A 3.3V CMOS Charge-Pumping Offset-Compensated Optical Charge-Mixer with 3% Phase Accuracy

A new type of CMOS electro-optical charge-mixer is presented, who´s functionality is based on the charge pumping (CP) phenomenon. The device uses two PMOS transistors with bulk-embedded photodiode to detect the intensity and phase of a modulated light signal. Using clocking between accumulation and inversion, the two transistors transfer to output charge packets that are synchronous and proportional to the light intensity. A device replica is used to compensate for both, background illumination and offset charge. This latter peculiarity depends on the photo-sensor bias voltage. The device is implemented in a standard 0.35mum CMOS and operates from a single 3.3V supply. Using a 12mW/cm ² pulsed light source with a pulse width of 500ns, the charge-mixer estimates the phase delay with an accuracy of 3%