The system design of polar modulation transmitter for GSM/WCDMA

Abstract

Most of the currently used commercial transmitters for GSM/EDGE/WCDMA are implemented using two separate architectures. GSM uses offset PLL (translation loop) and EDGE/WCDMA uses zero-IF (homodyne) architecture. This approach is reliable but high cost and inefficient because of low circuit commonality. An enhanced polar modulation transmitter architecture based on GSM power amplifier (PA) is efficient, highly integrated and low in complexity. It doesn't need a separate WCDMA PA and uses the same building blocks in both GSM and WCDMA sides. Solution has difficulties in recombining amplitude and phase modulation as well as wide power control range. Those are reduced by performing digital and analog calibrations as well as by employing novel two-point power control approach and a RF VGA. System level simulations using a PA behavioural model from a commercial GSM PA module indicate that the transmitter provides considerable design margin against the ACLR and EVM requirements specified in the WCDMA standard.