Automatic rearview mirror system using a photosensor array

A system apparatus, structure and method for controlling a plurality of variable reflectance mirrors (or mirror segments), including a rearview mirror and side view mirrors, which change their reflectance level in response to a plurality of drive voltages applied thereto, for an automotive vehicle. The system includes a light sensing device and a control circuit formed as a single VLSI CMOS circuit. The light sensing device comprises a photosensor array having a field of view encompassing a rear window area and at least a portion of at least one side window area of the vehicle. The logic and control circuit determines a background light signal from photosensor element signals generated by the photosensor elements in the photosensor array indicative of light levels incident on the photosensor elements. The circuit also determines a peak light signal in three different zones or sub-arrays of the photosensor array. The zones or sub-arrays may correspond to three mirrors or mirror segments. The peak light signals in each of the zones and a common background light signal are used to determine independent and separate control signals, which are then output to separate mirror drive circuits for independently controlling the reflectance level of the rearview mirror and the left and right side view mirrors, or alternatively the segments of a mirror.
Description
This application is a divisional of application Ser. No. 08/023,918 filed Feb. 26, 1993, now U.S. Pat. No. 5,550,677.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an automatic rearview mirror system for automotive vehicles which automatically changes reflectance level in response to glare causing light, and more particularly relates to an improved automatic rearview mirror system using only a rearwardly facing sensor.
2. Description of Related Art
Automatic rearview mirrors and mirror systems have been devised for varying the reflectance level of a variable reflectance rearview mirror by reducing the reflectance automatically in response to annoying glare light, as seen rearwardly of the rearview mirror or mirrors by a driver of the vehicle, and by increasing automatically the reflectance to a normal or maximum reflectance level when the annoying glare light subsides. These automatic mirrors have been changed over the years in an effort to improve their performance characteristics and associated level of glare protection.
Early automatic rearview mirrors used a rearwardly facing sensor and control circuit to change mirror reflectance. One example of such a "single-sensor" type mirror is described in U.S. Pat. No. 4,266,856. In these prior art single-sensor type mirrors, the rear glare light was incident on a rearwardly facing sensor or photocell, such as a photodiode, photoresistor or phototransistor. These mirrors suffered from various problems, however, including the problem that these mirrors would become increasingly sensitive and even "lock-up" in their minimum reflectance level or state as the driver encountered significantly higher light levels in town or city driving. This required the driver to repeatedly adjust the mirror's sensitivity control to prevent such problems.
To overcome the problems of single-sensor type mirrors, a non-rearwardly facing photocell for sensing "ambient" light was added. It was believed that the desired reflectance necessary to relieve the driver from glare depended not only on glare light but also on ambient light. Accordingly, these "two-sensor" type mirrors used two separate photocells, one generally facing rearwardly and one generally facing forwardly (or other non-rearwardly facing direction) of the mirror or vehicle. The signals from these two photocells were then compared in some fashion, and when, for example, the glare light from the rear was comparatively high with respect to the "ambient" light, a control circuit would apply a control signal to reduce mirror reflectance. Some examples are described in German Laid-Open Patent No. 3,041,692; Japanese Laid-Open Patent No. 58-19941; and U.S. Pat. Nos. 3,601,614; 3,612,666; 3,680,951; 3,746,430; 4,443,057; 4,580,875; 4,690,508; and 4,917,477. In many of these prior art automatic rearview mirrors, light generally forward of the mirror or vehicle was incident on the second photocell.
These arrangements, however, also had problems. In some of these mirrors the forwardly facing or "ambient" light sensor was inaccurate because it did not correctly measure ambient light levels since it did not include light generally rearward of the mirror or vehicle. Some examples include the devices described in U.S. Pat. Nos. 4,443,057 and 4,917,477. Other prior art devices overcame these deficiencies by providing a control circuit which correctly measured ambient light as a combination of both the forward and rear light levels. Examples of this significantly different approach are described in U.S. Pat. Nos. 4,793,690 and 4,886,960.
The prior art two-sensor type systems generally provided improved performance over prior art single-sensor type systems but were also more complex and costly. In part, this was because using separate forwardly and rearwardly facing photocells required that the performance characteristics of the two separate photocells, such as photoresistors, be matched appropriately to ensure consistent performance under various operating conditions. Matching photocells such as photoresistors, however, generally involves complex, expensive and time consuming operations and procedures.
Both the prior art single-sensor and two-sensor type mirrors presented additional problems when they were also used to control the exterior side view mirrors. This is because such prior art systems used a common control or drive signal to change the reflectance level of both the interior rearview mirror and the exterior left and/or right side view mirrors by substantially the same amount. In U.S. Pat. No. 4,669,826, for example, a single-sensor type mirror system used two rearwardly facing photodiodes to control both an interior rearview mirror and the left and/or right side view mirrors based on the direction of incident light from the rear. Another example includes the two-sensor type system described in U.S. Pat. No. 4,917,477.
In rearview mirror systems, however, each of the interior rearview and exterior side view mirrors may reflect different source light levels. More specifically, the inside rearview mirror, left side view mirror and right side view mirror each enable the driver to view a different portion or zone of the total rearward area. Of course, there may be some overlap of the image information contained in each of the three zones. The situation is further complicated with multi-lane traffic because each of the mirrors reflects different light levels caused by the headlights of the vehicles which are following, passing or being passed. As a result, in the prior art systems, when the reflectance level of the interior rearview mirror was reduced to decrease the glare of headlights reflected therein, the reflectance level of the exterior left and right side view mirrors was also reduced by substantially the same amount, even though, for example, the side view mirrors might not be reflecting the same level of glare light, if any. Accordingly, rear vision in the exterior left and right side view mirrors could be improperly reduced.
Other prior art two-sensor type systems used a common ambient light sensor and several rearwardly facing sensors, one for each of the mirrors. An example is the alternate system also described in U.S. Pat. No. 4,917,477. This approach is not satisfactory, however, because it reduces system reliability and increases complexity and cost.
Finally, some prior anti-glare mirrors used several sensors to control the segments of a variable reflectance mirror. One example is disclosed in U.S. Pat. No. 4,632,509, which discloses a single-sensor type mirror using three rearwardly facing photocells to control three mirror segments depending on the direction of incident light from the rear. See also U.S. Pat. No. 4,697,883. These prior mirror systems generally have the same problems as the other single-sensor type mirrors. Some other anti-glare mirrors are generally disclosed in U.S. Pat. Nos. 3,986,022; 4,614,415; and 4,672,457.
Consequently, there is a need for an automatic rearview mirror system for an automotive vehicle having improved reliability and low cost, which accurately determines or otherwise discriminates light levels that the driver will experience as glare without the need for a separate forwardly facing photocell. In addition, as noted above, there is also a need for an automatic rearview mirror system of high reliability and low cost, which accurately determines light levels that the driver will experience as glare, and which can control independently the reflectance of a plurality of mirrors according to the light levels actually reflected by each of the rearview and exterior side view mirrors without the need for additional and separate rearwardly facing photocells. There is also a need for an automatic rearview mirror system that can independently control the segments of a variable reflectance mirror while accurately determining light levels that the driver will experience as glare in each segment of the mirror without the need for additional and separate forwardly and rearwardly facing photocells.

