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A wideband radio frequency power amplifier (RF PA) is implemented with a stack of 16 low-breakdown-voltage thin-oxide transistors in a standard 45-nm CMOS SOI technology. A combination of dynamic-biasing and stacking prevents all breakdown mechanisms when the PA operates under large voltage swings and facilitates an output impedance close to 50 Ω without a need for an output-matching network. Using a post-fabrication process, the conductive Si substrate of the CMOS SOI PA is etched away and replaced by a semi-insulating aluminum nitride (AlN) substrate to reduce the effect of substrate parasitic capacitances and improve the PA's performance. A small-signal gain of 12.2 dB at 1.8 GHz is achieved with a - 3-dB bandwidth from 1.5 to 2.6 GHz. For high-reliability operation, the PA is biased with a 15-V power supply and a small transistor current density of 0.2 mA/μm and delivers a saturated output power (PSAT) of 30.2 dBm and a peak power-added efficiency (PAE) of 23.8%. For a wide range of measured frequencies from 1.5 to 2.4 GHz and under a lower supply voltage of 12 V, PSAT and P1 dB remain above 27.9 and 24.8 dBm, respectively, with peak PAE above 20%. In terms of output power, efficiency, and linearity, the CMOS PA on AlN substrate outperforms its Si counterpart, while both PAs deliver good power performance despite utilizing thin-oxide low-breakdown-voltage transistors.
Microwave Theory and Techniques, IEEE Transactions on (Volume:60 , Issue: 12 )
Date of Publication: Dec. 2012