Abstract:
An approach is provided for digital triggering a recording of one or several signals sampled at individual sampling instants on a digital oscilloscope. The triggering is carried out when the interval between two recurrent triggering events is less or greater than a time threshold value.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention relate to digital triggering of signals. 
     2. Discussion of the Background 
     A digital oscilloscope can now present analog signals very accurately on a display device after sampling the analog signal over time and digitize the sampled values of the analog signal at the individual sampling times by means of analog-digital conversion. 
     The triggering of the digitized signals to be presented on the display device of the digital oscilloscope is now also realized in digital manner. In the document DE 39 36 932 A1, an analog signal converted into the digital data format is compared in a comparator with reference to overshooting or undershooting a threshold value stored in a register. The first overshooting or undershooting of the threshold value by one of the sampled values of the analog signal to be presented is identified by the triggering system as a triggering time and leads to a triggering impulse, which is used in the display device for recording the signals to be presented synchronously with the triggering impulse. 
     The digital triggering of DE 39 36 932 A1 implements only a static triggering on the basis of a single signal-level comparison with one threshold value. The fact that a dynamic triggering on the basis of a time-dependent signal feature—for example, a triggering on the basis of a signal slope of the signal, a duration of a signal impulse or a time delay of a signal impulse by comparison with a reference impulse—is not yet possible using a digital triggering system of this kind is disadvantageous. 
     SUMMARY OF THE INVENTION 
     In accordance with various embodiments of the invention, a system and method are provided for digital triggering of signals, in which time-dependent signal features of the signal to be presented on the digital oscilloscope can be used as a triggering condition for a digital triggering, and of providing a corresponding digital oscilloscope. 
     Embodiments of the invention include a method for digital triggering, a system for digital triggering, and a digital oscilloscope. 
     According to an embodiment of the invention, a digital triggering of this kind, instead of one triggering event based upon one level comparison with one threshold value, as in the conventional art, two triggering events based upon two level comparisons each with one threshold value are identified, and the time difference between the two triggering events is used as the triggering condition for a dynamic triggering. The digital triggering is implemented in the case of an overshooting and also in the case of an undershooting of a threshold value by the time difference between the two identified triggering events. In this manner, a digital triggering is possible alternatively with a positive or negative signal slopes with a signal impulse up to a maximum impulse duration or from a minimum impulse duration or with a signal-impulse delay up to a maximum impulse delay or from a minimum impulse delay. 
     According to another embodiment of the invention, the time difference between the first and second triggering event is determined via the number of sampling times of the signals to be triggered between the two triggering events. On the one hand, as a result of the time discretization, a first inaccuracy in the precise determination of the first and second triggering events arises in the timing of the exact overshooting or undershooting of the threshold value by the time-discretized signal—reference signal—used in each case for the triggering; and, on the other hand, a second inaccuracy arises a result of a possible synchronicity error between the respectively-determined first or second triqgeritng event and the sampling raster of the signals to be presented on the digital oscilloscope. 
     The first inaccuracy, resulting from the imprecise determination of the first and second triggering events, is resolved by determining the levels of intermediate points between the last preceding sampling time and the next following sampling time of the reference signal(s) before and respectively after the first and second triggering event by means of interpolation, and by comparing the determined levels of the intermediate points with reference to overshooting or undershooting the threshold value(s). In this manner, the times of the first and second triggering events can be determined significantly more precisely. 
     The second inaccuracy resulting from the synchronicity error means that the occurrence of the triggering condition can be either unambiguously identified or unambiguously not identified or neither unambiguously identified nor unambiguously not identified. The triggering condition is unambiguously identified or unambiguously not identified, if the determined number of sampling times between the first and second triggering event either overshoots an upper threshold value or undershoots a lower threshold value. If the determined number of sampling times is disposed between the first and second triggering event between this upper and lower threshold value, then the occurrence of the triggering condition can neither be unambiguously identified nor unambiguously not identified. In this case, the display of the signals to be presented on the digital oscilloscope cannot be started via a triggering impulse and must be postponed until an unambiguous identification of the triggering condition. 
