A Comparison of Polar and Quadrature RF-PWM

All-digital implementations of PWM-based wireless transmitters are gaining popularity. Unlike baseband PWM, RF-PWM has relaxed filtering requirements and is preferred due to a smaller chip size. This paper is aimed to highlight the differences between polar and quadrature implementations of RF-PWM-based transmitters. Using mathematical models and simulations, performance of the two implementations is compared. The mathematical analysis indicates that the quadrature implementation is expected to have higher quantization noise compared to the polar because of the shorter duty cycles at maximum amplitude. The simulations, using a 10 MHz LTE uplink signal at 2 GHz carrier frequency, confirm this and also show the effect of RF pulse swallowing on the error vector magnitude (EVM).