Cascaded 4:1 AMUX-DAC Using Novel Clocking and Advanced DSP

The analog bandwidth of digital-to-analog converters (DACs) implemented in CMOS, which are generally used in commercial optical transmission systems, has been stagnating in recent years with new technology nodes. A promising concept enabling higher signal bandwidths is cascaded analog multiplexing (AMUX). In this work, we discuss the system-level aspects of a 4:1 cascaded AMUX and propose a novel clocking scheme, combining multiple advantages of previous methods. Successively, we use the scheme to demonstrate PAM-4 and PAM-8 signal generation at 60GBd using advanced DSP, quadrupling the sample rate of four DAC-generated signals with three 2:1, 130nm SiGe AMUX modules.