Broadband HBT Doherty Power Amplifiers for Handset Applications

A Doherty power amplifier for IEEE 802.16e mobile worldwide interoperability for microwave access (m-WiMAX) is fully integrated on a 1.2 × 1.2 × mm² die using a 2-μm InGaP/GaAs hetero-junction bipolar transistor (HBT) process. The direct input power dividing technique is employed on the chip. Broadband input and output matching techniques are used for broadband Doherty operation, and their effects are analyzed. A peaking amplifier 1.5 times larger than a carrier amplifier delivers high efficiency for m-WiMAX signal with a 9.6-dB crest factor and an 8.75-MHz bandwidth (BW). The PA with a supply voltage of 3.4 V has an EVM of 2.3% and a PAE of 31.5% at an output power of 24.75 dBm as well as an operating frequency of 2.6 GHz. A PAE over 30.3% and an output power of greater than 24.6 dBm with an EVM less than 3.15% and a gain variation of 0.2 dB are achieved across 2.5-2.7 GHz without any assisting linearization technique. After compensating AM-AM and AM-PM nonlinearity using a digital feedback predistortion algorithm, the PA exhibits a PAE of over 27% and an output power of over 23.6 dBm across 2.2-2.8 GHz while maintaining an EVM below 2.7%.