A monolithically integrated, high speed optical front-end for optical sensing application in standard 0.35-micron CMOS technology is reported. The proposed receiver consists of an integrated photodiode, a transimpedance amplifier, a mixer, an IF amplifier and an output buffer. By treating the n-well in standard CMOS technology as a screening terminal to block the slow photo-generated bulk carriers and interdigitizing shallow <i>p</i><sup>-</sup> junctions as the active region, the integrated photodiode operates up to several gigahertz with no process modification. With multi-inductive-series peaking technique, the improved regulated cascade (RGC) transimpedance amplifier achieves an experimentally measured -3 dB bandwidth of more than 6 GHz and a transimpedance gain of 51 dB(omega), which is the fastest reported TIA in CMOS 0.35-micron technology. The 5 GHz broadband mixer produces a conversion gain of 13 dB which greatly minimizes the noise contribution from the IF amplification stage. The optical front-end of the active pixel demonstrates a -3 dB bandwidth of 4.9 GHz while consuming a current of 40 mA from 3.3 V power supply. This work presents the highest bandwidth for fully integrated CMOS optical receivers reported to date.