A 3.3 V 12.5 Gb/s 0.2/22m SiGe BiCMOS Laser Diode Driver Using Bias Current

Abstract

A low supply voltage fully-integrated 12.5 Gb/s laser diode driver IC was realized in a 0.2 m 60 GHz SiGe BiCMOS process. A three-fold power consumption reduction versus existing drivers was achieved by using a 3.3 V supply and a dynamic emitter follower having a local positive feed- back loop that boosts the drive strength of the leg that controls the turning-off output switch, without taking additional supply power. Low voltage operation was achieved by replacing the tail current source of the output switch with a resistor and setting the current value with a common-mode feedback loop. A direct on-chip summation of bias and modulation currents was realized by using a bias modulation canceling circuit and a cascode current generator with series damping resistor. The signal path peaking and ringing was reduced with RC compensation networks that critically damp both the last emitter follower which drives a large load capacitance and the output switch parasitic LC circuit. A virtually constant dynamic performance was achieved for a wide range of modulation currents by using adjustable voltage swings and tail currents in the driver back-end stages. Laser diode driver IC specifications include: 3–3.6 V supply voltage, 70 mA supply current (excluding output current), 20–100 mA modulation cur- rent range, 1–100 mA bias current range, 12 ps/112/112deterministic jitter, 25 ps rise/fall time, 10% to 90% pulsewidth adjustment and 1.5 1.5 mm/50die area.