77GHz CMOS-based Power Amplifier

Fujitsu Laboratories, Ltd. has developed a millimeter-waveband power amplifier (PA) using standard 90nm CMOS process technology. Targeting millimeter-wave applications, Fujitsu Labs developed a standard CMOS modeling technology and design techniques to minimize high-frequency signal loss, thereby enabling the development of the world’s first CMOS-based PA that operates at 77GHz. The technology realizes CMOS radio frequency (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 ideal for measuring with high resolution and accuracy the distance between two points, as well as for high-capacity data transmission. As such, the millimeter wave is starting to be applied to automotive radar systems and to wireless transmission systems. Typically, compound semiconductors have been used in the RF front-end circuits of these systems in order to realize 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 miniaturization – 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.

Fujitsu Labs developed the following two technologies that make it possible to apply standard CMOS technology to millimeter-wave amplifiers.

  1. Modeling technology for transistors and passive components operating in the millimeter waveband
    Fujitsu Labs established a transistor model that shows the operating characteristics at millimeter-waveband and developed parameter-extraction method technology. Researchers also optimized the structure of transmission lines, capacitors, and other passive components, and developed structures that minimize resistive losses.
  2. 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 previous levels, and also reduced signal loss to 0.4 decibels (0.4 dB).

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

Fujitsu Labs’ new technology makes it possible to implement 77GHz automotive radars 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 – which had been expensive to produce in the past – 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 plans to utilize 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.

More info: Fujitsu Laboratories