We report novel event-driven noise reduction circuits with correlated double sampling (CDS) technique for pulse-frequency-modulation (PFM) analog-to-digital converters (ADCs). PFM-ADCs are promising for pixel-parallel 3-D integrated image sensors with excellent imaging performance. The developed ADC with CDS consists of comparators, capacitors, and timing control logic circuits that are designed to generate the triggered clocks to cancel kTC noise in a pixel. We confirmed that the prototype ADC showed noise reduction effects and also an excellent linearity with a wide dynamic range of 120 dB, which indicates the feasibility of high-quality pixel-wise image sensors.
We describe a high optical performance 3.4 μm pixel pitch global shutter CMOS image sensor with a light guide structure. The sensitivity and the parasitic light sensitivity are 28,000 e-/lx·s and -89 dB, respectively. Moreover, the incident light angle dependence of sensitivity and parasitic light sensitivity has been improved by the light guide structure. The pixel achieves 1.8 e- temporal noise and full well capacity of 16,200 e- with charge domain memory in 120 fps operation by multiple accumulation shutter technology.
This paper reports a spectral imaging system using a high signal to noise ratio(SNR) 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, 1.5×10＾7 e- FWC, 190-1100nm spectral sensitivity, with very high quantum efficiency. Also showed that the developed multi-bandpass filter can select four wavelengths: 630nm, 800nm, 960nm and 1050nm with 10nm FWHM. Using the developed spectral imaging system, a diffusion of 5mg/dl glucose into physiological saline solution was captured images under 960nm and 1050nm wavebands, at which absorptions of water molecules and glucose appear within UV to NIR waveband respectively.
In this work, statistical analyses of random telegraph noise (RTN) at in-pixel source followers using array test circuit are reported with following two focuses. The first one is the impact of time constants and number of states toward readout noise in CMOS image sensors. The other one is the impact of transistor shapes. SF transistors with various shapes including rectangular, trapezoidal and octagonal structures were analyzed and reduction effect of RTN is summarized.
Automotive LIDAR is a significant sensor that can grasp the circumstances around the vehicle necessary for automated driving and advanced driving assistant system. The research and development for LIDAR has been advanced by many research institutes and companies. We are also conducting research aiming for compact size and high sensitivity for automotive LIDAR.
In the last decade, the image sensors for 3D measurement are employed widely and require the stability and reliability especially for mobile devices and automobiles in strong background light. Compared to strong background light, the intensity of the reflected light incident on the image sensor is very low, so environmental tolerance is required, and in particular, an image sensor not dependent on the background light is required. In this study, three-dimensional shape acquisition system is using modulated light with a specific frequency. After the photocurrent by background light is sampled using a current mirror, the pixel circuit can compensate the photocurrent by background light when signal light is accumulated. A TEG of the pixel circuit is fabricated in the ROHM 0.18μm process, and the signal to background light ratio (SBR) in the simulation is -43.5 dB.
A 4.1Mpix 280fps stacked CMOS image sensor with array-parallel ADC architecture is developed for region control applications. The combination of an active reset scheme and frame correlated double sampling (CDS) operation cancels Vth variation of pixel amplifier transistors and kTC noise. The sensor utilizes a floating diffusion (FD) based back-illuminated (BI) global shutter (GS) pixel with 2.4e-rms readout noise. An intelligent sensor system with face detection and high resolution region-of-interest (ROI) output is demonstrated with significantly low data bandwidth and low ADC power dissipation by utilizing a flexible area access function.
In new markets such as in-vehicle cameras and sensing applications that are rising rapidly in recent years, there is a growing need for image sensors that have a wider dynamic range and are more resistant to the image of moving subjects with high sensitivity and low noise. We have developed a single exposure CIS (CMOS image sensor) which has multiple gain switching functions for each pixel and has a dynamic range exceeding 91dB.
The required incorporation of an additional in-pixel retention node for global shutter complementary metal-oxide semiconductor (CMOS) image sensors means that achieving a large saturation signal presents a challenge. This paper reports a 3.875-μm pixel single exposure global shutter CMOS image sensor with an in-pixel pinned storage (PST) and a lateral-overflow integration capacitor (LOFIC), which extends the saturation signal to 224 ke−, thereby enabling the saturation signal per unit area to reach 14.9 ke−/μm^2. This pixel can assure a large saturation signal by using a LOFIC for accumulation without degrading the image quality under dark and low illuminance conditions owing to the PST.