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InGaP/GaAs heterojunction photosensor powered by an on-chip GaAs solar cell for energy harvesting

In this study, an InGaP/GaAs heterojunction phototransistor (HPT) and a GaAs solar cell were monolithically integrated into an HPT epitaxial wafer, and the battery-free operation of the HPT was demonstrated for energy harvesting. Although the thickness and doping condition of the layers were optimized for the HPT performance, but not for the solar cell performance, the obtained short-circuit current was high enough to operate the InGaP/GaAs HPT in a two-terminal (2T) configuration. A collector photocurrent of 0.63 mA was obtained when the energy-harvesting InGaP/GaAs 2T-HPT was exposed to white light with a power density of 35 mW/cm², and it linearly increased with the power density. For a potential application of the energy-harvesting InGaP/GaAs HPT as a photosensor in space, the device was irradiated with electrons of 1 MeV energy and 10¹⁵ cm⁻² fluence. No significant degradation of the fabricated energy-harvesting 2T-HPT after the high-energy electron irradiation guarantees its battery-free operation in space.

A heterojunction phototransistor (HPT) is more attractive as a photosensor than a photodiode because of its high photoresponse even at low bias voltage and immunity from avalanche noise. In particular, the GaAs-based HPT with an AlGaAs emitter demonstrated a high performance. Recently, the InGaP emitter has replaced the AlGaAs emitter in the AlGaAs/GaAs HPT owing to its superior material properties. The photosensor may be widely used in space, where it needs to be operated without a battery. An HPT has a process compatibility with a heterojunction bipolar transistor (HBT) for the fabrication of monolithically integrated photoreceivers. The InGaP/GaAs HPT also has good compatibility with the GaAs heteroface solar cell for a battery-free operation. Solar cells made of III–V compound semiconductors have been developed and used in space owing to their high conversion efficiency, lower temperature coefficient, and superior radiation resistance. The significant potential of high-efficiency GaAs heteroface solar cells for space applications has been extensively investigated by many researchers.Compared with Si, which has been widely used as a material of terrestrial solar cells, III–V compound semiconductors have a superior radiation resistance for the same electron energy and fluence. In particular, the InGaP solar cells demonstrated a radiation resistance superior to that of GaAs solar cells. Since the migration energy of radiation-induced defects and the activation energy of defect annealing in InGaP are lower than those in GaAs, InGaP has a higher radiation resistance than GaAs. In this study, radiation resistant InGaP was used as a window layer in a GaAs heteroface solar cell.
In space, high-energy electron or particle irradiation often induces a significant degradation of the performance of semiconductor devices. Since the battery-free operation of an InGaP/GaAs HPT monolithically integrated with a GaAs solar cell is also proposed for use in space in this paper, the effects of high-energy electron irradiation on the fabricated energy-harvesting HPTs were studied by 1 MeV electron irradiation.

