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The linear amplifier with nonlinear components (LINC) is highly efficient because it uses a highly efficient nonlinear power amplifier (PA). However, the linearity performance of the LINC system is easily degraded by amplitude and phase mismatches between the two paths. In this paper, we propose a novel mismatch calibration technique for the LINC system that calibrates both phase and amplitude mismatches with only phase control. The technique detects mismatches between two paths without any iteration using predefined five test vector signals. In addition, this technique corrects the path mismatches using unbalanced phase control. Therefore, the proposed scheme does not require additional amplitude mismatch control blocks such as dc/dc converters or low drop output regulators (LDO). The linearity performance of the proposed LINC system is measured with 7-MHz bandwidth orthogonal frequency-division multiplexing (OFDM) signals. According to the measurement results, the proposed technique significantly enhances linearity. The measurement results also shows that the proposed LINC system satisfies the error vector magnitude (EVM) requirement for a 16-state quadratic amplitude modulation (QAM) signal (-24 dB) and a 64-QAM signal (-31 dB) up to 3.8- and 2.35-dB amplitude mismatches, respectively, with any phase mismatch.
Date of Publication: Nov. 2011