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We present a theoretically comprehensive treatment of outphasing systems that utilize radio-frequency high-efficiency PAs. We separately analyze encoding and clipping distortions and how they accounts for most of the nonlinearities in outphasing systems. With that insight, we have designed an inherently linear outphasing system at high efficiency. We have implemented these techniques in a 90-nm Class-B prototype that uses signal-dependent time-varying circuits under close digital control to achieve 56%, 44%, and 30% efficiency for GSM, EDGE, and WCDMA modulations, while demonstrating linearity commensurate with demanding specifications on adjacent channel leakage.