Random telegraph noise (RTN) that occurs at in-pixel source follower (SF) transistors and column amplifier is one of the most important issues in CMOS image sensors (CIS) and reducing RTN is a key to the further development of CIS. In this paper, we clarified the influence of transistor shapes on RTN from statistical analysis of SF transistors with various gate shapes including rectangular, trapezoidal and octagonal structures by using an array test circuit. From the analysis of RTN parameter such as amplitude and the current-voltage characteristics by the measurement of a large number of transistors, the influence of shallow trench isolation (STI) edge on channel carriers and the influence of the trap location along source-drain direction are discussed by using the octagonal SF transistors which have no STI edge and the trapezoidal SF transistors which have an asymmetry gate width at source and drain side.
This paper describes the impacts of random telegraph noise (RTN) with various time constants and number of states to temporal noise characteristics of CMOS image sensors (CISs) based on a statistical measurement and analysis of a large number of MOSFETs. The obtained results suggest that from a trap located relatively away from the gate insulator/Si interface, the trapped carrier is emitted to the gate electrode side. Also, an evaluation of RTN using only root mean square values tends to underestimate the effect of RTN with large signal transition values and relatively long time constants or multiple states especially for movie capturing applications in low light environment. It is proposed that the signal transition values of RTN should be incorporated during the evaluation.
This paper explains a new method to model a photodiode for accurate quantum efficiency simulation. Individual photo-generated particles are modeled by Boltzmann transport equation, and simulated by Monte-Carlo method. Good accuracy is confirmed in terms of similarities of quantum efficiency curves, as well as color correction matrices and SNR10s. Three attributes - "initial energy of the electron", "recombination of electrons at the silicon surface" and "impurity scattering" - are tested to examine their effectiveness in the new model. The theoretical difference to the conventional method with drift-diffusion equation is discussed as well. Using the simulation result, the relationship among the cross-talk, potential barrier, and distance from the boundary has been studied to develop a guideline for cross-talk suppression. It is found that a product of the normal distance from the pixel boundary and the electric field perpendicular to the Z-axis needs to be more than 0.02V to suppress the probability of electron leakage to the adjacent pixel to less than 10%.
This paper demonstrates a multi spectral imaging system utilizing a linear response, high signal to noise ratio (SNR) and wide spectral response CMOS image sensor (CIS), and an electrically tunable multi bandpass optical filter with narrow full width at half maximum (FWHM) of transmitted waveband. The developed CIS achieved 71dB SNR, 1.5x107 e- full well capacity (FWC), 190-1100nm spectral response with very high quantum efficiency (QE) in near infrared (NIR) waveband using low impurity concentration Si wafer (~1012 cm-3). With the developed CIS, diffusion of 5mg/dl glucose into physiological saline solution, as a preliminary experiment for non-invasive blood glucose measurement, was successfully visualized under 960nm and 1050nm wavelengths, at which absorptions of water molecules and glucose appear among UV to NIR waveband, respectively.
In new markets such as in-vehicle cameras, surveillance camera and sensing applications that are rising rapidly in recent years, there is a growing need for better NIR sensing capability for clearer night vision imaging, in addition to wider dynamic range imaging without motion artifacts and higher signal-to-noise (S/N) ratio, especially in low-light situation. We have improved the previously reported single exposure type wide dynamic range CMOS image sensor (CIS), by optimizing the optical structure such as micro lens shape, forming the absorption structure on the Si surface and adding the back side deep trench isolation (BDTI). We achieved high angular response of 91.4%, high Gr/Gb ratio of 98.0% at ±20°, 610nm, and high NIR sensitivity of QE 35.1% at 850nm, 20.5% at 940nm without degrading wide dynamic range performance of 91.3dB and keeping low noise floor of 1.1e-rms.
This paper demonstrates to separate multi-path components caused by specular reflection with temporally compressive time-of-flight (CToF) depth imaging. Because a multi-aperture ultra-high-speed (MAUHS) CMOS image sensor is utilized, any sweeping or changing of frequency, delay, or shutter code is not necessary. Therefore, the proposed scheme is suitable for capturing dynamic scenes. A short impulse light is used for excitation, and each aperture compresses the temporal impulse response with a different shutter pattern at the pixel level. In the experiment, a transparent acrylic plate was placed 0.3m away from the camera. An objective mirror was placed at the distance of 1.1 m or 1.9m from the camera. A set of 15 compressed images was captured at an acquisition rate of 25.8 frames per second. Then, 32 subsequent images were reconstructed from it. The multi-path interference from the transparent acrylic plates was distinguished.
The pixels in the conventional image sensors are placed at lattice positions, and this causes the jaggies at the edge of the slant line we perceive, which is hard to resolve by pixel size reduction.
The authors have been proposing the method of reducing the jaggies effect by arranging the photo diode at pseudorandom positions, with keeping the lattice arrangement of pixel boundaries that are compatible with the conventional image sensor architecture. In this paper, the authors discuss the design of CMOS image sensor with pseudorandom pixel placement, as well as the the evaluation on image measurement accuracy of line parameters using Hough transform.
A novel user interaction system combining an aerial display and a gesture interaction is expected to provide an excellent user experience. However, its psychometric effectiveness has not been sufficiently explored. In this reported study, we performed a usability test of the system that comprised an aerial display, gesture interaction, and suitable software content. Using a statistical analysis employing the Kruskal Wallis test and a factor analysis of the experimental results, the importance of a suitable combination of aerial display and gesture interaction as well as the novelty of the aerial display were demonstrated. Following this, a two-dimensional aerial display was considered to be adequately useful for a typical spatial user interaction system.
Since multicast distribution using a wireless local area network (WLAN) system is broadcast distribution for each group, it can efficiently use bandwidth and is suitable for broadcast-type video delivery services. However, the conventional multicast distribution scheme for WLAN systems has several issues. A multicast is transmitted at a single transmission rate because of the distribution by a group with multiple stations (STAs). Thus, the STAs far from the access point (AP) cannot receive multicast data at a high transmission rate. On the other hand, in the case of a low transmission rate, it is impossible to transmit high-bit-rate video, and the channel utilization efficiency decreases. Furthermore, since there is no retransmission control function, packet loss occurs immediately when a propagation error or packet collision occurs. In conventional related works, the communication quality suitable for multicast distribution over a WLAN is insufficient.
We propose a multicast distribution scheme for WLAN to solve these issues. The proposed scheme transmits using multiple transmission rates according to the location of the STAs using scalable video coding (SVC) technology. Furthermore, the optimum transmission rate can be selected on the basis of the quality of experience (QoE) indicator and the conditions at the locations of the STAs, and the communication quality can be guaranteed. In this study, we confirm that the proposed scheme maintains a high communication quality, even when the multicast distribution area is expanded compared with that obtained by the conventional scheme.
This paper presents a full-HD autostereoscopic display with a wide viewing zone based on time-division multiplexing slanted parallax barrier with subpixel-based slit control. A slanted directional diffuser placed between the barrier panel and the image panel suppresses moir_ by mixing light from RGB subpixels. By constituting the parallax barrier along with this slanted diffusion line, control of the barrier by subpixel unit is enabled. By introducing subpixel-based phase shift and slit width control to time-division quadruplexing parallax barrier, viewing zone free from crosstalk is enlarged notably. Theoretical viewing zone is calculated and compared with the experimental results using a prototype hardware. The overall crosstalk of the prototype is also measured to confirm the effectiveness of the proposed method.