D. Stoppa

Novel CMOS image sensor with a 132-dB dynamic range

A CMOS image sensor providing an ultrawide dynamic range with a piecewise linear response is presented. The active pixel is based on a novel architecture which implements a voltage comparator and an analog memory to detect and store the information on the integration time needed to reach saturation, while also maintaining the standard integrated photo-current signal. A 128/spl times/64 pixel array has been designed and fabricated in 0.35-/spl mu/m, 3.3-V CMOS technology. The chip measures 2.67/spl times/4.90 mm/sup 2/ with a pixel size of 24.65/spl times/24.65 /spl mu/m/sup 2/ and a fill factor of about 11%. The sensor has been fully characterized and the measured dynamic range turned out to be 132 dB with a power consumption of 14 mW at video frame rate. The sensor features also good noise performance with a temporal noise of 0.2% (1.7%) and a fixed pattern noise of 0.4% (1.5%) at low (high) irradiance.

Avalanche Photodiodes in Submicron CMOS Technologies for High-Sensitivity Imaging

Vacuum based devices, such as Photo Multiplier Tubes (PMT) and Micro Channel Plates (MCP), have been for many years the sensors of choice for most applications calling for photon counting and timing (Renker, 2004). While providing very good sensitivity, noise and timing characteristics, these photodetectors feature a number of disadvantages: they are bulky, fragile, and sensitive to magnetic fields; they require very high operation voltages, and have large power consumption; in their high-performance models, providing good spatial resolution, they are still very expensive. For high-sensitivity imaging applications, suitable solutions are represented by CCD cameras coupled with either MCP Image Intensifiers (I-CCDs) or Electron Multipliers (EM-CCDs) (Dussault & Hoess, 2004). However, besides being very expensive, their performance is not completely satisfactory in extreme time resolved measurements. For reasons of cost, miniaturization, ruggedness, reliability, design flexibility, integration density, and signal processing capabilities, a fully solid-state solution (and, particularly, CMOS technology) would be highly desirable. Among the advanced CMOS image sensors so far reported, the most promising ones in terms of high sensitivity and fast timing are those based on Single Photon Avalanche Diodes (SPADs). SPADs are avalanche photodiodes operated in the so-called Geiger mode, i.e., biased above breakdown, so as to be sensitive to single photons (Cova et al., 1996). Although these sensors have been developed for more than 30 years, in particular owing to the group of Prof. Cova at Politecnico di Milano, and single devices have reached outstanding performance (Ghioni et al., 2007), only recently the perspective of making a SPAD-based camera has become feasible. The first SPAD-based pixel arrays in CMOS technology have been demonstrated only a few years ago (Rochas et al., 2003a), but since then further developments rapidly followed, also facilitated by the availability of commercial, High-Voltage CMOS technologies (HV-CMOS) aimed at integrated circuits for power electronics, as well as of specially tailored “imaging” processes, which have been boosted by the huge market of

A versatile photodiode SPICE model for optical microsystem simulation

We report on the definition and the implementation in ANACAD Eldo simulator of a photodiode circuit macro-model to be used in the design of optical smart sensors such as position sensing detectors (PSDs) and digital cameras. The optical power waveform as well as its spectrum can be easily defined by the user, allowing for a high flexibility of the model. The effectiveness of the proposed macro-model is highlighted by comparing Eldo simulation results with both numerical device simulation results and experimental data.

A 138 dB dynamic range CMOS image sensor with new pixel architecture

A 128/spl times/64 pixel image sensor in 0.35 /spl mu/m 3.3V CMOS technology achieves 138 dB dynamic range by adapting single-pixel integration time to the local illumination conditions. Video frame rate is achieved with 0.2% rms temporal noise and 14 mW power in a test chip.

