Patent Publication Number: US-2022228908-A1

Title: Optoelectronic sensor component for measuring light with built-in redundancy

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present patent application is a national stage entry according to 35 U.S.C. § 371 of PCT application No.: PCT/EP2020/064678 filed on May 27, 2020; which claims the priority of German patent application 10 2019 114 537.6 filed on May 29, 2019, all of which are incorporated herein by reference in their entirety and for all purposes. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to optoelectronic sensor components, and in particular ambient light sensors. 
     BACKGROUND 
     An ambient light sensor is an integrated optoelectronic sensor that detects the intensity of the ambient light and outputs a signal that is proportional to the ambient light intensity. Known ambient light sensors typically comprise a photodiode assembly and a signal processing circuit. 
     Ambient light sensors are built into the dashboards of motor vehicles, for example, where they measure the light intensity in the passenger compartment. On the basis of this measurement, the backlighting of the displays of the dashboard can then be adapted accordingly. 
     In the field of motor vehicles, in particular, sensors used therein are subject to the requirement that they are suitable for integrity checking. This ensures that the function of each sensor can be checked and a sensor that has possibly failed can thus be identified. 
     Present-day ambient light sensors do not satisfy these requirements. 
     Furthermore, in the field of motor vehicles, there is the requirement for controlling the display brightness of the displays of the dashboard by way of proximity detection and gesture recognition. This requires a proximity detection function in combination with an ambient light detection function. Proximity measurements can be carried out by proximity sensors. These sensors comprise infrared emitters, which illuminate the target object, and infrared detectors, which measure the signal reflected from said target object. The distance to the target object can be calculated on the basis of the intensity of the reflected signal measured by the sensor. 
     The function checking that is already employed in the case of discrete photodiode-based detectors might then be considered for being applied to integrated optoelectronic sensors such as ambient light sensors, for instance. Such function checking functions as follows: the supply voltage of the photodiode is reversed. As a result, the photodiode is no longer operated in the reverse direction, but rather in the forward direction. The resulting forward current is measured. If the measured forward current lies within a predefined range, an entirely satisfactory function of the photodiode is deduced. 
     This integrity check cannot be carried out in the case of integrated optical sensors, however, since there the supply voltage of individual photodiodes cannot be reversed straightforwardly without deactivating the entire integrated circuit. 
     It would therefore be desirable to have a sensor architecture which enables a different, reliable and simple integrity check, and which moreover is suitable for integrated circuits. 
     Said architecture should be configured in particular in such a way that it can be implemented in an integrated optoelectronic sensor component such as an ambient light sensor, for instance. 
     Accordingly, it is desirable to specify an optoelectronic sensor component which enables plausibility or function checking to be carried out in a simple and convenient manner. The function checking should be possible in particular in real time during ongoing operation of the optoelectronic sensor component. 
     SUMMARY 
     An optoelectronic sensor component for measuring light may include a first signal channel for providing a first electrical signal, which represents the intensity of light incident on the sensor component, a second signal channel, which is separate from the first signal channel in terms of signaling, for providing a second electrical signal, which is independent of the first electrical signal and which likewise represents the intensity of the light incident on the sensor component, a first light-sensitive detection assembly, which is configured for generating the first electrical signal and is assigned to the first signal channel, and a second light-sensitive detection assembly, which is configured for generating the second electrical signal and is assigned to the second signal channel, wherein both detection assemblies have an identical spectral sensitivity and are thus redundant with respect to one another. 
     By virtue of two separate detection assemblies being provided, said detection assemblies having an identical spectral sensitivity and thus being redundant with respect to one another, the optoelectronic sensor component yields the same measurement signal twice in the case of an entirely satisfactory function. That can be used for redundancy-based plausibility monitoring. In other words, an additional redundant light-sensitive detection assembly is used to detect the same incident light. Comparison of the mutually redundant signals allows a possible malfunction of the sensor component to be deduced. 
