A Novel Approach for Mitigation of AM/PM Delay Mismatch in Polar Transmitters

One of the major challenges in polar modulators is the time delay adjustment between the amplitude (AM) and phase modulation (PM) paths when they are mixed at the analog mixer. Such delay mismatch between both paths leads to undesirable distortion effects in Error Vector Magnitude (EVM) as well as Adjacent Channel Interference (ACI) levels. In this brief, we first present a theoretical model that shows the distortion caused by the delay mismatch. We then present a new digital compensation scheme that mitigates such distortion in a power efficient manner when compared to traditional approaches based on programmable delay elements. The proposed technique has been verified by simulations, achieving improvements in EVM and ACI. As a result it allows the polar transmitter (TX) comply with regulatory requirements.