Abstract:
A method for measuring transmission characteristics of a transmission path between a transmitter and a receiver. A first transmitter sends a first signal into a first transmission path. The first signal is detected by the receiver. A second transmitter sends a second signal into a second transmission path having known characteristics or characteristics that can be predetermined. The second signal is superimposed with the first signal. A transmission signal is intermittently distributed between the first and second transmitters in a controlled manner. The signal received by the receiver comprises first and second signal components to be assigned to the first and second transmitters, respectively. The first signal component averaged over a predefined time period essentially is exactly as large as the averaged second signal component and the deviation between the averaged signal components is at least intermittently used as control signal for the switching between the first and second transmitters.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT/EP2012/072092, filed Nov. 8, 2012, which claims priority to EP 11192161.5, filed Dec. 6, 2011, both of which are hereby incorporated herein by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    The present invention pertains to a method and a device, as well as a sensor, for measuring a signal transmission channel from a transmitter to a sensor via a transmission path. 
         [0003]    A transmission channel from a transmitter to a sensor needs to be determined in many fields of application. For example, it may be required to determine the distance of a reference object from other objects. In this case, for example, the amplitude attenuation of a light signal caused by the distance can be used in the form of 1/r 4  for distance measurements. 
         [0004]    In many known compensation methods, the actual transmission signal is superimposed with a compensation signal at the sensor in such a manner that the sensor in total receives a nearly constant signal. Examples include: 
         [0005]    DE10001955A1; 
         [0006]    DE10024156A1; 
         [0007]    DE19839730C1; 
         [0008]    DE9309837U1; 
         [0009]    DE10001943C1; 
         [0010]    DE10346741B3; 
         [0011]    DE102004025345B3; 
         [0012]    DE102005013352A1; 
         [0013]    DE102005010745B3; and 
         [0014]    DE102007005187B4. 
         [0015]    All these methods have the following common features:
       the compensation signal and/or the transmission signal is an amplitude-controlled analog signal;   the transmission signal has a constant duty factor and/or is essentially monofrequent.       
 
         [0018]    The analog compensation signal is the significant disadvantage of all these methods. It requires an adjustable amplifier or, in other words, an analog multiplier that usually cannot be manufactured in a temperature-stable manner without substantial effort. Such a system is difficult to produce. It particularly requires very complex analog in-production inspections. 
       SUMMARY 
       [0019]    This disclosure teaches a purely digital activation of the transmitter and/or the compensation transmitter and thus reduces the aforementioned problems. 
         [0020]    The inventive method for measuring the transmission characteristics of at least a first transmission path comprises at least a first transmitter that sends at least one signal into said first transmission path. The signal is detected in at least a first receiver after it passes through at least a section of said first transmission path. In said receiver, the signal is superimposed in an additive manner with at least a second signal of a second transmitter from at least one transmission path that with respect to its characteristics is essentially known or is predetermined or can be predetermined. The method is characterized in that a transmission signal is at least intermittently distributed between at least said first transmitter and said second transmitter in a controlled manner. This switching allows a distribution of the transmission signal between the first transmitter and the second transmitter that preferably consists of a compensation transmitter. The distribution of the transmission signal may be realized in a continuously variable manner between 0% and 100%. This means that any desired distributions are possible. The switching preferably is a (controlled) switching, during which the distribution is realized in such a manner that the transmission signal is adjusted to 100% for the first transmitter while it is adjusted to 0% for the second transmitter and vice versa. The transmission signal preferably is at least intermittently switched between the two transmitters in a time-dependent or in a phase-dependent controlled manner. The control is preferably realized in such a manner that, referred to the signal received by the receiver, the first signal component averaged over a predefined time period, which is to be assigned to the first transmitter, essentially is exactly as large as the second signal component averaged over the predefined time period, which is to be assigned to said second transmitter. 
         [0021]    According to the method, the deviation of the first signal component averaged over the predefined time period from the second signal component averaged over said predefined time period is—referred to the signal received by the receiver (referred to as receiver signal or receiver output signal)—at least intermittently used as control signal for the distribution, particularly for the controlled switching of the transmission signal between at least the first transmitter and the second transmitter. 
         [0022]    The transmission signals for the first transmitter and the second transmitter may consist of unmodulated or modulated signals. When using modulated signals such as, for example, frequency-modulated or amplitude-modulated signals, an optional filter or demodulator is provided in the circuit of the sensor and preferably demodulates the receiver output signal directly or after its amplification by means of an amplifier. However, the demodulation may optionally also be carried out later during the processing of the receiver signal. 
         [0023]    In the context of this disclosure, it was recognized that a change of the modulation and of the overall design of the system are required in order to realize a purely digital activation of the transmitter or transmitters. 
