A 224-Gb/s PAM-4 Linear Distributed Driver for Silicon-Photonic Modulators in SiGe BiCMOS

A 224-Gb/s PAM-4 linear distributed driver for silicon-photonic (SiPh) Mach-Zehnder modulators (MZM) is presented in 180-nm SiGe BiCMOS. Equalization is integrated to enhance high-frequency components, compensating for SiPh MZM roll-off and interconnect loss. The driver employs a distributed amplifier structure with BJT-based drive cells. Within each cell, a capacitive-division topology minimizes the effect of BJT’s input resistance. The artificial transmission line (ATL) of the amplifier features an m-derived termination for improved port impedance matching. A trimming shield technique in the layout design addresses non-idealities, such as high-frequency peaking and reflections. Experimental results demonstrate a typical bandwidth of 65 GHz with $\gt9-\mathrm{dB}$ maximum equalization capability. Eye diagrams for NRZ/PAM-4 modulation schemes and various bit rates are measured with a maximum output swing of $3.917 \mathrm{~V}_{\text {ppd }}$. Error-free performance up to 224 Gb/s PAM-4 is confirmed through bathtub-curve tests.