Abstract:
Detection circuits ( 1 ) for detecting movements of movable objects ( 2 ) such as joysticks are provided with first detectors ( 100 ) for detecting first movements of the joysticks in first directions, comprising first detection units ( 101 ) for detecting a presence/absence of light spots ( 3 ), locations of the light spots ( 3 ) depending on said first movements, and with second detectors ( 200 ) for detecting second movements of the joysticks in second directions, comprising second detection units ( 201 ) for detecting first second intensities of the light spots ( 3 ), intensities of the light spots ( 3 ) depending on said second movements. Such detection circuits ( 1 ) are less sensitive to misalignment of components during an assembly and simpler to produce and less costly. The second detectors ( 200 ) are entirely located within the light spot ( 3 ) independently from positions of the joysticks and the first and third detectors are partly located within the light spot ( 3 ) dependently on positions of the joysticks. The detection units ( 101 ) comprise photo diodes ( 120 ) and transistors ( 121 ) for digitizing the signals from the photo diodes ( 120 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a detection circuit for detecting movements of a movable object, and also relates to a detection arrangement, to a device and to a method. 
         [0002]    Examples of such a movable object are joysticks and multi functional keys, and examples of such a device are consumer products, such as mobile phones, personal computers, personal digital assistants and remote controls, and non-consumer products, without excluding further examples. 
       BACKGROUND OF THE INVENTION 
       [0003]    A prior art detection arrangement is known from U.S. Pat. No. 6,326,948, which discloses an input device comprising a base with a slide surface, a movable body slidable on the slide surface, a light emitting element for emitting light, a reflective portion which is provided for the movable body and has a reflective surface for reflecting the light emitted by the light emitting element, and a plurality of light receiving elements for receiving the light reflected by the reflective portion. 
         [0004]    In the prior art detection arrangement, horizontal movements are detected by comparing amounts of light received by the plurality of light receiving elements. To detect vertical movements, a diaphragm is placed between the movable body and the light receiving elements, such that a size of a light spot on the light receiving elements increases when the movable body is pushed down. The vertical movements are therefore detected by detecting a total amount of light received by the plurality of light receiving elements. 
         [0005]    The known detection arrangement is disadvantageous, inter alia, owing to the fact that it requires a diaphragm to be able to detect vertical movements. Such a diaphragm is sensitive to misalignment of components during an assembly and makes a production more complex and more expensive. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the invention, inter alia, to provide a detection circuit that does not require a diaphragm between its movable object and its detectors. 
         [0007]    Further objects of the invention are, inter alia, to provide to a detection arrangement, a device and a method that do not require a diaphragm. 
         [0008]    The detection circuit according to the invention for detecting movements of a movable object comprises:
       a first detector for detecting a first movement of the movable object in a first direction in a plane of the detection circuit, which first detector comprises a first detection unit for detecting a presence or an absence of a light spot at a location of the first detection unit, a location of the light spot depending on said first movement, and   a second detector for detecting a second movement of the movable object in a second direction perpendicular to the plane of the detection circuit, an intensity of the light spot depending on said second movement, which second detector comprises a second detection unit for detecting a first intensity or a second intensity of the light spot at a location of the second detection unit, the first and second intensities being different intensities unequal to zero.       
 
         [0011]    By detecting at a first location a presence or an absence of a light spot, for example a horizontal movement of the movable object can be detected. By detecting at a second location an intensity of the light spot, for example a vertical movement of the movable object can be detected, and it is no longer necessary to use a diaphragm. 
         [0012]    The detection circuit according to the invention is further advantageous, inter alia, in that it is less sensitive to misalignment of components during an assembly and simpler to produce and less costly. 
         [0013]    An embodiment of the detection circuit according to the invention is defined by further comprising:
       a third detector for detecting a third movement of the movable object in a third direction in the plane of the detection circuit, which third detector comprises a third detection unit for detecting a presence or an absence of the light spot at a location of the third detection unit, the location of the light spot depending on said third movement, the first and third directions being non-parallel directions.       
 
         [0015]    The respective first and second and third directions are for example x and y and z directions in case of the plane of the detection circuit being a horizontal plane, without excluding further options. 
         [0016]    An embodiment of the detection circuit according to the invention is defined by the first detector comprising further first detection units and the third detector comprising further third detection units, the first detection units being aligned parallel to the first direction and the third detection units being aligned parallel to the third direction. A plurality of first detection units and a plurality of third detection units allow the movements in the first and third directions to be detected more accurately. The pluralities of first and third detection units are for example lines of a cross, with the second detection unit being located at the crossing or close to the crossing or with a plurality of second detection units being located close to the crossing, at the line or lines of the cross or close to the lines of the cross. 
