Fujitsu Laboratories has developed a millimetre-waveband power amplifier (PA) using standard 90nm CMOS process technology.
Targeting millimetre-wave applications, Fujitsu Labs developed a standard CMOS modelling technology and design techniques to minimise high-frequency signal loss, thereby enabling the development of a CMOS-based PA that operates at 77GHz.
The technology realises 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 millimetre-wave automotive radar systems.
This technology will be presented at the International Solid-State Circuits Conference (ISSCC) 2008 to be held in San Francisco from February 3-7. (Session 31.3).
The millimetre 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 millimetre 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 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 millimetre wave circuits to achieve operation that was previously achieved through compound semiconductors.
Practical application of standard CMOS technology in millimetre-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 millimetre-wave amplifiers.
Modelling technology for transistors and passive components operating in the millimetre waveband
Fujitsu Labs established a transistor model that shows the operating characteristics at millimetre-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.
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).
Results
The combination of these two technologies resulted in a 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 millimetre-waveband technologies in both automotive radar systems and wireless communications systems is anticipated in the future.
Future developments
Fujitsu Labs 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 millimetre-wave automotive radar systems and wireless communications systems.