Optical detector unit and multispectral optical sensor

Abstract

An optical detector unit (10) comprising an optical sensor (16) arranged on a substrate (24), wherein said optical sensor (16) comprises a number of detector pixels (32) each generating a multispectral sensor signal, should allow for sectored viewing applications at a particular lean and simple setup at reduced manufacturing costs. This in accordance with the invention is achieved in that said optical detector unit (10) comprises an interference filter element (40)jointly covering the pixels (32), and further comprising a double-diffuser system (42), said double-diffuser system (42) comprising a first diffuser element (44) positioned directly on top of said interference filter element (40) and a second diffuser element (46) positioned in a predefined distance (d) above said first diffuser element (44).

Description

[0001] Optical Detector Unit and Multispectral Optical Sensor

[0002] DESCRIPTION

[0003] Technical background of the invention

[0004] The invention relates to an optical or spectral detector unit . The invention more particularly relates to an optical detector unit comprising an optical sensor arranged on a substrate to detect received photons , said optical sensor comprising a number of sensor pixels each generating a multispectral sensor signal and j ointly covered by an interference filter element . The invention furthermore relates to a multispectral sensor comprising such an optical detector unit .

[0005] Background

[0006] Optical or multispectral sensors are increasingly being used in such diverse areas of technology as smart phones and mobile devices , smart homes and buildings , industrial automation, medical technology, connected vehicles , etc . At the same time sensor data becomes more complex and is expected to meet the requirements for high accuracy . Further, color and spectral light sensing on a chip-scale have various applications in color identi fication, data authentication, spectroscopy, and other industrial and consumer-level optical detection applications . In a number of important applications , in particular for camera applications , such sensors are used as ambient light sensors for so-called "auto white balance" functionality, in order to provide essential background information for appropriate correction functionalities and thereby in general improve imaging quality .

[0007] Common multispectral sensors are often based on an array of pixels and on-pixel filters for each pixel . For spectroscopic applications the filters can be chosen to have linear independent filter characteristics . In order to accomplish an ac- curate spectral measurement of a given source , incoming radi- ation should be known in order to compensate for di f ferent response of individual pixels . This way an amplitude of a spectral signal of a pixel can be used to calculate a spectral reconstruction of a light source under study .

[0008] However, a homogenous distribution of incoming radiation on the pixel array is an ideal condition . In real systems , in contrast , variations of the actual irradiation detected at the sensor ' s level may vary between di f ferent channels , due to geometry ef fects limiting the individual field of views ( FOV) , dominant angle of incidence (AOI ) of incoming irradiation, etc . Geometry ef fects in such systems may be caused by misalignments of individual components due to manufacturing tolerances etc . In particular for uses in ambient light sensor devices , however, homogeneity of incoming light distribution at detector level may be of special signi ficance . In order to provide highly reliable homogenous distribution, di ffusors may be used in a position before incoming radiation reaches the pixels in order to mix the incoming light as well as possible and to pass on the light to the sensor array in a homogenous , ideally in a Lambertian, manner . Further, the spectral sensitivity of an interference filter-based multi- spectral sensor depends strongly on the angular distribution of light hitting the filter on the detector array .

[0009] Further, in many existing sensor devices for a mean limit of the field of view (" FOV" ) a lid aperture is used in combination with a di f fuser on top or, with respect of the direction of incoming light , in front of the aperture in order to collect and mix incoming light from a rather wide incident angle (up to 180 ° ) . The position of the lid with respect to the sensor array underneath, however, can vary largely because of tolerances and lack of precision in the packaging during the assembly process . Such variation in relative position may generate variations in amplitude and spectra shape of sensitivity, because of variations in angular power distribution . Depending on the array position, each channel will be af fect- ed in a di f ferent way . Variations in angular distribution will generate variations in spectral sensitivity .

[0010] Depending on the performance of an associated di f fuser, the system accuracy may also depend on the position of a dominant radiation spot . A wide di f fuser obj ect will scatter the light more homogeneous to the inside into the detector array than a dominant and small point . Typically, each di f fuser with a common transmittance ratio also has an ideal Lambertian spread and will also vary the power distribution depending on the position ( tilt vs . detector ) and spectra sensitivity .

