Abstract:
In one embodiment a circuit arrangement for disturber detection comprises an input for receiving an input signal, the input being adapted to be coupled to an antenna, a receiver circuit coupled to the input which is configured to provide a demodulated signal as a function of the input signal, and a disturber rejection circuit which is coupled to an output of the receiver circuit. Therein the disturber rejection circuit is configured to provide a first signal indicative of a low energy disturber and/or a second signal indicative of a square envelope disturber, the first and second signals being provided as a function of the demodulated signal at respective outputs of the disturber rejection circuit. Furthermore, a lightning detector and a method for disturber detection are described.

Description:
[0001]    The present invention refers to the field of lightning detectors and especially to a circuit arrangement and a method for disturber detection. 
       BACKGROUND 
       [0002]    A lightning detector is a system which can detect the presence of incoming thunder storms with lightning activities. Lightning is the result of flowing current due to the electrostatic charge separation in clouds. Typically this current is massive and can flow from the cloud to the ground or inside the cloud. The current flow generates an electromagnetic field. 
         [0003]    From an electromagnetic point of view, lightning flashes produce very wide band signals. To monitor such a wide band frequency range with portable devices is very challenging. Lightning is a complex phenomenon made up of several different events: breakdown, return stroke, in-cloud activities and subsequent stroke. Scientific literature establishes that by analyzing the phenomenon using a narrow band system many details could be lost and it would no longer be possible to distinguish between the basic elementary processes which constitute lightning. Nevertheless, this approach is suitable for detecting lightning itself. 
         [0004]    The subject application focuses on a narrow band radio frequency receiver which is to be used in a lightning detector. The receiver scans around a few hundred kilohertz up to a couple of megahertz as the central frequency. The challenge that comes with this lightning detection involves so-called manmade disturbers. Manmade disturbers can be classified in three different categories, namely low-energy signals, square envelope signals and continuous jamming noise. 
         [0005]    There are known lightning detectors which evaluate the pattern of the incoming signal and subsequently perform an assessment. For this the received signal is digitized using, for instance, an analog-to-digital converter. An external unit then generates a histogram out of the sampled signal. These known systems are usually implemented in a digital signal processor, DSP, with high computing power. Power consumption of such DSP is in the range of 10 to 100 milliampere. Besides this, the solution is quite expensive. 
         [0006]    One object consists of providing a circuit arrangement and method for disturber detection which enables reduced power consumption and an implementation at low cost. 
       SUMMARY 
       [0007]    In one embodiment a circuit arrangement for disturber detection comprises an input for receiving an input signal, a receiver circuit coupled to the input and a disturber rejection circuit which is coupled to an output of the receiver circuit. The input is adapted to be coupled to an antenna. The receiver circuit is configured to provide a demodulated signal as a function of the input signal. The disturber rejection circuit is configured to provide a first signal indicative of a low energy disturber and/or a second signal indicative of a square envelope disturber. The first and second signals are provided as a function of the demodulated signal at respective outputs of the disturber rejection circuit. Furthermore, the disturber rejection circuit is configured to further provide an interrupt signal indicative of a continuous jammer. The interrupt signal is provided as a function of the demodulated signal. 
         [0008]    The input receives the input signal via the antenna. The receiver circuit demodulates the input signal and provides the demodulated signal. The disturber rejection circuit analyzes the demodulated signal and provides the first signal which indicates the presence of a low energy disturber and/or the second signal which indicates the presence of a square envelope disturber. 
         [0009]    As the circuit arrangement analyzes the demodulated signal, which is an analog signal, conversion of the input signal into a digital signal is avoided. Thereby, a low power and low cost implementation is enabled. 
         [0010]    A low energy disturber signal is characterized by fast transitions of its envelope and a short decay time. Typically, these signals are caused by manmade sparks, e.g. in switches, engines or the like. A square envelope disturber is normally emitted by systems using pulse width modulation, for example, DC/DC converters. 
