59-dBOmega 68-GHz Variable Gain-Bandwidth Differential Linear TIA in 0.7-µm InP DHBT for 400-Gb/s Optical Communication Systems

We report a variable-gain and variable-bandwidth differential linear transimpedance amplifier (TIA-VGA) realised in a 0.7-μm indium phosphide (InP) double heterojunction bipolar transistor (DHBT) technology. The circuits yields 59-dBΩ / 900-Ω differential transimpedance gain with 20-dB control and 68-GHz -3-dB bandwidth with 30-GHz control. Output-referred 1-dB-compression single-ended amplitude is larger than -4-dBm (400mV_pp) up to 60GHz. High quality On-Off-Keying (OOK) eye diagrams are measured at 64 GBd. Consuming less than 475 mW, this circuit exhibits the largest bandwidth for a linear TIA-VGA, to our knowledge, along with wide-range gain and bandwidth controls. This makes it a particularly suitable and flexible candidate for high-symbol-rate photoreceivers dedicated to next generation 400-Gb/s and 1-Tb/s optical communication systems.