Watt-Level CMOS Doherty Power Amplifier

Toshiba has developed a 2.4 GHz complementary metal-oxide semiconductor (CMOS) Doherty power amplifier (PA) capable of watt-level output power. For radio-frequency (RF) PAs, CMOS implementation has recently been required to reduce the size, lower the cost, and improve the performance of mobile devices. However, CMOS implementation degrades the peak output power and efficiency of a PA. To overcome these problems, Doherty PA technology was utilized to enhance the output power of CMOS PAs. A Doherty PA generally consists of main- and sub-PAs, and improves power efficiency by turning off the sub-PA in the low output power range.

2.4 GHz 1.1 W CMOS Doherty PA

The newly developed Doherty power combiner uses a 65 nm CMOS process and reduces magnetic interference between passive components while requiring less than half the area for passive components compared with conventional combiners. The new combiner also provides the world's highest peak output power(*) of 1.1 W for a CMOS Doherty PA and achieves a power-added efficiency of 23% at the 6 dB power back-off level, which is a performance index used to determine whether to use a PA in wireless local area network (LAN) terminals. Degradation of device reliability is one of the challenges to be solved when fabricating a Doherty PA with a deepsubmicron, low-threshold-voltage CMOS process. As a solution, we developed a reliability enhancement technique that is expected to provide an approximately 75% improvement in theoretical time-to-failure (TTF) for IEEE 802.11b wireless LAN signals.

(*) As of June 2012, at the 2012 IEEE Symposium on VLSI Circuits (as researched by Toshiba)

IEEE: Institute of Electrical and Electronics Engineers

Output spectra of wireless LAN (IEEE 802.11b/g) signals