This laser diode driver operates at 2.5 Gbps. It contains a driver, a reference voltage generator, an automatic power control circuit and digitally controlled blocks of bias current and modulation current. The TSMC 0.35 μm 1P4M CMOS digital process is used to fabricate this chip. APC is used to maintain the laser diode output power and it works when photodetector gain ranges from 1/80 to 1/120. A dynamic pull-up and pull-down circuit of the output driver is used to improve the eye diagram. The experimental results demonstrate that it works at 2.5 Gbps and the APC digital control blocks of bias current and modulation current also work well.