Sensor device, sensor module, imaging system and method to operate a sensor device

Abstract

An optical detector unit (2) comprising an array (26) of photodetectors (28) grouped into a number of macropixels (60) such that each macropixel (60) is provided with a time-to-digital converter (66) to which output signals of the photodetectors (28) of the respective macropixel (60) may be delivered via a sequence of compression trees (76, 80, 104) shall be provided that helps overcome deficiencies caused by misaligned spots (62) of incoming radiation, and in particular should allow for reliable compensation of effects due to shifting of detected incoming light spots (62) on the sensor array (26). In accordance with the invention, this is achieved by that the photodetectors (28) of each macropixel (60) further are grouped into a number of zones (72) such that the photodetectors (28) of each zone (72) with respect to their signal outputs are jointly connected to a first level compression tree (76) associated with said zone (72), wherein said first level compression tree (76) with respect to its signal outputs is connected to the time-to-digital converter (66) of the respective macropixel (60) via a number of subsequent higher order compression trees (80, 104)), and wherein the first level compression tree (76) of a zone (72) of a macropixel (60) with respect to its output signal is connect-ed to the subsequent compression tree (104) of its macropixel (60) via an associated multiplexer (96) and further is switchably connected to a number of multiplexers (96) each associated with zones (72) of other macropixels (60).

Description

[0001] SENSOR DEVICE , SENSOR MODULE , IMAGING SYSTEM AND METHOD TO OPERATE A SENSOR DEVICE

[0002] DESCRIPTION

[0003] Technical background of the invention The invention relates to an optical detector unit , in particular for use in mobile devices . In particular, it relates to an optical detector unit comprising an array of photodetectors grouped into a number of macropixels such that each macropixel is provided with a time-to-digital converter to which output signals of the photodetectors of the respective macropixel may be delivered via a sequence of compression trees . The invention furthermore relates to an optical sensor device and an imaging system, comprising such a detector unit , and to a method to operate an optical sensor unit .

[0004] Background

[0005] Optical 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 and connected vehicles , etc . In particular in smart phones and mobile devices , protection for personal mobile phone data is becoming increasingly important . For the convenience of the user, advanced technologies for locking and unlocking of the devices is of particular signi ficance .

[0006] This , as one of a plurality of options , may be ef fected by 3D stereoscopic image sensing technology . In particular, electronic products with face recognition functions have gradual- ly appeared on the market . Taking a mobile phone as an example , the mobile phones with face recognition function includes at least a flood illuminator, a dot proj ector and an infrared camera . The face recognition process of a mobile phone includes three steps in sequence : proximity sensing (determining whether an object approaches a mobile phone) , flood illuminating sensing, and dot projecting sensing. It is worth noting that the method of sensing by the flood illuminator includes emitting a light source (e.g., infrared light) with a larger irradiation angle by the flood illuminator and projecting onto the surface of an object (e.g., a human face) . Afterwards, the infrared light reflected from the object is received by the infrared camera, and then calculating by a processor or the like, roughly determines whether the object is a human face. When the object is determined to be a human face, the dot projector emits a plurality of light spots projected onto the human face, and an infrared camera is used to receive the changing of the reflected light spot, to calculate the virtual face surface contour. This in turn may be used to accurately determine whether the detected face is the user of the mobile phone or other authenticated person .

[0007] In such, but also in other applications suitable for measuring 3D information for a target, the time of flight (TOF) of the signal emitted from a dot projector and, after reflection at the target, received in an associated detector in a sensor system may be measured. The measured time then can be converted into a digital value characteristic for the distance of the target from the sensor system in a time-to-digital converter ("TDC") . Compared to flood illuminated systems, dot projector based systems focus the light into dots which are projected to the scene or target by using a dot projector on the illuminator side. A main advantage of such systems is that the signal generated in the emitter as a consequence of the focusing is concentrated into the dots which results in a higher intensity level (=higher signal level) at the detector and therefore better performance.

[0008] The detector associated with such dot projector may be based upon the use of single-photon avalanche diodes, or SPADs for short. A SPAD is a solid-state photodetector which finds increasing application in optical sensors including spectroscopy, medical technology, consumer and security applications amongst others . SPAD arrays combine high sensitivity and spatial resolution, e . g . for highly accurate distance measurements in time-of- f light sensors . In a SPAD array, groups of individual SPADs may be formed to j ointly deliver detector signals for the detector . For example , a given zone in a SPAD array, also referred to as "macropixel" , embedded in direct time of flight system may be assigned to a zone in an image to create 3D spatial image data . In other words : a macropixel may be provided with an associated time-to-digital converter and is an array of SPADs which belongs to a detector segment in the sense that the output signals of the individual photodetectors of the macropixel may be delivered to the time-to- digital converter of this macropixel . In such systems the respective macropixel may be associated with a certain 2D section of the image of the target or scene , and the third dimension parameter for this 2D section may then be added via the TOF value detected by the respective macropixel thereby completing a 3D data set for the respective section of the scene .

[0009] In dot proj ector based systems as mentioned above , a signi ficant advantage may be seen in that not illuminated SPADs of an individual macropixel can be disabled which reduces the noise level of the system ( lower noise level ) . In addition, focusing the light in illumination dots is increasing the intensity level within these dots which increases the signal level of the enabled pixels . However, in order to avoid undesired reduction of sensor resolution, and to provide high sensor accuracy, it is desirable to make sure that each reflected dot is correctly illuminating the area of the macropixel associated therewith . In real case applications , however, the dots or their reflections at sensor level typically are not uni formly distributed to the scene ; for example , in the center of the scene the distance may be closer than at the edges . Further, parallax ef fects may cause a shi ft of the dots in dependency of the distance to the target . Summary

[0010] The obj ect of the invention is therefore to provide an improved optical detector unit comprising an optical sensor with an array of detector elements or pixels , that helps overcome the deficiencies identi fied above , and in particular allows for reliable compensation of ef fects due to shi fting of detected incoming light spots on the sensor array . Further, an improved optical sensor device should be provided, as well as an improved method for operating such a sensor unit .

