A Linear Modulator Driver With Over 70-GHz Bandwidth 21.8-dB Gain and 3.4-Vppd Output Swing for Beyond 120-GBd Optical Links

• Published in: IEEE transactions on microwave theory and techniques Vol. 72; no. 7; pp. 4080 - 4091
• Main Authors: Niu, Shengpu, Ahmed, Riaz, Lambrecht, Joris, Declercq, Jakob, Verbeke, Marijn, Verplaetse, Michiel, Moeneclaey, Bart, Wang, Cheng, Kerrebrouck, Joris Van, Singh, Nishant, Bauwelinck, Johan, Yin, Xin
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.07.2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amplification; Bandwidth; Bandwidths; Gain; Impedance matching; Integrated circuits; Linearity; Links; Modulation; Modulator driver; Optical fiber communication; Power consumption; Power efficiency; Power measurement; Pulse amplitude modulation; pulse amplitude modulation-4 (PAM-4); Resistors; SiGe BiCMOS; Signal measurement; traveling wave; Traveling waves; Variable gain
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2023.3342624

This article investigates a linear differential modulator driver for optical communication links beyond 120 GBd. The driver was implemented in a 55-nm SiGe BiCMOS technology with an <inline-formula> <tex-math notation="LaTeX">f_{T}/f_{\text {MAX}} </tex-math></inline-formula> of 330/370 GHz, featuring a traveling wave output stage driven by a lumped variable gain amplifier (VGA) and a predriver. The fabricated IC achieved a maximum low-frequency gain of 21.8 dB with more than 10-dB gain control capability and a 3-dB bandwidth of over 70 GHz. Power measurement results show the driver is able to deliver a constant output swing of 3.56 Vppd while keeping the THD below 2%, with the differential input swing varying from 0.3 to 1.03 Vppd at 1 GHz. In the large-signal measurement, the chip delivered 72, 106, 112, and 128 GBd pulse amplitude modulation-4 (PAM-4) signals with differential output swings of 4, 3.59, 3.434, and 3.425 Vppd, respectively. The chip's total power consumption is 725 mW, resulting in a power efficiency of 2.83 pJ/bit. Overall, this is the first time an optical modulator driver reported the ability to accommodate such a wide input swing and demonstrated the operation at a data rate of 256 Gb/s. These features make it a desired candidate for beyond 120-GBd optical links.