A Balanced Darlington Cell for a 3-230-GHz InP Distributed Amplifier

This article presents a novel Darlington cell that improves the gain-bandwidth product and output power of distributed amplifiers (DAs). By employing two diode-connected transistors to a conventional Darlington pair, the voltages and currents of two transistors inside the pair are balanced, and output power is improved. Moreover, the new cell's high input impedance and high current gain allow the DA to have lower input line loss and wider bandwidth. A 3-230-GHz indium phosphide DA is designed and characterized to verify the concept. The Darlington DA prototype provides an average gain of 13 dB over 3-230-GHz bandwidth while keeping input and output return losses below −7 dB up to 220 GHz. Across several frequency bands from 10-65, 70-110, 110-170, and 170-220 GHz, the average saturated output power is 21.2, 20, 18.5, and 13.3 dBm, respectively. The maximum output 1-dB compression point and third-order intercept point are 17.6 and 30.4 dBm, respectively. The measured peak power-added efficiency is 10.5% at 70 GHz and 5.5% at 170 GHz. The Darlington DA consumes 110 mA from a 6.6-V supply.