     In accordance with non-limiting embodiments, the sensor component can have one, a plurality or all of the following features, in all technically possible combinations:
         at least one signal processing circuit for conditioning the first and second electrical signals;   the two detection assemblies and each signal processing circuit are embodied as a single integrated circuit with a common voltage supply;   a first signal processing circuit for conditioning the first electrical signal and a separate second signal processing circuit for conditioning the second electrical signal;   the spectral sensitivity of both detection assemblies has a photopic profile;   a further light-sensitive detection assembly and an assigned further signal channel, wherein the further detection assembly is configured for detecting, in particular only, infrared light;   a further light-sensitive detection assembly and an assigned further signal channel, wherein the further detection assembly has an identical spectral sensitivity to the first and second detection assemblies and is shielded vis à vis ambient light, such that it can supply a reference signal for darkness;   each detection assembly comprises at least one photodiode;   a light-sensitive total measurement area subdivided into a number of measurement elements, wherein the measurement elements are formed by the photodiodes of the detection assemblies;   the first detection assembly defines a first light-sensitive measurement area and the second detection assembly defines a second light-sensitive measurement area, wherein the area of the first measurement area is an integral multiple of the area of the second measurement area;   the sensor component is an ambient light sensor.       

     The further light-sensitive detection assembly and the assigned further signal channel for detecting infrared light can be used for example in applications in which a proximity detection function is also desired alongside the ambient light detection function. For the proximity detection function, for example, an emitter configured to emit, in particular only, infrared light can be used to illuminate a target object. By means of the further light-sensitive detection assembly and the assigned further signal channel for detecting infrared light, the intensity of the infrared light reflected from the target object can be measured in addition to the intensity of the ambient light. The intensity of the reflected light can be used to calculate the distance between the detection assembly and a target object. 
     Likewise, the further light-sensitive detection assembly and the assigned further signal channel for detecting infrared light can supply a reference signal for infrared light, which reference signal can be subtracted from the signal of the first and second detection assemblies in order to adapt the spectral sensitivity of the two detection assemblies even better to a photopic profile. Accordingly, the spectral sensitivity of the human eye can be modeled in the best possible way. This can be done for example in a manner similar to the determination of a reference signal for dark current, by the infrared signal detected by the detection assembly being subtracted from the signal of the first and second detection assemblies. 
     A system for measuring light with function checking may include a sensor component having the features mentioned above and a device for checking the function of the sensor component, wherein the function checking device is configured to compare the two electrical signals generated by the first two detection assemblies and to deduce a malfunction of the sensor component ( 100 ) depending on the result of the comparison. 
     The light measuring system may have one, a plurality or all of the following features, in all technically possible combinations:
         the comparison effected by the function checking device consists in forming the difference between the two electrical signals generated and deducing a malfunction if the absolute value of the difference exceeds a specific threshold value;   the function checking device is furthermore configured to compare the reference signal with the first two electrical signals and to deduce a malfunction of the sensor component if the absolute value of at least one of the two electrical signals is less than the absolute value of the reference signal.       

     A system for electronic control based on measuring light may include a sensor component as defined above and an electronic control unit, wherein the sensor component and the control unit are connected to one another via a digital communication interface, such that the sensor component can transmit its measurement results in the form of digital data to the control unit, wherein the system provides a method for checking the error-free data transmission between the sensor component and the control unit, e.g. by means of a checksum, a cyclic redundancy check or an error correction method. 
     The two systems defined above may be combined in a non-limiting embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments will now be described in greater detail with reference to the drawings, wherein: 
         FIG. 1  is a block diagram of a first embodiment of a sensor component comprising one photodiode per channel and a common signal processing circuit; 
         FIG. 2  is a block diagram of a second embodiment of a sensor component comprising one photodiode per channel and one signal processing circuit per channel; 
         FIG. 3  is a block diagram of a third embodiment of a sensor component comprising four photodiodes per channel; and 
         FIG. 4  is a block diagram of one possible hardware implementation of a sensor component in the form of a chip with a measurement area subdivided into individual pixels. 
     
    
    
     Identical elements, elements of the same kind or elements having the same effect are indicated in the figures with the same reference signs. The figures and the proportions of the elements shown in the figures with respect to one another are not to be regarded as to scale. Rather, individual elements may be shown exaggeratedly large for better representability and/or for better comprehensibility. 