         [0011]    In an example application the antenna that is to be connected to the circuit arrangement comprises an LC resonator. It can be realized, for instance, as a loop antenna which is based on a parallel LC resonator. The input signal received via the antenna can also be called “radio signal”. 
         [0012]    Signals generated by a jammer are characterized by a longer duration with an increased noise level. The interrupt signal signifies the presence of a continuous jammer and enables an adaptation of threshold values used in the disturber detection circuit arrangement with respect to the noise level. 
         [0013]    In another embodiment the circuit arrangement further comprises a monitor circuit coupled to the output of the receiver circuit. The monitor circuit is prepared to provide an enabling signal as a function of the demodulated signal and a first threshold signal. 
         [0014]    The monitor circuit observes the demodulated signal and provides the enabling signal as soon as the level of the demodulated signal exceeds the first threshold signal. 
         [0015]    The first threshold signal thereby comprises an adjustable signal representative of a noise level of the input signal. 
         [0016]    The monitor circuit can also be called a threshold watchdog. 
         [0017]    By means of the interrupt signal the first threshold signal can be adapted when the noise level of the received signal exceeds a preset maximum value of acceptable noise due to the presence of a continuous jammer. Thereby, the robustness with respect to manmade disturbers is improved and the presence of lightning can still be detected even if a continuous jammer is nearby. 
         [0018]    In another embodiment the circuit arrangement is adapted to be operated in either a listening mode or an active mode as a function of the enabling signal. 
         [0019]    In a further development in the listening mode, the disturber rejection circuit is switched off and in the active mode the disturber rejection circuit is switched on. 
         [0020]    Consequently, in the listening mode in which the level of the demodulated signal is below the first threshold signal and the enabling signal remains at low, just the receiver circuit is active and consumes power. Only if the level of the demodulated signal exceeds the first threshold signal does the circuit arrangement enter the active mode in which the disturber rejection circuit is switched on and subsequently checks the shape of the demodulated signal in order to classify it as a disturber or as a lightning. 
         [0021]    As the disturber rejection circuit does not consume any power during the listening mode, the power consumption of the circuit arrangement is greatly reduced. 
         [0022]    In one development the first signal is provided as a function of the demodulated signal and a noise signal. 
         [0023]    A duration of the demodulated signal which is put in relation to the noise signal is used to differentiate between lightning and a potential manmade disturber. The duration of lightning is in the range of 10 milliseconds which is considerably longer than the duration of an impulse caused by a manmade spark, which is in the range of 100 nanoseconds to 50 microseconds. 
         [0024]    The noise signal can, for instance, be provided by low pass filtering of the demodulated signal. 
         [0025]    In a further development the second signal is provided as a function of the demodulated signal and a peak hold signal. 
         [0026]    Holding a peak of the demodulated signal and comparing it with the demodulated signal at a slightly later point in time determines the decay time of the demodulated signal. A short decay time indicates that the impulse in the input signal which exceeded the first threshold signal is caused, for instance, by a DC/DC converter and not by lightning. 
         [0027]    In another embodiment the receiver circuit comprises an amplifier which is coupled to the input and is configured to provide an amplified signal as a function of the input signal and a demodulator. The demodulator is coupled to the output of the amplifier and is configured to provide the demodulated signal as a function of the amplified signal at the output of the receiver circuit. 
         [0028]    In the receiver circuit the input signal is amplified, e.g. by means of a low noise amplifier, and demodulated. 
         [0029]    The demodulator can, for instance, be implemented using an envelope detector which extracts the envelope of the amplified radio signal. 
         [0030]    The receiver circuit can also be denoted as the analog frontend. The bandwidth of the receiver circuit is meant to be greater than the antenna bandwidth so that the gain throughout the antenna bandwidth is constant. 
         [0031]    In a further embodiment the monitor circuit comprises a first comparator having an input for receiving the demodulated signal, another input for receiving the first threshold signal and an output for providing the enabling signal as a function of a difference between the modulated signal and the first threshold signal. 
         [0032]    In another embodiment the circuit arrangement further comprises a filtering circuit coupled to the output of the receiver circuit. The filtering circuit is configured to provide the noise signal representative of the noise of the input signal as a function of the demodulated signal. 
