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multiple parallel transistors in the power splitter circuit. After the signal is amplified by each transistor, it is combined again using the combiner circuit, thereby enabling high-power output. At frequencies above 70 GHz, however, due to the interference of high-frequency complex signal distribution, the signal undergoes attenuation in the power splitter and combiner circuits, preventing the achievement of the desired power output. As a result, it was necessary to construct a power splitting and combination model for use in the millimeter-wave band, and develop a design that takes the complex signal distribution into consideration while enabling the desired output to be achieved.
Newly Developed Technology
Fujitsu developed the following technologies in order to resolve the aforementioned issues.
(1) Optimizing the GaN HEMT passivation layer
After analyzing the reason why electrons escaped from the electron channel layer and accumulated in the passivation layer, Fujitsu traced the issue to the existence of defects in the crystallization of the SiN used as part of the passivation layer. By enhancing the layer’s SiN composition and crystalline structure, Fujitsu was able to build a passivation layer with minimal crystalline defects, making it difficult for electrons to accumulate. As a result, the technology was successful in amplifying high- frequency current to over two times the power of existing technology.
(2) Building a power division and combination model through electromagnetic analysis
By performing electromagnetic analysis on the complex signal distribution of the high-frequency signal, based on the physical properties of the power splitter and combiner circuits, Fujitsu successfully designed a highly precise circuit that reduces signal attenuation in the two circuits. As a result, Fujitsu was able to increase design precision by roughly 15%.
Results
The above technologies were employed to develop a power amplifier for use in millimeter-wave W-band wireless equipment. The newly developed amplifier
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www.compoundsemiconductor.net October 2010
Fujitsu and Fujitsu Laboratories plan to work to further improve the performance and expand the frequency spectrum of the new GaN HEMT power amplifier, while at the same time employing the technology in a wide range of applications, including millimeter-wave-enabled trunk lines and ultra-high- speed wireless network access.
Notes
(1) Gallium-nitride (GaN): A wide band-gap semiconductor material that operates stably at high temperatures and with a higher breakdown-voltage than semiconductor technologies based on previous materials, such as silicon (Si)- or gallium-arsenide (GaAs)-based technologies.
(2) High Electronic Mobility Transistor (HEMT): A field-effect transistor that takes advantage of operation of the electron layer at the boundary between different semiconductor materials that is relatively rapid compared to that within conventional semiconductors. Fujitsu pioneered its development in 1980, and the technology now underpins much of today’s ICT infrastructure, including satellite transceivers, wireless equipment, GPS-based navigation systems, and broadband wireless networking systems.
(3) W-band: Name for the radio band from 75 to 110 GHz. Used for high-speed wireless
achieves a maximum output of 1.3W, which, among GaN HEMT power amplifiers, represents the world’s highest output in this frequency band using single integrated circuit.
Furthermore, the new technology achieves a transmission output equivalent to 16 times that of existing amplifiers that use GaAs. When employed in combination with the GaN HEMT receiver amplifier developed by Fujitsu last year, it is expected that transmission ranges will be able to be extended by approximately six times in comparison to transceivers that employ GaAs. This will enable millimeter-wave band wireless communications equipment to be deployed in a wider range of fields, while at the same time ensuring high-quality communications in which ample signal output can be obtained even when there is signal attenuation due to rain and other factors.
Future Developments
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