[0011] With respect to the optical detector unit comprising an array of photodetectors grouped into a number of macropixels such that each macropixel is provided with a time-to-digital converter to which output signals of the photodetectors of the respective macropixel may be delivered via a sequence of compression trees , this obj ect in accordance with the invention is achieved in that the photodetectors of each macropixel further are grouped into a number of zones such that the photodetectors of each zone with respect to their signal outputs are j ointly connected to a first level compression tree associated with said zone . This first level compression tree with respect to its signal outputs may be connected to the time- to-digital converter of the respective macropixel via a number of subsequent higher order compression trees . The first level compression tree of a zone of a macropixel with respect to its output signal in an aspect of the invention is connected to the subsequent compression tree of its macropixel via an associated multiplexer . In order to also take into account incoming events detected in neighbouring macropixels and thereby compensate for said misalignments , in one aspect of the invention the first level compression tree of a zone of a macropixel with respect to its output signal further is switchably connected to a number of multiplexers each associated with zones of other macropixels .

[0012] Preferred embodiments are subj ect of the dependent claims . The invention is based on the consideration that in order to compensate misalignment ef fects , the ef fective detector area of a macropixel may be adj usted dynamically to - to the degree possible - also include individual pixels of neighbouring macropixels i f they also are hit by the incoming radiation spot . In particular, this may be achieved by making pixels of neighbouring macropixels available to additionally contribute to the signals detected directly at the original macropixel .

[0013] In accordance with an aspect of the invention and in the benefit of reliable connectivity and short signal transport times , the photodetectors of each zone with respect to their signal outputs may be hard-wire or " fixed wire" connected to their first level compression tree .

[0014] As mentioned above , in one aspect and in a basic concept of the present invention, a multiplexing structure connecting photodiodes of neighbouring macropixels to a j oint TDC channel is provided . This in particular allows to take into account individual readings of photodiodes that originally will belong to neighbouring macropixels . In order to achieve this in a particularly ef ficient way, in a preferred aspect of the invention all or some of the macropixels may be divided into four zones , each of which then may correspond to one quarter of the respective macropixel . In accordance with one aspect of the invention, the intended extension of the ef fective area of a macropixel may be achieved by taking into account the crossing point region in which for corners of neighbouring macropixels are arranged next to each other . Preferably, the macropixels are arranged in a quadratic pattern such that any four of said macropixels neighbour each other in an area around a common crossing point .

[0015] In one aspect , for each macropixel in this arrangement the zone may be taken into account that within the respective macropixel is next to the crossing point . Thus , in one aspect of the invention the output of those zones of neighbouring macropixels that directly neighbour their common crossing point should be provided as additional input to the TDC of each of the neighbouring macropixels .

[0016] In a preferred embodiment , for each zone of said macropixels directly neighbouring said common crossing point , its first level compression tree is switchably connected to the multiplexers associated with said other zones of said macropixels directly neighbouring said common crossing point . In particular, in one aspect of the invention this connection between the zones next to the crossing point may be considered to form a 2nd level compression tree based on a ring structure formed by these zones and their respective interconnections . In other words , in this aspect of the invention the ring structure encompasses the four neighbouring macropixels next to their common crossing point . A quarter of this ring structure is located on the respective corner of each macropixel . By connecting various photodiodes , e . g . by abutment , the ring structure may be established . The resulting configuration by nature can be seen similar to a bus interface with a single driver and four receivers .

[0017] In one aspect of the present invention, the ring structure is provided in order to make the output of the 1 st level compression trees of the zones available as an additional input signal to each of the neighbouring macropixels . Thus , in one aspect of the invention, the ring structure comprises one signal ring for each of the zones of interest . The switchable connection of said first level compression tree of the respective zone of a macropixel with the multiplexers each associated with zones of other macropixels thus constitutes a 2nd level compression tree for the connection with the respective time-to-digital converter .

[0018] With respect to the optical sensor device , the obj ect mentioned above is achieved in that an optical detector unit of the type identi fied above is provided for use in the sensor device . In a preferred embodiment , the sensor device may further comprising an optical emitter unit . The optical emitter unit in yet another preferred embodiment may comprises an op- tical emitter arranged in a chamber with an aperture in a housing also comprising a chamber in which said detector unit is arranged . In one aspect of the invention said optical emitter unit and said detector unit may be arranged as a time-of- f light module .

[0019] With respect to the method of operating an optical sensor unit , the obj ective mentioned above in accordance with the invention may be achieved with a method comprising the steps of :

[0020] - detecting received photons by means of an optical sensor arranged in a chamber of a housing through an aperture of said chamber, wherein the optical sensor comprises an array of photodetectors grouped into a number of macropixels such that each macropixel is provided with a time-to-digital converter to which output signals of the photodetectors of the respective macropixel may be delivered via a sequence of compression trees ,

[0021] - on the incident of an incoming photon arriving at a photodetector, generating a sensor signal and delivering said sensor signal to a time-to-digital converter associated with the macropixel of said photodetector, and

[0022] - further delivering said sensor signal to a time-to-digital converter associated with another macropixel .