         [0033]    The filtering circuit is realized, for instance, by using a low pass filter. It generates the noise signal from the demodulated signal. The noise signal is also designated as the AC ground noise. A time constant which is realized by the filtering circuit is much greater than a time constant of a filter which is implemented inside the demodulator. This enables detection of the level of noise of the demodulated signal. 
         [0034]    In another embodiment the disturber rejection circuit comprises a first identification circuit configured to provide the first signal, a second identification circuit configured to provide the second signal and an interrupt generation circuit. The interrupt generation circuit is configured to provide the interrupt signal as a function of the noise signal and a fourth threshold signal. 
         [0035]    The fourth threshold signal comprises, for example, a reference voltage representing a noise threshold. Whenever the noise signal crosses this noise threshold, the interrupt signal is provided signifying that high input noise is received in the input signal via the antenna. The interrupt signal indicates the presence of a continuous jammer in the vicinity of the circuit arrangement. This jammer is also classified as disturber in the disturber rejection circuit. 
         [0036]    In a further development the first identification circuit comprises a second comparator which is configured to provide a duration signal as a function of the difference between the demodulated signal and the noise signal, the difference being relative to a second and a third threshold signal. Furthermore, the first identification circuit comprises a first counter coupled to an output of the second comparator. The first counter is configured to provide the first signal as a function of a length of an input of the duration signal. 
         [0037]    As soon as the difference between the demodulated signal and the noise signal exceeds the second threshold signal the duration signal at the output of the second comparator changes to a high state. Whenever the difference subsequently reduces to below the third threshold signal, the duration signal changes to a low state. The first counter determines the length in time of this impulse of the duration signal. If the length of this impulse exceeds a preset value characteristic of the duration of a manmade spark, the first signal goes to high indicating lightning. Otherwise the first signal remains low signifying a disturber. 
         [0038]    In another embodiment the second identification circuit comprises a peak holder circuit, a third comparator coupled to an output of the peak holder circuit, a latch coupled to an output of the third comparator and a second timer coupled to an output of the latch. The peak holder circuit is configured to provide the peak hold signal as a function of an impulse of the demodulated signal. The third comparator is configured to provide a comparison signal as a function of a difference between the peak hold signal and the demodulated signal. The latch is configured to provide an envelope signal as a function of the comparison signal and the duration signal. The second counter is configured to provide the second signal as a function of a length of an impulse of the envelope signal. 
         [0039]    An impulse of the demodulated signal is identified and stored for a certain amount of time in the peak holder circuit and reflected in the peak hold signal. Whenever the difference between the peak hold signal and the demodulation signal exceeds a preset value, the comparison signal at the output of the third comparator is set to high. This high state sets the latch so that the envelope signal at the output of the latch also goes to high. The latch is reset by a falling edge of the duration signal resulting in a falling edge of the envelope signal. The second counter determines the length of an impulse of the envelope signal. The second signal is set to high if this length surpasses a preset value characteristic of a square envelope disturber. This high indicates lightning. Otherwise, in the presence of a disturber with short impulse duration, the second signal remains low. 
         [0040]    The duration in time of an impulse of an envelope signal is proportional to the decay time of the input signal. The decay time of a disturber is much shorter than the decay time of lightning. Consequently, a square envelope disturber can be identified by means of the second signal. 
         [0041]    In one embodiment a lightning detection circuit comprises a circuit arrangement for disturber detection as described above and a logic unit coupled to the outputs of the circuit arrangement for disturber detection. The logic unit has an output for providing a detection signal indicative of a lightning event as a function of the first and second signals provided at the outputs of the circuit arrangement for disturber detection. 
         [0042]    The logic unit evaluates the first and second signals. In case first and second signals are high, the detection signal is also set to high, signifying the detection of lightning in the input signal. If the first and/or the second signal at the outputs of the circuit arrangement for disturber detection remain low, a disturber is detected. The detection signal also remains low. The impulse in the input signal caused by the disturber is filtered out. If the first and the second signal are high, the detection signal goes to high indicating the presence of lightning. A subsequent circuit may use the detection signal to estimate the distance to the leading edge of a thunder storm, for example. 