         [0017]    An embodiment of the detection circuit according to the invention is defined by the second detector being entirely located within the light spot independently from a position of the movable object and the first and third detectors being partly located within the light spot dependently on the position of the movable object. The size of the light spot is preferably such that all second detection units of the second detector are located within this light spot independently from the position of the movable object and is preferably such that all second detection units of the second detector are located partly within this light spot and partly outside this light spot dependently on the position of the movable object. The position of the movable object determines a location of the light spot at the detection circuit. 
         [0018]    An embodiment of the detection circuit according to the invention is defined by further comprising:
       a source for generating a light signal, the movable object comprising a reflector for reflecting the light signal to the detection circuit, the light spot resulting from the reflected light signal.       
 
         [0020]    By locating the source such as a light emitting source or an infrared light emitting heat source in the detection circuit and by providing the movable object with a reflector, it is no longer necessary to disadvantageously locate a source into the movable object. 
         [0021]    An embodiment of the detection circuit according to the invention is defined by the first detection unit comprising a first photo element for generating a first photo element signal, which first photo element is coupled to a first transistor for digitizing the first photo element signal, and the second detection unit comprising a second photo element for generating a second photo element signal, which second photo element is coupled to a second transistor for digitizing the second photo element signal. By digitizing the photo element signals immediately behind the photo elements, such as photo diodes or photo transistors, complex and expensive analog-to-digital converters and amplifiers are avoided. 
         [0022]    An embodiment of the detection circuit according to the invention is defined by the detection circuit being an integrated detection circuit based on at least one technique of a thin film poly silicon technique and a single crystal silicon substrate technique and a light emitting diode technique and an organic light emitting diode technique. Such an integrated circuit may advantageously comprise the photo elements, the transistors and the source, to form one robust circuit. 
         [0023]    The detection arrangement according to the invention comprises the detection circuit according to the invention and further comprises the movable object. 
         [0024]    An embodiment of the detection arrangement according to the invention is defined by the detection arrangement being a diaphragm-less arrangement. Such a diaphragm only introduces disadvantages. 
         [0025]    An embodiment of the detection arrangement according to the invention is defined by the first movement of the movable object in the first direction in the plane of the detection circuit resulting from the movable object being tilted and the second movement of the movable object in the second direction perpendicular to the plane of the detection circuit resulting from the movable object being pushed down. The tilting and pushing down are user-friendly movements. 
         [0026]    The device according to the invention comprises the detection circuit according to the invention and further comprises a man-machine-interface that comprises the movable object. 
         [0027]    An embodiment of the device according to the invention is defined by the man-machine-interface further comprising a display, which display is an integrated display comprising the detection circuit. This way, the movable object forms for example part of the display and does not need to be built separately, which makes a production easier and less costly. The movable object may for example be located on a margin of a display area of the integrated display. 
         [0028]    Embodiments of the detection arrangement according to the invention and of the device according to the invention and of the method according to the invention correspond with the embodiments of the detection circuit according to the invention. 
         [0029]    The invention is based upon an insight, inter alia, that a diaphragm is to be used in case one kind of detector has to detect two different kinds of movements, and is based upon a basic idea, inter alia, that different kinds of detectors are to be used for detecting different kinds of movements. 
         [0030]    The invention solves the problem, inter alia, to provide a detection circuit that does not require a diaphragm between its movable object and its detectors. The detection circuit according to the invention is further advantageous, inter alia, in that it is less sensitive to misalignment of components during an assembly and simpler to produce and less costly. 
         [0031]    These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments(s) described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    In the drawings: 
           [0033]      FIG. 1  shows diagrammatically a detection arrangement according to the invention in cross section, 
           [0034]      FIG. 2  shows a detection circuit in cross section and in top view for a non-moved movable object (left side) and for a moved movable object (right side), 
           [0035]      FIG. 3  shows detector layouts for a detection circuit according to the invention in top view, 
           [0036]      FIG. 4  shows a detector layout in greater detail for a detection circuit according to the invention in top view, 
           [0037]      FIG. 5  shows photo diodes and transistors of a detection circuit according to the invention, 
           [0038]      FIG. 6  shows a detector layout in greater detail for a detection circuit according to the invention in cross section, 
           [0039]      FIG. 7  shows a first integrated detection circuit according to the invention in cross section, 
           [0040]      FIG. 8  shows a second integrated detection circuit according to the invention in cross section, 
           [0041]      FIG. 9  shows a third integrated detection circuit according to the invention in cross section, and 
           [0042]      FIG. 10  shows a device according to the invention. 