[0023] Preferably, the method may further comprise the step of using a switchable multiplexer to optionally deliver said sensor signal to said time-to-digital converter associated with said another macropixel .

[0024] The maj or advantages achieved by the invention may be seen in that due to the basic concept of the invention of using detector signals of individual photodetectors , i f needed, as additional input for neighbouring macropixels , a higher ef ficiency and accuracy of data detection may be achieved even in the case of misalignment of incoming radiation spots with respect to the assigned macropixels . In principle , by the concept of the invention, the ef fective sensor area assigned to an individual macropixel may be modified or shifted by additionally taking into account the output signals out of neighbouring macropixels or their respective neighbour zones. The use cases for this mode of operation in accordance with one aspect of the invention in particular may be seen in that one or more spots of light falls on the crossing point or intermediate boundaries between various neighbouring macropixels. In reaction, with the concept of the invention compensating offsets may be realized. In particular, all neighbouring zones can be connected to the TDC of a certain macropixel. Any kind of spatial offset is possible. Various spots of incoming light may be distributed non-uniformly over the scene and therefore over the focal plane area of the sensor device. By rearranging the interconnection of the macropixels to the TDCs in the way identified above, the effective detector areas of the macropixels can be aligned to the pattern of the spots 62.

[0025] Brief Description of the Preferred Embodiments

[0026] Preferred embodiments and aspects of the invention are described further in connection with a drawing. In this drawing,

[0027] FIG. 1 shows an embodiment of an optical sensor device;

[0028] FIG. 2 an array of photosensors of the sensor device of

[0029] FIG. 1 in top view;

[0030] FIG. 3 a macropixel of the sensor device of FIG. 1 in top view (FIG. 3a: top tier, FIG. 3b: bottom tier) ;

[0031] FIG. 4 a block diagram of details of the readout circuit;

[0032] FIG. 5 the schematics of a multiplexing structure;

[0033] FIG. 6 an ensemble of four neighbouring macropixels in top view; FIG . 7 a block diagram of a multiplexer structure ; and

[0034] FIG . 8 an array of photosensors of the sensor device of FIG . 1 .

[0035] Identical parts are labelled by the same reference numerals .

[0036] Detailed Description of the Preferred Embodiments

[0037] FIG . 1 shows an example of an optical sensor device 1 in cross section . The embodiment of the sensor device 1 shown is intended to be used in a mobile device , in particular a smart phone , as a 3D sensor, in particular for face recognition purposes . It is noted, however, that the device 1 may be used in other appropriate applications as well , and the present disclosure should not be understood to be restrictive to the shown use case only . The optical sensor device 1 shown in FIG . 1 comprises both a detector unit 2 and an emitter unit 4 , that in the embodiment shown may be provided in a common sensor package of the sensor device 1 . It is noted that the present invention relates to the design of the optical detector unit 2 alone and therefore , within the scope of the present invention, may very well be used in an optical detector unit 2 alone .

[0038] In at least one embodiment an imaging system comprises at least one sensor device according to the aspects discussed below and a host system wherein the at least one sensor device 1 is embedded in . The host system comprises one of a mobile device , a 3D-camera, or a spectrometer, for example . For example , the mobile device can be a mobile phone , Smartphone , computer, tablet or the like . The sensor device 1 can be implemented into the mobile device using the detector unit 2 . This way the sensor device can be used as an optical sensor, e . g . rangefinders , proximity sensors , color sensors or time- of- f light sensors .

[0039] The optical sensor device 1 comprises an opaque housing 6 with two chambers : a first chamber 8 as part of the emitter unit 4 and a second chamber 10 as part of the detector unit 2 . The opaque housing 6 is arranged on a substrate or carrier 12 and comprises a light barrier 14 which divides the housing 6 into the first and second chamber 8 , 10 and therefore may be interpreted as the separation line between detector unit 2 and emitter unit 4 . The first and second chambers 8 , 10 are further confined laterally by a frame body 16 arranged in the housing 6 . A cover section or lid 18 , also part of the housing 6 , is located opposite to the carrier 12 and thereby covers the chambers 8 , 10 . The cover section 18 , the frame body 16 , and the light barrier 14 are manufactured from a continuous piece of material , such as a mold material , for example .

[0040] The carrier or substrate 12 provides mechanical support and electrical connectivity to electronic components which are integrated into the multispectral sensor 1 . For example , the carrier 12 comprises a printed circuit board, PCB (not shown) . However, in other embodiments (not shown) the carrier 12 can also be part of the housing and 6 electronic components are embedded into the housing 6 by molding for example .

[0041] An optical emitter 20 is located inside the first chamber 8 . The optical emitter 20 is arranged on and electrically connected to the carrier 12 , e . g . to the PCB . The optical emitter 20 is a laser diode , such as a VCSEL or VECSEL, for example . These types of lasers are configured to emit light at a speci fied wavelength, e . g . in the UV, visual or infrared part of the electromagnetic spectrum . In some embodiments the optical emitter 20 is tuneable to emit within a range of specified wavelengths . The speci fied emission wavelength, or an emission spectrum, lies in the IR or UV / Vis . The emission may be narrow- or broadband . For example , vertical-cavity surface-emitting lasers , VCSEL, or vertical-external-cavity sur- f ace-emitting-lasers , VECSEL, predominantly emit in the IR or NIR, e . g . at 940 nm . In the embodiment shown, in view of the intended use as 3D detector device , the emitter 20 in one aspect of the invention is designed as a NIR emitter 20 with dominant emission at about 940 nm . The advantage of this selection of the wavelength may be seen in that light of this wavelength, while invisible for the human eye , is well detectable in Si based detectors , and sunlight is partly absorbed, thus reducing ef fects of ambient light .