         [0043]    The above-mentioned first, second, third and fourth comparators may each be realized as a so-called window comparator or as a comparator with hysteresis. 
         [0044]    The mentioned first and second counters can also be implemented by means of a respective timer. 
         [0045]    In one embodiment a method for disturber detection comprises the following steps:
       receiving an input signal,   demodulating the input signal and providing a demodulated signal,   providing a first signal indicative of a low energy disturber,   providing a second signal indicative of a square envelope,   providing an interrupt signal indicative of a continuous jammer, the interrupt signal being provided as a function of the demodulated signal,   wherein the first and second signals are each provided as a function of the demodulated signal.       
 
         [0052]    The described method for disturber detection is, for example, implemented within the circuit arrangement for disturber detection according to the invented principle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0053]    The text below explains aspects of the invention in detail using exemplary embodiments with reference to the drawings. Components and circuit elements that are functionally identical or have the identical effect bear identical reference numbers. In so far as circuit parts or components correspond to one another in function, a description of them will not be repeated in each of the following figures, wherein: 
           [0054]      FIG. 1  shows an exemplary embodiment of a lightning detection circuit with an exemplary embodiment of a circuit arrangement for disturber detection; 
           [0055]      FIG. 2  shows exemplary signal diagrams for the first identification circuit of  FIG. 1 ; 
           [0056]      FIG. 3  shows exemplary signal diagrams for the second identification circuit of  FIG. 1 ; 
           [0057]      FIG. 4  shows exemplary signal diagrams for the interrupt generation circuit of  FIG. 1 ; and 
           [0058]      FIG. 5  shows an exemplary state transition diagram for  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0059]      FIG. 1  shows an exemplary embodiment of a lightning detector with an exemplary embodiment of a circuit arrangement for disturber detection. The circuit arrangement for disturber detection comprises an input I for receiving an input signal In and three outputs O 1 , O 2 , O 3 . It further comprises a receiver circuit with an amplifier LNA and a demodulator DEM, and a monitor circuit coupled to an output of the receiving circuit. The monitor circuit comprises a first comparator CMP 1 . The circuit arrangement for disturber detection further comprises a filtering circuit LP coupled to the output of the receiver circuit as well as a disturber rejection circuit DRC. The input I is prepared to be coupled to an antenna A. The receiver circuit is coupled to the input I. 
         [0060]    In the receiver circuit the input signal In is amplified by the amplifier to a radio signal Rf and demodulated by the demodulator to the demodulated signal Env. The first comparator CMP 1  receives the demodulated signal Env and a first threshold signal Th 1 . It provides an enabling signal En as a function of the difference between the demodulated signal Env and the first threshold signal Th 1 . The filtering circuit LP receives the demodulated signal Env and provides therefrom a noise signal Acg by means of low pass filtering of the demodulated signal Env. 
         [0061]    The disturber rejection circuit DRC comprises a first identification circuit providing a first signal S 1  with a second comparator CMP 2  and a first counter CT 1 . The first signal S 1  is provided at an output O 1 . The disturber rejection circuit DRC further comprises a second identification circuit with a peak holder circuit PKH, a third comparator CMP 3 , a latch LT and a second counter CT 2 . The second identification circuit provides the second signal S 2  at an output O 2 . Finally, the disturber rejection circuit DRC comprises an interrupt generation circuit with a fourth comparator CMP 4  for providing an interrupt signal Int at an output O 3  of the circuit arrangement for disturber detection. 
         [0062]    In the first identification circuit the second comparator CMP 2  receives the demodulated signal Env and the noise signal Acg. The second comparator CMP 2  provides a duration signal Oute depending on a difference between the demodulated signal Env and the noise signal Acg in relation to a second and a third threshold signal Th 2 , Th 3 . The first counter CT 1  receives the duration signal Oute and provides first signal S 1  as a function of the duration of an impulse of the duration signal Oute. 
