Wave transmission lines and networks – Long line elements and components – Strip type
Reexamination Certificate
1999-08-19
2001-07-10
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Long line elements and components
Strip type
C333S128000, C333S033000
Reexamination Certificate
active
06259337
ABSTRACT:
BACKGROUND
The present invention relates generally to high power amplifiers, and more particularly, to an improved coplanar waveguide structure that forms an improved inductor for use with monolithic microwave integrated circuit high power amplifiers.
Prior art relating to monolithic microwave integrated circuit (MMIC) high power amplifier output matching circuit designs includes the following. Certain prior art MMIC high power amplifiers use microstrip based circuitry. Circuit loss diminishes with wider microstrip line width. The loss of the output matching circuit is of the order of 0.5 dB for conventional X-band power MMIC amplifiers. Microstrip based circuitry is not compatible with flip-chip module assembly techniques.
Other prior art MMIC high power amplifiers use a coplanar waveguide with a very wide signal carrying strip to meet dc current carrying requirements. Current crowding of coplanar waveguide with large strip-to-gap ratio leads to a low Q factor, and higher circuit loss. Flip-chip amplifier efficiency suffers when such lower Q, critical resonant circuit elements are employed.
It would therefore be desirable to have a coplanar waveguide structure for use with monolithic microwave integrated circuit high power amplifiers that improves upon conventional designs.
SUMMARY OF THE INVENTION
The present invention provides for a coplanar waveguide structure for use with a monolithic microwave integrated circuit high power amplifier. The coplanar waveguide structure comprises a coplanar transmission line segment having more than two ground plane electrodes and a plurality of signal/dc current carrying electrodes. The current carrying electrodes are each separated from an adjacent ground plane electrode by a gap. The coplanar waveguide structure forms an improved inductor for the monolithic microwave integrated circuit high power amplifier. A center ground plane electrode is preferably at least twice the width of the signal carrying electrode. The gaps between the signal carrying electrode and the ground electrodes are preferably at least one half the width of the signal carrying electrode to minimize current crowding.
The present invention uses a high Q planar inductor that is compatible with flip-chip MMIC technology. The effective width of the signal carrying metal strip is able to handle the dc current required for operation of the high power amplifier without risking current metal migration.
The present invention makes use of closely spaced, parallel coplanar waveguide (CPW) segments shorted at one end to form a shunt inductor at the output of high power flip-chip, monolithic microwave integrated circuit (MMIC) amplifiers. As a part of the output matching circuitry, the shunt inductors are at resonance with the drain-source capacitance of output-transistors at the RF signal frequency. Because there is less current crowding at the edge of the conductors, the coplanar inductor configuration offers higher circuit Q-factor compared with conventional CPW inductors with an identical strip width and characteristic impedance. The reduction in output matching circuit loss is critical to high efficiency operation of very high power flip-chip MMIC amplifiers, such as those used in active array radar.
The present invention improves the power added efficiency (PAE) of flip-chip, high power MMIC amplifiers for active array antenna applications. The present invention provides higher monolithic microwave integrated circuit amplifier efficiency through lower circuit loss at the output impedance transformer section. The use of a higher Q-factor coplanar inductor at the drain electrode of the output transistors serves to reduce signal loss per cycle. The reduction in RF power loss at the output of a high power amplifier directly impacts the power added efficiency of circuit operation. Higher RF amplifier efficiency leads to lower prime power demand, power supply size reduction, improved thermal management and lower system manufacturing cost.
The present invention may be used in all field effect transistor (FET) amplifiers, including MESFET and high electron mobility transistors (HEMT) based high power monolithic microwave integrated circuit (MMIC) amplifiers. The present invention will have beneficial impact on MMIC based, active array radar systems, and communication systems, developed by the assignee of the present invention.
REFERENCES:
patent: 5528203 (1996-06-01), Mohwinkel et al.
Alkov Leonard A.
Glenn Kimberly E
Lee Benny
Lenzen, Jr. Glenn H.
Raytheon Company
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