Sensor system for determining the transmission properties of a transmission path between transmitter and receiver in the form of coupling factors

Abstract

A sensor system (10) for determining the transmission properties in the form of coupling factors (16, 18) of a transmission path (12, 14) between a transmitter (20, 22) and a receiver (30) comprises a first and a second transmitter (20, 22), a receiver (30), and a processing unit (40). Both transmitters (20, 22) each transmit a transmission signal (100, 102) into the transmission path (12, 14). The receiver (30) receives the transmission signals (100, 102) and outputs a reception signal (110, 112, 114), wherein the two transmission signals (100, 102) are controlled by the processing unit (40) such that the reception signals (110, 112, 114) are equal.The processing unit (40) comprises an offset generator (60) for generating an offset signal (130) and is designed to feed the transmitters (20, 22) with feed signals (140, 142), to determine a difference signal (116) from the received signals (110, 112, 114), and based thereon to generate a control signal (120) for the feed signals (140, 142), which control signal is controlled such that the difference signal (116) is controlled to a predetermined amplitude value during a measurement and, during a further measurement, to superimpose an offset signal (130) of the offset generator (60) on the difference signal (116); and to determine the coupling factors (16, 18) of the transmission path (12, 14) from the determined signals.

Description

[0001] The present invention relates to a sensor system for determining the transmission characteristics of a transmission path between a transmitter and a receiver in the form of coupling factors, comprising a first and a second transmitter, a receiver, and a feedback-based processing unit. The invention further relates to a corresponding processing unit and a corresponding method.

[0002] In many applications of measurement or sensor systems, a transmission channel or transmission path between a transmitter and a receiver must be determined. For example, if the distance of a reference object from other objects is to be determined, or if an object and its movement are to be detected, such feedback-based systems are used. For example, for distance detection in vehicles, the amplitude attenuation of a light signal is used to measure distance using optical systems.

[0003] Many feedback systems operate according to the Halios principle, in which the actual transmission signal is superimposed with a compensating signal at the receiver. By controlling the corresponding transmitters, a nearly constant signal can be received at the receiver or sensor. Examples of such measurement systems are disclosed in DE 10 2005 013 325 A1, DE 10 2005 010 745 B3, DE 10 2007 005 187 B4, EP 2 783 232 B1, or EP 2 788 786 B1.

[0004] What all methods have in common is that the compensation signal and / or the transmitter signal is an analog signal with controlled amplitude and the transmitter signal has a constant duty cycle.

[0005] In addition to distance measurement, such sensors are also used as rain sensors or for gesture recognition. Here, the transmission path is described by the coupling factors between the transmitter and the receiver. From the change in the coupling factors, a raindrop on the window, for example, can be detected. For example, with two optical measuring paths with two LEDs and a photodiode as the receiver, the relative changes in the coupling factors are measured during rain detection, which is controlled by a Halios control loop to the same receive current of the receiver. However, it is not possible to also determine the absolute optical coupling factors during the measurement. With the known control systems, the control or measurement must be interrupted or stopped to determine the absolute coupling factors. This deactivates rain detection, which is disadvantageous and can sometimes lead to dangerous situations.

[0006] However, there is a need to determine the absolute coupling factors, for example, to detect a constant film of water or dew on the windshield when used as a rain sensor. Furthermore, the absolute coupling factors can be used to optimally adjust the gain of such a measurement system. The same applies to gesture recognition measurements.

[0007] The object of the present invention is therefore to improve a feedback sensor system and in particular to optimize the safety and reaction time of such a system.

[0008] The present object is achieved by a processing unit having the features of claim 1, by a sensor system having the features of claim 3 and by a method having the features of claim 16.

[0009] In a first aspect, the present invention relates to a processing unit for a feedback-based sensor system with a first and second transmitter and a receiver for determining the transmission properties of a transmission path between the transmitters and the receiver in the form of coupling factors, comprising an input interface for receiving a receiver signal from the receiver, which comprises transmission signals generated by the transmitters after passing through the transmission path; a feedback loop with a control unit for generating feed signals for the transmitters based on the received signal such that a received signal is present at the input interface which is regulated and has an amplitude of zero; an offset generator for generating an offset signal in order to generate adjusted feed signals and thus carry out a control in order to adjust to a predetermined amplitude value of the received signal that is not equal to zero;an algorithm unit with an algorithm for determining the coupling factors of the transmission link from the received signals, the feed signals, and the matched feed signals; and an output interface for outputting the feed signals to the transmitters, for generating transmission signals in the transmitters based on the feed signals, and for outputting the determined coupling factors.

[0010] In a further aspect, the invention relates to a sensor system for determining the transmission properties of a transmission path between transmitter and receiver in the form of coupling factors, comprising a first and second transmitter, a receiver, and a feedback-based processing unit, preferably a processing unit as previously mentioned; wherein both transmitters are configured to each transmit a transmission signal based on a feed signal into the transmission path, the receiver is configured to receive the transmission signals and output a reception signal; the two transmission signals are regulated by the processing unit such that the reception signals based on the transmission signals are equal; and the processing unit comprises an offset generator for generating an offset signal; and the processing unit is configured to generate feed signals for the transmitters;to feed the transmitters with the feed signals; to determine a difference signal from the received signals; to generate, based on the difference signal by means of a control unit, a control signal on which the feed signals supplied to the transmitters are based, and which is designed such that the difference signal is controlled to a predetermined amplitude value equal to zero; to superimpose an offset signal from the offset generator on the difference signal during a further measurement of the received signals; and to determine the coupling factors of the transmission path from the determined signals.

