CMOS Light Field Image Sensor Building Block for Detection of Multicolor LED Blink Sequence From Heterogeneous Locations

A light field image sensor is fabricated on a standard complementary metal-oxide-semiconductor (CMOS) process. The sensor uses two grating layers of various layer-tolayer distances to take advantage of Talbot effect. The horizontal placement of the upper grating relative to the lower one has three types of configurations. By shifting the upper grating to the left or right or aligned position relative to the lower grating, light incident from left, right, and center can be differentiated. Furthermore, color selectivity is analyzed by varying grating slit spacing to favor a particular color's wavelength to reach Talbot depth. We designed photodiodes each having area of 14 × 15 um
²
. We used a 180-nm five-metal CMOS process and achieved an angle differentiation accuracy error within 1.8° for the direct incidence on aligned configuration and within 3.6° of the expected angle for the leftand right-shifted configurations. In addition, we experimented with applying various wavelengths of light even to sensor structures favoring other wavelengths to analyze their effects. Combining these sensor characteristics, we show that red, green, and blue lights, clustered together at three different locations, can be recognized by a set of light field sensors. The sensor set can differentiate 6 different combinations of 3 different color blink sequences per cluster location, thus totaling 18 types of spatial temporal signals. Moreover, repeated measurements showed good immunity to noise. The standard deviation of the measured results between each repetition was less than 5 mV.