This paper presents a novel CMOS bias topology serving as not only a bias circuit but also an adaptive linearizer for SiGe HBT power amplifier (PA) IC. The novel bias circuit can well keep the base-to-emitter voltage (V<inf>be</inf>) of RF amplifying HBT constant and adaptively increase the base current (I<inf>b</inf>) with the increase of the input power. Therefore, the gain compression and phase distortion performance of the PA is improved. A three-stage 5-GHz band PA IC with the novel bias circuit for WLAN applications is designed and fabricated in IBM 0.35 μm SiGe BiCMOS technology. Under 54 Mbps OFDM signal at 5.4 GHz, the PA IC exhibits a measured small-signal gain of 29 dB, an EVM of 0.9% at 17 dBm output power and a DC current consumption of 284 mA.
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