Pierre-André Besse

Design and characterization of a CMOS 3-D image sensor based on single photon avalanche diodes

The design and characterization of an imaging system is presented for depth information capture of arbitrary three-dimensional (3-D) objects. The core of the system is an array of 32 /spl times/ 32 rangefinding pixels that independently measure the time-of-flight of a ray of light as it is reflected back from the objects in a scene. A single cone of pulsed laser light illuminates the scene, thus no complex mechanical scanning or expensive optical equipment are needed. Millimetric depth accuracies can be reached thanks to the rangefinders optical detectors that enable picosecond time discrimination. The detectors, based on a single photon avalanche diode operating in Geiger mode, utilize avalanche multiplication to enhance light detection. On-pixel high-speed electrical amplification can therefore be eliminated, thus greatly simplifying the array and potentially reducing its power dissipation. Optical power requirements on the light source can also be significantly relaxed, due to the arrays sensitivity to single photon events. A number of standard performance measurements, conducted on the imager, are discussed in the paper. The 3-D imaging system was also tested on real 3-D subjects, including human facial models, demonstrating the suitability of the approach.

Parallel single molecule detection with a fully integrated single-photon 2X2 CMOS detector array

We present parallel single molecule detection (SMD) and fluorescence correlation spectroscopy (FCS) experiments with a fully integrated complementary metal oxide semiconductor (CMOS) single-photon 2x2 detector array. Multifocal excitation is achieved with a diffractive optical element (DOE). Special emphasis is placed on parallelization of the total system. The performance of the novel single-photon CMOS detector is investigated and compared to a state-of-the-art single-photon detecting module [having an actively quenched avalanche photodiode (APD)] by measurements on free diffusing molecules at different concentrations. Despite the order of magnitude lower detection efficiency of the CMOS detector compared to the state-of-the-art single-photon detecting module, we achieve single molecule sensitivity and reliably determine molecule concentrations. In addition, the CMOS detector performance for the determination of the fraction of slowly diffusing molecules in a primer solution (two-component analysis) is demonstrated. The potential of this new technique for high-throughput confocal-detection-based systems is discussed.

Toward a 3-D camera based on single photon avalanche diodes

A three-dimensional (3-D) imager is presented, capable of computing the depth map as well as the intensity scale of a given scene. The heart of the system is a two-dimensional array of single photon avalanche diodes fabricated in standard CMOS technology. The diodes exhibit low-noise equivalent-power high-dynamic range, and superior linearity. The 3-D imager achieves submillimetric precision at a depth-of-field of a few meters. This precision was achieved by averaging over 10 000 measurements. The imager operates using a standard laser source pulsed at 50 MHz with 40-mW peak power and requires no mechanical scanning mechanisms or expensive optical equipment.

Hall detection of magnetic resonance

We propose a detection method for magnetic resonance experiments based on the use of a Hall effect device. To demonstrate its feasibility, we have measured the quasistatic and radio-frequency magnetic fields generated by the unpaired electrons contained in a (50 μm)3 grain of diphenylpicrylhydrazil, excited into magnetic resonance in a 10 mT static magnetic field. The proposed technique has the same versatility of the conventional inductive method but, potentially, allows one to perform magnetic resonance spectroscopy and imaging studies with submicron spatial resolution.

A CMOS 3D camera with millimetric depth resolution

A 3D imager is presented, capable of capturing the depth map of an arbitrary scene. Depth is measured by computing the time-of-flight of a ray of light as it leaves the source and is reflected by the objects in the scene. The round-trip time is converted to a digital code independently for each pixel using a CMOS time-to-digital converter. To reach millimetric accuracies an array of 32/spl times/32 highly sensitive, ultra-low jitter CMOS detectors capable of detecting a single photon is used. The scene is illuminated using a cone of low power pulsed laser light, thus no mechanical scanning devices or expensive optical equipment are required.

A differential relaxation oscillator as a versatile electronic interface for sensors

Abstract A simple and versatile electronic interface circuit for sensors is presented. The novel interface circuit is based on a relaxation oscillator in differential configuration. In such a configuration, the sensitivity is strongly increased and compensations are made possible. It can be applied to resistive, capacitive and inductive sensors or detectors. Experimental and simulation results confirm the theory built up. High sensitivity is measured. Non-idealities of electronic components set the limit of attainable sensitivity.

CMOS imager based on single photon avalanche diodes

In this paper we report on a 32/spl times/32 optical imager based on single photon avalanche diodes integrated in CMOS technology. The maximum measured dynamic range is 120dB and the minimum noise equivalent intensity is 1.3 /spl times/ 10/sup -3/ lx. The minimum integration time per pixel is 4 /spl mu/s. The output of each pixel is digital, thereby requiring no complex read-out circuitry, no amplification, no sample and hold, and no ADC.

A method for spark rejection in ultraviolet flame detectors

A novel method is presented to render ultraviolet (UV) flame detectors insensitive to ignition spark radiation. The method involves isolating the signal due to the sparks from the UV sensor output and subtracting a DC signal proportional to it from the output of the flame detector sensor system. A practical demonstration of the method is given using a commercially available UV flame detector with the addition of an analog circuit to perform the necessary signal processing. A selectivity improvement to spark radiation of greater than 130 has been obtained. The method is robust in that it is independent of the distance between the light source and the flame detector and has been designed to work with different spark generators found on the market. The analog circuit is simple, requiring few components, thus ensuring rugged, fail-safe operation and low cost.

Scaling down an inductive proximity sensor

Abstract We analyse the problem of scaling down an inductive proximity sensor made of superposed multiple-turn flat coils. We scale down linearly all the geometrical dimensions. Then the nominal inductance is scaled down proportionally to the scale factor. The coupling factor of the superposed coils remains constant. However, for both ferromagnetic and non-ferromagnetic targets, the sensitivity remains constant when the frequency is scaled by the inverse square of the reduction factor. But the parasitic effects in the sensor coil become more important for small device dimensions. Therefore these effects are expected to set the ultimate limit in the miniaturization of the integrated inductive proximity sensors.

Temperature compensation of an integrated low power inductive proximity microsensor

Abstract A simple temperature compensation method for inductive proximity microsensors based on the differential relaxation oscillator has been developed and successfully tested. With this compensation and for the temperature range from −20°C to +80°C, an accuracy better than ±10 μm at 1 mm distance to an aluminum target has been measured. The microsensor has been integrated with a 3-V, 1-μm CMOS read-out circuit using a gold bumping layer to form a 3.8-mm side flat coil. The power consumption of the whole compensated microsystem is lower than 10 mW. To achieve this, the temperature behaviors of the whole microsensor and of its building elements, namely the sensing coil (nearby a target) and the read-out circuit, have been studied and a compensation method has been developed. The inductance of the integrated coil is temperature-independent in the frequency range up to 12 MHz, whereas its resistance depends mainly on the temperature coefficient of the conductor resistivity. The resonance frequency of the coil is not affected by temperature. In its principle, the electronic circuit has a temperature-dependent drift in the sensing distance range. This drift can, however, be compensated using a negative temperature coefficient resistor. Analytical derivations and simulation tools have been used for the choice of the optimal coefficient for a specific sensing distance range.