Mukul Sarkar

Biologically Inspired CMOS Image Sensor for Fast Motion and Polarization Detection

A complementary-metal-oxide semiconductor (CMOS) image sensor replicating the perception of vision in insects is presented for machine vision applications. The sensor is equipped with in-pixel analog and digital memories that allow in-pixel binarization in real time. The binary output of the pixel tries to replicate the flickering effect of an insects eye to detect the smallest possible motion based on the change in state of each pixel. The pixel level optical flow generation reduces the need for digital hardware and simplifies the process of motion detection. A built-in counter counts the changes in states for each row to estimate the direction of the motion. The designed image sensor can also sense polarization information in real time using a metallic wire grid micropolarizer. An extinction ratio of 7.7 is achieved. The 1-D binary optical flow is shown to vary with the polarization angle of the incoming light ray. The image sensor consists of an array of 128 × 128 pixels, occupies an area of 5 × 4 mm2 and it is designed and fabricated in a 180-nm CMOS process.

Integrated polarization analyzing CMOS Image sensor for autonomus navigation using polarized light

Navigation is important both for insects to perform living tasks and robots to perform assigned tasks. We propose a CMOS image sensor for autonomous agent navigation which mimicks the navigational patterns of insects using the variations in the degree of skylight polarization. The polarization pattern of the skylight varies in a systematic way both in the plane (e-vector) and the degree of polarization according to the suns position. The proposed CMOS image sensor is able to sense polarization information in real time using a metallic wire grid micro-polarizer oriented in various directions on top of the pixel. The degree of polarization is computed from the sensed polarization information, the variations of which can be used as a compass. The image sensor consist of an array of 128×128 pixels, occupies an area of 5×4mm2 and it has been designed and fabricated in a 180nm CMOS process.

A Biologically Inspired CMOS Image Sensor

Biological systems are a source of inspiration in the development of small autonomous sensor nodes. The two major types of optical vision systems found in nature are the single aperture human eye and the compound eye of insects. The latter are among the most compact and smallest vision sensors. The eye is a compound of individual lenses with their own photoreceptor arrays. The visual system of insects allows them to fly with a limited intelligence and brain processing power. A CMOS image sensor replicating the perception of vision in insects is discussed and designed in this book for industrial (machine vision) and medical applications. The CMOS metal layer is used to create an embedded micro-polarizer able to sense polarization information. This polarization information is shown to be useful in applications like real time material classification and autonomous agent navigation. Further the sensor is equipped with in pixel analog and digital memories which allow variation of the dynamic range and in-pixel binarization in real time. The binary output of the pixel tries to replicate the flickering effect of the insects eye to detect smallest possible motion based on the change in state. An inbuilt counter counts the changes in states for each row to estimate the direction of the motion. The chip consists of an array of 128x128 pixels, it occupies an area of 5 x 4 mm2 and it has been designed and fabricated in an 180nm CMOS CIS process from UMC.

Integrated Polarization-Analyzing CMOS Image Sensor for Detecting the Incoming Light Ray Direction

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, it occupies an area of 5×4 mm2 and it has been designed and fabricated in a CMOS 180nm process. The integrated grid polarizer is oriented in various directions to compute the Stokes parameters which can be used to determine the degree of polarization of the incoming light ray.

Integrated polarization-analyzing CMOS image sensor for detecting incoming light ray direction

A complementary metal-oxide-semiconductor (CMOS) image sensor used to detect the incoming light ray direction using polarization information is presented. The chip consists of an array of 128 × 128 pixels, and each pixel is embedded with a metallic wire-grid micropolarizer. It occupies an area of 5 × 4 mm2, and it has been designed and fabricated in a 180-nm CMOS process. Extinction ratios of 6.3 and 7.7 were achieved in two different polarization sense regions. The Stokes parameters, which are needed to evaluate the degree of polarization (DOP) and electric-field vector intensity, are computed from the pixel with the micropolarizer oriented at 0°, 45°, and 90°. We show that the variations in the DOP and the e-vector pattern with the incoming polarized light ray direction can be used as a directional reference source for autonomous agent navigation. We also show that the measurement results of ellipticity and azimuthal angles for the incoming light ray using the Stokes parameters can allow on-chip position detection based on the angle of the incoming light ray with little complexity. A very high correlation coefficient bigger than 0.94 was obtained between the measured and theoretical incoming light ray angles.

