| The importance of RF amplifiers linearization has been emphasized with the rapid development of the third generation mobile communication systems and the wide useness of linear modulation techniques. Modulated signals with varying envelop will generate intermodulation distortion which can not be eliminated by filter when those signal pass the RF power amplifiers. The power amplifier is known to be the most power consuing component in a transmitter, hence it is desirable to operate the power amplifier as efficient as possible,i.e.,near the saturation region which is at the operating region that the signals are most susceptible to nonlinear distortion. Many linearization techniques have developed to meet transmitter linearity requirement and power efficiency.Several linearization techniques are summarized and compared after the characteristics and classes of power amplifiers and description of nonlinear distortion are presented. This paper proposes a RF predistorter based on low-frequency even-order intermodulation components due to the simplicity, low cost and moderate distortion improvement of predistortion linearization. The third-order(IM3) and fifth-order(IM5) intermodulation distorted products can be generated by using second-order intermodulation components. Two double-balanced diode mixers are implemented as intermodulation products' generators. Power amplifier linearity has been improved by independently controlling the amplitudes and phases of IM3 and IM5. Simulation results show that IM3 reduction of 20dB and IM5 reduction of 18dB are achieved respectively at 1.95GHz. |
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