[0011] Further aspects of the invention relate to a corresponding method and a computer program product with program code for carrying out the steps of the method when the program code is executed on a computer, as well as a storage medium on which a computer program is stored which, when executed on a computer, effects execution of the method described herein.

[0012] Preferred embodiments of the invention are described in the dependent claims. It is understood that the features mentioned above and those to be explained below can be used not only in the respective combinations specified, but also in other combinations or alone, without departing from the scope of the present invention. In particular, the method and the computer program product can be implemented according to the embodiments described for the device in the dependent claims.

[0013] According to the invention, several measurements are carried out using the processing unit of the sensor system in a closed-loop process. First, a measurement is carried out as is known from the previous Halios system. The offset generator is switched off and the measurement is carried out without an offset signal. The two transmission signals from the transmitters, for example from optical transmitters, are controlled in such a way that a difference signal with zero amplitude is present at the receiver. The control loop measures the time-varying coupling factor difference of the two optical channels (transmission path) between a transmitter and the receiver. In a rain sensor, the difference in the coupling factors changes, for example, when raindrops influence the transmission path. The change is brief until the sensor system has adjusted the control loop.However, in order for a rain sensor to detect dew or a constant film of water on the windscreen, the absolute coupling factors must be determined.

[0014] In contrast to the prior art, in which the transmitter control is deactivated and the feed signals are transmitted with a constant amplitude (open-loop method) to determine the absolute coupling factors, the invention performs a further measurement using the closed-loop method, in which an offset signal is introduced into the control loop. This results in control to a non-zero amplitude value of the difference signal. Different feed signals are used for the transmitters in this second measurement than in the measurement without an offset signal.

[0015] Using the feed signals from the two measurements and the known behavior of the control loop and its components, including the amplifiers and, if applicable, converters, the coupling factors between the transmitters and the receiver can be easily determined or calculated using an algorithm. Preferably, the differential photocurrent required to calculate the coupling factors can be derived from the set gain, the converter behavior, and the demodulator value (difference signal at the demodulator output).

[0016] According to the invention, the absolute coupling factors of the two transmission channels are determined in the background while the control loop is running. This means that the two transmitters are switched alternately in the control loop, switching back and forth between them. The other transmitter is not active while one transmitter is transmitting. Preferably, the other transmitter is operated at a minimum value.

[0017] Using the processing unit according to the invention, it is therefore possible to continue operating a sensor system, such as a rain sensor, while the absolute coupling factors are being determined. The control process no longer needs to be stopped. Object detection or rain detection can continue continuously. Furthermore, by determining the absolute coupling factors, the control loop gain can be easily adjusted, allowing the coupling factor difference to be calculated from the control loop's integration signal.

[0018] In the sensor system according to the invention, in addition to the standard control without an offset signal, a measurement is also performed using an offset signal introduced into the control loop. The control loop is adjusted to a different, different received signal at the receiver, allowing the control loop and thus object or rain detection to continue. The resulting change in the signals also allows for the absolute coupling factor to be determined.

[0019] In a preferred embodiment of the processing unit, a feed source is additionally used to generate a minimum feed signal for the transmitters. The processing unit is also designed to alternately activate the two transmitters and feed them with a "normal feed signal". While one of the transmitters is fed with the feed signal ((high) current), the other transmitter is preferably not switched off, but is supplied with the minimum feed signal (minimum current) generated by the feed source. This feed signal is preferably different from zero. A minimum feed signal is a feed signal that can be output by the transmitter driver (or a transmitter source) as the smallest possible signal. The difference between the feed signal and the minimum feed signal is smaller during control than when the second transmitter is switched off.While this reduces the signal-to-noise ratio (SNR), for very small transmission signals, it has the advantage that the circuitry and control system do not have to operate close to the transmitter's "switch-off point" (e.g., a transmitter LED). Another advantage is that the transmitter driver does not have to constantly switch its operating mode between ON and OFF. This leads to delayed switch-on and switch-off edges. These delays and the signal edges can then also be asymmetrical. When using the minimum feed signal, the transmitter does not have to be switched off. The switching state remains, which means that the transmission signal is symmetrical and regular.

[0020] In a preferred embodiment of the sensor system, the transmitters are also alternately supplied with the supply signal. More preferably, the other transmitter is supplied with a minimum supply signal. This minimum supply signal is preferably at most 10% of the supply signal, i.e., the maximum value of the supply signal or the normal value of the supply signal if the normal value (current value) is at least 2 mA. More preferably, the minimum supply signal is at most 5%, 4%, 2%, 1%, or 0.5% of the supply signal. With a normal value of the supply signal (or current value) of at most 0.1 mA, the minimum supply signal can also be larger, preferably up to 50% of the normal value, more preferably up to 70%, very preferably up to 90%. The minimum supply signal can also be zero, but this can lead to overshoots during control.

