Dual-Mode Supply Modulator IC With an Adaptive Quiescent Current Controller for Its Linear Amplifier in LTE Mobile Power Amplifier

Abstract

This article presents a hybrid envelope tracking (ET) supply modulator (SM) integrated circuit (IC) based on a Class-AB linear amplifier (LA) with supply voltage and temperature insensitive quiescent current. For ET mode, to further improve efficiency of the ET-SM, the supply voltage of the LA can be modulated using an additional dc-dc converter according to the average output power. An adaptive quiescent current controller for the LA of the ET-SM is proposed to maintain its quiescent current for large variations in voltage and temperature. Due to the insensitive quiescent current over the voltage of the LA, the supply voltage to the LA can be controlled in a wider range for the average output power, which allows the power amplifier (PA) in the ET mode to have a greater improvement in efficiency. The size of the output stage of the LA is also discretely reconfigured using 3-bit digital control to reduce the power consumption of the LA according to the output power level. For the low average output power levels, the operation mode is changed to APT mode, which supplies a reduced dc voltage according to the reduced average output power to the PA. The proposed SM, dc/dc converter and PA ICs were designed and implemented using CMOS processes for 0.9 GHz LTE application. Using an LTE uplink signal with a signal bandwidth of 5 MHz and a PAPR of 7.5 dB, a PAE of 38.4% at an average output power of 24.0 dBm was obtained under an ACLR of −30.0 dBc for the overall ET-PA. At a 6 dB back-off for the average output power, a PAE of 24.6% was achieved using the ET mode. A maximum PAE improvement of 8.0% point using the proposed SM IC was achieved compared to the stand-alone PA.