A CMOS Sensor based on Single Photon Avalanche Diode for Distance Measurement Applications

This paper describes the design of a 64x2-pixel array, fabricated in a conventional industrial high-voltage 0.8μm CMOS technology, and aimed at 3D measurements based on the time-of-flight technique. Light signals are detected using a photodiode biased above its breakdown voltage so that an extremely high sensitivity can be achieved exploiting the intrinsic multiplication effect of the avalanche phenomenon. A single photon avalanche diode and dedicated read-out electronics for light pulses arrival-time estimation have been implemented in a 38times180-μm2 pixel with an expected power consumption of about 20 muW. To increase the distance measurement resolution a multiple pulse measurement is used, extracting the mean value of the light pulse arrival-time directly in each pixel; this innovative approach dramatically reduces the dead-time of the pixel read-out, allowing a high frame rate imaging to be achieved

A CMOS photosensor test-chip for smoke detection applications

We report on a CMOS integrated photosensor specially tailored for smoke detection applications. A test chip consisting of an integrated photodiode, which reveals the light scattered by smoke particles, and of the related read-out electronics, has been designed and fabricated in 0.8 /spl mu/m CMOS technology. The circuit design is based on the Switched Capacitor (SC) technique, and accomplishes low noise specifications by means of an accurate design of the first read-out stage and by employing Correlated Double Sampling (CDS) filtering blocks. Circuit simulations and preliminary results from the electrical characterization of the first chip prototype allowed the basic design methodology to be validated.

A CMOS ASIC for differential read-out of ISFET sensors

We report on a CMOS ASIC especially taylored for the differential read-out of ISFET sensors, to be used for remote monitoring of water pollution and for biomedical diagnostic and analysis. The circuit design is based on switched-capacitors technique, which allows a high resolution to be achieved. The first chip prototypes have been fabricated in 0.8 /spl mu/m, 5 V CMOS technology, and are currently being tested. Preliminary results from the electrical characterisation of the chip are reported, which validate the design approach.

Linear-Mode Gain-Modulated Avalanche Photodiode Image Sensor for Time-of-Flight Optical Ranging

In this paper, a CMOS image sensor based on avalanche photodiodes (APDs) for time-of-flight optical ranging is presented. In-pixel phase-sensitive detection was obtained thanks to the modulation of APD avalanche gain. A pixel based on this principle with 30-μm pixel pitch and 25.7% fill factor was designed, and a 64 × 64 APD image sensor was fabricated in a 0.35-μm standard CMOS process. The maximum demodulation contrast measured on the array exceeds 85% at 25-MHz modulation frequency. High-frequency modulation was demonstrated on single test pixels, where a demodulation contrast as high as 80% was measured at 200-MHz modulation frequency. A 3-D camera working at a frame rate up to 200 frames/s was realized and characterized.

CMOS distance sensor based on single photon avalanche diode

This paper reports on a novel image sensor employing a Single Photon Avalanche Diode (SPAD) as light-sensing device. The sensor is specifically designed for Time-OfFlight 3D imaging applications. An active pixel containing a SPAD and a read-out channel has been designed. An averaging circuit is included in the pixel, allowing an increased resolution with a reduction of the overall measurement time. A 64x2 pixel linear array has been fabricated in a conventional industrial high-voltage 0.8μm CMOS technology, together with some test structures aimed at SPAD characterization. An electro optical characterization of the test structures has been performed. The pixel array, although tailored for 3D imaging, can be also used to acquire the intensity map of a scene. A characterization of the operation in both modalities is presented.

A novel 3D staring system for driver assistance

This paper reports on the development of an intelligent electro-optical device for the 3D detection of drive scenarios and obstacles recognition; the work is being carried out in the frame of a national program, under the acronym OPTO3D and involving Centro Ricerche Fiat, Istituto per la Ricerca Scientifica e Tecnologica and University of Trento. The system is finalized to automotive drive assistance functions, particularly to the pre-crash application. It is based on a new CMOS image sensor that enhances the passive 2D vision through the on-pixel integration of distance information, with high dynamic range. The 3D detection is based on a novel active imaging technique, derived from the time of flight concept. Novel intelligent processing algorithms support the objects recognition.