     DETAILED DESCRIPTION 
     The various sensor components  100 ,  200 ,  300  and  400  shown in the figures are in each case a combined ambient light and proximity sensor. Such sensors yield an output signal which increases with increasing intensity of light L incident on the sensor (see the arrows in the figures). The intensity of the light L prevailing in the environment in which the sensor is situated can thus be measured with the aid of such sensors. In addition, the sensor is also able to detect the approach of a human body part. 
     Such sensors can be installed in the dashboard of a motor vehicle, for example, where they serve for measuring the lighting conditions prevailing in the passenger compartment. The backlighting of the dashboard displays can then be adapted on the basis of the measurement result. By virtue of the proximity detection, commands issued by an occupant of the vehicle can also be recognized. 
     Of course, the sensors shown in the figures can also be used in other fields. 
       FIG. 1  is a block diagram of a first embodiment  100  of an optoelectronic sensor component. The sensor component  100  is present in the form of an integrated circuit. The sensor component  100  can be realized as a semiconductor chip, for example. The sensor component  100  comprises four light-sensitive detection assemblies  102 ,  104 ,  106  and  108  and a common signal processing circuit  110 . The semiconductor chip  100  is supplied with power via a terminal VDD. The chip usually comprises a grounding terminal GND as well. 
     The chip  100  has four further terminals, numbered consecutively from  1  to  4  in the figure. The semiconductor chip  100  additionally has a measurement area, not illustrated here, for measuring the incident ambient light L. The detection assemblies  102 ,  104 ,  106  and  108  are part of the measurement area. 
     In the present example, each of the four detection assemblies respectively consists of one photodiode  102  to  108 . Each respective photodiode  102  to  108  corresponds to a signal channel  112  to  118  for providing an electrical signal. The four signal channels  112 ,  114 ,  116  and  118  are each separate from one another in terms of signaling. They each provide an electrical signal that is independent of the other electrical signals. 
     The first two photodiodes  102  and  104  have an identical spectral sensitivity. They are thus redundant with respect to one another. In other words, they thus yield the same signal for the same incident ambient light L. The spectral sensitivity in the case of the photodiodes  102  and  104  may have a photopic profile. That is to say that the spectral sensitivity of the two detection assemblies  102  and  104  is modeled on that of the human eye. 
     The third detection assembly  106  has a photodiode having a different spectral sensitivity than that of the first two photodiodes  102  and  104 . The photodiode  106  is a photodiode that is sensitive to, in particular only, infrared radiation (IR photodiode). The fact that the photodiode  106  is a different photodiode than the other two photodiodes  102  and  104  is identified by the black dot in the photodiode triangle. 
     The fourth detection assembly  108  comprises a photodiode of the same type as the first two photodiodes  102  and  104 . This means that the spectral sensitivity of the fourth photodiode  108  is identical to that of the photodiodes  102  and  104 . The difference, however, is that the fourth photodiode  108  is shielded vis àvis the ambient light L by an opaque cover, for example. This is identified by the cross in the photodiode triangle. 
     Consequently, the first signal channel  112  represents the intensity of the light L incident on the sensor component  100 . Likewise, the second signal channel  114  represents the intensity of the ambient light L incident on the sensor component  100 . The third signal channel  116  represents the intensity of the infrared light incident on the sensor component  100 . The fourth signal channel  118 , by contrast, yields a constant reference signal for darkness. 
     However, the fourth detection assembly  108  can also have a different spectral sensitivity than that of the photodiodes  102 ,  104  and  106 . Accordingly, besides detection assemblies having a spectral sensitivity having a photopic profile and a spectral sensitivity in the infrared range, the chip  100  can also comprise a detection assembly that is sensitive to other spectral ranges. 
     All of the photodiodes  102  to  108  are connected to the same signal processing circuit  110 . The signal processing circuit  110  thus performs the conditioning of all signals supplied by the photodiodes  102  to  108 . This is done serially, for example, such that the signal processing circuit successively converts the signals of the four different photodiodes. 
     The signal processing circuit  110  typically comprises an amplifier and an analog-to-digital convertor. 
