A Digitally Modulated Class-E Polar Amplifier in 90 nm CMOS

In this paper a digital amplitude modulator for a polar transmitter is presented. The instantaneous output power is modulated by adjusting the amplifiers 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 $\pi/4$ 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 90 nm CMOS. It achieves a peak output power of 9 dBm with a PAE of 30% when powered from a 1.2 V supply. The measured EVM is 2.6% for a 6 dBm $\pi/4$ DQPSK modulated signal with 2 Mb/s signal rate at 2.4 GHz RF frequency.