A wideband envelope-tracking CMOS linear transmitter without digital predistortion

Abstract

In this work, an effective linearization technique to linearize both AM-PM and AM-AM distortions in CMOS envelope tracking (ET) transmitter is developed using dual shaping tables. AM-AM response is linearized using iso-gain shaping table. A variable phase shifter is integrated with the RF power amplifier (RF PA), which linearizes AM-PM response of CMOS ET PA in conjunction with the iso-gain shaping table. In this way, no additional digital predistortion (DPD) is required to linearize the CMOS ET PA. The 2-stage RF PA with the integrated phase compensation circuit is fabricated in 0.28-µm SOI CMOS process. The ET transmitter system demonstrated using the CMOS envelope amplifier (EA) shows an overall system PAE of 42.2% with −34.5 dBc E-UTRA ACLR with 40 MHz BW LTE signal centered at 0.837 GHz. The proposed method overcomes the bandwidth limitation of the conventional methods relying on DPD and/or feedback loops, and can be applied to wide bandwidth LTE signals.