ISSCC news: Fujitsu tips 77GHz CMOS PA

Feb. 4, 2008 – At this week’s International Solid-State Circuits Conference (ISSCC), Fujitsu Labs says it will show a power amplifier (PA) built with 90nm process technologies that operates at 77Ghz, realizing CMOS RF frontend circuitry with a power amplifier that integrates with baseband circuitry on a chip, for use in millimeter-wave automotive radar systems.

Typically, compound semiconductors have been used in the RF frontend circuits of millimeter wave systems to realize high gain and output of high-frequency signals, though CMOS technology offers high levels of integration and functionality and has been making strides in operational speeds due to miniaturization, Fujitsu notes in a statement. But significant signal loss has been a persistent barrier to application of standard CMOS technology in millimeter-wave circuitry, and boosting gain in an amplifier requires taking into account parasitic capacitance, and suppressing signal loss in a matching circuit.

In a statement, Fujitsu explained the two technology developments it says enables use of standard CMOS technology in millimeter-wave amplifiers. First were models to show operating characteristics for transistors and passive components at millimeter-waveband, and parameter extraction. Also, researchers optimized the structure of transmission lines, capacitors, and other passive components, and developed structures to minimize resistive losses.

Second, they developed a “short stub” matching circuit (meaning one end of the transmission line is connected to the inside of the circuit, and the other to a power source or ground, so that the RF signal electrical potential is always zero), and integrated it with the power-supply circuitry in a way that further reduces signal losses to 0.4dB. This also shrinks the matching circuit’s required chip space by 90%.

The combination of these two technologies resulted in a PA operating at 77GHz, achieving 8.5dB gain and 6.3dBm saturated output power, showing the ability to implement 77GHz automotive radars using inexpensive standard CMOS technologies, the company notes. It also made a 60GHz version with 8.3dB gain and 10.6dBm saturated power output, showing the technology also can extend the transmission range of wireless communications to the 60GHz band. Future work will focus on increasing output power.

Combining baseband circuitry with RF frontend circuitry on one chip also saves chip real estate, the company added, opening up opportunities in automotive radar systems and wireless communications systems.


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