[0011] The knowledge about the setup depending on spectra sensitivity is important to generate a useful trans fer matrix for spectral reconstruction . However, especially for colored scenes , the typical white balancing by the "gray world theory" or the "brightest pixel theory" ( assuming the dominant contribution from a dominant radiation spot ) are restricted in balancing performance , and detailed color and spectral information about the ambient light is expected to improve the performance without color shi ft .

[0012] Further, especially in smart phone applications , camera systems with increasing performance may be provided . Improved cameras of this type may allow for optimi zed evaluation of detected color and spectral information in various sectors of the scene , such as center of the selected scene , borders of the scene , areas outside of the selected scene . It therefore may be highly desirable to provide improved ambient light sensors that are able to match increased camera performance by also taking into account the speci fics of the various scenarios or scenes supported by the camera for the respective white balancing .

[0013] For this purpose , ambient light sensors suitable for so- called sectored viewing with detectors allowing for a sectored view to a target scene may be provided . This , however, may cause the necessity to blur or smoothen the incoming radiation in order to properly assign the detected photons to the various individual sectors of view . In particular, de- signs for the sectored viewing of color and / or spectral sensors based upon micro-lens array ("MLA" ) packages have been suggested . In such designs , for each spectral channel a single , associated optical path is provided for generating a monochromatic image on a detector array . Regarding the tolerances in MLA production or deposition processes , however, as well as the relatively high tolerances in packaging processes , the viewing angle of each spectral channel can tilt in a di f ferent direction, requiring further compensation . This results in signi ficant ef forts in final testing and custom operating of such devices . Further, because of the relatively low pixel counts and the ef fects of dominant structure movements in such devices , an optical system may be needed to blur and smoothen the scenery image and the detection .

[0014] Summary

[0015] The obj ect of the invention is therefore to provide an improved optical detector unit of the type identi fied above , that helps overcome the deficiencies identi fied above , in particular in a lean and simple setup in order to reduce manufacturing costs . It is another obj ect of the present invention to provide an optical detector unit of the type identified above that is particularly beneficial in structural smoothing, enabling the use of interference filters on a detector array independently of the angle of irradiation (AOI ) and therefore is particularly useful for sectored viewing applications . Further, an improved multispectral sensor should be provided .

[0016] With respect to the optical detector unit of the type identified above , this obj ect is achieved in that the optical detector unit further comprises a double-di f fuser system, said double-di f fuser system comprising a first di f fuser element positioned directly on top of said interference filter element and a second di f fuser element positioned in a predefined distance above said first di f fuser element . Preferred embodiments are subj ect of the dependent claims .

[0017] The invention is based on the consideration that , in comparison to MLA based design concepts for a sectored view sensor, a signi ficant part of the potential deficiencies mentioned above are considered to be consequences of the relatively complex design and manufacturing process for the micro-lens arrays . In particular, a main source of errors and inaccuracies in the present consideration is associated with the relative adj ustment of the individual components in relation to each other, particularly in view of the inevitable manufacturing tolerances . As an alternative solution, in favour of AOI-independent detector properties the desired smoothing and optical blur leading to smoothing of the proj ected aperture without any angular and spectral dependence for the interference filter transmission may be achieved by the combination of a ( Potentially directly processed) thin film di f fuser directly on top of the detector array with a second di f fuser that is separated by an optical spacer . In this principal design, the properties of the two di f fusers may be combined by using the smoothing function of an upper, distant second di ffuser with the function of an angular ef fect compensation of a lower first di f fuser directly on top of the interference filter that can perform the near field angular mixing to an at least partial Lambertian characteristics .

[0018] In other words : in one aspect of the present invention, the upper or second di f fuser layer, together with the thickness of the spacer between the two di f fusers , define the smoothing width of the incoming radiation . At the level of the detector area, the lateral power distribution becomes a Gaussian smoothing . The width of this smoothing function depends on the di f fusing ratio ( thickness and material of the di f fuser ) as well as the following spacer thickness . In addition and in synergetic combination therewith, the lower or first di f fuser performs the near field angular mixing to a partially Lambertian characteristics . Thus , any AOI that is hitting the position of the lower, "on chip" di f fuser is spread again into a partial Lambertian distribution . The mixing condition on each position is done in the same way . In consequence , due to the combination of the two di f fusers suggested by the invention, the structure of incoming radiation is scattered ( also referred to as smoothing of the obj ect structure and aperture border ) , and the passing filter conditions become independent from position or direction of incoming radiation .

