Keita Yasutomi

Image-sensor-based visible light communication for automotive applications

The present article introduces VLC for automotive applications using an image sensor. In particular, V2I-VLC and V2V-VLC are presented. While previous studies have documented the effectiveness of V2I and V2V communication using radio technology in terms of improving automotive safety, in the present article, we identify characteristics unique to image-sensor-based VLC as compared to radio wave technology. The two primary advantages of a VLC system are its line-of-sight feature and an image sensor that not only provides VLC functions, but also the potential vehicle safety applications made possible by image and video processing. Herein, we present two ongoing image-sensor-based V2I-VLC and V2VVLC projects. In the first, a transmitter using an LED array (which is assumed to be an LED traffic light) and a receiver using a high-framerate CMOS image sensor camera is introduced as a potential V2I-VLC system. For this system, real-time transmission of the audio signal has been confirmed through a field trial. In the second project, we introduce a newly developed CMOS image sensor capable of receiving highspeed optical signals and demonstrate its effectiveness through a V2V communication field trial. In experiments, due to the high-speed signal reception capability of the camera receiver using the developed image sensor, a data transmission rate of 10 Mb/s has been achieved, and image (320 × 240, color) reception has been confirmed together with simultaneous reception of various internal vehicle data, such as vehicle ID and speed.

LED and CMOS Image Sensor Based Optical Wireless Communication System for Automotive Applications

An optical wireless communication (OWC) system based on a light-emitting-diode (LED) transmitter and a camera receiver has been developed for use in the automotive area. The automotive OWC system will require Mb/s-class data rates and the ability to quickly detect LEDs from an image. The key to achieving this is improvements to the capabilities of the image sensor mounted on the camera receiver. In this paper, we report on a novel OWC system equipped with an optical communication image sensor (OCI), which is newly developed using CMOS technology. To obtain higher transmission rates, the OCI employs a specialized “communication pixel (CPx)” capable of responding promptly to optical intensity variations. Furthermore, a new quick LED detection technique, based on a 1-bit flag image which only reacts to high-intensity objects, is formulated. The communication pixels, ordinary image pixels, and associated circuits (including 1-bit flag image output circuits) are then integrated into the OCI. This paper describes the design, fabrication, and capabilities of the OCI, as well as the development of the LED and image sensor based OWC system, which boasts a 20-Mb/s/pixel data rate without LED detection and a 15-Mb/s/pixel data rate with a 16.6-ms real-time LED detection.

Optical Vehicle-to-Vehicle Communication System Using LED Transmitter and Camera Receiver

This paper introduces an optical vehicle-to-vehicle (V2V) communication system based on an optical wireless communication technology using an LED transmitter and a camera receiver, which employs a special CMOS image sensor, i.e, an optical communication image sensor (OCI). The OCI has a “communication pixel (CPx)” that can promptly respond to light intensity variations and an output circuit of a “flag image” in which only high-intensity light sources, such as LEDs, have emerged. The OCI that employs these two technologies provides capabilities for a 10-Mb/s optical signal reception and real-time LED detection to the camera receiver. The optical V2V communication system consisting of the LED transmitters mounted on a leading vehicle and the camera receiver mounted on a following vehicle is constructed, and various experiments are conducted under real driving and outdoor lighting conditions. Due to the LED detection method using the flag image, the camera receiver correctly detects LEDs, in real time, in challenging outdoor conditions. Furthermore, between two vehicles, various vehicle internal data (such as speed) and image data (320 × 240, color) are transmitted successfully, and the 13.0-fps image data reception is achieved while driving outside.

A Low-Noise High Intrascene Dynamic Range CMOS Image Sensor With a 13 to 19b Variable-Resolution Column-Parallel Folding-Integration/Cyclic ADC

A low temporal noise and high dynamic range CMOS image sensor is developed. A 1Mpixel CMOS image sensor with column-parallel folding-integration and cyclic ADCs has 80μV_rms (1.2e^-) temporal noise, 82 dB dynamic range using 64 samplings in the folding-integration ADC mode. Very high variable gray-scale resolution of 13b through 19b is attained by changing the number of samplings of pixel outputs. The implemented CMOS image sensor using a 0.18-μm technology has the sensitivity of 10-<i>V</i>/lx·s, the conversion gain of 67- μV/e^-, and linear digital code range of more than 4 decades.

A 0.27e-rms Read Noise 220-μV/e-Conversion Gain Reset-Gate-Less CMOS Image Sensor With 0.11-μm CIS Process

A low temporal read noise and high conversion gain reset-gate-less CMOS image sensor (CIS) has been developed and demonstrated for the first time at photoelectron-counting-level imaging. To achieve a high pixel conversion gain without fine or special processes, the proposed pixel has two unique structures: 1) coupling capacitance between the transfer gate and floating diffusion (FD) and 2) coupling capacitance between the reset gate and FD, for removing parasitic capacitances around the FD node. As a result, a CIS with the proposed pixels is able to achieve a high pixel conversion gain of 220 μV/e- and a low read noise of 0.27erms- using correlated multiple-sampling-based readout circuitry.

