Analysis and Implementation of DC-coupled Compact and Power Efficient Lumped Driver for Single-Ended Optical Modulators in SiGe 250 nm BiCMOS Technology

In this paper, a differential to single-ended DC-coupled compact and power efficient lumped driver for single-ended optical modulators using the IHP 250nm SiGe BiCMOS SG25H5 technology, featuring f(t)/f(max) of 220 / 290 GHz, has been analyzed and reported. The amplifier is composed of a differential to single-ended common-emitter variable gain stage, a fixed gain common-emitter stage and a cascode amplifier. Emitter followers have been used between the stages for DC leveling purposes. Peaking inductors for both input and output stages have been used to shape the frequency response in different frequency ranges, while degeneration resistors have been employed for improving the linearity of the circuit. Measurement results show that the proposed design has a low frequency gain of 15 dB and a 3 dB bandwidth of 53 GHz, along with a total harmonic distortion at 1 dB compression of 8% and an in band group delay variation of +/- 3 ps. Time-domain measurements show operation up to 60 Gbps non-return-to-zero and 36 GBaud 4-levels pulse amplitude modulation, together with an output voltage swing at 1 dB compression of 0.8 V-ppd. The fabricated circuit has a footprint of (0.2x0.3) mm(2) and a power dissipation of 175 mW resulting in a compact and power efficient DC-coupled differential to single-ended design, suitable for single-ended optical devices, which is very rare to be found in the literature.