Linear Power Amplifier Based On Wcdma

For implement of wide band modulation, multi-carries and elimination of adjacent channel interference to satisfy BER requirement in WCDMA system,which is most popular in 3G technology, the linearity requirement of the base station power amplifier becomes tighter. Feedforward is generally known as the best performing linearization technique for its advantages, such as broadband, stability, etc.This paper introduces the theories of power amplifier nonlinear characters and feedforward technique. According to the RF specifications in 3GPP for WCDMA transmitter power amplifier, an adaptive feedforward amplifier system is completed including EDA simulation, circuits layout and main mechanical structure design. Compared with traditional feedforward, this paper presents an adaptive control method based on power detection minimization. With strong and fast digital signal processing ability, the adaptive system can control feedforward amplifier parameters exactly and suppress non-linear products at last by detecting changes of signals and environments.Test results show that under 2-tone test in 5MHz tone spacing, the power amplifier system achieves -50dBc IMD3 with 20w output power, improved 20dB in IMD3 compared with the one without linearity. Estimated value of ACLR comes to 53dB,which satisfies the 3GPP requirement for WCDMA base-station transistor. Further tests with alterative input power indicate a steady suppression to the IMD3 controlled by the adaptive system.