On-chip synchronous detection for CMOS photodetector

A detector-associated circuit with a novel approach for implementing synchronous detection is proposed. A suggested phase-switching technique for synchronous demodulation obviates the need to employ a precise analog multiplier. By using a switched-phase amplifier to combine operations of additional amplification and phase-switching, the circuitry is substantially simplified. This approach enables voltage lowering, power and surface savings. The circuit is designed to operate under a low supply voltage down to 2 V, using a double-poly 0.8-μm CMOS process. It is to be integrated with a CMOS photodiode for optical detection. The sensitivity of such a detection system is evaluated via noise analysis and simulations. A modulated optical signal of about 20 fW/mm² is still detectable.