[0042] For example , in a direct-time-of- f light detector system, such VCSEL may be operated in pulsed mode (<500ps pulse width with high peak power ) . The VCSEL may therefore be bonded directly to a driver IC in order to avoid too long interconnections (which might have too high an inductance for the steep edges of the drive signal of the VCSEL ) . Above the VCSEL, a microlens array may be mounted which generates the dots and determines the field of illumination .

[0043] As part of the optical detector unit 2 , an optical sensor 22 is arranged inside the second chamber 10 and on the carrier 12 . In this particular embodiment , the optical sensor 22 is integrated into a single semiconductor sensor die 24 together with other electronics . The optical sensor comprises an array 26 of individual optical detector elements or pixels 28 which will be discussed in further detail below . In at least one embodiment the photodetectors 28 comprise photodiodes , single-photon avalanche diodes , SPADs , and / or avalanche photodiodes , APDs . The proposed sensor device can be used with di fferent types of photodetectors , in particular, those which are compatible with time-to-digital converters . The pixels 28 in the embodiment shown and in accordance with one aspect of the invention are implemented as single-photon avalanche diodes , or SPADs . Further, on the receiver side , an imaging lens , an interference filter (bandpass 940nm) , and optional mircolenses above the sensor surface may be provided . The CMOS die may be connected to the SPAD die via hybrid bonding .

[0044] As further part of the optical detector unit 2 , an array 30 of optical filters 32 is arranged in the second chamber 10 above the optical sensor 22 . The optical filters 32 are attached to the optical sensor 22 and all have the same transmission characteristic in order to match the spectrum as emitted by the emitter 20 for proper detection of reflected signals from the emitter 20 . The optical filters 32 may be interference filters such as an optical cut-of f filter, bandpass , long or short pass filter, dielectric filters , Fabry- Perot filters and / or polymer filters . Since , however, in the embodiment shown a single wavelength of about 940 nm is used, the optical filter arrangement instead also may be a continuous coating .

[0045] In order to allow for proper passage of light or radiation, the cover or lid 18 of the housing 6 , in each of both subunits detector unit 2 and emitter unit 4 , is provided with a first aperture 36 and a second aperture 38 . The first and the second apertures 36 , 38 are positioned above the optical emitter 20 and the optical sensor 22 , respectively . In fact , the apertures 36 , 38 lie within an emission cone of the optical emitter 20 and a field of view ( FOV) of the optical sensor 22 , respectively . The emission cone includes all points in space that may, at least theoretically, be illuminated by the optical emitter 20 , e . g . for a fixed emitter position and orientation . Similarly, the field of view of the optical sensor 22 includes all points in space from where , at least theoretically, light reflected at an external target 40 may traverse towards the optical sensor 22 , e . g . for a fixed detector position and orientation .

[0046] Optionally, optical systems can be arranged inside the first and second chambers 8 , 10 , respectively . For example , a first optical stack 42 comprises a lens or system of lenses and is attached to the optical emitter 20 inside the first chamber 8 . The emitter 20 in combination with its optical stack is designed as a dot proj ector system 44 . Accordingly, the optical stack 42 is designed to focus the light emitted by emitter 20 into dots which are proj ected to the scene or target 40 . In addition, the optical stack 42 may have optical filters or protective glass layers or windows , for example . The first and second chambers 8 , 10 may be sealed with an optical window, respectively .

[0047] Furthermore , a second optical stack 48 may comprise a lens or system of lenses and is attached to the optical sensor 22 in- side the second chamber 10. For example, the second optical stack 48 may comprise an array of micro-lenses wherein individual micro-lenses are associated with respective pixels 28 of the optical sensor 22. The array of micro-lenses may have additional black aperture layers and determine the FOV of the optical sensor 22. The micro-lenses can be adjusted in their optical properties (focal length, lens diameter, distance between lens and pixel 28, etc.) such that each associated pixel 28 of the optical sensor 22 is detecting light only from a defined region of the target 40. The optical properties of the micro-lenses may be adjusted in a way that the defined regions of the target 40 do not overlap. In addition, the second optical stack 48 may have further optical layers, e.g. optical filters, angular filters or protective glass layers or windows, for example. Furthermore, the second optical stack 48 may also have an additional lens to narrow the FOV of the optical sensor 22, e.g. to 10 degrees or smaller. Such optics such as a single lens or objective lens are used to gather light being reflected from the external target 40 and to image onto the sensor device 2, e.g. CMOS or CCD photo sensor. An optical band-pass filter typically passes the light with the same wavelength as the emitter unit 20.

[0048] A control unit 52 is integrated into the semiconductor sensor die 24 alongside with the optical sensor 22. The control unit 52 comprises a driver for the optical emitter 20. For example, the control unit 52 initiates emission of light by the dot projector system 44. Emission of the dot projector system 44 can be modulated, e.g. pulsed or modulated by a continuous wave. In operation, the optical emitter 20 emits light at the specified wavelength which illuminates the target 40.

[0049] Further, the control unit 52 also is a control unit for the optical sensor unit 2. For example, it provides sensor signals which are generated by the optical sensor 22. The control unit 52 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, amplifiers which too are located in the semiconductor sensor die 24 . The semiconductor die 24 may have a printed circuit board PCB providing electrical communication to the individual components of the multispec- tral sensor . In particular, the control unit 52 comprises means for time-of- f light measurements , i . e . measuring the time di f ference between a signal emitted by the emitter 20 and an incoming signal at sensor 22 as a reflection at target 40 .

