A Novel Approach to Implementing On-Chip Synchronous Detection for CMOS Optical Detector Systems

A phase-switching approach suppresses the need to employ a precise multiplier for synchronous demodulation. An improved solution for implementing on-chip synchronous detection consists of using a switched-phase amplifier, which combines pre-amplification and phase-switching operations. This enables circuit simplification, voltage lowering, and power and surface savings. A detector-associated circuit realising pre-amplification and synchronous demodulation is proposed. It includes a transimpedance amplifier, a switched-phase amplifier and a low-pass filter. All these building blocks are designed to operate under a minimum supply of 2 V, using a double-poly, 0.8-m CMOS process. The designed circuit is to be integrated with a CMOS optical detector for portable applications. System-level simulations (including the detector model) are performed to validate the system operation, and to estimate performances. The sensitivity of the system in terms of minimum detectable optical signal (which is synchronously modulated) is evaluated to be 2.2 10^–14 W/mm² in normal measuring conditions.