AMPLITUDE MODULATION CIRCUIT IN POLAR TRANSMITTER AND METHOD FOR CALIBRATING AMPLITUDE OFFSET IN POLAR TRANSMITTER

摘要

An amplitude modulation circuit in a polar transmitter and a method for calibrating amplitude offset in the polar transmitter are provided. The amplitude modulation circuit includes a digital-to-analog converter (DAC), a low pass filter (LPF), a gm stage, and a calibration module. The DAC is coupled to an amplitude modulation signal input. The LPF is coupled to the DAC, and the gm stage is coupled to the LPF. The calibration module has an input coupled to the gm stage, and an output coupled to a node on a path between the DAC and the gm stage. The method includes: generating an amplitude offset calibration signal according to an amplitude modulation signal generated from the gm stage; and transmitting the amplitude offset calibration signal via the output of the calibration module to a node on a path between the DAC and the gm stage so as to calibrate the amplitude offset.