A Broadband InP Darlington Amplifier with Two-Way Distributed Power Combining

This paper presents a broadband InP two-way distributed power-combining Darlington amplifier. To simultaneously enhance output power, maintain wide bandwidth, and preserve reliability, a cascaded distributed power-combining topology is proposed. A distributed driver stage is co-designed with reduced collector line impedance to effectively extend the bandwidth. Furthermore, a linearized Darlington pair with capacitive stepping techniques is employed to increase input impedance by 7 to 10 times compared to conventional common-emitter amplifiers, further improving both output power and bandwidth. The proposed amplifier prototype operates across a wide frequency range from near DC to 250 GHz, achieving a peak Psat of 17 dBm, a peak OP1dB of 13.9 dBm, and a flat in-band gain of 17.4 dB. In a 64-QAM modulation test at 156 GHz, it demonstrates an error vector magnitude (EVM) of -26.1 dB and a signal-to-noise ratio (SNR) of 24 dB at an average output power of 6.4 dBm.