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Low-cost miniaturized UV photosensor for direct measurement of DNA concentration

Highly sensitive measurement of DNA concentration on portable, easy-to-use, low-cost miniaturized equipments without sample waste is challenging.
The DNA peak optical absorbance at λ=260 nm is a well-known property already used in the spectrometric measurement of DNA concentration. Existing apparatus are large-sized, expensive and require a manipulation of DNA. In the current work, a low-power, suitable and miniaturized photosensor aiming at a sensitive and direct measurement of DNA concentration has been designed. Direct measurement, i.e. without sample manipulation, implies UV transmission through the translucid tube wall from the closed tube containing the DNA sample in solution.
To allow measurements at such low wavelengths, we designed and fabricated photodiodes in SOI technology to ensure a high responsivity in the UV range. Measurements of the photodevice confirmed its responsivity spectrum and magnitudes. These fully integrable photodiodes, fabricated in SOI CMOS technology, can be coupled to a complete signal processing microsystem.
Direct measurements at 280 nm optical wavelength of serially diluted DNA within a closed tube (range: 40 pg/μL to 400 ng/μL in a volume of 45 μL) generated a monotonic relation between the DNA concentration and the mean of the diode photocurrent induced by light transmission through DNA solution and tube container. Absorbance of the incident UV ray was inversely proportional to DNA concentration. The photosensor compared favorably with other DNA quantitative methods (spectrophotometry, fluorometry, real-time PCR) in terms of sensitivity.
Originalities of this work are the use of a thin-film SOI photosensor, the low-cost, portable and adaptable system and the potential of the device for direct measurement of nucleic acid concentration within tube containers without sample manipulation or waste.

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Toshiba Matsushita Display Develops Photosensor Touch-Panel

Toshiba Matsushita Display Technology Co., Ltd. (TMD) has developed an LCD panel that enables finger-touch input using photosensors under a range of light conditions from dark indoor to bright outdoor. Through enhanced sensitivity of the photosensors integrated onto the LCD panel's glass substrate and optimized signal processing functions, the panel detects reflection from a finger using backlight in dark indoor and finger shadows using external light in bright outdoor.

The prototyped panel is a transmissive LCD panel using a 2.8-inch (7.1 cm diagonal) WQVGA (400 x 240 pixels) resolution, low-temperature polycrystalline Si (p-Si) TFT with approximately 65,000 display colors. The range of ambient light intensity, in which finger-touch input is available, extends from 0 to 100,000 lx.

The panel has become able to recognize finger-touch input in a wide range of light intensity by switching its recognition modes between finger shadows using external light and finger reflections using its built-in backlight depending on the situation. The panel not only recognizes finger shadows but also supports input using an optic pen. TMD will present this panel at the Flat Panel Display International (Display 2007) show to be held at Tokyo Big Sight from April 11 to 13.

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Beam extrapolation and photosensor testing for the T2K experiment

Our understanding of the physics of neutrino oscillations has evolved rapidly over the past decade or so, with results from the SNO, Super-K, MINOS and CHOOZ experiments, among others, producing results favouring a three-neutrino mixing model, and significantly constraining the parameter space for the mixing.

There are still several important questions to be answered however: we do not know whether theta_13 is non-zero, or whether (sin^2 (2*theta_23)) is maximal; also, we do not know the sign of the mass splitting Delta M^2, or whether CP-violation occurs in the lepton sector. The latter is possibly the most exciting of all - leptonic CP-violation is a requirement for leptogenesis, and could therefore indicate a solution to the matter-antimatter asymmetry problem in cosmology. The T2K long-baseline neutrino experiment is one of a new generation of neutrino projects, which will make more precise measurements of theta_13 and theta_23 than has been achieved by previous experiments. It uses the Super-K water Cerenkov detector at Kamioka as a far detector, and also has a suite of new near detectors.