     In this approach, by way of an example, the individual sampled values of the signals to be presented on the digital oscilloscope must be buffered in a FIFO memory and the unambiguous occurrence or the unambiguous non-occurrence of the triggering condition are determined in a further, subsequent determination of the exact times of the first and second triggering events, and therefore of the exact time difference between the first and second triggering event if the presence of the triggering condition is identified in the fine analysis, the sampled values of the signals to be recorded, which have been buffered in the FIFO memory, are retrospectively presented on the display of the digital oscilloscope via a triggering impulse. 
     It should also be mentioned that, in the case of an overshooting of a threshold value, the upper and lower threshold values for the number of sampling times between the first and second triggering event for the unambiguous identification or unambiguous non-identification of the triggering condition adopt a different value—first lower and first upper threshold value—by contrast with the case of an undershooting of a threshold value—second lower and second upper threshold value. Additionally, the upper and lower threshold value for a threshold-value comparison of the time difference between the first and second triggering time with the “&gt;=” or respectively “&lt;=” inequality condition provides different values by contrast with a threshold-value comparison of the time difference between the first and second triggering time with the “&gt;” or respectively “&lt;” inequality condition. 
     According to yet another exemplary embodiment of the invention a method and the system are provided for the digital triggering of signals on the basis of two triggering events separated by a time difference, and the digital oscilloscope are explained in greater detail below with reference to the drawings. 
     Still other aspects, features, and advantages of the present invention are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the present invention. The present invention is also capable of other and different embodiments, and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary embodiments are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements and in which: 
         FIG. 1  shows a block-circuit diagram of a conventional digital oscilloscope; 
         FIG. 2  shows a block-circuit diagram of a system for digital triggering of signals on the basis of two triggering events separated by a time difference, according to an exemplary embodiment of the present invention; 
         FIG. 3  shows a block-circuit diagram of a sub-system for fine analysis of triggering conditions, according to an exemplary embodiment of the present invention; 
         FIG. 4  shows a block-circuit diagram of a digital oscilloscope according to an exemplary embodiment of the present invention; 
         FIGS. 5A ,  5 B,  5 C,  5 D,  5 E,  5 F show time characteristics of various triggering conditions, according to various embodiments of the present invention; 
         FIG. 6  shows a flow chart of a method for digital triggering of signals based on two triggering events separated by a time difference according to an exemplary embodiment of the present invention; and 
         FIG. 7  shows a flow chart of a sub-routine for fine analysis of triggering conditions, according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before describing the method and system for digital triggering of signals on the basis of two triggering events separated by a time difference with reference to  FIGS. 2 to 7  and the associated digital oscilloscope, the digital oscilloscope according to the prior art will first be presented with reference to  FIG. 1 . This is necessary for the further understanding of the invention. 
     Using a pre-amplifier  1 , which provides a variable amplification factor, the digital oscilloscope according to the prior art shown in  FIG. 1  matches the level of the amplitudes of the measured signals present at its input with the measurement range of the display device  4 . After the level matching, the pre-amplified, analog measured signals are supplied to an analog-digital converter  2  for conversion into a corresponding digital data format. The digitized measured signal is checked with reference to a triggering condition by a digital triggering system  3 . If this triggering condition is identified, a triggering impulse for triggering the digital oscilloscope is generated at the output of the digital triggering system  3 . The sampled values of the digitized measured signals, which are registered simultaneously with the triggering impulse or directly following the triggering impulse in time, are presented on the screen of the display unit  4  of the digital oscilloscope. 