[0019] In a preferred embodiment and according to one aspect of the invention, the detector pixels are laterally arranged on the substrate in an array with a regular lateral central distance between neighbouring pixels . In yet another aspect and in an embodiment preferred even further, this regular lateral distance between centres of neighbouring pixels on the substrate is chosen as a guide parameter for the selection of the geometry in the double-di f fuser system . Preferably, the predefined distance between the first and second di f fuser elements is in the range of 0 . 75 to 1 . 25 times said regular lateral centre distance , preferably more or less equal to said lateral centre distance .

[0020] In one aspect of the invention, the predefined distance between the first and second di f fuser elements is established by means of a spacer element . For the spacer element , various designs are possible within the scope of the invention . In particular, in a preferred embodiment and in accordance with one aspect of the invention, the spacer element may be a solid element completely filling the space between said first and second di f fuser elements , in particular a thin glass (preferably wafer scale or mounted piece / tile ) or a stack of multiple layers of transparent layers of li ft of f material . In yet an alternative preferred embodiment and in accordance with another aspect of the invention, the spacer element may be designed as a frame element positioned at the outer rim of said first and second di f fuser elements thereby providing an unfilled open space or aur gap between said first and second di f fuser elements .

[0021] According to another aspect of the invention, the ensemble of the substrate carrying the optical sensor and the double- di f fuser system associated therewith may be arranged in an optical chamber with an aperture in a housing . The aperture element , depending on the individual use case and potential other parameters or requirements , may be positioned distanced from the substrate carrying the sensor unit and the doubledi f fusor system positioned on top, thereby leaving some type of gap between the surface of the second or upper di f fuser and the aperture . This gap, in one aspect of the invention, in the chamber between the second di f fuser element and the aperture may be filled with a solid element , e . g . a glass element . In an alternative embodiment , the chamber between the second di f fuser element and the aperture may be kept unfilled and thus provides an air-gap .

[0022] Each pixel may comprise a photodiode as the signal-generating unit . According to a preferred aspect of the invention, the detector channels each comprise at least one of said pixels and an optical filter associated therewith . As in comparable sensor designs , in such a design the filter determines the transmission characteristic of the respective sensor pixel . In an embodiment of the invention, such ensemble of pixel or photodiode with associated optical filter may be provided in a stacked or package type of design in close proximity to each other . In particular, in a preferred embodiment , an interference filter suitable for the detector spectral channel formed by the respective detector array is provided . In yet another aspect of the present invention which is considered independently inventive , a j oint interference filter may be provided for all pixels of the same detector array or the same detector channel .

[0023] In an aspect of the invention, the detector unit is manufactures in an integrated chip design, preferably combining the concept identi fied above with modern wafer level chip scale packaging ("WLCSP" ) technologies in order to obtain a reliable , yet cost-ef fective compact and miniaturi zed sensor design using only few components . In an aspect of the invention, the detector unit is designed in WLCP technology . With respect to the multispectral sensor, the obj ect mentioned above is achieved in that the multispectral sensor comprises an optical detector unit of the type identi fied above . Further, in a preferred embodiment and in accordance with yet another aspect of the invention, the multispectral sensor is intended for use as an ambient light sensor, in particular for use in camera systems , and preferably in applications for sectored viewing of the ambient light sensor .

[0024] The maj or advantages achieved by the invention may be seen in that due to the basic concept of the invention of providing the double-di f fuser systems , reliable structural smoothing of incoming radiation and high performance use of the interference filters on the detector array without signi ficant impact of the respective AOI may be achieved . Therefore , the detector unit , at high accuracy and reliability, even for sectored view applications may be designed without the necessity to use special optical or MLA elements , and therefore is particularly suitable for advanced production technologies and miniaturi zed designs . In consequence , enhanced optical and spectral performance may be achieved at lowered costs and lowered number of components .

