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
Shengpu Niu, Riaz Ahmed, Joris Lambrecht, Jakob Declercq, Marijn Verbeke, Michiel Verplaetse, Bart Moeneclaey, C. Wang, Joris Van Kerrebrouck, Nishant Singh, Johan Bauwelinck, Xin Yin
Abstract
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 xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_T$</tex-math> </inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{\text{MAX}}$</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.