         [0024]    According to this disclosure, the method is utilized in a sensor or a device for measuring the transmission characteristics of a transmission path. According to this disclosure, the sensor comprises a control circuit. The control circuit includes a signal generator, a first and a second multiplier, an integrator and a comparator. This control circuit is preferably realized in the form of a digital logical unit or finite-state machine or in the form of a data processing system, wherein the data processing system comprises at least a memory and a central processing unit (central unit, CPU). With respect to the digitizing of the control circuit, the drivers for the first and the second transmitter are also designed in the form of digital-to-analog converters. It is preferred to utilize a single bit digital-to-analog converter (DAC). It is likewise preferred to alternatively utilize a multiple bit DAC. The receiver amplifier of the inventive sensor consists of an analog-to-digital converter (ADC, analog-digital converter) that converts the receiver signal of the receiver into a digital signal that is then additionally processed in the digital control circuit. 
         [0025]    Consequently, a conversion of the digital signals into analog signals does not take place until they are delivered to the transmitters. The analog receiver signal of the receiver that may be designed, for example, in the form of a photodiode if the transmitters consist of LEDs is digitized directly behind the receiver. The processing takes place digitally. 
         [0026]    The purely digital activation of the compensation transmitter has the advantage that it can on the one hand be tested much easier, e.g., with the aid of a “scan-path”- and on the other hand usually realized with a smaller chip surface than a comparable analog solution corresponding to the prior art. 
         [0027]    The first transmission path is the transmission path (link) to be monitored, e.g., the space in front of a vehicle. If the transmission characteristics of the transmission path including objects positioned in the transmission path between the transmitter and the receiver are known, the position of the detected objects is also known. In this manner, an object detection can be designed. At least the respective distance of the transmitter or the receiver from the object can be detected. If so required, several first transmitters need to be used in order to detect the position in space, the motion and/or the speed of the objects. Several receivers may alternatively also be used. 
         [0028]    The transmitter referred to as second transmitter is a comparison or compensation transmitter that serves for making the device and the method at least as much as possible independent of interfering influences. The second transmitter sends a signal directly to the receiver via a second transmission path that differs from the first transmission path. The characteristics of the second transmission path are known or can be predetermined. 
         [0029]    According to this disclosure, the first and the second transmitter are activated in a controlled manner by means of a control signal. In this case, a controlled switching of the transmission signal between the two transmitters is designed, preferably by means of a switch. 
         [0030]    According to this disclosure, the above-described sensor, which preferably is largely realized digitally, can be used in a device for measuring the transmission characteristics of a transmission path. The sensor has a sensor output, at which a switching signal used for switching over the transmission signal between the first and the second transmitter is delivered to a processing unit. A device of this type can be used, for example, in a motor vehicle in order to detect objects in the vicinity of the motor vehicle. The device may consist, for example, of a parking aid or a distance meter. 
         [0031]    Of course, these teachings are not limited to optical signals, in which case the transmitters are designed in the form of LEDs and the receiver is designed in the form of a photodiode. The transmitters may also consist of coils, capacitors, capacitive plates, antennas or other control means in order to emit the corresponding flows including fluidic material flows. In this case, the receiver is realized accordingly, for example, in the form of a photodiode, a coil, an antenna or the like. 
         [0032]    In addition to processing visible or invisible light signals such as, for example, infrared radiation, it is also possible to use acoustic signals, i.e., sound waves in the audible or inaudible range. The circuit of the sensor needs to be adapted accordingly in this case. For example, the transmitters are replaced with loudspeakers and the receiver is replaced with a microphone. It is possible to utilize a modulated carrier frequency, in particular, when using sound waves, as well as when using optical signals. With respect to the processing of modulated signals, an optional demodulator also needs to be arranged in the sensor in order to demodulate the signal prior to its further processing. 
         [0033]    The use of optical signals or ultrasonic signals is particularly advantageous if the sensor is utilized in a vehicle. The transmission characteristics of a transmission path are also measured in this case. In this manner, objects in the vicinity of the vehicle can be detected. The method can be utilized, for example, as a distance radar with a signal in the form of optical radiation (radar radiation) or as a parking aid when ultrasound (acoustic signal) or infrared radiation is used. A processing unit in the vehicle is preferably supplied with the switching signal of the sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: 
           [0035]      FIG. 1  shows a block diagram of a device for carrying out the method; 
           [0036]      FIG. 2  shows an exemplary timing of the signals in  FIG. 1 ; 
           [0037]      FIG. 3  shows a block diagram of a device (sensor) for carrying out the method with acoustic signals; 
           [0038]      FIG. 4  shows an exemplary timing of the signals in  FIG. 1  when using modulated carrier frequency signals in accordance with  FIG. 2 ; 
           [0039]      FIG. 5  shows a block diagram of an implementation in the form of a microprocessor system, and 
           [0040]      FIG. 6  shows a block diagram of a simultaneous amplitude control and PWM control. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    The following description merely refers to an exemplary embodiment. Prior to describing the embodiment in greater detail, it should therefore be noted that it is not limited to the respective circuit components or the respective procedural steps because these components and steps can vary. Essential parts of the method may alternatively be realized, in particular, in the form of software or a digital logical unit, as described below. The terms used in this description are merely intended for describing special embodiments and should not be interpreted in a restrictive sense. Whenever the singular or indefinite articles are used in the description and in the claims, this also refers to a plurality of these elements as long as the overall context does not clearly indicate otherwise. 
