A 3D image sensor based on current assisted photonic mixing demodulator in 0.18 µm CMOS technology

A Time-Of-Flight (TOF) range image sensor using current assisted photonic mixing demodulator is presented. The demodulator structure, featuring a remarkably small pixel size (10 × 10 μm²), is used to realize a 160 × 120 pixel array of ranging sensor fabricated in standard 0.18 μm CMOS technology. The third dimension, i.e. depth information, can be determined by correlating the reflected modulated light signal from the scene with a reference signal synchronous with the light source modulation signal. Initial results demonstrate that the demodulator structure is suitable for a real-time 3D image sensor. A good charge separation efficiency and demodulation capabilities are achieved up to modulation frequencies larger than 20 MHz. The impact of important parameters such as wavelength, modulation frequency and voltage on this test device are also experimentally evaluated. The prototype camera system is capable of providing real-time distance measurements of a scene through modulated-wave TOF measurements with a modulation frequency of 20 MHz. In the distance measurement, the sensor array provides a linear distance range from 1.2m to 3.7m with maximum accuracy error 3.3% and maximum pixel noise 8.5% at 3.7m distance.