[0050] For example , in operation the external target 40 is positioned in the FOV of the optical sensor device 1 . The control unit 52 initiates pulsed emission of light by means of the optical emitter 20 through the first aperture 36 and towards the external target 40 . Typically the illumination unit 20 emits modulated light with high speeds up to some 100 MHz . Alternatively, a single pulse per frame such as 30 Hz can be used . The emitted light has the speci fied wavelength . In reaction, the external target 40 will reflect the incoming light signal , and the reflected signal may be detected in sensor 22 .

[0051] The optical sensor device 1 in one aspect of the invention may be intended to be used in or with a 3D camera . In a 3D- camera imaging system two types of images may be generated : a regular 2D image and an additional ID image with distance information . These two images can be combined to yield a 3D image . In this context , the sensor device 1 may be used to provide , in particular on the basis of a time-of- f light measurement , the ID image with the distance information . In order to properly match this image with the "regular" 2D image , the sensor device 1 is designed to provide the ID-distance information in a way that can be combined with the 2D image information . For this purpose , in an aspect of the invention the photodetectors 28 of the detector unit 2 are provided in the form of the array 26 . The array 26 , an excerpt of which is shown in top view in FIG . 2 , comprises the individual photodetectors 28 in a regular lateral arrangement . In order to provide the desired information, the photodiodes 28 or pixels 28 are arranged and grouped into so-called macropixels 60 , each of which in an aspect of the invention in with regard to the space requirements of the evaluation electronics positioned underneath comprises 8x8 = 64 individual photodiodes 28 in a regular arrangement . Regarding lateral si ze , the dimensions of the pixels 28 are chosen such that , under normal operating conditions , the spots 62 of incoming light or radiation cover 2x2 = 4 individual pixels 28 . Thus , under normal operation, only 4 of said 64 individual pixels 28 will be needed to properly detect incoming radiation, whereas the remaining pixels 28 may be left inactive . Within each macropixel 60 , the active photodiodes 28 or pixels 28 of the respective macropixel 60 logically are connected in an "OR" mode such that all pixels 28 hit by incoming radiation will be triggered and thus contribute to the generation of an output signal .

[0052] The control unit 52 further comprises a readout circuit 64 that in turn comprises at least one control terminal . The readout circuit 64 provides a readout path for each of the photodetectors 28 . An array of time-to-digital converters 66 , TDCs for short , may be electrically connected to converter output terminals of the readout circuit 64 such that output signals of the photodetectors 28 may be delivered to the time-to-digital converters 66 . In particular, for each macropixels 60 an associated time-to-digital converter 66 is provided such that output signals of the photodetectors 28 of the respective macropixel 60 may be delivered to the associated TDC 66 .

[0053] In general , the accuracy and reliability of the output signals provided by the optical sensor 22 may be limited and lowered by a number of factors . In particular, both static and dynamic sources for potential errors in the signals may be of relevance . As an example of static sources for such errors , geometry factors may become relevant . Further, however, misreadings intrinsic to the measuring concept and resulting from ef fects like that the incoming spots 62 are not uni form- ly distributed to the scene or target 40 ( closer distance in the centre than at the edges ) or parallax ef fects may cause certain shi fts of the spots 62 in relation to the array 26 may occur in dependency of the distance to the target .

[0054] In a preferred embodiment and in one aspect of the invention, as can be seen clearly in FIG . 2 , all or a selected number of macropixels 60 may be arranged in a quadratic pattern such that any four of these macropixels 60 neighbour each other in an area around a common crossing point 70 . In this layout , a relatively large area can be covered reliably by a regular arrangement of individual photodetectors 28 , and production costs due to the intrinsic symmetry of the design can be kept low . By way of example , for such quadratic pattern, some possible positions of individual spots 62 relative to the array 26 and thus relative to their respective macropixels 60 are shown in FIG . 2 :

[0055] - Spots 62a - 62c are falling into di f ferent areas entirely within the macropixel 60 .

[0056] - Spot 62d is falling on the vertical border 68 between two neighbouring macropixels 60 .

[0057] - Spot 62e is falling on the hori zontal border 68 between two neighbouring macropixels 60 .

[0058] - Spot 62 f is falling on the central crossing point 70 of four neighbouring macropixels 60 .

[0059] In the latter cases the light energy of the respective Spot 62d, 62e , 62 f is distributed over multiple macropixels 60 , resulting in an underrepresentation of the light energy in the original , "correct" macropixel 60 . This may result in reduced accuracy of the system .

[0060] In order to overcome this , in one aspect of the present invention a multiplexing scheme is provided which allows to connect photodiodes 28 of neighbouring macropixels 60 to a j oint TDC channel , thereby allowing to take into account individual readings of photodiodes 28 that originally will belong to neighbouring macropixels 60 . The sensor device 1 therefore allows for compensating an optical of fset on a de- vice-basis . Thus , 2D image and an additional ID image can be aligned with higher accuracy .

[0061] In one aspect of the present invention, this is achieved by a design in which, logically, the array 26 of photosensors 28 of one or each macropixel 60 is arranged into a number of subgroups or zones 72 of pixels 28 . FIG . 3 shows a macropixel 60 in top view . The readout architecture associated with the macropixel 60 can be implemented as a separate tier and arranged above or below the array 26 , which may be arranged as another tier . However, the readout architecture may also be implemented next to the array 26 or between photodetectors 28 or on a backside of the array 26 as shown in the drawing . The readout architecture comprises the array 26 and the readout circuit 64 .