         [0042]    The disclosed embodiment is initially explained with reference to  FIGS. 1  (block diagram) and  2  (signal diagram). 
         [0043]    An inventive sensor  100  comprises a signal generator  1  that generates a signal  2 , typically a clock signal. Depending on the position of the switch  3 , this signal  2  is routed to a transmitter  4  in the form of a transmitter input signal  26  via a driver component realized in the form of an amplifier  24  or to a compensation transmitter  5  in the form of a compensator input signal  25  via a driver component realized in the form of the amplifier  23 . In this example, the respective transmitters consist of a transmission LED  4  and a compensation transmission LED  5 . Instead of such an optical system that is based on LEDs and photodiodes and described in greater detail below, it would also be conceivable, for example, to utilize other systems that
       are based on inductively transmitted signals and in which the transmitters and receivers consist of coils or   are based on capacitive signals and in which capacitor plates are used as transmitters and receivers or   are based on inductively transmitted signals with transmitters in the form of coils and receivers in the form of Hall plates or   are based on electromagnetic waves and in which antennas are used as transmitters and receivers; or   are based on sound waves with transmitters in the form of loudspeakers and receivers in the form of microphones; or   are based on modifiable material flows, for example, in tubes, flowing liquids or gases or other fluids, wherein the transmitters consist, for example, of reagent injectors and the receivers consist, for example, of sensors such as, in particular, colorimetric sensors or chromometers; or   are based on another modifiable or modulation-capable energy flux and/or impulse current with corresponding transmitters and receivers.       
 
         [0051]    All of these systems utilize the same basic principle described below. 
         [0052]    The transmitter  4  sends a signal  7  into a transmission path  6  and said signal is received by a receiver  8  after it passes through the transmission path  6 . In this case, the signal  7  can be modified by the transmission path  6 . This can occur, for example, due to objects  9 , on which the signal  7  is reflected before it reaches the receiver  8 . 
         [0053]    A signal  27  of the receiver  8  is based on the received signal  7 . The signal  27  is amplified in an amplifier  10  and, if applicable, impedance-converted. The output signal  11  of the amplifier  10  is multiplied by the signal generator signal  2  of the signal generator  1  in a multiplier  12  in order to obtain a new signal  13 . 
         [0054]    Depending on the digital sign signal  14  that is generated in a sign generator  22  in dependence on a switching signal  28 , this signal  13  is respectively multiplied by −1 or +1 in order to obtain the signal  15 . This respectively results in an up-integration or down-integration of the signal  13  in the downstream integrator or decimation filter  16 . Its analog output signal  17  is converted into the digital sign signal  21  by a comparator  18 . This digital sign signal  21  is delayed by one clock cycle of the signal  2  by means of a delay circuit  29  in order to obtain the switching signal  28 . Based on the switching signal  28 , it is determined if the transmitter  4  is connected to the signal generator  1  and the signal  2 , i.e., if it transmits, or if the compensation transmitter  5  is connected to the signal generator  1  and the signal  2 . 
         [0055]    Consequently, the sign signal  21  is decisive for the position of the switch  3  during the next clock cycle of the signal  2 . This method essentially corresponds to a superimposed pulse-width modulation (PWM modulation) of the signal  2 , wherein the PWM modulation for generating the signal  26  for the first transmitter  4  takes place inverse to the PWM modulation for generating the signal  25  for the compensation transmitter  5 . 
         [0056]    The compensation transmitter  5  itself sends a signal  19  into another transmission path  20  that also ends at the receiver  8 . The signals  7 ,  19  of the first transmission path  6  and the second transmission path  20  are added up at the receiver. The signal  27  is formed of the two signals  7 ,  19  at the output of the receiver  8 . 
         [0057]    In contrast to the well-known evaluation of a so-called “optical bridge” in accordance with the Halios method that is described, for example, in DE 10 2007 005 187 and in which the composite signal  27  (alternating component) passed through the two transmission paths  6 ,  20  is adjusted to zero in the receiver, the time average of the two signal components  27   a ,  27   b  (via the transmission paths  6 ,  20 ) is adjusted to zero at the receiver  8  in this case. The signal component  27   a  is based on the signal  7  of the first transmitter  4  and the signal component  27   b  is based on the signal  19  of the second transmitter  5 . 