         [0063]    The peak holder circuit PKH of the second identification circuit receives the demodulated signal Env and holds an impulse or a peak occurring within the demodulated signal Env for the duration of an impulse of the duration signal Oute. A peak hold signal Ph is provided accordingly. The third comparator CMP 3  compares the peak hold signal Ph to the demodulated signal Env and provides a rising edge of a comparison signal Cs at its output as soon as the difference between peak hold signal Ph and demodulated signal Env exceeds a certain preset threshold. The preset threshold can be, for instance, 40%. By means of the rising edge of the comparison signal Cs, the latch LT is set. The latch may be implemented, for example, by means of an RS flipflop. When setting the latch LT, an envelope signal Sig_id at its output reflects a rising edge. The latch LT is reset by a falling edge of the duration signal Oute. The second counter CT 2  determines a duration of an impulse of the envelope signal Sig_id and provides the second signal S 2  accordingly. 
         [0064]    The interrupt generation circuit receives the noise signal Acg and a fourth threshold signal indicative of a noise floor threshold and provides the interrupt signal Int when the noise signal Acg exceeds the fourth threshold signal Th 4 . 
         [0065]    The lightning detection circuit additionally comprises a logic unit LOC which is coupled to the first and second outputs O 1 , O 2  of the circuit arrangement for disturber detection. The logic unit LOC provides a detection signal Det at an output O of the lightning detector as a function of the first and second signals S 1 , S 2 . 
         [0066]    The dynamic behaviour of the circuit arrangement for disturber detection will be explained below with the help of signal diagrams of  FIGS. 2 to 4 . 
         [0067]      FIG. 2  shows exemplary signal diagrams for the first identification circuit of  FIG. 1 . All the signals depicted are related to time. The upper diagram of  FIG. 2  shows the input signal In, the second and third threshold signals Th 2 , Th 3  and the difference between the demodulated signal Env and the noise signal Acg. The lower diagram of  FIG. 2  shows the duration signal Oute. Whenever the difference between the demodulated signal Env and the noise signal Acg surpasses the second threshold signal Th 2 , the duration signal Oute goes to logic high. As soon as the difference between the demodulated signal Env and the noise signal Acg decreases below the third threshold signal Th 3 , the duration signal Oute goes back to logic low. In an exemplary implementation the second threshold signal Th 2  is set to approximately 60 milli volts above the noise signal Acg and the third threshold signal is set to approximately 120 milli volts above the noise signal Acg. 
         [0068]    The first counter CT 1  in  FIG. 1  determines a duration of an impulse of the duration signal Oute. An impulse duration between 100 nanoseconds and 50 microseconds signifies the presence of a disturber, whereas an impulse duration of around 10 milliseconds signals the presence of lightning. 
         [0069]      FIG. 3  shows exemplary signal diagrams for the second identification circuit of  FIG. 1 . The upper diagram shows the peak hold signal Ph, the demodulated signal Env and the input signal In. The diagram in the middle of  FIG. 3  shows the duration signal Oute. The diagram in the bottom of 
         [0070]      FIG. 3  shows the envelope signal Sig_id. 
         [0071]    The peak hold signal Ph samples an impulse of the demodulated signal Env and stores it for a certain amount of time. The difference between the peak hold signal Ph and the demodulated signal Env represents the drop ratio of the input signal In, also denoted as the decay time. The third comparator CMP 3  of  FIG. 1  supervises the decay time of the input signal In and provides an impulse at its output if the difference between the peak hold signal Ph and the demodulated signal Env surpasses a preprogrammed value, e.g. 40%. In this event, the envelope signal Sig_id goes to logic high. Together with a falling edge of the duration signal Oute, the envelope signal Sig_id also goes to logic low. 