[0021] In a preferred embodiment of the sensor system, the supply signal is a supply current. This is preferably at most 100 mA, more preferably at most 10 mA, more preferably at most 6 mA, and particularly preferably at most 4 mA.

[0022] Preferably, the minimum supply signal is a minimum supply current that is no greater than 10% of the maximum or normal supply current, or no greater than 50% for a supply current of at most 0.2 mA, no greater than 70% for a supply current of at most 0.1 mA, or no greater than 90% for a supply current of at most 0.05 mA. Preferably, the minimum supply current is at most 0.8 mA, more preferably at most 0.4 mA, and very preferably at most 0.2 mA.

[0023] In a preferred embodiment of the sensor system, the coupling factors are determined using an algorithm implemented in the processing unit. The algorithm can, for example, be implemented in an algorithm unit such as that provided in the inventive processing unit. Using the algorithm, the coupling factors of the transmission links are determined from the received signals, the feed signals, and the adjusted feed signals or the minimum feed signals.

[0024] Preferably, the receiver and transmitter are optical components, such as photodiodes or light-emitting diodes (LEDs). Alternatively, the receiver and transmitter can also be capacitive components, resulting in a capacitive transmission path.

[0025] In principle, the sensor system uses analog technology. However, digital technology has become more popular in recent years, particularly because the components are inexpensive and easy to use. In a preferred embodiment, the processing unit of the sensor system comprises a receiver circuit that has an amplifier (with a filter, e.g., bandpass or highpass) and an ADC (analog-to-digital converter) for digitization. The processing unit further comprises a multiplexer for processing the input signals, a demodulator designed as a comparator, preferably as a subtractor, and an output circuit that has a DAC (digital-to-analog converter) for generating analog feed signals for the transmitters. This enables control using digital technology. The control unit in the processing unit is accordingly implemented using digital technology. The feed signals remain analog, as does the signal received by the receiver.

[0026] In a further preferred embodiment, the output circuit of the digital sensor system has a minimum signal source for generating the minimum feed signal. The output circuit further comprises a multiplexer for feeding one of the transmitters with a feed signal and the other transmitter with the minimum feed signal. Preferably, the minimum feed source is a minimum current source, and the minimum feed signal is a minimum feed current. The minimum feed signal is generated as an analog signal and transmitted directly to the corresponding transmitter.

[0027] In a preferred embodiment of the sensor system, the offset generator is arranged upstream of the control unit in the processing direction. The offset signal is thus superimposed, preferably added, with the difference signal generated in the demodulator, so that the superimposed signal, including the offset signal, is processed in the control unit. This ensures that the transmission paths are preferably brought into an "artificial imbalance." They are therefore not regulated to zero, i.e., their AC amplitude value, or the difference value between two signal components of the two transmitters contained in the received signal, is not equal to zero, or the amplitude is not equal to zero.

[0028] In a preferred embodiment of the sensor system, the control unit is a PI controller. Other controllers can also be used.

[0029] The present invention also relates to a rain sensor with a sensor system as described above, wherein the transmitter light sources are preferably LEDs and the receiver is a photodiode. Using the sensor system or the inventive rain sensor, not only raindrops but also a film of moisture or dew on a window can be detected.

[0030] In a preferred embodiment, the sensor system can be designed as a gesture recognition system.

[0031] In addition, the present invention also relates to a vehicle with a sensor system or rain sensor as described above.

[0032] The method according to the invention is used to determine the transmission properties of a transmission path in the form of coupling factors of a sensor system based on feedback compensation between a first and a second transmitter and a receiver. Both transmitters each transmit a transmission signal based on a feed signal into the transmission path. The transmission signal from the respective transmitter is received by the receiver. The two transmission signals are regulated by a processing unit such that the reception signals based on the transmission signals are equal. The processing unit has an offset generator for generating an offset signal. The method comprises several steps, wherein at least one first measurement is initially performed, followed by at least one second measurement.It is possible to perform several first measurements and several second measurements to improve the quality, for example, first several first measurements and then several second measurements.

[0033] Likewise, the at least one first measurement and the at least one second measurement can be performed "quasi-parallel," i.e., with very rapid switching between the measurements, so that the data for calculating the absolute coupling factor can be determined virtually simultaneously. In this case, several first and then several second measurements can also be performed.

[0034] Carrying out a first measurement comprises the steps of generating feed signals for the transmitters, wherein the feed signals can be or are different for each transmitter, and alternately feeding the transmitters with the feed signals, wherein the other transmitter is switched off or preferably supplied with a minimum feed signal. A further step involves transmitting transmission signals based on the feed signals into the transmission path to the receiver. A step of receiving the transmission signals by means of a receiver is followed by a step of generating reception signals in the receiver. This is followed by a step of determining a difference signal from the reception signals. In a further step, the reception signals are regulated and a control signal based on the regulated reception signals is generated such that the difference signal has an amplitude equal to zero.A further step involves generating the feed signals based on the control signal.

[0035] After performing this first measurement, a second measurement is performed, which comprises the steps described above and additionally includes a step of generating an offset signal, preferably generated using an offset generator. This is followed by a step of superimposing the difference signal with the offset signal, i.e., preferably adding the difference signal and the offset signal. In a further step, the difference signal is controlled and the control signal is generated such that the difference signal has an amplitude other than zero. The control system is thus artificially imbalanced.