[0025] In other words , according to the concept of the invention, of providing the double-di f fuser system, a particularly cheap, low cost solution with respect to the used materials and processes is provided . The solution is easy to implement , in particular by making use of standard processes like spin coating or li ft of f - thin film technologies for applying the di f fusers , and thus highly beneficial in comparison to MLA stack technology . Further, the smoothing ef fects are easily adj ustable by simple adj ustment or tuning of the distance between the two di f fusers .

[0026] Brief Description of the Preferred Embodiments

[0027] Preferred embodiments and aspects of the invention are described further in connection with a drawing . In this drawing, FIG . 1 shows a smartphone in backside view;

[0028] FIG . 2 shows a camera system, in particular for use in the smartphone of FIG . 1 ;

[0029] FIG . 3 shows a detector array of an optical detector unit of the camera system of FIG . 2 ;

[0030] FIG . 4 shows an optical detector unit of the camera system of FIG . 2 in cross section;

[0031] FIG . 5-7 each show another alternative embodiment of an optical detector unit of the camera system of FIG . 2 in cross section .

[0032] Identical parts are labelled by the same reference numerals .

[0033] Detailed Description of the Preferred Embodiments

[0034] FIG . 1 shows a smartphone 1 in backside view . The smartphone 1 is equipped with a camera system 2 , which, as its maj or components , comprises the actual camera 4 , also referred to as the "camera detection system" 4 , and a multispectral sensor 6 , serving as an ambient light sensor 6 , associated therewith . The camera sensor system 4 , the details of which are of lesser signi ficance for the invention disclosed here , and the ambient light sensor 6 are mounted at the back of a common cover glass 8 , which may be the cover glass 8 of the smartphone 1 as such . The ambient light sensor 6 is used mainly for so-called "auto white balance" functionality in the camera system 2 , in order to provide essential background information for appropriate correction functionalities and thereby in general improve imaging quality of the camera system 2 .

[0035] FIG . 2 shows an example of the camera system 2 in cross section that in the embodiment shown is integrated into a mobile device such as the smartphone 1 . It is noted, however, that the concept presented below may very well be used in other systems or devices , such as wearables . The ambient light sensor 6 comprises an optical detector unit 10 in the form and design of an optical sensor chip . It is noted that the concept proposed herein can be applied for various types of optical sensor chips and optical devices and that the present invention relates to the design of the optical detector unit 10 alone and therefore , within the scope of the present invention, may very well be used in an optical detector unit 10 in other applications .

[0036] The optical detector unit 10 comprises a housing 12 with a sensor chamber 14 in which the actual optical functional sensor unit 16 is positioned . In order to allow for proper passage of light or radiation to reach the optical functional sensor unit 16 through the housing 12 , the housing 12 is provided with an opening or aperture 18 . For sake of illustration, the field of view of the camera sensor system 4 and the field of view of the ambient light sensor 6 are also shown in FIG . 2 , symboli zed as cones 20 , 22 , respectively . As can be seen from FIG . 2 , the cone 22 representing the FOV of the ambient light sensor 6 is signi ficantly larger than the cone 20 representing the FOV of the actual camera 4 , due to the general desire for ambient light sensors to have a huge field of view and, i f possible , to detect light from the complete solid angle .

[0037] The housing 12 of the optical detector unit 10 of the ambient light sensor 6 is arranged on a substrate or carrier 24 . A cover section or lid 26 forming the aperture 18 and also part of the housing 12 is located opposite to the carrier 24 and thereby covers the chamber 14 . The carrier or substrate 24 provides mechanical support and electrical connectivity to electronic components which are integrated into the optical detector unit 10 . For example , the carrier 24 may comprise a printed circuit board, PCB (not shown) . However, in other embodiments (not shown) the carrier 24 can also be part of the housing 12 , and electronic components may be embedded into the housing 12 by moulding for example . In yet an alternative embodiment , the circuitry may be designed in TSV technology ("through silicon via" ) . A through-chip via is a vertical electrical connection (via ) that passes completely through a silicon wafer or die . The contacting of the chip in this technology is brought to the backside of the chip and processed as a BGA (ball grid array) . The advantage is that everything may be mounted at wafer level ( Si , filter, glass , optic, aperture , di f fuser . . . ) .