[0062] As can be seen from the top view on the top tier of a macropixel 60 shown in FIG . 3a, the array 26 of photodiodes 28 ( or - in the embodiment shown - SPADs ) is , in accordance with one aspect of the invention, sub-divided into four subgroups or zones 72a - 72d . Due to the quadratic shape of the macropixel 60 , each zone 72a - 72d is shaped as a subquadrant of the macropixel 60 and located in one of the corners of the macropixel 60 . Each zone 72a - 72d comprises 4x4 = 16 photodiodes 28 . For the sake of convention, in the following, for quadratic structures , for each macropixel 60 its upper right zone 72 shall be named zone 72a, its lower right zone shall be named zone 72b, its upper left zone 72 shall be named zone 72c, and its lower left zone shall be named zone 72d . The 16 photodiodes 28 of each zone 72a - 72d, with respect to the readout circuit 64 , are grouped using a 16-to- l first level compression tree 76 , which in an aspect of the invention may be hard-wired in a fixed wired scheme in the readout circuit 64 .

[0063] Correspondingly, as shown for the bottom tier of the macropixel 60 in top view in FIG . 3b, the CMOS logic of a macropixel as implemented in the readout circuit 64 comprises a frontend 74 for each zone 72a - 72d of photodiodes 28 . The respective frontend 74 in turn comprises quench and 1stlevel compression tree 76 of the respective zone 72a - 72d . Accordingly, the photodetectors 28 of the macropixel 60 are grouped into the zones 72 such that the photodetectors 28 of each zone 72 with respect to their signal outputs are j ointly connected to the first level compression tree 76 associated with the respective zone 72 . Further, the readout circuit 64 comprises the TDC 66 of the respective macropixel 60 and data processing logic 78 . In the embodiment shown, with the photodiodes 28 being implemented as SPADs , the SPAD anode may be connected to the quench via hybrid bonding connections .

[0064] FIG . 4 shows a block diagram of details of the readout circuit 64 for the respective zones 72a - 72d . As represented there , the individual photodiodes 28 or SPADs ( 16 per zone 72 ) in their output , by hard-wiring, are connected to a j oint 16-to- l 1stlevel compression tree 76 .

[0065] As mentioned above , in one aspect and in a basic concept of the present invention, a multiplexing structure connecting photodiodes 28 of neighbouring macropixels 60 to a j oint TDC channel is provided, in particular for allowing to take into account individual readings of photodiodes 28 that originally will belong to neighbouring macropixels 60 . In particular, in accordance with one aspect of the invention, the output of those zones 72 of neighbouring macropixels 60 that directly neighbour their common crossing point 70 should be provided as additional input to the TDC 66 of each of the neighbouring macropixels 60 . This multiplexing structure , which in one aspect of the invention is intended to overcome undesired effects of misarranged spots 62 on the array 26 , is shown in the schematic of FIG . 5 . In this multiplexing structure , in one aspect of the invention a 2nd level compression tree 80 based on a ring structure 82 is implemented in the readout circuit 64 .

[0066] FIG . 5 shows , in top view, the area in the vicinity of a common crossing point 70 of four neighbouring macropixels 601 , 602 , 603 , 604 . For macropixel 601 , zone 72bl is shown, where- as for macropixels 602, 603, 604 their neighbouring zones 72d2, 72a3, and 72c4 are shown. In the embodiment shown in FIG. 5, the ring structure 82 encompasses the four neighbouring macropixels 601, 602, 603, 604 next to their common crossing point 70. A quarter of the ring structure 82 is located on the respective corner 84 of each macropixel 60. By connecting various photodiodes 28, e. g. by abutment, the ring structure 82 may be established. The resulting configuration by nature can be seen similar to a bus interface with a single driver and four receivers.

[0067] In one aspect of the present invention, the ring structure 82 is provided in order to make the output of the 1stlevel compression trees 76 of the zones 72bl, 72d2, 72a3, and 72c4 available as an additional input signal to each of the neighbouring macropixels 601, 602, 603, 604. Thus, in one aspect of the invention, the ring structure 82 comprises one signal ring 86 for each of the zones of interest, i. e. zones 72bl, 72d2, 72a3, and 72c4. Each signal ring 86, via an output 88, is connected to an input 90 of the TDC 66 of each of the neighbouring macropixels 601, 602, 603, 604. In other words, in each zone 72bl, 72d2, 72a3, and 72c4, a multiplexer is implemented which allows to connect each of the signal rings 86 to the TDC 66 of a certain one of the macropixels 601, 602, 603, 604. This multiplexer may be controlled by USE_ZX_X signals. Further, each signal ring 86, via ring input 92, is connected to the output 94 of the 1stlevel compression tree 76 of one of the zones 72bl, 72d2, 72a3, and 72c4.

[0068] In the preferred embodiment as shown, connecting the corner zones 72bl, 72d2, 72a3, and 72c4 of four macropixels 601, 602, 603, 604, in an aspect of the invention the ring structure 82 accordingly comprises four individual rings 86, each of which is driven by the output 94 of exactly one of the zones 72bl, 72d2, 72a3, and 72c4. In the embodiment shown, level 1 compression tree 76 of Zone 72a3 is driving the ring interconnect 86a, zone 72bl is driving the ring interconnect 86b, zone 72c4 is driving the ring interconnect 86c and zone 72d2 is driving the ring interconnect 86d. In an aspect of the invention, the layout implementation of the ring structure 82 may be implemented very symmetrically in order to avoid timing errors on each line . In each zone 72bl , 72d2 , 72a3 , and 72c4 , a multiplexer 96 is provided which allows to activate the connection of each of the signal rings 86 to the TDC 66 of a certain macropixel 601 , 602 , 603 , 604 . This multiplexer 96 may be controlled by USE control signals . In particular, in one aspect of the invention, each of the signal rings 86 may be activated separately and independently by an associated multiplexer 96 .