           [0043]      FIG. 11  shows an alternative detection arrangement according to the invention. 
           [0044]      FIG. 12  shows a device with the alternative detection arrangement of  FIG. 11 . 
           [0045]      FIG. 13  shows a cross-sectional view (a) and top view (b) of a device according to the invention in the form of an accelerometer at zero acceleration. 
           [0046]      FIG. 14  shows a cross-sectional view (a) and top view (b) of the device in  FIG. 13  when an acceleration is applied in the X direction. 
           [0047]      FIG. 15  shows an example of a packaged device. 
           [0048]      FIG. 16  shows an extra mass added to the movable object in the form of a metal ring (a) or a metal layer (b). 
           [0049]      FIG. 17  shows a cross-sectional view of the accelerometer in 3D operation mode: without acceleration (a) and with an acceleration applied in the Z-direction (b). 
           [0050]      FIG. 18  shows a cross-sectional view of a 3D accelerometer having a separate detection component for the Z-direction. 
           [0051]      FIG. 19  shows the operation principle of the Z-component and detection circuit: no acceleration (a) and with an acceleration (b). 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0052]    The detection arrangement  10  according to the invention shown in the  FIG. 1  in cross section comprises a detection circuit  1  according to the invention. The detection circuit  1  such as for example an ASIC die comprises detectors  100 , 200 , 300  such as for example photo diodes and a source  4  such as for example a light source like any kind of LED and is located in a package  6 . A spring  8  is attached to the package  6 , and a movable object  2  is coupled to the spring  8 . This movable object  2  comprises a reflector  5  and a virtual rotation point  7 . Solder balls  9  of the package  6  allow the package  6  to be connected to for example a device  20  shown in the  FIG. 10 . Further, x and y and z directions are shown in the  FIG. 1 . 
         [0053]    The detection circuit  1  shown in the  FIG. 2  in cross section and in top view for a non-moved movable object (left side) and for a moved movable object (right side) discloses in the cross sections, to explain a basic principle of the detection circuit  1 , the detectors D 1 -D 4  and the source S and an image  11  of the source S at an other side of the reflector  5 . In the top views, the four detectors D 1 -D 4  are shown surrounding the source S. Signals from the detectors D 1  and D 2  are subtracted from each other via a differential circuit to get a y direction signal and signals from the detectors D 3  and D 4  are subtracted from each other via a differential circuit to get an x direction signal. 
         [0054]    When the movable object  2  such as a joystick is in a non-moved position or rest position (left side), the reflector  5  is parallel to the substrate and light emitted from the source S is reflected by the reflector  5  and casts a light spot  3  back onto the substrate. In other words the image  11  of the source S behind the reflector  5  shines a light cone through an opening created by the reflector&#39;s outline. The size of the reflector  5 , the distance between the source S and the reflector  5  and the dimension of the detectors D 1 -D 4  may be chosen such that the light spot  3  covers approximately half of the detectors area. Due to the symmetry of the system, the reflected light spot  3  is centered on the detectors D 1 -D 4 . In other words, all detectors D 1 -D 4  are equally exposed to light and therefore the output signals in X and Y directions are zero. 
         [0055]    When the joystick is tilted slightly to the right around a virtual pivot in the middle of or above the reflector  5 , the image  11  is moved along a circle or a curve to a new position. The light cone is therefore also tilted and consequently the light spot  3  is displaced to the left and slightly elongated. Now the symmetry is broken: D 3  receives more light than D 4  while D 1  and D 2  are still equally shined. On the output X, a non-zero signal is detected which is proportional to the tilt angle of the joystick in the X direction; while the signal on the output Y remains zero. Similarly, a tilt in any direction (X and Y) can be detected by all four detectors D 1 -D 4 . The mentioned way of connecting the detectors D 1 -D 4  is only an example. There exist different ways to extract the X and Y signals from the four detectors D 1 -D 4 . 
         [0056]    In another implementation, the tilt of the joystick to a certain direction, thus the X and Y signals, are translated into the speed of a cursor on a display moving towards that direction. By tilting the joystick a user is able to move the cursor into a desired direction. The speed of the movement depends on the tilt angle. To stop the movement, the user needs to release the joystick and let it return to the rest position. 