         [0072]    The duration in time between the rising edge of the envelope signal Sig_id and its subsequent falling edge is determined in the second counter CT 2  of  FIG. 1  and is reflected in the second signal S 2 . A short impulse of the envelope signal Sig_id is an indication for a square envelope of the input signal In. This is depicted, for example, in the second impulse of the envelope signal Sig_id at the bottom of  FIG. 2 . As can be discerned from the upper diagram, the second series of impulses in the input signal In has a square envelope resulting typically from a PWM system like a DC/DC converter. The first series of impulses in the input signal In has a triangular shaped envelope which is reflected in an impulse having a much longer duration in the envelope signal Sig_id depicted in the left impulse of the bottom diagram. 
         [0073]    Consequently, a non-square envelope resulting from lightning can be differentiated from a square envelope resulting from a disturber. 
         [0074]      FIG. 4  shows exemplary diagrams for the interrupt generation circuit of  FIG. 1 . The upper diagram shows the demodulated signal Env, the noise signal Acg, the input signal In and the fourth threshold signal Th 4 . The lower diagram shows the interrupt signal Int. It can be seen that due to a jammer which produces a continuously high noise signal reflected in the input signal In, the noise signal Acg at the output of the filtering circuit LP of  FIG. 1  exceeds the fourth threshold signal Th 4 . This results in a rising edge of the interrupt signal Int. When the noise signal Acg decreases below the level of the fourth threshold signal Th 4 , the interrupt signal Int goes back to low. 
         [0075]    As a result, the absolute value of the noise floor in the input signal In is monitored continuously and a superordinate system is warned by an impulse of the interrupt signal Int that a continuous noise has jammed the analog frontend of the disturber detection circuit of  FIG. 1 . The level of the first threshold signal Th 1  can subsequently be adapted to keep the disturber detection circuit arrangement in the listening mode as long as possible which consumes only little power as the disturber rejection circuit is switched off. 
         [0076]    Advantageously, by using the circuit arrangement for disturber detection false triggers caused by manmade disturbers can be detected and subsequently rejected so that the lightning detector is only activated in the case of real lightning. 
         [0077]      FIG. 5  shows an exemplary state transition diagram for the circuits of  FIG. 1 . Four states  10 ,  11 ,  12  and  13  are depicted. State  10  represents the listening mode in which the demodulated signal Env from  FIG. 1  is continuously monitored by comparison with the first threshold signal Th 1  in the monitoring circuit of  FIG. 1 . As soon as the demodulated signal Env exceeds the first threshold signal Th 1 , the enabling signal En is generated and the active mode is entered. States  11 ,  12  and  13  each belong to the active mode. In state  11  the disturber rejection circuit DRC of  FIG. 1  is activated. Evaluation of the shape of the demodulated signal Env is conducted in the first and second identification circuit, as well as in the interrupt generation circuit of  FIG. 1 . If the first signal S 1  remains at low because of a too short impulse of the duration signal Oute and/or if the second signal remains at low because of a too short impulse of the envelope signal Sig_id signifying a square envelope and/or if the interrupt signal Int is at high, state  13  is entered. A disturber is consequently detected. Subsequently state  10  is assumed and the circuit goes back to the listening mode. 
         [0078]    If, on the other hand, in state  11  the first signal S 1  and the second signal S 2  are at logic high concurrently with a logic low in the interrupt signal Int, lightning is detected and state  12  is assumed. The detection signal Det of  FIG. 1  is set to logic high to inform a superordinate circuit. Subsequently, state  10  is assumed again with power-saving in the listening mode. 
         [0079]    The logic circuit LOC can be realized by using, for example, an AND or an OR gate. 
         [0080]    As the circuit arrangement according to an aspect of the invention is based on an analog frontend and subsequent analog and digital circuit components, only analog signals have to be analyzed within the circuit components. This enables a low cost implementation as an expensive DSP for digital evaluation in the high frequency range can be avoided. The generated digital signals, for example, the duration signal Oute and the envelope signal Sig_id, have a considerably lower frequency than the input signal In. This further reduces the power consumption. 
         [0081]    Despite using a narrow band frontend, disturbers can be securely detected and subsequently rejected. By continuously monitoring the demodulated signal and only activating the disturber rejection circuit if this demodulated signal surpasses a certain threshold, energy is saved.