[0069] In consequence of this design, and in accordance with one aspect of the invention, each zone 72bl , 72d2 , 72a3 , and 72c4 is able to drive a dedicated ring 86 . Thus , for each of the macropixels 60 , each of its three neighbouring zones 72 , respectively can signal wise be connected to its respective TDC channel . As a result , a quarter ( due to the division of each macropixel 60 into four zones 72 ) of each of the neighbouring macropixels 60 can be connected to a TDC channel of the respective macropixel 60 . In an aspect of the invention, the interconnection is implemented highly balanced in order to avoid timing errors of the signals .

[0070] FIG . 6 shows an ensemble of four neighbouring macropixels 60 in top view, showing in more detail how the interconnection described above may be placed between the four corners 84 of four abutting macropixels 60 . Four independent macropixels 60 are shown, each of which is subdivided into four zones ( 72a to 72d) . Each macropixel 60 comprises a TDC 66 (positioned on bottom tier ; by indication, the TDC 66 of the upper left macropixel 60 is shown only) . In normal operation, the four zones 72a to 72d of each macropixel 60 are connected to its TDC 66 . The multiplexer ring structure 82 in the region of neighbouring corners 84 allows to connect zones 72 from neighbouring macropixels 60 to the TDC 66 of each macropixel 60 . In the example shown here , the multiplexer 96 of the upper left macropixel 60 is activated by a respective USE control signal , and thus the connection of the neighbouring zones 72 of the three neighbouring macropixels 60 to the upper left TDC 66 is activated .

[0071] Consequently, each of the respective zones 72 in this state is driving one of the implemented signal rings 86 , thereby feeding their signals as an additional signal contribution to the TDC 66 of the upper left macropixel 60 . In other words , as a consequence of activating the multiplexer 96 on the upper left macropixel 60 , the SPAD events of the neighbouring zones 72 are guided to the upper left TDC 66 . As a result , the ef fective detection surface of the upper left macropixel 60 is increased by the respective neighbouring zones 72 , effectively providing an of fset of one quarter in x and y direction . This is indicated by indicated area 98 in FIG . 6 . The use case for this mode of operation in accordance with one aspect of the invention is that one spot 62 of light falls on the crossing point 70 of the four macropixels 60 shown . Of course , other use cases may be addressed in which other of fsets may be reali zed . In particular, all neighbouring zones 72 can be connected to the TDC 66 of a certain macropixel 60 . Any kind of spatial of fset is possible .

[0072] A block diagram of the multiplexer structure provided for the sensor device in accordance with one aspect of the invention is shown in FIG . 7 . A quadrant or zone 72 , as described above , in a preferred embodiment comprises 4x4= 16 individual photodiodes 28 or SPADs , which are grouped by a 16 to 1 ( level 1 ) compression tree 76 to form the respective zone 72 .

[0073] Each of the outputs 100 of the level 1 compression tree 76 of each zone 72 is connected to the respective zone multiplexer 96 . In addition, it may be connected by its corresponding wire 102 to the ring 86 which is connected to the neighbouring zones 72 . As a consequence of this interconnection, the zone multiplexer structure 96 may be considered a compression tree 80 for the zone 72a - 72d . The USE signals control signals for the multiplexers 96 then allow to activate the connection with the event signals of any of the sixteen SPADs of the respective zones 72 . Within each macropixel 60 , two additional 2-to- l compression trees 104 ( Level 3 ) are provided which complete the connection to the TDC 66 . In other words , in the embodiment shown and in one aspect of the present invention the first level compression tree 76 of each zone 72 with respect to its signal outputs is connected to the time- to-digital converter 66 of its respective macropixel 60 via a 2ndlevel or first higher order compression tree 80 ( as provided by the multiplexing ring structure 82 ) and further via subsequent higher order ( 3rdlevel ) compression trees 104 . In detail , and in accordance with one aspect of the invention, the first level compression tree 76 of each zone 72 of a macropixel 60 with respect to its output signal is connected to the subsequent compression tree 104 of its macropixel 60 via the associated multiplexer 96 , and it further is switchably ( due to the functionality of the activatable multiplexer 96 ) connected to a number of multiplexers 96 each associated with zones 72 of other macropixels 60 .

[0074] In particular and in accordance with one aspect of the invention, for the regular, quadratic pattern shown above , in which the ring structure 82 between neighbouring zones 72 is provided, the first level compression tree 76 of each of the zones 72 directly neighbouring the common crossing point 70 may be switchably connected to the multiplexers 96 associated with said other zones 72a, 72b, 72c, 72d of said macropixels 60 directly neighbouring said common crossing point 70 .

[0075] FIG . 8 , in a representation similar to that of FIG . 2 , a number of possible use cases in accordance with aspect of the invention are shown . Various spots 62 of incoming light may be distributed non-uni formly over the scene and therefore over the focal plane area of the sensor device 1 . By rearranging the interconnection of the macropixels 60 to the TDCs 66 in the way identi fied above , the ef fective detector areas of the macropixels 60 can be aligned to the pattern of the spots 62 . In particular ( the shi fts are indicate by framed zones 106 each) :

[0076] Spot 62g is falling into the correct macropixel area, and no rearrangement is needed . For spots 62h, 62 i a spatial of fset by one quadrant to the right is provided .

[0077] For spot 62 k, a spatial of fset by one quadrant downwards is provided .

[0078] For spots 621 , 62m a spatial of fset by 1 quadrant down and right is provided .

[0079] It is noted that the embodiments of the optical sensor device 1 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 , modi fications , 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 .