[0036] Following this second measurement, the method according to the invention comprises the step of determining the coupling factors from the feed signals of the transmitters of the two measurements. Overall, different feed signals and different received signals or difference signals are present. From these values, the coupling factors of the respective transmission paths between a transmitter and the receiver can be determined, as explained further below. This can preferably be done using an algorithm.

[0037] In a preferred embodiment, the method comprises further steps. When performing the first and second measurements, a step of generating a minimum feed signal is performed, wherein the minimum feed signal is preferably provided by a minimum feed source. A further step involves feeding one transmitter with the feed signal and feeding the other transmitter with the minimum feed signal. During a further measurement, the other transmitter is fed with the feed signal and the one transmitter with the minimum feed signal, so that the feeding with the feed signal and the minimum feed signal always alternate.

[0038] The invention thus relates to a method for determining the transmission characteristics of a transmission link in the form of coupling factors of a measurement system based on feedback compensation between a first and second transmitter and a receiver. Both transmitters each transmit a transmission signal based on a transmission current into the transmission link, which is received by the receiver. The transmission signals are regulated by a processing unit such that the reception signals based on the transmission signals are identical. The processing unit comprises an offset generator for generating an offset signal.

[0039] The procedure has the following steps: - Generating a transmission stream for one of the transmitters; - generating a minimum transmission current for the other of the transmitters by means of a minimum current source; - alternately feeding the transmitters with the transmission streams; - Receiving the transmission signals by means of a receiver as a received signal; - Determining a difference signal of the received signals; - regulating the received signals and generating a control signal based on the regulated received signals; - Feeding back the control signal and generating the transmission current for one transmitter; - Repeat the steps for the other transmitter; - Carrying out the preceding steps with the additional step of superimposing the received signal in each case with an offset signal from the offset generator; - Determining the coupling factors of the transmission path from the detected or generated signals and currents.

[0040] The invention is described and explained in more detail below using selected embodiments in conjunction with the accompanying drawings. They show: Fig. 1 shows a sensor system according to the invention with a processing unit; Fig. 2 a schematic diagram of the sensor system shown above with optical transmitters and transmission path; Fig. 3 an optical sensor system with a processing unit based on digital technology; Fig. 4 a vehicle with a sensor system designed as a rain sensor according to Fig. 3.

[0041] Fig. Figure 1 shows a schematic diagram of the sensor system 10 according to the invention for determining the transmission properties in the form of coupling factors for a transmission path 12 between a transmitter 20 and a receiver 30. In addition to the first transmitter 20, the sensor system 10 has a second transmitter 22, which also sends a transmission signal to the receiver 30. The two transmission paths 12, 14 are shown schematically here and are represented by the coupling factors 16, 18, which describe the transmission paths 12 and 14, respectively.

[0042] A processing unit 40 processes the received signal 110 generated by the receiver 30, which is present at an input interface 42 of the processing unit 40. The received signal 110 is amplified by an amplifier 44 (with a filter (not shown) such as a bandpass or highpass) and fed to a control unit 50. The control unit 50 preferably comprises a PI controller.

[0043] A generated control signal 120 is supplied to the respective transmitters 20, 22 as a feed signal 140 or 142, respectively, with the feed signals 140, 142 being output at an output interface 46. The feed signals 140, 142 are each amplified by an amplifier 52, 54.

[0044] Between the amplifier 44 (input amplifier) ​​and the control unit 50, a superposition element 62 is arranged, which superimposes an offset signal 130 of an offset generator 60 on the amplified received signal 110.

[0045] According to the invention, with the sensor system 10, first one transmitter 20 is fed with a feed signal 140, so that a first received signal 110 is present in the receiver 30. The second transmitter 22 is switched off. In a next step, the transmitter 22 is fed with the feed signal 142, with the transmitter 20 switched off. A received signal 110 based on the transmitted signal of the transmitter 22 is then present at the receiver. The control by means of the control unit 50 regulates the two feed signals 140, 142 so that the received signals 110 (generated by the two transmitters 20, 22) are equal and a resulting difference signal has an amplitude of zero. In a further measurement, the offset signal 130 is superimposed on the amplified received signal 110. The control is then carried out to a predetermined offset value. This measurement is also carried out with the two transmitters 20, 22.The coupling factors 16, 18 can be easily determined from the regulated supply signals 140, 142 and the signals present at the output of the amplifier 44, as will be described below.

[0046] Fig. Figure 2 shows a special embodiment of the sensor system 10, in which the transmitters 20, 22 are designed as LEDs 21, 23. The two LEDs 21, 23 are fed with the respective supply signals 140, 142 and transmit a transmission signal 100, 102 into the transmission paths 12 and 14, respectively, characterized by the coupling factors 16, 18. The two transmission signals 100, 102 are superimposed and reach the receiver 30, designed as a photodiode 32. The control loop and signal processing are carried out according to the sensor system 10 according to Fig. 1.