     Terminal No.  1  is the data output of the chip  100 . Via the latter, the signals supplied by the detection assemblies  102 ,  104 ,  106  and  108  and processed by the signal processing circuit  110  are output. Terminal No.  2  is a clock input for providing a clock frequency to the chip  100 . Terminal No.  3  is a so-called interrupt pin. Via this output, the chip  100  can notify e.g. an external control unit that a great change in the light intensity is taking place. Terminal No.  4  is a so-called address pin. Via this input, e.g. an external control unit can set an address of the sensor, in respect of the fourth photodiode  108 . 
       FIG. 2  shows a second embodiment  200  of an optoelectronic sensor component. The sensor component  200  has a construction comparable to that of the sensor component  100  from  FIG. 1 . It differs merely in that each signal channel  212 ,  214 ,  216  and  218  is assigned to a dedicated and separate signal processing circuit  210   a  to  210   d . In the case of the sensor component  200 , therefore, the signals of the four different photodiodes  202  to  208  can be processed in parallel and simultaneously. In contrast to the sensor component  100  from  FIG. 1 , the provision of a respective dedicated signal processing circuit  210   a  and  210   b  for the two redundant channels  212  and  214  makes it possible to preclude undesired deviations between the two output signals that may occur as a result of the serial signal processing. Moreover, a defective signal processing circuit can be identified in the case of this second embodiment. 
     Accordingly, an infrared signal of the photodiode  206  can be measured in parallel with an ambient light signal of the photodiodes  202  and  204 . 
     The block diagram in accordance with  FIG. 3  shows a third embodiment  300  of a sensor component. The special feature in the case of this variant is that not just a single photodiode, but rather an entire group of photodiodes is assigned to each of the four channels  312 ,  314 ,  316  and  318 . In this example, each group of diodes comprises four photodiodes connected in parallel. The provision of a plurality of photodiodes per channel results in a greater signal yield. Moreover, possible slight differences between the characteristic curves of the photodiodes, which can result in undesired deviations between the signals of the two redundant channels when just one photodiode per channel is used, are thus of less significance. Such differences between characteristic curves may be e.g. a consequence of fluctuations in process parameters during fabrication of the photodiodes. 
     As in the example in  FIG. 2 , here as well each individual channel  312  to  318  has its dedicated signal processing circuit  310   a  to  310   d.    
       FIG. 4  shows a hardware realization of an optoelectronic sensor component  400 . In this embodiment, the sensor component  400  is embodied as an integrated semiconductor chip. The semiconductor chip  400  has six contacts  420 ,  422 ,  424 ,  426 ,  428  and  430 . A total measurement area  432  is formed in the center of the semiconductor chip  400 . The total measurement area  432  is the light-sensitive region of the sensor component  400 . In the present example, the total measurement area  432  is embodied in square fashion. 
     The six contacts  420  to  430  frame the total measurement area  432 . The contact  420  at the top left serves for supplying voltage to the semiconductor chip  400 . The contact  422  at the top right is the data output. The measurement signals supplied by the sensor chip  400  are read out via this contact  422 . The contact  422  can be embodied as an I2C interface. The contact  424  in the middle on the left serves for grounding the semiconductor chip  400 . The contact  426  in the middle on the right serves for connecting a timer (clock) for the purpose of data transmission e.g. via an I2C interface. The contact  428  at the bottom left serves for addressing. The contact  430  at the bottom right is an interrupt. 
     The total measurement area  432  is subdivided into a number of individual measurement elements. In the present case, there are 4×4=16 measurement elements. The individual measurement elements are identified by the numbers  1  to  4 . The individual, here square, measurement elements each correspond to an individual photodiode. 
     The number of the measurement element ( 1  to  4 ) indicates to which of the four measurement channels of the ambient light sensor  400  the respective measurement element is assigned. In a manner comparable to the example in  FIG. 3 , four photodiodes are assigned to each measurement channel. The measurement channels  1  and  2  are once again embodied in a redundant fashion. The associated photodiodes have the same spectral sensitivity (e.g. they simulate the sensitivity of the human eye) and serve for detecting the same spectral range. The measurement channel serves for detecting the infrared light. The measurement channel  4  in turn is assigned to four shielded photodiodes that supply the reference signal already mentioned. 