         [0058]    During slow interferences in comparison with the clock frequency of the signal generator  1 , e.g., during a change of extraneous light when LEDs are used—this does not represent a considerable disadvantage. The utilization of a Delta-Sigma method makes it possible to eliminate the controlled power sources required in conventional circuits, for example, for activating the transmission LEDs  4 ,  5  in case LEDs are used. The (digital) bit stream at the output  21  is essentially identical to the sign signal  14 . It merely leads by one clock cycle and is inverted. It represents the disbalance of the two signal transmission paths  6 ,  20 , i.e., the deviation between the signal components  27   a ,  27   b . Depending on the respective application, the resolution is ensured with a corresponding decimation filter  16 . 
         [0059]      FIG. 3  shows a special embodiment of the inventive sensor  100 . Acoustic signals  7 ,  19  are used in this sensor  100 . The transmitter  4  and the compensation transmitter  5  are therefore realized in the form of loudspeakers. The receiver  8  consists of a microphone. The signals  7 ,  19  consist of sound waves or ultrasonic waves that are processed by the sensor  100 . The transmitters  4 ,  5  and the receiver  8  need to be respectively adapted to the sound waves used. When using ultrasonic waves, it is possible, for example, to utilize dynamic and electrostatic loudspeakers or, in particular, piezoelectric loudspeakers or piezoelectric quartz or ceramic oscillators. 
         [0060]    When sound waves are used, the loudspeakers  4 ,  5  can also emit modulated carrier frequencies. A filter or a demodulator  30  needs to be provided downstream of the receiver  8  in order to further process these signals in the sensor  100 . The optional demodulator  30  is preferably arranged between the amplifier  10  and the multiplying element  12 . The use of demodulated signals is illustrated in  FIG. 4 . This figure shows that the signals  25 ,  26  and  27  are modulated signals. Due to the utilization of the filter  30 , the other signals in the processing remain unchanged in comparison with the signals illustrated in  FIG. 2 . 
         [0061]    As already mentioned, this method may also be realized in the form of software, for example, by utilizing a microcomputer platform, particularly a digital signal processor platform (DSP platform). This is explained briefly and sufficiently for a person skilled in the art below with reference to  FIG. 5 . 
         [0062]    The signal  27  of the receiver  8  is converted into a purely digital signal  31  that is fed to a digital processing unit  32  by means of an analog-to-digital converter (ADC)  30 . In this context, it is important that the ADC  30  may also consist of a single bit or a multiple bit ADC. Whenever the term digital processing unit  32  is used in this context, it refers to its functionality essentially being based on Boolean functions. Depending on the respective intended use, a person skilled in the art will typically realize this digital processing unit  32 , for example, in the form of a DSP platform, a microcomputer platform or digital logical unit, etc. It is usually sensible that this digital processing unit  32  has at least two digital or analog output signals  35 ,  36 , by means of which the driver components (amplifiers)  24 ,  23  of the transmitters  4 ,  5  are activated. It is self-evident that, depending on the viewpoint, the drivers  24 ,  23  may also be considered as part of the digital processing unit  32  if they also deliver digital output signals  26 ,  25 . With respect to their function, however, the drivers  24 ,  23  may also consist of digital-to-analog converters  24 ,  23  (D/A converters) that not only switch the signals  26 ,  25  on or off, but also output these signals such that their amplitude corresponds to the predefined and in this case digital signals  35 ,  36  ( FIG. 5 ). 
         [0063]    It is furthermore sensible that the digital processing unit  32  is capable of communicating with a master system and of exchanging the determined data in suitable form, particularly in digital or analog form, via an interface  33  that is realized in digital or analog manner or in accordance with a more complex standard or protocol depending on the respective intended use. The circuit illustrated in  FIG. 5  may represent, e.g., a proximity sensor of a motor vehicle whereas the master system forms a part of the motor vehicle electronics that respectively carries out the activation, evaluation and display of the signals and their further processing. 
         [0064]    In certain instances, a system of the type described with reference to  FIGS. 1 and 2  will require a higher resolution than that achieved with the above-described complementary PWM modulation of the signals  26  and  25 . It may therefore be sensible to utilize an expanded circuit according to  FIG. 6 , in which an analog/digital converter (ADC)  42  converts the integrator signal  17  into a digital value  43 . This digital value is once again delayed by one clock cycle in a delay unit  29  and after corresponding adaptation  39 ,  44 ,  45  respectively the digital value controls an adjustable amplifier  38 ,  41  in such a manner that the signal  2  is not only switched, but an amplitude control is also realized. Consequently, the signal  37  for the compensation transmitter  5 , as well as the signal  40  for the transmitter  4 , is controlled with respect to its amplitude. Although this means that the advantage of realizing the system in digital technology as far as possible is lost, the overall resolution is increased in comparison with the prior art. 
         [0065]    While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.