[0047] In principle, the sensor systems 10 can be configured according to the Fig. 1 and Fig. 2 using analog technology. However, it is advantageous to implement the processing unit 40 using digital technology. Such an embodiment of a sensor system 10 is shown in Fig. 3. The transmitters 20, 22 are also embodied here as LEDs 21, 23, and the receiver 30 as a photodiode 32. The transmission paths 12, 14 are represented by the coupling factors 16, 18. The system according to the invention is designed to determine the two absolute values ​​of the coupling factors 16, 18, so that, for example, when the sensor system 10 is designed as a rain sensor, dew or a film of water on the windshield, i.e., in the transmission paths 12, 14, can also be detected. The sensor system 10 according to the invention, as shown in the Fig. The method shown in Figures 1 to 3 is suitable for detecting the absolute coupling factors 16 and 18 during operation, i.e., in a closed-loop process. This allows a rain sensor to operate continuously. There is no danger from interrupted processing.

[0048] The processing unit 40 comprises an input circuit 70, which includes the amplifier 44, and a downstream ADC converter 72, which converts the analog received signals 112, 114 into digital signals. The digital signals are further processed by a multiplexer unit 74, so that a difference can be formed and amplification can take place in a subsequent demodulator unit 76. The demodulator value present at the output of the demodulator unit 76 corresponds to the difference between the received signals 110 of the two LEDs 21, 23 multiplied by the gain of the amplifier 44 and the gain of the ADC converter 72. From this value, the coupling factors 16, 18 can ultimately be determined using several measurements.

[0049] The difference signal 116 present at the output of the demodulator unit 76 results from the difference between the two received signals 112, 114, which are compared with each other and formed in the multiplexer unit 74 from the respective received signals 110.

[0050] The difference signal 116 is fed to the control unit 50, where the corresponding control can be implemented, for example, using a PI controller. The generated control signal 120 is amplified in a DAC gain stage 78, i.e., preferably digitally multiplied or scaled with a configurable gain, so that the subsequent DAC converters 80, 82 can optimally utilize their control range. The control signal 120 is then split into two channels for the two transmitters 20, 22 and into two DAC input signals 150, 152 by a multiplexer (not shown here), which are converted into analog signals by two digital-to-analog converters (DAC converters 80, 82) and then amplified by two drivers (DAC amplifiers 84, 86) and fed as feed signals 140, 142 to the corresponding LEDs 21 and 23, respectively.

[0051] For a measurement, the two transmitters 20, 22 are operated alternately, whereby the other transmitter 20, 22, which is not supplied with the supply signal 140, 142, can be switched off or de-energized. However, within the scope of the invention, it has proven advantageous if the second transmitter 20, 22, not supplied with the supply signal 140, 142, is also supplied with a minimum current or minimum supply signal 140, 142. This makes the transmitted signal 100, 102 more stable and the signal shape more symmetrical. The processing unit 40 therefore comprises two supply sources 88, 90, each of which generates a minimum supply signal 160, 162, which is supplied to the transmitter 20, 22 instead of the respective supply signal 140, 142. While one transmitter 20 is fed with the feed signal 140, the second transmitter 22 is fed with the minimum feed signal 162 from the feed source 90, or vice versa. Switching back and forth is accomplished, for example, by means of a multiplexer.Alternatively, the minimum feed signals 160, 162 of the feed sources 88, 90 can be superimposed with the respective DAC output signal 154, 156 of the DAC amplifier 84, 86 by means of an adder 96, 98, so that the minimum current (minimum feed signal 160, 162) or the sum of the minimum current (minimum feed signal 160, 162) and the feed current (DAC output signal 154, 156 of the active DAC amplifier 84, 86) is applied as feed signal 140, 142 to the output interface 46 and feeds the LEDs 21, 23.

[0052] After carrying out the measurement and control in the sensor system 10 without an offset signal 130, a further measurement is carried out with an offset signal 130, whereby the value of the difference signal 116 is no longer controlled to an amplitude of zero, but to an amplitude deviating therefrom.

[0053] Using these two measurements and the known signals or currents for controlling the LEDs 21, 23, the two coupling factors 16 and 18 can be determined.

[0054] The goal is to calculate the coupling factors 16, 18 for the two transmission links 12, 14 using two controlled measurements in closed-loop operation. This requires two measurements with different feed signals 140, 142 or feed currents. The respective coupling factor 16, 18 results from the ratio between the feed signal 140, 142 or the corresponding feed current and the received signal 112, 114 or the corresponding received current.

[0055] The supply current (supply signal 140, 142) is referred to as LED current I LED The received current or the received signal 112, 114 is referred to below as photocurrent, I FotoTo determine the coupling factor, the supply current, LED current, and the photocurrent, received signal 112, 114, must be determined. The following applies: where CF is the coupling factor. Or, in other words, the received signal equals the feed current times the coupling factor.