These are largely scintillator-based, but use a novel photosensor, the silicon photomultiplier (SiPM), for light readout. T2K has been leading the effort understand and model these new sensors, and the present work will describe the current state-of-the-art in device characterisation, and also the effort to ensure the quality of the devices installed in the calorimeter of the ND280 near detector. An important part of a long-baseline analysis is the extrapolation of the neutrino flux measured at the near detector to predict that at the far detector. Methods to do this have been developed by previous experiments; however T2K uses an innovative configuration whereby the main detectors are displaced from the neutrino beam centre, removing much of the high-energy tail in the neutrino flux to reduce backgrounds from non-quasielastic events. This thesis evaluates the effectiveness of two extrapolation techniques, used by previous experiments, for the T2K configuration.

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Graphene photosensor integrated into computer chip

Today, most information is transmitted by light – for example in optical fibres. Computer chips, however, work electronically. Somewhere between the optical data highway and the electronic chips, photons have to be converted into electrons using light-detectors.

Scientists at the Vienna University of Technology have integrated a graphene photosensor with a standard silicon chip. The hybrid device can transform light of all important telecommunications frequencies into electrical signals. The scientific results have now been published in the journal Nature Photonics.

Optical fiber transmission uses wavelengths that are in the near-infrared portion of the spectrum. Typical wavelengths are 850nm, 1310nm, and 1550nm. Both lasers and LEDs are used as transmission sources; lasers usually for 1310 or 1550nm single-mode applications while LEDs typically for 850nm or 1300nm multimode applications.

Both academia and the industry are placing high hopes in graphene for many different applications. Two years ago, the team of Thomas Müller (Institute of Photonics, Vienna University of Technology) demonstrated that graphene is ideally suited to convert light into electrical current.

Müller commented, “There are many materials that can transform light into electrical signals, but graphene allows for a particularly fast conversion. So wherever large amounts of data are to be transmitted in a short period of time, graphene will in the future probably be the material of choice.”

Significant development

The researchers had to come a long way from the basic proof of what the material can do to actually using it in a chip – but now they have succeeded. The Viennese team worked together with researchers from the Johannes Kepler University in Linz.

Müller added, “A narrow waveguide with a diameter of about 200 by 500 nanometers carries the optical signal to the graphene layer. There, the light is converted into an electrical signal, which can then be processed in the chip. There have already been attempts to integrate photodetectors made of other materials, such as germanium, directly into a chip. However, these materials can only process light of a specific wavelength range.”

The researchers say that they can show that graphene can convert all wavelengths which are used in telecommunications equally well. The graphene photodetector is not only extremely fast, it can also be built in a particularly compact way: for example, 20 000 such detectors could fit onto a single chip with a surface area of 1cm². Theoretically, the chip could be supplied with data via 20,000 different information channels.

”These technologies are not only important for transmitting data over large distances. Optical data transmission also becomes more and more important for communication within computers”, says Thomas Müller. When large computer clusters work with many processor cores at the same time, a lot of information has to be transferred between the cores. As graphene allows switching between optical and electrical signals very quickly, this data can be exchanged optically. This speeds up the data exchange and requires much less electrical energy.

W The light signal arrives throuth a waveguide (left), in the 2 micrometer wide graphene sheet, electrical current is generated. G 
Graphene - a two dimensional sheet made of carbon atoms - can convert light into electrical current. "CMOS-compatible graphene photodetector covering all optical communication bands", Pospischil et al., Nature Photonics (2013), doi:10.1038/nphoton.2013.240

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A highly sensitive and low-noise IR photosensor based on a-SiGe as a sensing and noise filter

The a-SiGe TFT photosensor for embedded touch-screen panels (TSPs) was characterized by comparison with an a-Si sensor.

The photoresponse of an a-SiGe sensor at a 850-nm wavelength was much higher than that of a-Si, indicating that a-SiGe is a strong candidate material for an IR sensor.

In order to increase the signal-to-noise ratio, the incident visible light was filtered by incorporating a bandpass-filter layer. An a-SiGe IR-sensor-embedded LCD panel was successfully demonstrated, showing an excellent multitouch property independent of ambient-light conditions. This technology can be widely used in multifunctional TSPs.

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CVD-grown monolayered MoS2 as an effective photosensor operating at low-voltage

We report the fabrication of a photosensor based on as-grown single crystal monolayers of MoS2 synthesized by chemical vapor deposition (CVD).

The measurements were performed using Au/Ti leads in a two terminal configuration on CVD-grown MoS2 on a SiO2/Si substrate. The device was operated in air at room temperature at low bias voltages ranging from −2 V to 2 V and its sensing capabilities were tested for two different excitation wavelengths (514.5 nm and 488 nm). The responsivity reached 1.1 mA W−1 when excited with a 514.5 nm laser at a bias of 1.5 V.