     The system for digital triggering of signals on the basis of two triggering events separated by a time difference shown in  FIG. 2  provides a first comparator  5  for the identification of a first triggering event. A first reference signal S i  selected from all of the signals S to be presented on the digital oscilloscope is supplied to a first input  6  of the first comparator  5 . A threshold signal SW i , with which the first reference signal S i  is compared in the first comparator  5  with reference to overshooting or undershooting, is disposed at the second input  7  of the comparator  5 . The comparison with reference to overshooting or undershooting in the first comparator  5  is determined by the signal disposed at the third input  8 , which indicates a comparison with regard to positive or negative slope. The output  9  of the first comparator  5  is activated in the case of an overshooting or undershooting of the threshold signal Sw i  by the first reference signal S i . 
     In a similar manner, a second comparator  10  is provided for the identification of a second triggering event following the first triggering event. Either the first reference signal S i  supplied to the first input  6  of the first comparator  5  or a second reference signal S j , which provides a time delay by comparison with the first reference signal S i , is disposed at the first input  11  of the second comparator  10 . The threshold signal present at the second input  12  of the second comparator  10  is either the threshold signal SW i  also provided at the second input  7  of the first comparator  5  or a threshold signal SW j , which differs from this threshold signal SW i . The signal provided at the third input  13  of the second comparator  10  determines whether the threshold-value comparison in the second comparator  10  is to be implemented between the first reference signal S i  or respectively the second reference signal S j  and one of the two threshold signals SW i  or SW j  in the case of a positive or negative slope. The output  14  of the second comparator  10  is activated by the first or second reference signal S i  or respectively S j  in the case of an overshooting or undershooting of the threshold signal SW i  or respectively SW j . 
     With the first comparator  5  and the second comparator  10 , it is therefore possible, on the basis of two triggering events separated by a time difference—first and second triggering event—, to adjust and to identify the following substantial triggering conditions with reference to the first and respectively second reference signal S i  and respectively S j :
         identification of a positive or negative slope with a given minimum or maximum gradient in a reference signal S i  ( FIG. 5A ,  5 B);   identification of a digital reference-signal impulse S i  or an analog reference signal S i  with a given minimum or maximum length ( FIG. 5C ,  5 D); and   identification of a signal delay with a given minimum or maximum delay at the start or at the end of the signal between a first reference signal S i  and a second reference signal S j  with a time delay relative to the first reference signal S i  ( FIG. 5E ,  5 F).       

     The output  9  of the first comparator  5  is supplied to the start-input  15 , and the output  14  of the second comparator  10  is supplied to the stop-input  16  of the counter  17 . The sampling frequency Clk of the analog-digital converter  2  of the digital oscilloscope is disposed at a third input  18  of the counter  17 . The counter  17  counts the number n sampling times of the signals S to be presented on the digital oscilloscope between the first triggering event (output signal of the first comparator  5  disposed at the start-input  15  of the counter  17 ) and the second triggering event (output signal of the second comparator  10  disposed at the stop-input  16  of the counter  17 ). 
     The sampling times n counted by the counter  17  between the first and second triggering event at the output  19  of the counter  17  are supplied on the one hand to a first input  20  of a third comparator  21 , and on the other hand, to a first input  22  of a fourth comparator  23 . The second input  24  of the third comparator  21  receives the upper threshold value Gw o  stored in a register  25 . The second input  25  of the fourth comparator  23  is supplied with the lower threshold value Gw u  stored in a register  26 . 
     The first comparator  21  compares the number n, registered in the counter  17 , of sampling times between the first and second triggering event with the upper threshold value GW o  and activates the first; output  26  if the number n of sampling times is greater than or equal to the upper threshold value GW o , and activates the second output  27 , if the number n of sampling times is less than the upper threshold value GW o . The fourth comparator  23  compares the number n, determined in the counter  17 , of sampling times between the first and second triggering event with the lower threshold value GW u  and activates the first output  28 , if the number n of sampling times is greater than or equal to the lower threshold value GW u , and activates the second output  29 , if the number n of sampling times is less than the lower threshold value GW u . 
