An Analog and Digital Representation of Polarization Using Cmos Image Sensor

A CMOS image sensor with an integrated wire grid polarizer to sense the polarization of light is presented. The chip consists of an array of 128 by 128 pixels, and it has been designed and fabricated in a CMOS 180nm process. The sensed polarization information is represented and analyzed in both the analog and the digital domain. Extinction ratios of 6.3 and 7.7 were achieved in analog representation. I. SENSOR DESCRIPTION The three basic characteristics of light are intensity, color and polarization. The polarization can be detected using either with external polarization filters or with micropolarizers directly integrated on top of the photodetector. Micropolarizers can be made from organic materials [1] or using a metallic wire grid [2], [3]. The metallic wire grid micropolarizer can be made using the metal layers available with the standard CMOS technology. Our polarization sensing sensor has an embedded linear wire grid polarizer in each pixel. The linear wire grid polarizer was implemented using thin metal strips with a wire grid pitch of 480nm, as shown in figure 1. Figure 1: Wire grid Polarizer Figure 2 shows the sensor die photograph along with the implemented polarization regions. The array of 128 by 128 pixels was split into three regions: 1) a 64x128 array without a metal grid used for normal imaging applications, 2) a 64x64 array (sense region 1) consisting of 2 by 2 pixel arrays where two pixels (A and B) measure the intensity while the other two measure the 0o (D), and 90o (C) degree polarized intensity respectively and 3) a 64x64 array (sense region 2) consisting of 2 by 2 pixel arrays where one pixel records the intensity of the light (A) while the other 3 record the 0o (B), 45o (C) and 90o (D) polarized intensity. Each pixel contains a pinned photodiode, an analog comparator, two banks of analog memories and two SRAMs. The image sensor provides both analog and digital readout of each pixel. Figure 2: Sensor Regions with different Polarizing angles. AN ANALOG AND DIGITAL REPRESENTATION OF POLARIZATION USING CMOS IMAGE SENSOR Mukul Sarkar , David San Segundo Bello, Chris van Hoof, Albert Theuwissen 3 imec, Delft University of Technology, Harvest Imaging [email protected] The analog readout consists of a column level double differential sampling circuit (DDS), an output amplifier, a buffer and the column shift registers. The digital readout circuit consists of a 7-bit counter which counts the number of active high pixels row wise during the column progressive scan readout, and a column shift register.