This single-transistor circuit performs comparably to a prior four-transistor circuit.

Figure 1 shows a single-stage monolithic microwave integrated circuit (MMIC) power amplifier in which the gain element is a double-heterojunction bipolar transistor (DHBT) connected in common-base configuration. This amplifier, which has been demonstrated to function well at a frequency of 172 GHz, is part of a continuing effort to develop compact, efficient amplifiers for scientific instrumentation, wide-band communication systems, and radar systems that will operate at frequencies up to and beyond 180 GHz. The transistor is fabricated from a layered structure formed by molecularbeam epitaxy in the InP/lnGaAs material system. A highly doped InGaAs base layer and a collector layer are fabricated from the layered structure in a triple mesa process. The transistor includes two separate emitter fingers, each having dimensions of 0.8 by 12 µm. The common-base configuration was chosen for its high maximum stable gain in the frequency band of interest. The input-matching network is designed for high bandwidth. The output of the transistor is matched to a load line for maximum saturated output power under large-signal conditions, rather than being matched for maximum gain under small-signal conditions.

Figure 1. This Common-Base, Single-Transistor Amplifier is designed to provide useful power gain in the frequency band of 170 to 180 GHz.
In a test at a frequency of 172 GHz, the amplifier was found to generate an output power of 7.5 mW, with approximately 5 dB of large-signal gain (see Figure 2). Moreover, the amplifier exhibited a peak small-signal gain of 7 dB at a frequency of 176 GHz. This performance of this MMIC single-stage amplifier containing only a single transistor represents a significant advance in the state of the art, in that it rivals the 170-GHz performance of a prior MMIC three-stage, four-transistor amplifier. [The prior amplifier was reported in “MMIC HEMT Power Amplifier for 140 to 170 GHz” (NPO-30127), NASA Tech Briefs, Vol. 27, No. 11 (November 2003), page 49.]

Figure 2. These Gain and Output-Power Curves were derived from measurements on the amplifier of Figure 1 at a frequency of 172 GHz.
This amplifier is the first heterojunction- bipolar-transistor (HBT) amplifier built for medium power operation in this frequency band. The performance of the amplifier as measured in the aforementioned tests suggests that InP/lnGaAs HBTs may be superior to high-electron-mobility (HEMT) transistors in that the HBTs may offer more gain per stage and more output power per transistor.

This work was done by Vamsi Paidi, Zack Griffith, Yun Wei, Mattias Dahlstrom, Miguel Urteaga, and Mark Rodwell of the University of California at Santa Barbara and Lorene Samoska, King Man Fung, and Erich Schlecht of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Semiconductors & ICs category.

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Refer to NPO-40956, volume and number of this NASA Tech Briefs issue, and the page number.

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