CMOS Imager Chip Research Articles

A portable Raspberry Pi-based spectrometer for on-site spectral testing.

We designed a portable Raspberry Pi-based spectrometer, which mainly consists of a white LED acting as the wide-spectrum source, a reflection grating for light dispersion, and a CMOS imaging chip aiming at spectral recording. All the optical elements and Raspberry Pi were integrated using 3-D printing structures with a size of 118 mm × 92 mm × 84 mm, and home-built software was also designed for spectral recording, calibration, analysis, and display implemented with a touch LCD. Additionally, the portable Raspberry Pi-based spectrometer was equipped with an internal battery, thus supporting on-site applications. Tested by a series of verifications and applications, the portable Raspberry Pi-based spectrometer could reach a spectral resolution of 0.065 nm per pixel within the visible band and provide spectral detection with high accuracy. Therefore, it can be used for on-site spectral testing in various fields.

Direct spectral imaging of plasmonic nanohole arrays for real-time sensing

Plasmon-enhanced optical transmission through arrays of nano-structured holes has led to the development of a new generation of optical sensors. In this paper, to dramatically simplify the standard optical setups of these sensors, we position the nanoholes, an LED illumination source and a spacer layer directly on top of a CMOS imager chip. Transmitted light diffracts from the nanohole array, spreading into a spectrum over the space of a millimeter to land on the imager as a full spectrum. Our chip is used as a sensor in both a liquid and a gas environment. The spectrum is monitored in real-time and the plasmon-enhanced transmission peaks shift upon exposure to different concentrations of glycerol-in-water solutions or ethanol vapors in nitrogen. While liquids provide good refractive index contrast for sensing, to enhance sensitivity to solvent vapors, we filled the nanoholes with solvatochromic dyes. This on-chip solution circumvents the bulky components (e.g. microscopes, coupling optics, and spectrometers) needed for traditional plasmonic sensing setups, uses the nanohole array as both the sensing surface and a diffraction grating, and maintains good sensitivity. Finally, we show simultaneous sensing from two side-by-side locations, demonstrating potential for multiplexing and lab on a chip integration.

Automotive Three-Dimensional Vision Through a Single-Photon Counting SPAD Camera

We present an optical 3-D ranging camera for automotive applications that is able to provide a centimeter depth resolution over a $\mbox{40}^{\circ} \times \mbox{20}^{\circ}$ field of view up to 45 m with just 1.5 W of active illumination at 808 nm. The enabling technology we developed is based on a CMOS imager chip of 64 $\times$ 32 pixels, each with a single-photon avalanche diode (SPAD) and three 9-bit digital counters, able to perform lock-in time-of-flight calculation of individual photons emitted by a laser illuminator, reflected by the objects in the scene, and eventually detected by the camera. Due to the SPAD single-photon sensitivity and the smart in-pixel processing, the camera provides state-of-the-art performance at both high frame rates and very low light levels without the need for scanning and with global shutter benefits. Furthermore, the CMOS process is automotive certified.

Diffuse reflectance measurements using lensless CMOS imaging chip

To assess superficial epithelial microcirculation, a diagnostic tool should be able to detect the heterogeneity of microvasculature, and to monitor qualitative derangement of perfusion in a diseased condition. Employing a lensless CMOS imaging chip with an RGB Bayer filter, experiments were conducted with a microfluidic platform to obtain diffuse reflectance maps. Haemoglobin (Hb) solution (160 g/l) was injected in the periodic channels (grooves) of the microfluidic phantom which were covered with ~250 μm thick layer of intralipid to obtain a diffusive environment. Image processing was performed on data acquired on the surface of the phantom to evaluate the diffuse reflectance from the subsurface periodic pattern. Thickness of the microfluidic grooves, the wavelength dependent contrast between Hb and the background, and effective periodicity of the grooves were evaluated. Results demonstrate that a lens-less CMOS camera is capable of capturing images of subsurface structures with large field of view.

LED die‐on‐chip integration for fluorescence‐detection applications

Conventional fluorescence-detection systems typically involve a separate laser excitation source shining directly down towards the photodetectors, with the fluorescent sample in-between. A major issue with such systems is the strong excitation light signal that can saturate detection circuitry and/or make detection of the fluorescent signal difficult, even with optical filtering. A fluorescence-detection system is described consisting of light emitting diode dies bonded on top of a CMOS imaging chip. Such a system facilitates a high level of integration while potentially reducing the excitation light hitting the photodetectors. Model results are used to predict the shape of the imager response to excitation light. Experimental results confirm the validity of the model.