[0038] As part of the optical detector unit 10 , the optical sensor unit 16 is arranged inside the chamber 14 and on the carrier 24 . In this particular embodiment , the optical sensor unit 16 is integrated into a single semiconductor sensor die 28 together with other electronics . The optical sensor unit 16 comprises an array 30 of individual optical detector elements or pixels 32 each generating a multispectral sensor signal . The pixels 32 may be implemented as photodiodes , for example . In the embodiment shown, the substrate 24 together with the electronic components integrated therein is designed in the so-called wafer level chip scale packaging ("WLCSP" ) technology .

[0039] A control unit and a measurement unit (not shown) are integrated into the semiconductor sensor die 28 alongside with the optical sensor 16 . The measurement unit can be considered a control unit for the optical sensor unit 10 . For example , it may provide sensor signals which are generated by the optical sensor 16 . The control unit and the measurement unit may be implemented as control logic, state machines , microprocessor and the like . They may also comprise additional components such as analog-to-digital converters , time-to- digital converters , ampli fiers which too may be located in the semiconductor sensor die 28 . The semiconductor die 28 may have a printed circuit board PCB providing electrical communication to the individual components of the multispectral sensor . In operation, incoming radiation can be detected by means of the optical sensor 16 . Each sensor pixel 32 in reaction generates a multispectral sensor signal , respectively . The measurement unit therefore in total provides a set of multispectral sensor signals .

[0040] The array 30 of the pixels 32 may be designed in the way of a conventional multispectral sensor, with each pixel 32 being provided with an individuali zed optical filter having a speci fic transmission characteristic, thereby forming an individual channel of the sensor unit . In the embodiment shown by way of example only, however, the optical sensor 16 is designed with respect to the speci fic needs of modern camera systems . In such modern cameras , various options may be offered to the user that include focussing on certain scenes , taking into account areas neighbouring the focus area, etc . For such systems , the conventional design approach for ambient light sensing, i . e . the typical white balancing by the "gray world theory" or the "brightest pixel theory" , are restricted in balancing performance and thus may be not suf ficient for the requirements of enhanced camera performance .

[0041] In order to overcome this and to provide an ambient light sensor 6 enabled to properly support the camera 4 and produce enhanced and improved white balancing, the ambient light sensor 6 I the embodiment shown is designed to give sectored colour and spectral information of the scene and parts around ( centre of the scene , border of the scene and outside areas of the scene ) . In other words , the ambient light sensor 6 is designed for so-called sectored viewing applications . The sectored information of ef fective ambient light may then be used to produce a gradient white balancing of the image and to adj ust to di f ferent ambient light conditions in one scene . The design for sectored viewing in FIG . 2 is represented by dashed lines 34 , dividing the core 22 representing the FOV of the ambient light sensor 6 into a number ( in the embodiment shown three ) of sectors of the FOV of the ambient light sensor 6 .

[0042] In order to achieve this enablement for sectored view, in accordance with one aspect of the present invention, the pixels 32 of the ambient light sensor 6 are grouped into subarrays , in particular into monochromatic detector arrays 36 , each of which forming a respective detector spectral channel 38 with its own filter and optic, thereby allowing for an on-chip integration and wafer scaled package . In particular, a j oint or common interference filter element 40 is provided for all pixels 32 of an individual array 36 or channel 38 , thereby providing identical transmission characteristics for all pixels 32 of the respective array 36 or channel 38 . The geometrical design of the detector arrays 36 and their respective optical stack define the sectoring of the sensor ' s fields of view .

[0043] This arrangement of the pixels 32 into subgroups forming individual monochromatic detector arrays 36 is schematically shown in FIG . 3 which presents a top view onto the arrangement of the pixels 32 on the sensor die 28 . In the embodiment shown, a symmetric design is chosen for the monochromatic arrays 36 and their optical stacks such that each pixel 32 within the respective array 36 is associated with the same sector of a scene , which is necessary for colorimetric analysis . In consequence of this arrangement of the pixels 32 , in an aspect of the present invention the full field of view ( FOV) of the ambient light sensor 6 is split into FOV segments wherein the detector arrays 36 are detecting the average light of each segment . This setup of strictly separating into segments is not sensitive to position-dependent structures of incoming radiation, such as bright dot light sources . As long as such structure is part of the segment it is also part of the averaging of the segment . In the embodiment shown in FIG . 3 , twelve detector spectral channels 38 , each formed by an array 36 of pixels 32 , are provided .