Feedforward Effect in Standard CMOS Pinned Photodiodes

The charge handling capacity or the full well of the photodiodes used in CMOS image sensors is a very important characteristic because it affects the saturation level and the dynamic range of the image sensor. The scaling of the pixel size to increase the spatial resolution is also reducing the barrier separating the photon detection and the collection node in a standard pinned photodiode (PPD). The barrier reduction and the thermionic emission of the electrons allow some of the charges from the photodiode well to feed into the collection node, resulting in a feedforward voltage. In conventional readout of the pixels, this feedforward voltage is neglected and lost when the collection node is reset. The barrier height of the transfer gate (TG) determines the quantity of electrons held back in the photodiode well. Thus, the knowledge of this barrier height is very important in determining the true charge handling capacity of the photodiode potential well. Experiments with standard PPDs showed that a barrier height of around 0.5 V is needed to hold the electrons in the photodiode potential well. This is analogous to the barrier potential for charge-coupled devices reported in the literature. Furthermore, the barrier height dependence on the charge storing time in the photodiode well and the structural dimensions of the TG and photodiode length are also explored in this paper.

Integrated polarization-analyzing 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, it occupies an area of 5×4 mm2 and it has been designed and fabricated in a CMOS 180nm process. Extinction ratio of 6.3 and 7.7 were achieved. The sensor is used to classify materials based on the degree of polarization and the transmitted intensity after specular reflection on the material surface. The variation in the transmitted intensity among dielectrics and metals was successfully demonstrated.

An insect eye-based image sensor with very large field of view

In this paper we discuss the design of a novel miniaturized image sensor based on the working principle of insect facet eyes. The main goals are to design an imaging system which captures a large field of view (FOV) and to find a good trade-off between image resolution and sensitivity. To capture a total FOV of 124°, we split up this FOV into 25 different zones. Each of these angular zones is imaged by an isolated optical channel on our image sensor. There is an overlap between the zones to cover the full FOV but the different zones are imaged on separated regions at the image sensor. Every optical channel in the designed component consists of two lenses that are tilted with respect to each other and the optical axis. Because of this tilt of the lenses, we are able to minimize field curvature and distortion in the obtained images at the detector, and have an angular resolution below 1°. The optical system was implemented and optimized in the ray-tracing program ASAP. The parameters (in one channel) that are optimized to obtain this large FOV with a good image resolution and sensitivity are the radius of curvature of the two lenses, their conical factor and their tilt in two directions with respect to the optical axis of the complete system. The lenses are each placed on a pedestal that connects the lens to a planar substrate. We also add absorbing tubes that connect the two lenses in one channel to eliminate stray-light between different optical channels. The obtained image quality of the design is analyzed using our simulation model. This is determined by different parameters as there are: modulation transfer function, distortion, sensitivity, angular resolution, energy distribution in each channel and channel overlap. The modulation transfer function shows us that maximum contrast in the image is reached up to 0.3LP/°, distortion is maximal 21% in one of the 25 different channels, the sensitivity is 0.3% and the resolution is better than 1°.

A biologically inspired CMOS image sensor for polarization and fast motion detection

A CMOS image sensor replicating the perception of vision in insects is presented for machine vision applications. The image sensor can sense polarization information in real time using a metallic wire grid micro polarizer. The embedded polarizer uses the inherent property of materials to partially polarize the reflected light to classify among conductive materials. The sensor is also equipped with in-pixel analog and digital memories which allow in-pixel binarization in real time. The binary output of the pixel tries to replicate the “flickering effect” of the insects eye to detect the smallest possible motion based on the change in state of each pixel. A built-in counter counts the changes in states for each row to estimate the direction of the motion. The image sensor consists of an array of 128×128 pixels, occupies an area of 5×4mm2 and it has been designed and fabricated in a 180nm CMOS process.

Blood Pulsation Measurement Using Linearly Polarized Light

Blood molecules are optically active molecules. They have the ability to alter the polarization properties of light. This paper investigates the effect of blood pulsation variation on the polarization properties of linearly polarized light. This paper presents a new noninvasive noncontact blood pulsation measurement technique. Linearly polarized light has been allowed to transmit through the fingertips of a person and degree of linear polarization for transmitted part of the light has been calculated using polarized images. Experimental results show a strong correlation between the blood pulsation rate and the measured degree of linear polarization. The standard correlation coefficient value for the experiment with laser light source and two polarizers in the light path is 0.9484. Similarly for dc light source the correlation coefficient values are 0.9410 and 0.92 with two polarizers and one polarizer, respectively. Statistical analysis of the collected data has been done to measure the accuracy of the method. It shows that an accurate, low cost, and simple polarization-based blood pulsation measurement device can be developed by following the experiment performed with laser light source which could offer significant benefits to primary healthcare.