Abstract
This paper presents a digital amplitude modulator for a polar transmitter. The instantaneous output power is modulated by adjusting the amplifier's load through a digitally controlled impedance transformation network. The modulator is suited for modulation schemes with moderate peak-to-average power ratio (PAPR), such as π/4 DQPSK. The modulator may also be used for fine gain control in constant envelope modulation schemes. A class E amplifier with digital impedance amplitude modulation is integrated in 90nm CMOS. It achieves a peak output power of 9dBm with a PAE of 30% when powered from a 1.2V supply. The measured EVM is 2.6% for a 6dBm π/4 DQPSK modulated signal with 2Mb/s signal rate at 2.4GHz RF frequency.
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