An interface circuit design for an optical sensor based on a two-stage cascaded architecture is presented in this paper. The proposed design is a mixed signal solution that provides few advantages in terms of speed, power consumption, higher resolution with smaller number of storage units, and small area for future on-chip integration. Simulation and experimental results for five bits resolution (32 levels) are presented to validate the design. We are aiming for a single-chip integrated solution; however, for a quick proof of concept, the proposed design has been implemented as a PCB using discrete off-the-shelf components. The biasing current and power consumption from the PCB implementation are 192 mA and 1.3 W, respectively, at a 6.75-V supply voltage. © 2001-2012 IEEE.