LTE Power Amplifier for envelope tracking polar transmitters

The capacitance between the base and collector terminals of hetero-junction bipolar transistors (HBT) varies with an RF input signal, and degrades linearity and efficiency. A second harmonic control circuit and a feedback inductor between the base and collector terminals are employed to prevent the distortion of the signal, and improve the efficiency and the linearity. The PA circuit is realized in a 1.2 mm by 1.2 mm die using a 2 μm InGaP/GaAs HBT process. For a long term evolution (LTE) signal at a frequency of 2.535 GHz with a 7.42 dB crest factor, 16 QAM, and a 20 MHz bandwidth, the PA with a supply voltage of 4.5 V has an EVM of 2.78% and a PAE of 32.6% at an average output power of 26.9 dBm. The PA is operated in an envelope-tracking mode with a boosted supply modulator from 3.4 V to 4.5 V, and delivers a PAE of 34.2% at an average output power of 26.4 dBm, while meets the LTE spectrum mask.