[0044] A section of the optical detector unit 10 of the ambient light sensor 6 , comprising only one of the monochromatic detector arrays 36 , is shown in enlarged cross-sectional view in FIG . 4 . As is evident from FIG . 4 , the pixels 32 forming the monochromatic array 36 are arranged regularly within the array 36 , thereby being arranged on the substrate 24 with equal or regular lateral distances dl between neighbouring pixels 32. Further, in FIG. 4, the interference filter element 40 jointly or commonly provided a for all pixels 32 of the monochromatic array 36 or channel 38 shown here is clearly visible. As shown, the optical filter element 40 is positioned directly on top of the associated pixels 32. In various embodiments, the optical filter elements 40 may be an interference filter (as shown here) such as an optical cut-off filter, bandpass, long or short pass filter, dielectric filters, Fabry-Perot filters and / or polymer filters.

[0045] In order to enable the detector unit 10 of the ambient light sensor 6 for the intended sectored viewing capabilities, and to provide an optical detector unit 10 with improved performance, in accordance with an aspect of the present invention, the detector unit 10 in the embodiment shown is provided with a double-diffuser system 42. The double-diffuser system 42 comprises a first diffuser element 44 positioned directly on top of the interference filter element 40, and further a second diffuser element 46 positioned in a predefined distance d above the first diffuser 44 element. In the embodiment shown, and in accordance with one aspect of the invention, the predefined distance d between the two diffuser elements 44, 46 is chosen to be more or less equal to the average lateral distance dl between the centres of any two neighbouring pixels 32. In the preferred embodiment shown, the typical size of a pixel 32 may be 60 pm, the thickness of the diffusers 44, 46 may be around 5 - 10 pm, and the distance d between the diffusers 44, 46 may be around 60 pm, too.

[0046] As indicated by arrows 48, in FIG. 4 representing three incoming rays, the upper or second diffuser element 46 provides scattering or smoothing of incoming radiation, thereby eliminating potential structures therein due to dominant light sources or the like. In consequence, the lower or first diffuser element 44 can then effect the near field angular mixing of the transmitted radiation arriving there (as symbolized by arrows 50) to a partially Lambertian characteristic, basically for any AOI . Any AOI is hitting a position of the lower or first diffuser 44, mounted directly "on chip", thus is spread again into partially Lambertian distribution. The mixing condition on each position is done in the same way.

[0047] In summary, the second or top diffuser 46 provides the smoothing of the incoming radiation and therefore enables the AOI independent use of the interference filter element 40 deposited on the pixels 32. The upper diffuser layer 46 together with a spacer element 52 provided between the diffusers 44, 46 and establishing their distance d defines the amount of smoothing that can be reached in this setup, and thus due to the basic design of the systems smoothing is easily adjustable by simply tuning the distance d as given by the spacer element 52.

[0048] Both the space between the diffuser elements 44, 46 and the space within the sensor chamber 14 may be provided as air gaps, or instead be filled with appropriate material. In FIGs. 5 - 7, various embodiments of the optical detector unit 10 in this regard are shown. In one embodiment, as shown in FIG. 5, the spacer element 52 provided between the diffuser elements 44, 46 is a solid element 54, in particular made of thin glass or from multiple layers of transparent material. The inner space of the sensor chamber 14 in this embodiment, in contrast, is left empty, thereby providing an air-gap. In the embodiment shown in FIG. 6, in contrast, the spacer element 52 is designed as a frame element 56 positioned at the outer rim 58 of said first and second diffuser elements 44, 46, thereby providing an unfilled open space between the first and second diffuser elements 44, 46. The inner space of the sensor chamber 14 in this embodiment, in contrast, is designed as a solid element, in particular made of glass or from multiple layers of transparent material.

