Memory effect minimization and wide instantaneous bandwidth operation of a base station power amplifier

Abstract

Linear amplification and reduction of the memory effect of a wide bandwidth signal have been realized for a next generation base station power amplifier. Using a simple nonlinear LDMOS model, the third-order intermodulation distortion current is analyzed using a third-order power series. The limitations in shorting the envelope and second harmonics are studied. From the analysis, it is proven that the envelope is a more critical component than the second harmonic for the memory effect and linearity. In order to minimize the envelope voltages, a new matching topology is proposed, which consists Of a series LC circuit for shorting the device at a low frequency while maintaining a matchable impedance at the operating frequency. The proposed power amplifier was constructed using a 90 W PEP LDMOSFET at a 2.14 GHz, center frequency and tested for two-tone and multi-carrier WCDMA signals. The test results show that the memory effect and nonlinearity are drastically reduced for the proposed amplifier. For the two-tone signals, an asymmetry of less than 2 dB up to 60 MHz tone spacing is achieved for the IMD3 and up to 40 MHz for the IMD5. For the WCDMA 20FA signal with a bandwidth of 100 MHz, a linearity improvement of approximately 15 dB is achieved by minimizing the envelope impedances.