         [0057]    The detector layouts shown in the  FIG. 3  for a detection circuit  1  according to the invention in top view are examples only, such as squares in the  FIG. 3   a  or thin strips in the  FIG. 3   b  and the number of the detectors can be more than four in the  FIGS. 3   c  and  3   d . In the  FIG. 3   c , there are a number of small detectors aligning along four sides of the source. By counting the number of detectors which are covered by the light spot, X and Y signals can be obtained. This  FIG. 3   c  is shown in greater detail in the  FIG. 4 . In the  FIG. 3   d , the substrate contains a source S surrounded by an array of small detectors. The shape and position of the light spot which is corresponding to the tilt of the joystick, can be precisely determined by counting and locating the detector elements that are covered by the light spot. 
         [0058]    In addition, but not shown, the reflector may have different shapes. The reflector can be a concave mirror. A distance between a central point of the mirror and the source may preferably be between f and 2f, where f is the focal length of the mirror. In this case, the reflected light spot on the substrate is significantly smaller than in the case of a flat mirror. The concave mirror is preferably used in combination with arrays of detectors as shown in the  FIG. 3   d . Due to the small size of the light spot, the position of the light spot, thus corresponding to the tilt of the joystick, can be more precisely determined. 
         [0059]    The detector layout shown in the  FIG. 4  in greater detail in top view for a detection circuit  1  according to the invention comprises a first detector  100  comprising for example 18 detection units  101 - 118  and comprises a second detector  200  comprising for example 8 detection units  201 - 208  and comprises a third detector  300  comprising for example 18 detection units  301 - 318 . In an x direction from left to right the detection units  301 - 309  are followed by the detection units  205  and  206 , by the source  4 , by the detection units  207  and  208  and by the detection units  318 - 310 . In a y direction from above to below the detection units  101 - 109  are followed by the detection units  201  and  202 , by the source  4 , by the detection units  203  and  204  and by the detection units  118 - 110 . Further the light spot  3  is shown. 
         [0060]    In addition, a graph disclosing an intensity I versus a position P is shown. A dark area is indicated by  401 , a threshold is indicated by  403  and a lit area is indicated by  402 . In this example, a logical “1” is generated for the dark area and a logical “0” is generated for the lit area. 
         [0061]    The photo diodes  120 , 130 , 140  and the transistors  121 , 122 , 131 , 132 , 141 , 142  of a detection circuit  1  according to the invention are shown in the  FIG. 5 . Cathodes of the photo diodes  120 , 130 , 140  are coupled to a first reference terminal, and their anodes are coupled to first main electrodes of the transistors  121 , 131 , 141 . Second main electrodes of these transistors  121 , 131 , 141  are coupled to first main electrodes of the transistors  122 , 132 , 142  and are coupled to inputs of inverters  123 , 133 , 143 . The transistors  121 , 131 , 141  digitize the signal changes and the inverters  123 , 133 , 143  further digitize the signal and invert the digital signal. Second main electrodes of the transistors  122 , 132 , 142  are coupled to a second reference terminal. Control electrodes of the transistors  121 , 131 , 141  are coupled to each other. Control electrodes of the transistors  122 , 132 , 142  are coupled to each other. All control electrodes may be coupled to a further circuit for biasing purposes and for defining currents and for defining thresholds. 
         [0062]    In fact for each group of detection units  101 - 109 ,  110 - 118 ,  301 - 309 ,  310 - 318 , there may be a circuit as shown in the  FIG. 5 . About the detection units  201 - 208 , in a minimum situation there will only be one detection unit, for example detection unit  201  or  202 , in an extended situation there may be for example four detection units  201 ,  208 ,  204 ,  205  or  202 ,  203 ,  206 ,  207 , and in a maximum situation there may be eight or more detection units. Independently of the number of detection units  201 - 208 , each one may have its own circuit as shown in the  FIG. 5  or two or more may have together a circuit as shown in the  FIG. 5  etc. 
         [0063]    The detection units  202 , 203 , 206 , 207  are for example used to detect a press-to-select (press in a Z direction) action, hereafter called the Z photo detectors. Alternatively, for example all detection units  201 - 208  may be Z photo detectors. The rest are used for X and Y detection, hereafter called X/Y photo detectors. The Z photo detectors are preferably inside the light spot, regardless the position of the joystick. The positions of the Z photo detectors can be changed, for example a little more away from the source, and/or not in line with the X/Y photo detectors. 