[0056] The supply currents, i.e., the LED currents, can be determined from the set DAC input signals 150, 152 and the DAC gains of the DAC amplifiers 84, 86. The DAC gain factor corresponds to the gain of the respective LED 21, 23. This applies both to the (high) current of the respective LED 21, 23, i.e., the supply signal 140, 142, as well as to the minimum current, i.e., the minimum supply signal 160, 162. The minimum current is a constant, as low as possible current and is the lowest possible output current of the LED driver circuit supplied to the inactive LED 21, 23. The photodiode current or photocurrent, i.e., the received signal 110, cannot be directly applied to the amplifier 44 with its gain or gain G 44 However, the difference between the two received signals 112, 114 or the respective photocurrents can be measured as peak-to-peak output voltage V PP This is determined by: Vpp=(IPhoto1−IPhoto2)⋅G44

[0057] The conversion of an analog voltage value at the output of the amplifier 44 (V 44 ) into a digital value (ADC value, ADC value = output value at the ADC converter 72) is defined by: ADCvalue=V44⋅GADC, with G ADC = Gain of the ADC converter 72.

[0058] Ideally, the demodulator (demodulator unit 76) samples the output signal at amplifier 44 in the two active phases of the respective LEDs 21, 23 at the maximum or minimum peak value and in the phase of the other LED 23, 21 at the opposite minimum or maximum voltage peak value and determines the difference. Consequently, the peak-to-peak value of the amplifier output signal of amplifier 44 is determined. This means that the analog peak-to-peak value V pp by the theoretical peak-to-peak value ADC ppcan be replaced. The output value at ADC converter 72 is thus: ADCpp=(IPhoto1−IPhoto2)⋅G44⋅GADC

[0059] The ADC value of the two "phases" for LEDs 21, 23 is measured by two fast ADC measurements and is visible in the output voltage or output value DEM of demodulator unit 76. The following applies: DEM=(ADC1−ADC2)

[0060] The ADC peak-to-peak value, ADC pp , can be expressed by: ADCpp=(ADC1−ADC2) which corresponds to the difference between the ADC values ​​of LEDs 21 and 23.

[0061] This ADC pp can be equated with the demodulator output value DEM, resulting in: DEM=ADCpp DEM=(IPhoto1−IPhoto2)⋅G44⋅GADC

[0062] The photocurrents or photodiode currents for the two LEDs 21, 23 can be replaced using the coupling factors CF1, CF2 and the known supply currents or supply signals 140, 142. It should be noted that in each LED phase, both the high current (supply current or supply signal 140, 142) of one LED driver or one LED 21, 23 and the low current (minimum supply current or minimum supply signal 160, 162) of the other LED driver or the other LED 21, 23 are active. The following applies: IPhoto1=ILED1⋅CF1+Imin2⋅CF2 IPhoto2=ILED2⋅CF2+Imin1⋅CF1

[0063] Consequently, the demodulator output value DEM at the output of the demodulator unit 76 is: DEM=(ILED1⋅CF1+Imin2⋅CF2−ILED2⋅CF2−Imin1⋅CF1)⋅G44⋅GADC DEM=((ILED1−Imin1)⋅CF1−(ILED2−Imin2)⋅CF2)⋅G44⋅GADC

[0064] To simplify the equations, the differences between the high current and the low current of an LED 21, 23 or the corresponding LED channel are defined: IΔLEDX=ILEDX−IminX

[0065] It follows: DEM=(IΔLED1⋅CF1−IΔLED2⋅CF2)⋅G44⋅GADC

[0066] All variables in this equation are known except for the coupling factors CF1 and CF2. To determine the two coupling factors, two different equations must be set up. For this, two different measurements must be performed, either in the a) Open loop mode with different DAC values ​​or preferably b) in a closed control loop with different values ​​of the offset generator 60, i.e. different offset signals 130.

[0067] It is only necessary to assume that the coupling factors CF1 and CF2 do not change during the two measurements. This allows two suitable equations to be formulated: For the first measurement DEM1=(IΔLED11⋅CF1−IΔLED21⋅CF2)⋅G44⋅GADC For the second measurement DEM2=(IΔLED12⋅CF1−IΔLED22⋅CF2)⋅G44⋅GADC

[0068] The two equations can be set up as a system of equations and solved for the two coupling factors CF1 and CF2. This gives: CF1=DEM1⋅IΔLED22−DEM2⋅IΔLED21(IΔLED11⋅IΔLED22−IΔLED12⋅IΔLED21)⋅G44⋅GADC CF2=DEM1⋅IΔLED12−DEM2⋅IΔLED11(IΔLED11⋅IΔLED22−IΔLED12⋅IΔLED21)⋅G44⋅GADC

[0069] The denominators of the two coupling factors are identical. Therefore, the denominator only needs to be calculated once. For simplicity, the variable D is introduced here: D=(IΔLED11⋅IΔLED22−IΔLED12⋅IΔLED21)⋅G44⋅GADC

[0070] This results in the coupling factors: CF1=1D⋅(DEM1⋅ILED22−DEM2⋅IΔLED21) CF2=1D⋅(DEM1⋅ILED12−DEM2⋅IΔLED11)

[0071] In order to obtain the two measurements required to solve the equations in the closed loop, only two different offset signals 130 of the offset generator 60 have to be set.

[0072] According to the invention, the offset value or offset signal 130 is used to generate different supply currents or supply signals 140, 142. The offset value thus generates an offset in the digital Halios control loop and thus also changes the supply currents and the demodulator output value (DEM value). It is therefore also possible to generate two equations with different LED currents and different demodulator output values ​​in closed-loop mode.

