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CMOS-based PA operates at 77GHz

Posted: 07 Feb 2008     Print Version  Bookmark and Share

Keywords:power amplifier  CMOS technology  millimeter wave 

Fujitsu Laboratories Ltd has developed a millimeter-waveband power amplifier (PA) using standard 90nm CMOS process technology.

The company developed a standard CMOS modeling technology and design techniques to minimise high-frequency signal loss to produce what it claims to be the first CMOS-based PA that operates at 77GHz. The technology realises CMOS RF front-end circuitry that includes a PA, thereby enabling integration with baseband circuitry on a single chip, for use in millimeter-wave automotive radar systems.

The millimeter wave is designed for measuring with high resolution and accuracy the distance between two points, as well as for high-capacity data transmission. The millimeter wave is starting to be applied to automotive radar systems and wireless transmission systems. Typically, compound semiconductors have been used in the RF front-end circuits of these systems in order to realise high gain and output of high-frequency signals. On the other hand, for CMOS technology, which features high levels of integration and high-functionality, progress has been made in regard to operational speeds—attributable to ongoing miniaturisation—and it is now possible to apply millimeter wave circuits to achieve operation that was previously achieved through compound semiconductors.

Practical application of standard CMOS technology in millimeter-wave circuitry has been problematic due to the occurrence of significant signal loss. In order to boost the gain in an amplifier, a number of factors that are not evident on a circuit diagram, such as parasitic capacitance, need to be accurately reflected. In addition, signal loss in a matching circuit needs to be suppressed to enable maximum amplification performance.

Combined technologies
Fujitsu Labs developed two technologies that make it possible to apply standard CMOS technology to millimeter-wave amplifiers—Modeling technology and Matching circuit design. Fujitsu Labs established a transistor model that shows the operating characteristics at millimeter-waveband and developed parameter-extraction method technology. Researchers also optimised the structure of transmission lines, capacitors, and other passive components, and developed structures that minimise resistive losses.

To keep the circuitry compact, Fujitsu Labs developed a "short stub" matching circuit and integrated it with the power-supply circuitry in a way that would further reduce signal losses. This reduced the amount of chip space required by the matching circuit to one-tenth previous levels, and also reduced signal loss to 0.4dB.

The combination of the two technologies resulted in the first PA operating at 77GHz to achieve 8.5dB gain and 6.3dBm saturated output power. Furthermore, a separate PA operating at 60GHz was developed and achieved 8.3dB of gain and 10.6dBm saturated output power.

Furthermore, by combining baseband circuitry with RF front-end circuitry on one chip, millimeter-waveband transceiver chips—which had been expensive to produce in the past—can now be made considerably smaller. Widespread application of millimeter-waveband technologies in both automotive radar systems and wireless communications systems is anticipated in the future.

The company plans to utilise standard CMOS technologies to further develop amplifier circuits with higher output power, and integrated RF front-end circuits. Leveraging these technologies, Fujitsu Labs will conduct research to develop chips for millimeter-wave automotive radar systems and wireless communications systems.




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