         [0064]    In a detection circuit, a signal of each X/Y photo detector is compared to a corresponding reference signal, which results in a one bit digital signal. For instance if the X-Y photo detector is outside the light spot, the circuit shown in the  FIG. 5  results in a “1” for this photo detector, or in the other case, if the photo detector is inside the light spot, the circuit results in a “0”. The circuit is actually a one bit ADC (analog-to-digital converter). In other words, the circuit is a threshold detection (see the inset on the corner of  FIG. 4 ). For instance when the border of the light spot travels across a photo detector, a light intensity received on the photo detector is increased from the dark value  401  to the lit value  402 . Somewhere in the middle of these two levels, a threshold  403  is defined. That means when the border of the light spot travels about half way across the photo detector, the signal received on the detector should be switched from “1” (dark) to “0” (lit). In a later stage a digital circuit counts the number of photo diodes which are exposed to the light spot in each group, which represents the signal in that group. Signals X and Y will then be calculated by subtracting (digitally) signals of group  3  to group  4  and signals of group  1  to group  2 , respectively. The advantage of this digital detection method is that the electronic circuits are simpler. No analog circuits such as amplifiers and ADCs are required. The signals are digitalized right at every photo detector. 
         [0065]    The photo detectors such as photo diodes are reverse biased and for example connected in a current mirror circuit not shown. Via this current mirror circuit, a reference current may be defined. This reference current is mirrored to create equal and separate currents running through the photo diodes in the same group. Depending on the luminance condition of a photo diode  120 , the middle point, for example the coupling between the transistors  121  and  122 , can be at a low or a high value. For instance, when the photo diode is not lit, a voltage at this point is almost zero, but when the photo diode is exposed to light, its internal resistance drastically decreases (exponentially with a light intensity), that makes the point switching quickly to a high value. To ensure a fully digitalized signal, an extra threshold detection circuit such as an inverter e.g.  123  can be added. Finally at the output of each inverter, a digital signal can be obtained, which depends on the luminance condition of the photodiode. The outputs from the photo diodes in each group can be in a later stage fed into an encoder to have it converted into a binary number. Other suitable circuits than the encoder can be used as well. 
         [0066]    The detector layout shown in the  FIG. 6  in greater detail in cross section for a detection circuit  1  according to the invention discloses the detectors  200  and  300  and the source  4  and the reflector  5  and an image  12  of the source  4  in a non-moved position or rest position of the reflector  5  and the reflector  5  at a moved position or non-rest position  14  and an image  13  of the source  4  for this moved position or non-rest position and a light spot dimension  15 . 
         [0067]    When the joystick is pressed vertically, to for example select a certain item on a display as shown in the  FIG. 10 , the diameter of the spot of the reflected light on the substrate is not changed, but the light intensity of the spot is increased. In the beginning the reflector  5  is in the rest position. The light beams reflected at the edges of the reflector define the boundary of the reflected light spot on the substrate. This phenomenon can also be considered in an equivalent way: The image  12  of the light source (which is symmetrical to the source over the reflector), shines a light cone through an imaginary hole in the place of the reflector  5 . The solid angle of the cone in this case is α 0 . Given a fixed luminance power of the source, the light intensity on the substrate is proportional to α 0 /A, where A is the area of the reflected light spot. 
         [0068]    Now if the joystick is pressed vertically (click action), the reflector is supposed to travel to position  14  which is closer to the substrate than before. Applying a simple reflection rule, one can easily see that the size of the reflected light spot does not grow, but stays the same. However, due to the fact that the image  13  of the source now gets closer to the reflector, the solid angle α 1  of the light cone is now larger than α 0 . Consequently, the light intensity received by the substrate (˜α 1 /A, with A unchanged) is also increased. One or more Z photo detectors (e.g. 4) will sense this change and with a simple threshold detection circuit, a digital signal, corresponding to the vertical position of the stick, is generated. In principle, only one Z photo detector is necessary. However, to ensure a symmetrical movement of the stick, more than one Z photo detector (for instance 2-4) is to be preferred. The Z photo detectors can be arranged in the same rows as the X/Y photo detectors, or they can be located elsewhere, preferably provided that they are inside the light spot, regardless the position of the stick. 
         [0069]      FIG. 7  shows a first integrated detection circuit  1  according to the invention in cross section. The light source  503  is an Organic Light Emitting Diode (OLED) which is deposited and patterned onto a substrate  506 , which contains electronic devices such as thin film transistors (TFTs)  501 , photo diodes  502 , etc. based on a Low Temperature Poly-Silicon (LTPS) technique. The TFTs or LTPS photo diodes if not shielded are sensitive to light, therefore can be used as photo detectors. Besides, electronic circuits based on LTPS can be used to control and do signal processing for the device, that makes the device completely integrated. LTPS and OLED technologies have recently been combined on one common substrate to make the active-matrix OLED displays. Therefore, the use of this technique for the optical pointing device is an advantage in terms of technology reuse, high degree of integration and low-cost. The wavelength of the OLED can be chosen to suit the sensitive range of the LTPS-based photo detectors. Isolation layers are indicated by  500 , a transparent top electrode is indicated by  507 , a bottom electrode is indicated by  504 , gate oxide is indicated by  505 . 