A Time-Resolved CMOS Image Sensor With Draining-Only Modulation Pixels for Fluorescence Lifetime Imaging

This paper presents a time-resolved CMOS image sensor with draining-only modulation (DOM) pixels, for time-domain fluorescence lifetime imaging. In the DOM pixels using a pinned photodiode (PPD) technology, a time-windowed signal charge transfer from a PPD to a pinned storage diode (PSD) is controlled by a draining gate only, without a transfer gate between the two diodes. This structure allows a potential barrierless and trapless charge transfer from the PPD to the PSD. A 256 × 256 pixel time-resolved CMOS imager with 7.5 × 7.5 μm2 DOM pixels has been implemented using 0.18-μm CMOS image sensor process technology with PPD option. The prototype demonstrates high sensitivity for weak signal of less than one electron per light pulse and accurate measurement of fluorescence decay process with subnanosecond time resolution.

A 2.7e- temporal noise 99.7% shutter efficiency 92dB dynamic range CMOS image sensor with dual global shutter pixels

A low-noise global shutter CMOS image sensor is a next challenge to expand the market for CMOS image sensors. A low-noise global electronic shutter can be used for various applications such as high-speed imaging, machine vision and mechanical shutterless digital still cameras. A commonly used five transistor (5T) global shutter pixel using a floating diffusion memory suffers from large temporal noise due to kTC noise (reset noise) and large dark current [1]. Two-stage charge transfer pixels such as a seven transistor (7T) active pixel [2] and a dual pinned-diode active pixel presented by the authors [3] cancel the kTC noise. However, such structures have an issue of low shutter efficiency due to leakage from a photodiode to storage gate or diode. Furthermore, the 7T pixel suffers from dark current and transfer noise because of the use of surface-channel storage gates. The dual pinned-diode pixel of the previous design has problem of non-linearity due to poor charge transfer efficiency from a photodiode to storage diode.

High-speed charge transfer pinned-photodiode for a CMOS time-of-flight range image sensor

This paper presents a structure and method of range calculation for CMOS time-of-flight(TOF) range image sensors using pinned photodiodes. In the proposed method, a LED light with short pulse width and small duty ratio irradiates the objects and a back-reflected light is received by the CMOS TOF range imager.Each pixel has a pinned photodiode optimized for high speed charge transfer and unwanted charge draining. In TOF range image sensors, high speed charge transfer from the light receiving part to a charge accumulator is essential.It was found that the fastest charge transfer can be realized when the lateral electric field along the axis of charge transfer is constant and this conditon is met when the shape of the diode exactly follows the relationship between the fully-depleted potential and width. A TOF range imager prototype is designed and implemented with 0.18um CMOS image sensor technology with pinned photodiode 4transistor(T) pixels. The measurement results show that the charge transfer time is a few ns from the pinned photodiode to a charge accumulator.

A Two-Stage Charge Transfer Active Pixel CMOS Image Sensor With Low-Noise Global Shuttering and a Dual-Shuttering Mode

A complementary metal-oxide-semiconductor (CMOS) image sensor with low-noise global shuttering and a dual-shuttering mode is presented. The developed two-stage charge transfer pixel enables noise canceling by means of true correlated double sampling. The implemented prototype demonstrates for the first time that a noise level of less than three electrons can be achieved in a global-shutter CMOS image sensor while attaining high shutter efficiency of 99.7%. In the dual-shuttering mode, both a pinned storage diode signal and a floating diffusion signal are used for desirable functions such as wide-dynamic-range imaging, motion detection, and dual consecutive snapshot imaging.

A Low Noise Wide Dynamic Range CMOS Image Sensor With Low-Noise Transistors and 17b Column-Parallel ADCs

An extremely low temporal noise and wide dynamic range CMOS image sensor is developed using low-noise transistors and high gray-scale resolution (17b) folding-integration/cyclic analog-to-digital converter (ADC). Two types of pixel are designed. One is a high conversion gain (HCG) pixel with removing the coupling capacitance between the transfer gate and the floating diffusion, and the other is a pixel for wide dynamic range (WDR) CMOS imager with a native transistor as a source follower amplifier. The CMOS image sensor that is in combination with the proposed pixels and the high performance column ADC has achieved a low pixel temporal noise of 1.1erms-, a wide dynamic range of 87.5 dB with the video rate operation (30 Hz) and the vertical fixed pattern noise of 1.08-μVrms. The implemented HCG CMOS imager and WDR CMOS imager using 0.18 μm technology have the pixel conversion gain of 73.2- and 22.8-μV/e-, respectively.