This responsivity is one order of magnitude larger than that reported from photo devices fabricated using CVD-grown multilayered WS2. A rectifying-effect was observed for the optically excited current, which was four times larger in the direct polarization bias when compared to the reverse bias photocurrent. Such rectifying behavior can be attributed to the asymmetric electrode placement on the triangular MoS2 monocrystal.

It is envisioned that these components could eventually be used as efficient and low cost photosensors based on CVD-grown transition metal dichalcogenide monolayers.

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Circuit for a combustible gas sensor

A circuit for a combustible gas sensor comprising: a bridge circuit having first and second legs; a first node at a first midpoint in the first leg of the bridge circuit; a second node at a second midpoint in the second leg of the bridge circuit;

a first temperature responsive resistive sensor element coupled between the first node and a bottom of the bridge circuit and located in a flow of combustible gas;

a second temperature responsive resistive sensor element coupled between the bottom of the bridge and ground and located in the flow of combustible gas;

and a voltage control circuit coupled to the first and second nodes and to the top of the bridge circuit for maintaining closed loop control of first and second node voltages at the first and second nodes by varying a bridge voltage at the top of the bridge circuit wherein one of the first and second sensor elements includes a catalyst for stimulating reactions of reactive constituents in the flow of combustible gas.

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Combined-structure semiconductor gas sensor based on butane gas

A new combined-structure semiconductor gas sensor based on butane gas is reported in this paper. The combined structure sensor is a gas sensor that is based on the complementary feedback principle.

The sensor is composed of two sensitive materials A and B whose conductive types are the same. The materials A and B are all n-type materials. The results analysed from a theoretical viewpoint showed that the sensor had higher selectivity and better thermal stability when materials A and B satisfied certain conditions.

According to the sensor's structure and meeting conditions, we prepared the combined-structure gas sensor for butane gas. The experimental results showed that they are consistent with theoretical analysis and can be applied to monitor and control leakage of butane gas.

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Wireless Indoor Optical Positioning With a Differential Photosensor

An indoor optical positioning technique using a differentialphotosensor device is presented. The method is based on angle of arrival information estimated by the differential photosensor in an indoor environment with fixed optical beacons.

A photocurrent is generated by each of the three photodiodes in the photosensor by incident light from the optical beacons. The amplitudes of these photocurrents are a function of the incident angle of the light. Previously derived equations that express photocurrent amplitudes as a function of the azimuthal arrival angle, φ, and the polar arrival angle, θ, are modeled with second- and third-order polynomials, respectively, to determine the φ and θ angles from measured photocurrents.

Testing with optical beacons in various positions with respect to a fixed photosensor resulted in a root mean squared error for all estimated angles φ and θ of 2.8°. A positioning accuracy of better than 4 cm is achieved.

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A Review of Industrial Microwave Sensors

This paper reviews the field of microwave sensors. The field is broad and the applications numerous. This review will therefore only be able to present the broad outlines.

Firstly the historical perspective and the physical background are briefly described, and the general advantages and disadvantages are listed.

An overview of the various working principles of microwave sensors is given with a few examples of the applications mentioned. Important fields of applications and interesting examples are treated separately, starting with the measurement of moisture, which is the single most important field of applications in microwave sensors.

Applications in the petroleum industry are also mentioned, because they are relatively new, they play an exceptionally important economical role, and represent the field in which the author is currently working. Followed by some trends for the future.

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Optical oxygen sensor based on time-resolved fluorescence

A new, simple signal processing, low-cost technique for the fabrication of a portable oxygen sensor based on time-resolved fluorescence is described. The sensing film uses the oxygen sensing dye platinum meso-tetra (pentfluorophenyl) porphyrin (PtTFPP) embedded in a polymer matrix.

The experimental results reveal that the PtTFPP-doped oxygen sensor has a sensitivity of 2.2 in the 0-100% range. A preparation procedure for coating the photodiodes with the oxygen sensor film that produces repetitive and reliable sensing devices is proposed.

The developed time-resolved optical oxygen sensor is portable, low-cost, has simple signal processing, and lacks optical filter elements. It is a cost-effective alternative to traditional electrochemical-based oxygen sensors and provides a platform for other optical based sensors.

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Photosensor circuits including a regulated power supply

Photosensor circuits include a relay coil configured to control application of an alternating current (AC) power source to a load. The circuit includes a pulse width modulator circuit configured to generate a pulse width modulated signal having a pulse width that varies responsive to an average voltage across the relay coil. A drive transistor coupled to the relay coil controls the average voltage across the relay coil responsive to the pulse width modulated signal. A photo control circuit is configured to control application of the pulse width modulated signal to the drive transistor responsive to a detected light level. A power circuit coupled to the power source is configured to provide a regulated power signal to a comparator of the pulse width modulator circuit.