         [0070]      FIG. 8  shows a second integrated detection circuit  1  according to the invention in cross section. Si photo diodes  602  (used as photo detectors) and CMOS circuits  601  can be integrated on a single crystal Si substrate  603 . After the Si wafer is complete (after back-end-of-the-line process), the wafer is transferred to an OLED fab where an OLED structure is deposited and patterned on top of the Si wafer. The wafer is then diced into separated dies for use in for example an optical pointing device. A transparent top electrode is indicated by  607 , a bottom electrode is indicated by  605 , an OLED is indicated by  604 , an interconnection of the Si die is indicated by  600  and an isolation layer is indicated by  606 . 
         [0071]      FIG. 9  shows a third integrated detection circuit  1  according to the invention in cross section. Si photo diodes  702  (used as photo detectors) and CMOS circuits  701  can be integrated on a Si substrate  703 . After the Si wafer is complete (after back-end-of-the-line process), inorganic LED dies  704  are mounted (by the pick-and-place process and gluing) on top of the Si wafer. The wafer is then diced into separated dies for use in the optical pointing device. A bond wire is indicated by  707 , a bottom electrode is indicated by  705 , an interconnection of the Si die is indicated by  700 . 
         [0072]    Because a heat source emits infrared light, it can be used as an infrared light source as well. The heat source can be created easily on Si substrate for instance by a resistive heater (using metal resistor or poly resistor). Alternatively, visual light or infrared light can be created on Si by using light emission of silicon P-N junctions, for instance when the P-N junction is reversed-bias and under avalanching conditions, or using the so-called “latch-up” phenomenon of the CMOS transistors. The latch-up is an undesired phenomenon in an ICs when too much current flowing inside a couple of transistors in a loop which creates heat and infrared emission. Latch-up happens due to improper design or defects of the chip. However in this case, latch-up is deliberately created. Si photo diodes are sensitive to infrared wavelength therefore can be used to detect the infrared light coming from the heat source. 
         [0073]      FIG. 10  shows a device  20  according to the invention. It comprises a display  21  and a movable object  2  such as a joystick. The joystick is for example mounted on a joystick area  22  of the display area that comprises the detection circuit  1  and the source  4  between integrated electronics areas  23 , which form part of a display substrate  24 . The optical joystick is based on the active-matrix OLED display technology. The arrangement consists of an OLED light source and a number of photo detectors based on TFTs fabricated on a common substrate, and a joystick having a reflector, hung above the substrate. This arrangement can be used in devices such as mobile phones, PDAs and other handheld devices to navigate through the menus on the display. The detection circuit  1  may have any kind of detector layout, for example one of the layouts shown in the  FIG. 3  or a combination thereof, without excluding further layouts. 
         [0074]    A device for example contains a photonic die which is diced from a large substrate containing OLEDs, photo detectors and integrated electronics fabricated using the OLED display technology. As a supplement, the joystick may be integrated on an OLED display substrate and can be sold with the display, as an additional function of the display. In an OLED display in e.g. mobile phones, some margins surrounding the display area can be used for on-board electronics such as driving circuits of the display, connection pads, etc. at least some components for an optical joystick may be integrated in the margin of the display area, among other electronic circuits. The electronics of the joystick can also be integrated in the surrounding area of the display. The  FIG. 10  right side shows the combined display-joystick in a mobile phone, for example. The body of joystick and its suspension mechanism can be built on the display substrate (see  FIG. 10 , bottom-left), or can be a part of the top cover of the phone. 
         [0075]    For handheld devices the dimensions of the detection arrangement  10  are critical, because there is not much space available in e.g. a mobile phone. In particular the height of the detection arrangement should be as small as possible. The height of the detection arrangement in  FIG. 1  is largely determined by the height of the suspension  8 .  FIG. 11  shows schematically a very advantageous alternative embodiment of the detection arrangement  10 , wherein the space inside the movable object  2  in the form of a knob is used to house the suspension  8 ′. This measure can reduce the height significantly. The suspension  8 ′ protrudes from the package  6 . Instead of being housed inside the package, it now resides inside the knob  2 . The hollow space inside the knob should be sufficiently large to allow the movable object  2  (such as a joystick) to tilt and click without touching. This alternative embodiment allows to thin the package  6  thickness down to 1 mm or even 0.8 mm as shown in  FIG. 11 . The actual thickness of the package is more determined by the required mechanical strength of the package, rather than by the height of the components inside. The typical thickness of the package substrate  25  is about 0.2 mm and the thickness of the device substrate  1  is about 0.2 mm. Another advantage is that since a relatively large volume of the knob can be used to house the suspension  8 ′, the suspension design can be more relaxed in dimensions. 
