This paper describes a CMOS optical preamplifier suitable for infrared wireless data communications. The preamplifier consists of a differential CMOS variable-gain transimpedance amplifier embedded in a larger feedback loop used to reject photocurrents generated by ambient light. Fabricated in a commercial 0.35-/spl mu/m CMOS process, the preamplifier consumes 8 mW at 3 V, and provides 70 MHz bandwidth over a 77-dB dynamic range with a maximum transimpedance gain of 19 k/spl Omega/. The bandwidth is controlled within a factor of two over a 31-dB variation in gain.