Signal generation algorithm for digital polar transmitters with reduced receive band noise

Digital polar transmitters are under development for multiband handset applications, but typically lead to excess Rx band noise (RxBN). In this paper, a technique to improve the RxBN of a digital polar transmitter is demonstrated. Linear phase FIR filters are applied to both envelope and phase signals, so that the RxBN becomes relatively insensitive to transmitter non-idealities. At the same time, there is only small degradation of ACLR and EVM. Noise shaping algorithms are also applied to reduce the envelope quantization noise. For a WCDMA signal at 1.75 GHz, with a corresponding Rx band at 1.845 GHz, we demonstrate RxBN of -142 dBm/Hz in simulation and -125 dBm/Hz in experimental measurements.