An adaptive predistortion RF power amplifier with a spectrum monitor for multicarrier WCDMA applications

This paper presents an adaptive predistortion RF power amplifier for repeater systems with a spectrum monitor. For adaptive control of cancellation, we implement a spectrum monitor that improves the adjacent channel leakage ratio (ACLR) characteristics of the power amplifier by analyzing the output spectrums of RF power amplifiers directly and simultaneously. For experimental validation, we also implement a class-AB RF power amplifier that adopts a predistortion linearizer with the spectrum monitor and measure the characteristics for the wide-band code division multiple access (WCDMA) band. With an optimum gate bias voltage of the power amplifier, ACLRs of 22 and 20.5 dB are improved for the cases of one- and four-carrier WCDMA applications, respectively. The predistortion power amplifier with the spectrum monitor delivers a P_out of 37.5 dBm with an ACLR of -45 dBc for four-carrier WCDMA applications. Furthermore, excellent ACLR characteristics are consistently maintained with the minimization algorithm by adaptively controlling the vector modulator in the predistorter under various environments that include varying input power levels, temperatures, and operating frequencies