A Linear InGaP/GaAs HBT Power Amplifier Using Parallel-Combined Transistors With IMD3 Cancellation

In this letter, we present a linear InGaP/GaAs HBT power amplifier (PA) with parallel-combined transistors for small-cell applications. Ballast resistors with bypass resistors and capacitors are employed in parallel-combined transistors. When the resistors and capacitors are set to appropriate values, IMD3 components of the parallel-combined transistors are found to be out of phase with each other by 180° and are canceled out at the output. The experimental results show that the proposed HBT PA with parallel-combined transistors produces a saturated output power of 33.5 dBm at 0.88 GHz, with a power-added efficiency (PAE) of 46.1% at a 5-V supply voltage. To validate the effectiveness of the proposed HBT PA for linearity improvement, the implemented PA is also tested with a long-term evolution (LTE) signal (8.1-dB PAPR with 10-MHz bandwidth). The proposed PA achieves an adjacent channel leakage ratio (ACLR) below -45 dBc at an average power of 25.6 dBm with a PAE of 18.8% without applying predistortion.