THE GEOSPECTRAL CAMERA: A COMPACT AND GEOMETRICALLY PRECISE HYPERSPECTRAL AND HIGH SPATIAL RESOLUTION IMAGER

Abstract. Small unmanned aerial vehicles are increasingly being employed for environmental monitoring at local scale, which drives the demand for compact and lightweight spectral imagers. This paper describes the geospectral camera, which is a novel compact imager concept. The camera is built around an innovative detector which has two sensor elements on a single chip and therefore offers the functionality of two cameras within the volume of a single one. The two sensor elements allow the camera to derive both spectral information as well as geometric information (high spatial resolution imagery and a digital surface model) of the scene of interest. A first geospectral camera prototype has been developed. It uses a linear variable optical filter which is installed in front of one of the two sensors of the MEDUSA CMOS imager chip. A accompanying software approach has been developed which exploits the simultaneous information of the two sensors in order to extract an accurate spectral image product. This method has been functionally demonstrated by applying it on image data acquired during an airborne acquisition.

A UV sensitive integrated Micromegas with Timepix readout

This article presents a detector system consisting of three components, a CMOS imaging array, a gaseous-detector structure with a Micromegas layout, and a UV-photon sensitive CsI reflective photocathode. All three elements have been monolithically integrated using simple post-processing steps. The Micromegas structure and the CMOS imaging chip are not impacted by the CsI deposition. The detector operated reliably in He/isobutane mixtures and attained charge gains with single photons up to a level of 6 × 10 4. The Timepix CMOS array permitted high resolution imaging of single UV-photons. The system has an MTF50 of 0.4 lp/pixel which corresponds to approximately 7 lp/mm.

A CMOS Chip With Active Pixel Array and Specific Test Features for Subretinal Implantation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a CMOS imager chip that is aimed at subretinal implantation for partially restoring human vision. It has low supply voltage (<formula formulatype="inline"><tex Notation="TeX">$\pm$</tex></formula> 2 V) and all DC free terminals for long life wired operation. Stimulation voltage is increased to approximately 4 <formula formulatype="inline"><tex Notation="TeX">${\rm V}_{\rm pp}$</tex></formula> by low voltage drop design. 40 x 40 pixel cells including light sensors, amplifiers, control logic and electrode drivers are addressed sequentially to improve power consumption and spatial resolution of perception. Pad count is limited to 6, which requires a specific test procedure. The 3 x 3 mm<formula formulatype="inline"><tex Notation="TeX">$^{2}$</tex> </formula> design is fabricated in a 0.35 <formula formulatype="inline"><tex Notation="TeX">$\mu{\hbox{m}}$</tex></formula> CMOS technology optimized for optical performance. </para>

Charge sharing studies with a Medipix1 pixel device

The Medipix1 chip is a prototype (digital) CMOS imaging chip that emerged from particle detection in high energy physics experiments. It was designed at CERN following specifications from the Medipix1 Collaboration. This contribution aims at demonstrating the applicability of Medipix1 Si and GaAs pixel devices for alpha and X-ray particle detection. A study of “charge sharing” between pixels and test of “spatial resolution” using narrow beam and “edge” image contrast was performed. For photons with energy <35keV charge sharing between neighbouring pixels is negligible. On the contrary alpha-particles are detected in the form of clusters of adjacent pixels with typical cluster diameter of about 2.5 pixels. Possible applications of the device for position sensitive heavy charged particle detection (e.g. for surface analysis or for neutron detection) are considered.

Analog VLSI systems for image acquisition and fast early vision processing

This article describes a project to design and build prototype analog early vision systems that are remarkably low-power, small, and fast. Three chips are described in detail. A continuous-time CMOS imager and processor chip uses a fully parallel 2-D resistive grid to find an object's position and orientation at 5000 frames/second, using only 30 milliwatts of power. A CMOS/CCD imager and processor chip does high-speed image smoothing and segmentation in a clocked, fully parallel 2-D array. And a chip that merges imperfect depth and slope data to produce an accurate depth map is under development in switched-capa citor CMOS technology.