[0049] The embodiment shown in FIG. 7, instead, is a combination of the former two, featuring a solid element 54 used as spacer element 52 between the diffusers 44, 46 in combination with a solid element, in particular made of glass or from multiple layers of transparent material , as filler element for the inner space of the sensor chamber 14 .

[0050] The embodiments of the optical detector unit 10 discussed herein have been disclosed for the purpose of familiari zing the reader with novel aspects of the idea . Although preferred embodiments have been shown and described, many changes , modifications , equivalents and substitutions of the disclosed concepts may be made by one having skill in the art without unnecessarily departing from the scope of the claims .

[0051] In particular, the disclosure is not limited to the disclosed embodiments , and gives examples of as many alternatives as possible for the features included in the embodiments discussed . However, it is intended that any modi fications , equivalents and substitutions of the disclosed concepts be included within the scope of the claims which are appended hereto .

[0052] Features recited in separate dependent claims may be advantageously combined . Moreover, reference signs used in the claims are not limited to be construed as limiting the scope of the claims .

[0053] Furthermore , as used herein, the term " comprising" does not exclude other elements . In addition, as used herein, the article " a" is intended to include one or more than one component or element , and is not limited to be construed as meaning only one .

[0054] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a speci fic order . Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise speci fically stated in the claims or descriptions that the steps are to be limited to a speci fic order, it is in no way intended that any particular order be inferred . LIST OF REFERENCE NUMERALS smartphone camera system camera detection system ambient light sensor cover glass optical detector unit housing sensor chamber sensor unit aperture , 22 cone substrate lid sensor die array pixel dashed lines monochromatic detector array channel interference filter element double-di f fuser system first di f fuser element second di f fuser element , 50 arrow spacer solid element frame element outer rim

Claims

CLAIMS1. An optical detector unit (10) comprising an optical sensor (16) arranged on a substrate (24) , wherein said optical sensor (16) comprises a number of detector pixels (32) each generating a multispectral sensor signal and jointly covered by an interference filter element (40) , and further comprising a double-diffuser system (42) , said double-diffuser system (42) comprising a first diffuser element (44) positioned directly on top of said interference filter element (40) and a second diffuser element (46) positioned in a predefined distance (d) above said first diffuser element (44) .

2. The optical detector unit (10) of claim 1, in which the pixels (32) are laterally arranged on said substrate (24) in an array (36) with a regular lateral distance (dl) between centres of neighbouring pixels (32) .

3. The optical detector unit (10) of claim 2, in which said predefined distance (d) between said first and second diffuser elements (44, 46) is in the range of 0.75 to 1.25 times said regular lateral distance (dl) .

4. The optical detector unit (10) of any one of claims 1 to 3, in which said predefined distance (d) between said first and second diffuser elements (44, 46) is established by means of a spacer element (52) .

5. The optical detector unit (10) of claim 4, in which said spacer element (52) is a solid element (54) completely filling the space between said first and second diffuser elements (44, 46) .

6. The optical detector unit (10) of claim 4, in which said spacer element (52) is a frame element (56) positioned at the outer rim (58) of said first and second diffuser elements (44, 46) thereby providing an unfilled open space between said first and second diffuser elements (44, 46) .The optical detector unit (10) of any one of claims 1 to 6, wherein the ensemble of said substrate (24) carrying said optical sensor (16) and said double-diffuser system(42) is arranged in a sensor chamber (14) with an aperture (18) in a housing (12) , wherein said chamber (14) between said second diffuser element (46) and said aperture (18) is filled with a solid element.

8. The optical detector unit (10) of any one of claims 1 to 6, wherein the ensemble of said substrate (24) carrying said optical sensor (16) and said double-diffuser system (42) is arranged in an optical chamber (14) with an aperture (18) in a housing (12) , wherein said chamber (14) between said second diffuser element (44) and said aperture (18) provides an air-gap.

9. A multispectral sensor, comprising a number of optical detector units (10) of any one of claims 1 to 8.

10. The multispectral sensor of claim 9, which is designed as an Ambient Light Sensor (6) .

11. Camera system (2) comprising an ambient light sensor (6) having an optical detector unit (10) of any one of claims

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