A 2.5 Gbit/s transimpedance amplifier is realised using a 0.6 mum CMOS technology. By exploiting a regulated cascode configuration as the input stage, the amplifier achieves significant bandwidth improvement. The measured results demonstrate 2.2 GHz bandwidth for 0.5 pF photodiode capacitance with 55.3 dBOmega transimpedance gain.