BACKGROUND OF THE INVENTION
The present invention relates to photosensor circuits and, more particularly, photosensor circuits for light level switching control.

Photo controllers are devices that automatically turn electrical devices on and off in response to the ambient light level. They are used, for example, on street lights to automatically turn them off during the day and on at night. They are also used on billboard lighting systems to turn the billboard lights on early at night, off late at night during periods of low vehicular traffic, on again during early morning rush hour periods when high traffic levels resume, and then off during the daylight hours. Photo controllers may also be used in reverse, for example, to turn a golf course water fountain on during the day and off at night.

A variety of devices, including photo controllers, may make use of power converters to convert relatively high voltage alternating current to relatively low voltage direct current as is used in many conventional electronic devices. Some conventional power converters make use of large, high-voltage resistors to drop the voltage. However, these resistors are typically inefficient and generate high heat. The heat generated from the resistors may require that the resistors be housed in a large package and include heat dissipating elements, such as heat sinks. Also, the high heat generated by the resistors can lead to problems with reliability and longevity in the resistors and in other electronic components situated near the resistors.

Another conventional approach to power conversion is the use of a switch mode power converter. The switch mode power converters typically require six transistors or a micro-controller to implement. The requirement for multiple transistors or a micro-controller may cause the implementation of switch mode power converters to be cost prohibitive in some applications, such as in photo controllers.
A small, low cost, efficient switch mode power converter and a photosensor circuit including the same are described in U.S. Pat. No. 6,903,942 (“the '942 patent”), which is hereby incorporated herein by reference as if set forth in its entirety.

It is also known to provide a photosensor circuit including digital circuitry as incorporated in the 3100 Series photocontrol, available from TE Connectivity. The photosensor circuit for the 3100 Series photocontrol is shown in FIG. 1. As seen in FIG. 1, a microcontroller U1 outputs a signal GP4 that drives a drive transistor Q2 to turn on and off the drive transistor Q2 as part of a pulse width modulated control circuit including capacitors C5 and C6 and diode D2 (operating at a frequency of approximately 50 Hertz (Hz) to control the voltage across the relay coil of the relay K1. Relay K1 is shown as a normally open relay and, when light is detected by photransistor Q1, the coil current of relay K1 is turned off to turn off a load LOAD, such as a street light. A direct drive signal is provided by including capacitor C3 to adjust voltage levels of the signal to the base of the drive transistor Q2 from the signal GP4. In addition, a half wave rectifier (diode D1) is included to provide power for the photocontrol circuit.

A regulated power supply is also shown to provide the power supply signals VSS and VDD to allow operation of the microcontroller U1. In the illustrated embodiment, VSS is coupled to the AC line NEUTRAL to provide the DC ground reference. The VDD signal is provided by the resistor R7 coupled to the half wave rectifier D1. In addition, The VDD signal is coupled to the emitter of the drive transistor Q2. As such, current will also be provided through the drive transistor Q2 but only when the transistor is on.

A small, low cost, efficient switch mode power converter including a regulated power source for a microcontroller is also described in co-pending U.S. patent application Ser. No. 13/190,727 (“the '727 application”), which is hereby incorporated herein by reference as if set forth in its entirety.
Regulated power sources may also be used in photocontroller circuits not including a microcontroller, such as described in U.S. Pat. No. 8,026,470 (“the '470 patent”), which is hereby incorporated herein by reference as if set forth in its entirety.

SUMMARY OF THE INVENTION
Embodiments of the present invention provide photosensor circuits including a relay coil configured to control application of an alternating current (AC) power source having a negative half and a positive half of a line cycle to a load. A pulse width modulator circuit of the photosensor circuit is configured to generate a pulse width modulated signal having a pulse width that varies responsive to an average voltage across the relay coil. The pulse width modulator circuit includes a comparator. A drive transistor coupled to the relay coil that controls the average voltage across the relay coil responsive to the pulse width modulated signal. A photo control circuit of the photosensor circuit is configured to control application of the pulse width modulated signal to the drive transistor responsive to a detected light level. A power circuit, coupled to the power source, is configured to provide a regulated power signal to the comparator of the pulse width modulator circuit. The power circuit includes the drive transistor coupled between the relay coil and the regulated power signal and a second transistor coupled between a base of the drive transistor and the regulated power signal. The drive transistor conducts current passing through the relay coil to the regulated power signal when the drive transistor is on and the second transistor conducts current not passing through the relay coil to the regulated power signal when the drive transistor is turned off.