[0073] In a preferred embodiment, this calculation of the coupling factors 16, 18 is performed in an algorithm unit 64. The algorithm unit 64 receives all necessary signals, values, and corresponding currents. The coupling factors 16, 18 can be output to further units or processing units 40 via the output interface 46. It is also conceivable that the algorithm unit 64 is not integrated into the processing unit 40, but rather into other components. The corresponding signals must then be made available to the algorithm unit 64.

[0074] Fig. 4 shows a vehicle 92 with a sensor system 10 according to the invention as described above, wherein the sensor system 10 can also be designed as a rain sensor 94.

[0075] The invention has been comprehensively described and explained with reference to the drawings and the description. The description and explanation are to be understood as exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other embodiments or variations will become apparent to those skilled in the art upon use of the present invention and upon careful analysis of the drawings, the disclosure, and the following claims.

[0076] In the claims, the words "comprising" and "having" do not exclude the presence of further elements or steps. The undefined article "a" or "an" does not exclude the presence of a plurality. A single element or unit can perform the functions of several of the units recited in the claims. An element, unit, and system can be partially or completely implemented in hardware and / or software. The mere mention of some measures in several different dependent claims should not be understood to mean that a combination of these measures cannot also be advantageously used. A computer program can be stored / distributed on a non-volatile data carrier, for example, on an optical memory or on a solid-state drive (SSD).A computer program may be distributed together with hardware and / or as part of hardware, for example, via the Internet or via wired or wireless communication systems. Reference signs in the patent claims are not to be construed as limiting. Reference symbol 10 Sensor system 12, 14 transmission path 16, 18 coupling factor 20 channels 21 LED 22 channels 23 LED 30 recipients 32 photodiode 40 processing units 42 Input interface 44 amplifiers 46 Output interface 50 control unit 52, 54 amplifiers 60 Offset Generator 62 superposition element 64 Algorithm Unit 70 input circuit 72 ADC converters 74 Multiplexer unit 76 Demodulator unit 78 DAC gain stage 80, 82 DAC converters 84, 86 DAC amplifiers 88, 90 Food source 92 vehicles 94 Rain sensor 96, 98 adders 100, 102 transmission signal 110, 112, 114 reception signal 116 differential signal 120 control signal 130 Offset signal 140, 142 supply signal 150, 152 DAC input signal 154, 156 DAC output signal 160, 162 Minimum feed signal

