A polar transmitter using a new linear-assisted delta-modulation (LADM) envelope-amplifier has been developed for WCDMA applications. The LADM system is composed of a highly efficient switching block based on a 200-MHz-clock delta-modulator, which is implemented in a 0.18-mum CMOS IC, and a highly accurate linear block. In the LADM approach, the residual quantization noise and distortion of switching amplification are removed through the assistant linear process; thus, a sufficiently low ACPR of -45 dBc and a small EVM of 1.7% can be achieved without a pre-distortion technique. The developed polar transmitter nearly doubles the average efficiency in the 10- to 15-dB back-off region of class-AB PAs