matching circuit
102
and output impedance matching circuit
103
, the input impedance matching circuit
102
to package lead-throughs
104
, and the output impedance matching circuit
103
to package lead-throughs
105
.
The matching circuit in this type of internally impedance matched transistor circuit having a semiconductor element inside the same package typically includes striplines connected in series between the inputs and outputs of the semiconductor element and the wire inductance. The matching circuit is therefore usually a low-pass filter type circuit, and it is difficult to achieve a high-pass filter matching circuit. A low-pass filter matching circuit is a high impedance device in the frequency band in which a high frequency transistor is used, and a low impedance device in a low frequency band. Impedance is therefore also low in circuits external to the package at low frequency, the reflection coefficient increases at the reflection plane in a 50&OHgr; system and the stability coefficient is low. The system is therefore susceptible to low frequency oscillation.
Recent development of high output transistors has tended towards further increasing output, thus also increasing device size. As device size increases, input impedance drops and low frequency oscillation problems during high frequency band operation become even greater.
Internal matching circuits and transistors are also typically used with the top of the package sealed by a metal conductor or ceramic cover. This makes it difficult to add a new stabilization circuit internally to the package when anti-oscillation measures adding a stabilization circuit externally to the package are not effective.
It is to be noted that Japanese Patent Laid-open Publication No. 63-86904 teaches an internally impedance matched, high output field-effect transistor in which an anti-oscillation resistor is used between parallel connected transistors to suppress unnecessary oscillation in odd modes.
SUMMARY OF THE INVENTION
With consideration for the above-noted problems, it is an object of the present invention to provide an internally impedance matched transistor circuit for preventing low frequency oscillation during high frequency band operation by disposing an oscillation-preventing stabilization circuit comprising a resistor connected to ground through a capacitor.
To achieve this object, an internally impedance matched transistor circuit according to the present invention comprises, in a single package, a semiconductor element for signal processing a high frequency signal; an input impedance matching unit having an input impedance matching circuit for impedance matching between the semiconductor element and an input terminal to which a high frequency signal is applied from an external source, an output impedance matching unit having an output impedance matching circuit for impedance matching between the semiconductor element and an output terminal from which is output a high frequency signal processed by the semiconductor element, and an oscillation preventing stabilization circuit unit having an oscillation preventing stabilization circuit disposed proximally to the semiconductor element and comprising a resistor and a capacitor.
According to the present invention, the effects of gain drop in the fundamental frequency band can be reduced and a drop in gain in the low frequency band can be achieved, thereby suppressing unnecessary low frequency oscillation. Furthermore, by integrating a circuit for preventing oscillation in the same package, means for oscillation prevention are not necessary externally to the package.
The oscillation preventing stabilization circuit unit is preferably of a circuit design wherein the resistor and capacitor of the oscillation preventing stabilization circuit are connected in series with each other with the capacitor grounded, and the series circuit including the resistor and the capacitor is connected to the input terminal side of the semiconductor element.
Further preferably, a plurality of these semiconductor elements are connected in parallel to each other. In this case, adjacent semiconductor elements can be mutually connected by way of a resistor in the oscillation preventing stabilization circuit. It is therefore possible to suppress odd resonance mode loop oscillation
Capacitors of oscillation preventing stabilization circuits for adjacent semiconductor elements are preferably used in common. It is thus possible to reduce the number of capacitors, thereby reduce the number of packaged components, reduce the required packaging space inside the package, and thus reduce cost.
When a plurality of semiconductor elements are used, input and output terminals of adjacent semiconductor elements are further preferably used in common. In this case the same effects can be achieved when the output from two FETs (field-effect transistors) are passed as a composite output signal.
The capacitor of the oscillation preventing stabilization circuit is yet further preferably a surface oxidation type MOS capacitor. In this case an extremely thin dielectric can be achieved while required strength can be assured with the thickness of the underlying semiconductor layer. A low cost, high capacitance capacitor can thus be achieved in a small area, and cost can be reduced.
Further preferably, the capacitor and resistor of the oscillation preventing stabilization circuit are formed with the input impedance matching unit on a MOS substrate. It is thus possible to reduce the number of packaged components, reduce the required packaging space inside the package, and thus reduce packaging cost.


REFERENCES:
patent: 4631493 (1986-12-01), Vendelin et al.
patent: 5694085 (1997-12-01), Walker
patent: 5949287 (1999-09-01), Kurusu et al.
patent: 5955926 (1999-09-01), Uda et al.
patent: 6137367 (2000-10-01), Ezzedine et al.

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