A 24-Gb/s PAM-4 Tailless Current-mode Driver with Output Impedance Enhancing Technique in 14-nm FinFET

This paper presents a four-level pulse amplitude modulation (PAM-4) transmit driver utilizing the tailless current-mode structure. The PAM-4 driver operates at 24 Gb/s with a 1.3-V supply voltage, leveraging the advantage of the tailless approach. The low output impedance inherent to the tailless current-mode drivers is enhanced using a gain-boosting technique. The prototype chip was fabricated using a 14-nm FinFET process, achieving a vertical eye-opening of 44.6 mV at 24 Gb/s while consuming 60.3 mW. It achieved an energy efficiency of 2.513 pJ/bit. Through the gain boosting technique, the output impedance increased by approximately 100%.