Claims

[1] Processing unit (40) for a feedback-based sensor system (10) with a first and second transmitter (20, 22) and a receiver (30) for determining the transmission properties of a transmission path (12, 14) between the transmitters (20, 22) and the receiver (30) in the form of coupling factors (16, 18), comprising an input interface (42) for receiving a received signal (110, 112, 114) of the receiver (30), which comprises transmitted signals (100, 102) generated by the transmitters (20, 22) after passing through the transmission path (12, 14); a feedback loop with a control unit (50) for generating feed signals (140, 142) for the transmitters (20, 22) based on the received signal (110, 112, 114) such that a received signal (110, 112, 114) is present at the input interface (42) which is regulated and has an AC amplitude of zero; an offset generator (60) for generating an offset signal (130) to generate adjusted feed signals (140, 142) and thereby perform a control in order to adjust to a predetermined AC amplitude value of the received signal (110, 112, 114) not equal to zero; an algorithm unit (64) with an algorithm for determining the coupling factors (16, 18) of the transmission path (12, 14) from the received signals (110, 112, 114), the feed signals and the adapted feed signals (140, 142); and an output interface (46) for outputting the feed signals (140, 142) for the transmitters (20, 22) in order to generate transmission signals (100, 102) in the transmitters (20, 22) based on the feed signals (140, 142), and for outputting the determined coupling factors (16, 18). [2] Processing unit (40) according to claim 1, characterized bya feed source (88, 90) for generating a minimum feed signal (160, 162) for the transmitters (20, 22), wherein the processing unit (40) is designed to feed one transmitter (20, 22) with a feed signal (140, 142) and the other transmitter (20, 22) with the minimum feed signal (160, 162), which is preferably different from zero. [3] Sensor system (10) for determining the transmission properties of a transmission path (12, 14) between transmitter (20, 22) and receiver (30) in the form of coupling factors (16, 18), with a first and second transmitter (20, 22), a receiver (30), a feedback-based processing unit (40), preferably a processing unit (40) according to claim 1; where both transmitters (20, 22) are designed to each transmit a transmission signal (100, 102) based on a feed signal (140, 142) into the transmission path (12, 14), the receiver (30) is designed to receive the transmission signals (100, 102) and to output a reception signal (110, 112, 114); the two transmission signals (100, 102) are controlled by the processing unit (40) such that the reception signals (110, 112, 114) based on the transmission signals (100, 102) are equal; and the processing unit (40) comprises an offset generator (60) for generating an offset signal (130); and the processing unit (40) is designed to to generate feed signals (140, 142) for the transmitters (20, 22); to feed the transmitters (20, 22) with the feed signals (140, 142); to determine a difference signal (116) from the received signals (110, 112, 114); based on the difference signal (116), to generate a control signal (120) by means of a control unit (50), on which the feed signals (140, 142) supplied to the transmitters (20, 22) are based, and which is designed such that the difference signal (116) is controlled to a predetermined amplitude value equal to zero; in a further measurement of the received signals (110, 112, 114), to superimpose an offset signal (130) of the offset generator (60) on the difference signal (116); and to determine the coupling factors (16, 18) of the transmission path (12, 14) from the detected signals. [4] Sensor system (10) according to claim 3, wherein the transmitters (20, 22) are alternately fed with the feed signal (140, 142) and preferably the respective other transmitter (20, 22) is fed with a minimum feed signal (160, 162), which particularly preferably amounts to at most 10% of the feed signal (140, 142), further preferably at most 5%, 4%, 2%, 1% or 0.5%. [5] Sensor system (10) according to one of the preceding claims 3 to 4, wherein the supply signal (140, 142) is a supply current which is preferably at most 10 mA, more preferably at most 6 mA, particularly preferably at most 4 mA. [6] Sensor system (10) according to claim 4, wherein the minimum supply signal (160, 162) is a minimum supply current which is not greater than 10% of the maximum supply current and is at most 0.8 mA, preferably at most 0.4 mA, particularly preferably at most 0.2 mA. [7] Sensor system (10) according to one of the preceding claims, wherein the coupling factors (16, 18) are determined by means of an algorithm implemented in the processing unit (40). [8] Sensor system (10) according to one of the preceding claims, characterized by that the receiver (30) and the transmitters (20, 22) are optical components, preferably photodiodes (32). [9] Sensor system (10) according to one of the preceding claims, characterized bythat the processing unit (40) comprises: an input circuit (70) having an amplifier (44) and an ADC converter (72) for digitization, a multiplexer for processing the received signals (110, 112, 114); a demodulator designed as a comparator; and an output circuit with a DAC converter (80, 82) for generating analog feed signals (140, 142) for the transmitters (20, 22). [10] Sensor system (10) according to the preceding claim, characterized by in that the output circuit has a minimum signal source for generating the minimum feed signal (160, 162) and comprises a multiplexer for feeding one transmitter (20, 22) with a feed signal (140, 142) and the other transmitter (20, 22) with the minimum feed signal (160, 162), wherein the minimum signal source is preferably a minimum current source and the minimum feed signal (160, 162) is preferably a minimum feed current. [11] Sensor system (10) according to one of the preceding claims, characterized by that the coupling factors (16, 18) are based on the feed signals (140, 142) of two measurements, a first measurement being carried out without an offset signal (130) and the second measurement being carried out with an offset signal (130). [12] Sensor system (10) according to one of the preceding claims, characterized by that the offset generator (60) is arranged in front of the control unit (50) in the processing direction. [13] Sensor system (10) according to one of the preceding claims, characterized by that the control unit (50) is a PI controller. [14] Rain sensor (94) with a sensor system (10) according to one of the preceding claims 3 to 13, characterized by that the transmitters (20, 22) are light sources, preferably LEDs (21, 23), and the receiver (30) is a photodiode (32). [15] Vehicle (92) with a sensor system (10) according to one of claims 3 to 13 or with a rain sensor (94) according to the preceding claim. [16] Method for determining the transmission properties of a transmission path (12, 14) in the form of coupling factors (16, 18) of a sensor system (10) based on feedback compensation between a first and second transmitter (20, 22) and a receiver (30), wherein both transmitters (20, 22) each transmit a transmission signal (100, 102) based on a feed signal (140, 142) into the transmission path (12, 14), which is received by the receiver (30); the two transmission signals (100, 102) are controlled by a processing unit (40) such that the reception signals (110, 112, 114) based on the transmission signals (100, 102) are equal; and the processing unit (40) comprises an offset generator (60) for generating an offset signal (130); comprising the following steps: Carry out a first measurement with the following steps: - generating feed signals (140, 142) for the transmitters (20, 22); - alternately feeding the transmitters (20, 22) with the feed signals (140, 142); - transmitting transmission signals (100, 102) based on the feed signals (140, 142) into the transmission path (12, 14); - receiving the transmission signals (100, 102) by means of a receiver (30) and generating reception signals (110, 112, 114); - determining a difference signal (116) from the received signals (110, 112, 114); - regulating the received signals (110, 112, 114) and generating a control signal (120) based on the regulated received signals (110, 112, 114) such that the difference signal (116) has an amplitude equal to zero; - generating the feed signals (140, 142) based on the control signal (120); Perform a second measurement using the steps above and the additional steps: - generating an offset signal (130); - superimposing the difference signal (116) with the offset signal (130); - controlling the difference signal (116) and generating the control signal (120) such that the difference signal (116) has an amplitude other than zero; Determining the coupling factors (16, 18) from the feed signals (140, 142) of the transmitters (20, 22) and the difference signal (116) of the two measurements. [17] Method according to the preceding claim, characterized by the next steps: - generating a minimum feed signal (160, 162), preferably by means of a minimum feed source; - feeding one transmitter (20, 22) with the feed signal (140, 142) and feeding the other transmitter (20, 22) with the minimum feed signal (160, 162). [18] A computer program product comprising program code which, when executed by a computer, causes the computer to carry out the steps of the method according to claim 16 or 17.

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