         [0076]      FIG. 12  shows a device  20  with the alternative detection arrangement of  FIG. 11 . The device  20  is here a mobile phone. The package  6  with the solder balls  9  is connected to a printed circuit board (PCB)  21 . Other neighboring ICs on the PCB  22  may be present to provide other functionalities to the mobile phone. The knob  2  is embedded in a housing  23  of the mobile phone. The alternative detection arrangement can also be applied as a mouse pointer in notebooks, or as a pointing device on a display in mobile phones, PDAs, portable gaming devices, remote control and other handheld devices. 
         [0077]    In an advantageous embodiment of the invention, the detection arrangement is used as an accelerometer. The movable object is made of a transparent elastic material, such as polydimethylsiloxane (PDMS). The shape of the movable object is such that it can reflect light from the source back onto the substrate.  FIG. 13   a  shows a cross-section view of such a transparent elastic movable object in the shape of a solid bowl. Here the movable object is a 3D object of rotational symmetry. In this Figure, only the cross-section through the axis of symmetry is shown. The movable object has a flat top surface (AB) and a curved sidewall (BC, AD). 
         [0078]    Thanks to the low stiffness of the small foot of the bowl, the movable object can be tilted a few degrees under the influence of a fictitious force caused by a lateral acceleration. When no acceleration is applied to the device, the movable object stands up right in the rest position ( FIG. 13   a ) and the top surface of the movable object is parallel to the substrate. Light emitted from the light source S goes through the transparent elastic material of the movable object  2  and reaches the top surface AB. At this interface, the light is partly transmitted to the air above the surface and partly reflected back into the movable object, depending on the angle of incidence. When the angle of incidence is smaller than the critical angle θ c =n 0 /n 1 , in which no is the refractive index of the medium around the movable object (e.g. air) and n 1  is the refractive index of the material of the movable object, internal reflection at the surface occurs, meaning that only a small fraction of light is reflected and the rest is transmitted. In this example the elastic material is PDMS, which has an index of refraction of 1.4, resulting in θ c =45.6°. When the incidence angle is larger than θ c , total internal reflection will take place. In this case 100% of the light will be reflected back into the movable object structure (marked as the shaded regions in  FIG. 13   a ). The reflected light (both internal and total internal reflection) subsequently reaches the sidewall AD, BC of the movable object. Due to the curved surface of the sidewall, the angles of incidence are (almost) zero, which maximizes the transmission of the light from the movable object to the air. 
         [0079]    Ideally, the curved sidewall is a part of a spherical surface which has the center at the image S′ of the source S over the surface AB. Due to this geometry, the directions of the transmitted (refracted) light through the sidewall remain unchanged. 
         [0080]    The transmitted light finally casts a light circle back onto the substrate. The inner part of the circle has weak intensity which corresponds to the internal reflection region whereas the outer ring of the circle has strong intensity which corresponds to the total internal reflection region (see  FIG. 13   b ). The total internal reflection circle has the most important contribution to the operation of the accelerometer. 
         [0081]    In an alternative explanation of the principle, the image S′ of the light source above the top surface AB shines a light cone through an opening in the top surface (see  FIG. 13   a ,  14   a ). The sizes of the top surface, the height of the movable object and the dimensions of the detectors are chosen in such a way that the light circle (including the outer ring) covers approximately half of the detector areas. Due to the symmetry of the system, the reflected light circle is centered on the detectors. In other words, all detectors are equally exposed to the light and therefore the output signals X and Y are zero. 
         [0082]    When a lateral acceleration (supposed to be in the X direction) is applied to the device in  FIG. 13 , a fictitious force pushes the movable object sideway, which slightly tilts the movable object ( FIG. 14   a ). The top surface AB is tilted away from the rest position, which causes the image S′ to move to a new position and consequently the reflected light circle on the substrate is displaced to the right and slightly elongated. Now the symmetry is broken: D 4  receives more light than D 3  while D 1  and D 2  are still equally shined. This is because part of luminous flux previously received by D 3  is now transferred to D 4 . On the output X, a non-zero signal is detected which is proportional to the tilt angle of the movable object, thus the acceleration in the X direction; while the signal on the output Y remains zero. Similarly, an acceleration in any lateral direction (X and Y) can be detected by all four detectors D 1 -D 4 . The detectors can be connected in a different way and the X and Y signals from the four detectors can be extracted differently as mentioned in the example above. 