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General comments of UV Sensor

The UV sensor aims to measure the intensity of the ultraviolet part of the sun’s spectrum (as opposed to the ‘solar’ sensor which measures the visible and near IR part of the spectrum).

UV readings are also expressed in a different format from the ‘solar’ sensor readings: For the solar sensor, straightforward irradiance values in units of W/sqm are recorded. But the prime practical reason for monitoring UV levels is to guide human skin exposure, preventing sunburn and possible skin cancer risks.Therefore UV readings are expressed on a UV Index scale of 0-16 which weights the intensity by the wavelengths of the UV light most likely to cause skin damage. This seems to be explained reasonably well on the relevant Wikipedia page, where one index unit corresponds to an irradiance value of about 25W/sqm. Maximum midsummer UVI readings in the UK rarely exceed 7-8,although substantially higher readings are commonly registered at lower latitudes than the UK.
Davis Application Note #6 also provides further information on interpreting UV readings.

UV readings are technically difficult to make – the sensors need extensive individual calibration and the signal is low in amplitude hence causing noisy readings. This has two consequences. First, UV sensors are expensive because of the prolonged production and calibration process. (You may think that the Davis UV sensor is expensive, but sensitive high-end UV sensors are considerably more so.)
The second consequence is that, without moving to a still more sophisticated and costly sensor design, there is unavoidably some noise and short-term fluctuation in the sensor output, even under dark conditions when of course there should be zero UV readings. When the UV sensor was first introduced, Davis was troubled by support calls reporting overnight UV readings of 0.1 or 0.2 UVI, even occasionally higher, which were simply a consequence of noise in the dark current circuitry. The consensus was that these very low but false readings overnight were more of a concern to users than having good sensitivity at low UV levels. So the decision was taken that there would be a threshold in the displayed UV reading of 0.4 and below which any reading would show as zero and this is the solution that remains in place.

The result is of course that wintertime readings in higher latitudes such as the UK will typically show as zero unless the UVI value is above 0.3.

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Optical oxygen sensor based on RUDPP fluorescence quenching

An optical oxygen sensor system based on the process of fluorescence quenching is reported. The device detects the fluorescence quenching of a ruthenium complex, also known as RUDPP by sensing minute variations of a fluorescent membrane emission intensity.

A dual channel design consisting of a reference branch and a sensing branch is used. Both branches include modulated light from a bright blue LED acting as the excitation source coupled through an enclosed channel to a photo-diode. The sensing branch has the RUDPP fluorescence quenching membrane sandwiched between the blue LED and the photo-diode, while the reference branch is void of such membrane. To avoid membrane saturation in the sensing branch, the excitation source is modulated with a 350 Hz square wave.

The output signals of the two channels are amplified separately and subtracted from each other using a difference amplifier. Adjusting the difference amplifier output to zero effectively ensures excitation source interference cancellation. The photodiode in the sensing branch detects the intensity variations as a function of fluorescent quenching by oxygen. It was possible to isolate the fluorescent signal completely, based solely on electronic components, without the use of optical filters.

The output signal from the difference amplifier is further amplified (with an adjustable gain for calibration) and displayed. Sensor performance was tested and it exhibited both excellent sensitivity and response time, compared to the recent oxygen sensors reported by others. A decrease of less than 4 percent oxygen concentration was readily detectable. We conclude that this design establishes the feasibility of developing an optical oxygen sensor, relying solely on optoelectronic components for detection.

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Deep-UV sensors based on SAW oscillators using low-temperature-grown AlN films on sapphires

High-quality epitaxial AlN films were deposited on sapphire substrates at low growth temperature using a helicon sputtering system.

SAW filters fabricated on the AlN films exhibited excellent characteristics, with center frequency of 354.2 MHz, which corresponds to a phase velocity of 5667 m/s. An oscillator fabricated using AlN-based SAW devices is presented and applied to deep-UV light detection.

A frequency downshift of about 43 KHz was observed when the surface of SAW device was illuminated by a UV sensor with dominant wavelength of around 200 nm. The results indicate the feasibility of developing remote sensors for deep-UV measurement using AlN-based SAW oscillators.

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Resolved a false detection of the photo sensor under high-vacuum environment

The "photoelectric sensor" has been used to detect a presence of a glass substrate within the vacuum chamber, however, there was some trouble in many false detection due to fogging of the view port in evaporating.
Furthermore, there was another problem; the view port itself is expensively machined.

The client consulted major sensor manufacturers and tried a high-performance photo sensor, however, using it cannot prevent false detections.

A visit of our booth in the "Vacuum Exhibition" for mold technologies encouraged the client to know our switches and to contact us.

