Linearity Enhanced Broadband Darlington Power Amplifier IC Using InGaP/GaAs HBT for Handset Modules with Fractional Bandwidth of 50%
This letter presents a 0.6–1 GHz broadband Darlington power amplifier using a 2-µm InGaP/GaAs heterojunction bipolar transistor (HBT) process for mobile handset application. The Darlington structure is proposed for high performance broadband PA design, as it improves the gain-bandwidth products of the transistor itself without the problem of reducing the power added efficiency (PAE) of the circuit. A proposed simple tunable linearization circuit operates as a 2nd harmonic resonance circuit to improve linearity over 0.6–1 GHz and is designed to adjust the operating frequency differently according to the control voltage of the diode. Using the continuous wave (CW) signal, the implemented Darlington PA achieves an output power of 34.3–35.5 dBm, a PAE of 51–61% based on P3dB and a small-signal gain of 27.2–28.16 dB in a fractional bandwidth (FBW) of 50%. Using the 20 MHz 100 RB BW QPSK LTE signal with a PAPR of 7.22 dB were obtained E-UTRA ACLR of better than -40dBc at Pout of 27.5–28.5 dBm.