         [0083]    A preferred transparent elastic material used for the movable object is polydimethylsiloxane (PDMS). This material has an adjustable elasticity (Young&#39;s modulus in the range of about 360-1100 kPa), can be easily used in fabrication processes (using molding or lithography), has a transparency to visible light (wavelength 230-700 nm, refractive index is 1.4), has a low glass transition temperature (−125° C.), and has a constant modulus over a wide temperature range. 
         [0084]    A molding technique can be used to structure the PDMS movable object. Arrays of molded movable objects can be structured on a carrier substrate at the same step and are subsequently transferred and glued onto the substrate containing light sources and detectors. The alignment of the movable object with respect to the light sources and detectors can be done on wafer level. The current technique allows an alignment accuracy of a few microns or less. This is acceptable because the size of the movable object is in the range of a few hundred microns. Next, the sensors are packaged and then the substrate  26  with the package  27  is diced. Finally the sensor dies are molded inside an outer package  28  (see  FIG. 15 ). The package described above is only an example. Other ways of packaging are possible as well. The inner surface of the inner package  27  is light-absorbent, e.g. black and rough, to avoid unwanted reflections. The joint between the inner package  27  and the photonic substrate  26  is preferably hermetic to keep the structure free of contamination and to keep the air pressure inside constant, so that a constant damping coefficient is obtained. 
         [0085]    The sensitivity of the accelerometer increases when the mass of the movable object is increased. To create extra mass on the movable object, a metal ring  29  may be put on the movable object during the molding process (see  FIG. 16   a ). This ring is located on the rim of the structure; therefore it does not affect the optical paths of the light. Alternatively, a metal layer  30  can be deposited on top of the movable object  2  ( FIG. 16   b ). The role of this layer may be twofold: to increase the mass and to serve as a mirror. In this case, all light coming from the light source is reflected back onto the substrate, which increases the luminous intensity significantly. 
         [0086]    The accelerometer as described above is inherently sensitive to the third dimension (Z direction perpendicular to the substrate) as well.  FIG. 17  explains the operation in the Z direction. In  FIG. 17   a , the situation at zero acceleration is shown: the movable object is not stressed and stands up right, which is the same as in  FIG. 13 . If an acceleration in the Z direction is applied to the sensor, for instance as indicated by the arrow in  FIG. 17   b , the movable object structure is deformed so that its body gets lowered. Finite element simulation revealed that in this case mainly the foot of the structure is compressed while the body of the movable object remains almost unchanged. Consequently the top surface of the movable object moves closer to the substrate. This causes the width of the total internal reflection ring to increase (since the critical angle where total reflection starts remains the same while the reflection surface gets closer to the substrate) and the luminous intensity of the whole reflected light circle to increase due to shorter distance between the source and the detectors. As a result, the amount of light received by all detectors is increased equally. On the X, Y outputs, this increase cannot be seen, because they are connected in the differential mode. However, if the common mode is used, a signal corresponding to the Z-acceleration can be obtained. 
         [0087]    In an alternative embodiment shown in  FIG. 18 , a second sensing component for the Z-direction can be added to the previous X-Y components to form a 3D accelerometer. A transparent elastic movable object in the form of a cantilever can be structured on the same substrate in the neighborhood of the X-Y component, in the same molding step ( FIG. 18 ). In the Figure, the cross-section view of the cantilever is shown. In fact, the cantilever should be imagined as a 3D structure extruded from this cross-section into the direction perpendicular to the plane of the drawing. A light source is located under the foot of the cantilever and beneath the cantilever, two detectors D 5  and D 6  are added ( FIG. 18 ). The detectors are connected in the differential mode. The sidewalls of the foot of the cantilever are tapered in order to confine the light inside the structure, thus minimizing the cross-talk between the Z-component and the neighboring X-Y-component. 
         [0088]    The total reflected light in this case casts a rectangle of light on the substrate (see  FIG. 19   a ). The detectors are designed in such a way that in the rest position (no acceleration), the light rectangle overlaps both detectors and covers about half of each detector area. 
         [0089]    Depending on the Z-component of acceleration, the cantilever is bent upwards or downwards (see  FIG. 19   b ). Consequently the light rectangle will displace to the right or left, respectively, resulting in signal change on the output. Due to its shape, the cantilever is only sensitive to the acceleration in the Z direction and very much less sensitive to acceleration in the X and Y directions. 
         [0090]    It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.