The main focus of the issues

• Positioning the glass substrate under vacuum environment.
• Fogging of a view port in evaporating causes a false detection in the photo sensor.
• The view port is expensively machined.

Metrol's suggestions

Because the conventional "photoelectric sensor" detects workpieces with a reflection by emitted lights, they are subject to external conditions such as fogging, water drops and diffused reflections, etc., which consistently causes false detections.

Most engineers assume that "A sensor is useless under vacuum environment".

Metrol's "high vacuum class-compatible switch" is a mechanical precision positioning switch manufactured only with low outgas-compatible parts without any electric substrate.
The switch is compatible with high vacuum class up to 10^-5 Pa and capable of securely detecting the glass substrate even under high vacuum environment.

We customize the switch contact force to 0.5 N or less and the tip material to special resin respectively, so there is no risk of scratching the sensitive glass substrate.

Improvements

• Realization of positioning the wafer under the 10^-5 Pa high vacuum environment.
• No false detection by directly contacting the wafer.
• The need for the view port is eliminated, and the machining cost is reduced significantly.

Comment from Metrol representative

Because the signal points of the photo sensors such as "photoelectric sensor" and "fiber sensor" are invisible, adjusting the installation has taken more than two days.
Because the signal points of Metrol's contact-type "precision positioning switch" are visible, the installation positions can be specified on the CAD when designed.

In the semiconductor industry, we have many past adoption experiences also about positioning within vacuum devices such as "sputtering device", "organic EL evaporating device", "etcher", and "wafer carriers", etc.

If you have any trouble in positioning or detection of the presence under vacuum environment, please feel free to contact Metrol.

We look forward to hearing from you preparing our samples for the evaluation.

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Characteristics of semiconductor gas sensors II. transient response to temperature change

Temperature-stimulated transient responses of the conductance of SnO₂ gas sensors, as exemplified by the Taguchi Gas Sensor (TGS), are comprehensively studied. These responses are determined at many temperatures for sensors exposed to several fixed concentrations of oxygen in nitrogen. The dynamic response of conductance exhibits complex kinetics characterized by time constants which range, depending on ambient conditions, from seconds to days.

Measurement results are analyzed in the light of a proposed model of device behavior. This heuristic model is constructed by combining some fundamental experimental observations with kinetic predictions of the barrier layer theory of adsorption. The analyses result in identification of the physical mechanisms responsible for the complex kinetics and long time constants. We find that sensor conductance is controlled by an intergranular potental barrier consequent to oxygen adsorption.

The barrier potential exhibits an Elovich-type rate kinetic and its functional dependences on sensor temperature for several oxygen partial pressures are determined. In addition, the long-term drift of the TGS results from the diffusion of a native non-stoichiometric defect, an oxygen vacancy, evoked by changes in temperature or ambient oxygen pressure.

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UV sensor on Samsung Galaxy Note 4 doesn’t make sense

Yesterday Samsung announced their latest Galaxy Note, and the phone is packed full of the following key sensors: Barometer, UV, Heart Rate Monitoring, SpO2 (Dependent on market), and more.
Two of those stick out — SpO2 and UV. Having a pulse oximetry sensor (SpO2) in a phone would be tremendous, but with the “dependent on market” caveat we’ll have to wait and see. I suspect the “dependent on market” is secondary to concerns or considerations about FDA approval.
The UV sensor is getting more of the attention. In order to use the UV sensor, you have to maintain a more than 60 degree elevation angle against the sun with the back of the sensor.  Reports indicate Samsung will be using their S Health app to issue tips for sun exposure and sunscreen advice.
So should the UV sensor actually be used to make sunscreen and sun exposure advice? Short answer — I wouldn’t want my patients using a UV sensor for that purpose. There is no need for a sensor to do this when the EPA reports the UV index on a daily basis.
If a patient asked me about using the sensor, I would direct them to the EPA website, or, would recommend they use an Android app created by the EPA to help with this exact scenario.  The Android app recognizes your location, and gives you all the information you need — directly from the EPA.
In regards to wearing sunscreen, the American Academy of Dermatology has kept it simple. Use SPF of 30 or above, water resistent, broad spectrum coverage. Reapply every two hours when outdoors, and wear protective clothing. Apply one ounce, or enough to fill a shot glass — that’s a direct quote from the Academy. The American Academy of Dermatology has created a great Sunscreen FAQ, accompanied by an infographic that patient’s and doctors should use for guidance.
Just because a sensor can be packaged with a phone or a wearable doesn’t mean it makes sense.  We need to keep it simple — and not be titrating our sunscreen usage with a UV sensor on a phone.

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