Research On Linc Transmitter Techniques

With the development of modern wireless communication techniques, efficient spectrum modulation technique is used widely. As is known to all, efficient spectrum modulation is linear, so it requires a linear power amplifier. Actually most of the power amplifiers are nonlinear, so linearization of power amplifier has become a hot area for RF power amplifier. And with the development of 3G wireless communication, adjustment between the two conflicts of high efficiency and linearity has become a problem in modern wireless systems, and makes linear power amplifier hot in transmitter design. The LINC transmitter technology is an efficient and linear transmitter technology using non-linear device to achieve linear amplification, which is also an emerging power amplifier linearization technique.This paper mainly studies the implementation of LINC transmitters and influences of phase and gain imbalances on the linearity of the transmitter system. The article is divided into three parts, that is, construction of LINC transmitter system, test of LINC transmitter system, influences of non-linear distortion on system performances and methods to eliminate the non-linear distortion.The construction of LINC transmitter system mainly contains Signal Components Separator and signal recombination and system optimization. The signal decomposition is based on the principle of rectangular coordinates of vector signals, realized using DSP techniques using signal normalized, look-up tables and pipelining techniques to increase system processing speed and throughput. Signal recombination is achieved by the power combiner. The power combiner used in this paper is designed in ADS using microstrip lines with the S parameters as follows: S(1,1) less than -40dB, S(1,2) and S(3,3) less than -30dB,and S(1,3) less than -3dB.Then build up the test system for LINC transmitter based on the experimental platform and test the system performance. The result of hardware test shows that: the input signal with non-constant envelope is converted into two phase modulated signals with constant envelop by the Signal Components Separator in LINC transmitter, and the spectrum of the constant envelops signal is bad. After the signal recombination, the out-of- band distortion is eliminated and the signal maintains good linearity, which proves that LINC transmitter can use efficient non-linear power amplifier to achieve linear amplification.Finally, analyze the source of non-linear distortion in LINC transmitter, which is phase and gain imbalance between two spur tracks, and analyze the influence of non-linear distortion on system performance. At last use iterative method to compensate the nonlinear distortion and eliminate phase and gain imbalances.