     The 4×4 photodiodes are distributed on the total measurement area  432  as follows: the redundant photodiodes for measuring ambient light are situated in the corners and in the center of the square total measurement area  432 . The photodiodes for reference measurement and for measuring infrared light are arranged centrally on the outer sides of the square total measurement area  432 . 
     This pixel arrangement has the advantage that the geometry is symmetrical. In this regard, there is a shielded and an infrared photodiode on each outer side of the active optical area  432 . As a result, the signals are independent of the angle of light incidence. 
     In other words, the total measurement area  432  is thus subdivided into individual picture elements or pixels. 
     It was assumed in the description above that the measurement area covered by the photodiode(s) of the first channel and the measurement area covered by the photodiode(s) of the second measurement channel are of identical size. Alternatively, however, one measurement area can also be an integral multiple of the other measurement area. 
     A sensor component can be combined with a function checking device to form a system for measuring light with function checking. The function checking device then reads out the first two channels  1  and  2  of the sensor component. It compares the two signals read out and deduces a malfunction of the sensor component depending on the result of the comparison. The comparison may be effected by forming the difference between the two signals supplied by the channels. If the absolute value of the difference between the two signals exceeds a specific threshold value, it is assumed that the sensor component is faulty. Since the photodiodes of the first channel and the photodiodes of the second channel are embodied identically, the first two channels should also yield identical signals. If a significant deviation between the two signals occurs, there is thus some evidence that a malfunction of the photodiodes or of the signal processing circuit is present. 
     In addition, the function checking device can also compare the reference signal supplied by the fourth channel with the signals supplied by the first two channels. Since the associated photodiodes of the fourth channel are covered, the minimum signal expected when there is complete darkness prevailing in the environment of the sensor component is always present at output No.  4  of the sensor component. Accordingly, the absolute value of the signals of the first two channels should always be greater than or equal to that of the reference signal. If the absolute value of at least one of the two signals of the first two channels is less than the absolute value of the reference signal, a malfunction can likewise be assumed. 
     In the case where the measurement area of the first channel is an integral multiple N of the measurement area of the second channel, the signal I 1  supplied by the first channel will be greater than that of the second channel I 2  by an integral multiple N. The plausibility value P is then calculated here in accordance with the following equation: 
         P=N×I 2− I 1,
 
     wherein N is the integral multiple, I 1  is the signal of the first channel, and I 2  is the signal of the second channel. 
     Here, too, a malfunction is deduced if the absolute value of the plausibility value P exceeds a specific threshold value. 
     The sensor architecture having redundant optical channels can also be used to identify short circuits between the two redundant photodiode channels. For this purpose, a sequential measurement and parallel measurement have to be carried out on both redundant channels. If a short circuit exists between the two photodiode channels, the measurement result of the sequential measurement is double the magnitude of the measurement result of a parallel measurement. In the absence of a short circuit, the same measurement result is expected for both measurements. 
     The sensor component may also be combined with an electronic control unit to form a system for electronic control based on measuring light. The electronic control unit can be a so-called microcontroller (MCU), for example. The sensor component and the control unit are then connected to one another via a digital communication interface. This interface is formed for example by the contact  422  and the contact  426  in  FIG. 4 . As a result, the sensor component can transmit its measurement results in the form of digital data to the MCU. In this case, provision can be made of a method for checking the error-free data transmission between the sensor component and the MCU, for example by means of a checksum, a cyclic redundancy check or an error correction method. 
     LIST OF REFERENCE SIGNS 
     
         
           100 ,  200 ,  300 ,  400  Sensor component 
           102 ,  104 ,  106 ,  108  Light-sensitive detection assembly 
           110 ,  210 ,  310  Signal processing circuit 
           112 ,  114 ,  116 ,  118  Signal channel 
           212 ,  214 ,  216 ,  218  Signal channel 
           312 ,  314 ,  316 ,  318  Signal channel 
           420  Supply voltage terminal 
           422  Data output 
           424  Ground terminal 
           426  Clock generator terminal 
           428  Addressing pin 
           430  Interrupt 
           432  Total measurement area 
         L Ambient light