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4 February 2008


Fujitsu presents first 77GHz CMOS-based PA

At this week’s International Solid-State Circuits Conference (ISSCC) 2008 in San Francisco, CA, USA (3-7 February), Fujitsu Laboratories Ltd of Tokyo, Japan is presenting what it claims is the world’s first CMOS-based power amplifier (PA) that operates at a frequency of 77GHz.

The millimeter-wave PA uses standard 90nm CMOS process technology, with standard CMOS modeling technology and design techniques developed to minimize high-frequency signal loss. The technology enables the realization of CMOS RF front-end circuitry that includes a PA, allowing integration with baseband circuitry on a single chip. for use in millimeter-wave automotive radar systems.

Picture: Fujitsu Labs' 77GHz CMOS PA.

Such millimeter-wave circuitry is suited to measuring the distance between two points with high resolution and accuracy (and is hence starting to be applied to automotive radar systems), as well as being used for high-capacity data transmission in wireless systems.

RF front-end circuits of such systems typically use compound semiconductors to realize high gain and output of high-frequency signals. However, for CMOS technology, which allows high levels of integration and functionality, ongoing miniaturization has enabled silicon-based millimeter-wave circuits with comparable operating speeds, says Fujitsu.

Practical application of standard CMOS technology in millimeter-wave circuitry has been problematic due to the occurrence of significant signal loss. To boost the gain in an amplifier, a number of factors 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.

Fujitsu Labs says that, to enable it to apply standard CMOS technology to millimeter-wave amplifiers, it developed the following technologies:

Modeling technology for millimeter-wave transistors and passive components

Fujitsu Labs says that it established a transistor model that shows the operating characteristics in the millimeter waveband and developed parameter-extraction technology. Researchers also optimized the structure of transmission lines, capacitors, and other passive components, and developed structures that minimize resistive losses.

Matching circuit design

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 of the previous levels, and also reduced signal loss to 0.4dB.

Combining these technologies resulted in the first PA operating at 77GHz to achieve 8.5dB gain and 6.3dBm saturated output power. Also, a separate PA operating at 60GHz has been developed that achieves 8.3dB of gain and 10.6dBm saturated output power.

Picture: Input-output characteristics for Fujitsu Labs' 77GHz CMOS PA.

Fujitsu Labs reckons that its new technology makes it possible to implement 77GHz automotive radar using inexpensive standard CMOS technologies. These developments could also be used to extend the transmission range of wireless communications systems in the 60GHz band.

Furthermore, by combining baseband circuitry with RF front-end circuitry on one chip, millimeter-waveband transceiver chips can now be made considerably smaller. As a result, widespread application of millimeter-waveband technologies in both automotive radar systems and wireless communications systems is anticipated in the future.

Fujitsu Labs says it plans to use standard CMOS technologies to further develop amplifier circuits with higher output power, as well as integrated RF front-end circuits.

See related items:

Infineon ships first CMOS RF switch on silicon with GaAs performance

Axiom shipped 10 million CMOS PAs in 2007