[0080] 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 .

[0081] 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 .

[0082] 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 .

[0083] 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 .

[0084] LIST OF REFERENCE NUMERALS

[0085] 1 optical sensor device

[0086] 2 optical detector unit

[0087] 4 optical emitter unit

[0088] 6 opaque housing

[0089] 8 , 10 chamber

[0090] 12 substrate

[0091] 14 light barrier

[0092] 16 Frame Body

[0093] 18 lid

[0094] 20 emitter

[0095] 22 sensor

[0096] 24 sensor die

[0097] 26 array

[0098] 28 photodetector

[0099] 30 array

[0100] 32 optical filter

[0101] 36 , 38 apertures

[0102] 40 target

[0103] 42 , 48 optical stack

[0104] 44 dot proj ector system

[0105] 52 control unit

[0106] 60 macropixel

[0107] 62 spot

[0108] 64 readout circuit

[0109] 66 time-to-digital converter

[0110] 68 border

[0111] 70 crossing point

[0112] 72 zone

[0113] 74 frontend

[0114] 76 compression tree

[0115] 78 data processing logic

[0116] 80 compression tree

[0117] 82 ring structure

[0118] 84 corner

[0119] 86 signal ring

[0120] 88 output

[0121] 90 input 92 ring input

[0122] 94 output

[0123] 96 multiplexer

[0124] 98 shaded area 100 output

[0125] 102 wire

[0126] 104 compression tree

[0127] 106 framed zone

Claims

CLAIMS1. An optical detector unit (2) comprising an array (26) of photodetectors (28) grouped into a number of macropixels (60) such that each macropixel (60) is provided with a time-to- digital converter (66) to which output signals of the photodetectors (28) of the respective macropixel (60) may be delivered via a sequence of compression trees (76, 80, 104) , wherein the photodetectors (28) of each macropixel (60) further are grouped into a number of zones (72) such that the photodetectors (28) of each zone (72) with respect to their signal outputs are jointly connected to a first level compression tree (76) associated with said zone (72) , wherein said first level compression tree (76) with respect to its signal outputs is connected to the time-to-digital converter (66) of the respective macropixel (60) via a number of subsequent higher order compression trees (80, 104) , and wherein the first level compression tree (76) of a zone (72) of a macropixel (60) with respect to its output signal is connected to the subsequent compression tree (104) of its macropixel (60) via an associated multiplexer (96) and further is switchably connected to a number of multiplexers (96) each associated with zones (72) of other macropixels (60) .

2. The optical detector unit (2) of claim 1, wherein the photodetectors (28) of each zone (72) with respect to their signal outputs are hard-wire connected to their first level compression tree (76) .

3. The optical detector unit (2) of claim 1 or 2, wherein the switchable connection of said first level compression tree (76) of a zone (72) of a macropixel (60) with said number of multiplexers (96) each associated with zones (72) of other macropixels (60) constitutes a 2ndlevel compression tree (80) for the connection with the respective time-to- digital converter (76) .

4. The optical detector unit (2) of any one of claims 1 to3, wherein a number of macropixels (60) are divided into four zones (72a, 72b, 72c, 72d) each.

5. The optical detector unit (2) of any one of claims 1 to4, in which each zone (72) comprises 16 individual photodetectors (28) .

6. The optical detector unit (2) of any one of the preceding claims in which a number of macropixels (60) are arranged in a quadratic pattern such that any four of said macropixels (60) neighbour each other in an area around a common crossing point (70) .

7. The optical detector unit (2) of claim 6, wherein for each zone (72a, 72b, 72c, 72d) of said macropixels (60) directly neighbouring said common crossing point (70) , its first level compression tree (76) is switchably connected to the multiplexers (96) associated with said other zones (72a, 72b, 72c, 72d) of said macropixels (60) directly neighbouring said common crossing point (70) .

8. An optical sensor device (1) , comprising an optical detector unit (2) of any one of claims 1 to 7.

9. The optical sensor device (1) of claim 8, further comprising an optical emitter unit (4) .

10. The optical sensor device (1) of claim 9, in which said optical emitter unit (4) comprises an optical emitter (20) arranged in a chamber (8) with an aperture (36) in a housing (6) also comprising a chamber (10) in which said detector unit (2) is arranged.

11. The optical sensor device (1) of claim 9 or 10 in which said optical emitter unit (4) and said detector unit (2) are arranged as a time-of-f light module.

12. Image system comprising the optical sensor device (1) of any one of claims 8 to 11 and a host system where the sensor device (1) is embedded in, wherein the host system is one of a mobile device, a 3D-camera, or a spectrometer.

13. Method to operate the optical detector unit (2) of any one of claims 1 to 7, the method comprising the steps of:- detecting received photons by means of an optical sensor (22) arranged in a chamber (10) of a housing (6) through an aperture (38) of said chamber, wherein the optical sensor (22) comprises an array (26) of photodetectors (28) grouped into a number of macropixels (60) such that each macropixel (60) is provided with a time-to- digital converter (66) to which output signals of the photodetectors (28) of the respective macropixel (60) may be delivered via a sequence of compression trees (76, 80, 104) ,- on the incident of an incoming photon arriving at a photodetector (28) , generating a sensor signal and delivering said sensor signal to a time-to-digital converter (66) associated with the macropixel (60) of said photodetector (28) , and- further delivering said sensor signal to a time-to-digital converter (66) associated with another macropixel (60) .

14. The method of claim 13, further comprising the step of:- using a switchable multiplexer (96) to optionally deliver said sensor signal to said time-to-digital converter (66) associated with said another macropixel (60) .

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