| A design based on the character of WCDMA was performed for improving the linearity of the power amplifier. There were many technologies in the application; the design applied an analogy predistortion for the former aim according to the need of program. There was different from a traditional analogy predistortion, the traditional analogy predistortion was used for a couple of diodes for setting up the circuit that acquire the IM distortion and adjusted the potentiometer for controlling the distortion of the phase and gain. For improving the linearity of power amplifier, the distortion should add with a distortion from a main power amplifier, but they had inverse phase and identical gain. The design applied MAX2009 to achieve there served targets. The RF signal through the driver model was serried with the MAX2009. By testing we will get and record the input power of phase and gain compressions, at the beginning of the phase and gain of the main power amplifier compressions. After setting the relative parameters of the MAX2009, the initial points of the phase and gain compression from the MAX2009 get together with the starting of that form the main power amplifier, which called Breakpoint. While the slope of the phase and gain expansion from MAX2009 get inverse with the slope of the phase and gain from the main power amplifier. It will optimize the linearity of PA, when the Breakpoint is emerging, which keep the current index with that of the previous as a constant. For simplifying the later program, the parameters were controlled by the certain MCU. After setting the signal PAR as 10.57dB, the frequency from 2110 to 2170MHz, the output power as 38W, we can the following results: the ACPR of PA is improved 4dB, and the IM3 gets optimized 5.7dB, the efficiency is enhanced 5.5%. Although the method was not good enough at the improvement of linearity compared with DPD, MAX2009 is valuable technique at the aspect of cost and application. |