     The definition of the registers  25  and  27  with upper and lower threshold values GW o  and GW u , for example, first and second upper threshold values GW o1 , GW o2  and first and second lower threshold values GW u1 , GW u2 , is implemented by a superordinate process-control unit, not illustrated here, of the system for digital triggering of signals on the basis of two triggering events separated by a time difference. In this context, it should be stated that the occurrence of the triggering condition or the non-occurrence of the triggering condition cannot be unambiguously inferred from the number n, determined by the counter  17 , of sampling times between the first and second triggering event; in fact, for given values of the number n of sampling times between the first and second triggering event, either the unambiguous occurrence or the unambiguous non-occurrence of the triggering condition must be determined retrospectively by a separate fine analysis. 
     This indeterminacy in the identification of the triggering conditions results from the inaccuracy n the exact determination of the first and second triggering events synchronicity errors between the sampling raster and the precise first or respectively second triggering event, the maximum value of which can be up to one sampling time, and from a lack of precision in the threshold-value comparison, which is determined by the use of “&gt;=” or “&lt;=” instead of a “&gt;” or “&lt;” as comparison operators. For these reasons, the upper and lower threshold value can differ by a maximum factor of three, and can accordingly determine up to two intervening values for the number n of sampling times between the first and second triggering event, for which neither an identification of the triggering condition is unambiguously present nor unambiguously not present. A superordinate process-control unit, which is not illustrated, of the system for digital triggering accordingly defines the registers  25  and  26  in agreement with the comparison operator—“&gt;=”, “&lt;=”, “&gt;” or “&lt;” selected in the comparison of the time difference Δt between the first and second triggering event with the time threshold value SW t  with respectively appropriate upper and lower threshold values GW o  and GW u . 
     The signal at the first output  26  of the third comparator  21  —n≧GW 0 —and the signal at the first output  28  of the second comparator  23 —n≦GW u —are each supplied to one of the two inputs  31  and  32  of a multiplexer  30 . Dependent upon a signal disposed at a third input  33  of the multiplexer  30 , which indicates an overshooting or undershooting of a specified time threshold SW t  by the time difference Δt between the first and second triggering event, the multiplexer  30  connects either the activated signal of the first output  26  of the third comparator—n≧GW o —in the case of an overshooting of the time threshold SW t —or the activated signal of the first output  28  of the fourth comparator  23 —n≦GW u —in the case of an undershooting of the time threshold SW t —through to the output  34  of the multiplexer  30 , which acts as a triggering impulse s TR  for triggering the signals S to be presented on the digital oscilloscope. 
     The third and fourth comparator  21  and  23 , the associated registers  25  and  26  storing the upper and lower threshold value GW o  and GW u  and the multiplexer  30  therefore provide a unit  54  for the identification of triggering conditions. 
     The activated signal at the second output  27  of the third comparator  21 —n&lt;GW o —and the activated signal at the second output  29  of the fourth comparator  23 —n&gt;GW u —are supplied respectively to one of the two inputs  35  and  36  of an AND gate  37  and generate the signal FA for fine analysis of the triggering condition at the output  38 . In this fine analysis, the sampled values of the reference signal(s) S i  and respectively S j  are evaluated in order to achieve a more-accurate determination of the first and second triggering events and therefore of the time difference Δt between the first and second triggering events. A subsequent threshold comparison of the precisely-determined time difference Δt between the first and second triggering event with a time threshold SW t  allows an unambiguous identification or non-identification of the triggering condition. 
     In the sub-system for the fine analysis of triggering conditions according to  FIG. 3 , the sampled values of the signals S to be presented on the digital oscilloscope are supplied to several delay elements  39   1 ,  39   2 , . . . ,  39   N  connected in series, in which they are delayed respectively by the sampling time T i  of the analog-digital converter  2 . The signals disposed at the individual outputs of the individual delay elements  39   1 ,  39   2 , . . . ,  39   N , which are each delayed relative to one another by a different number of sampling cycles T i  and therefore represent the sampled values of the signals S to be presented on the digital oscilloscope, which have been buffered since the identification of the first triggering event, are supplied to the input of a switch  40  and passed on, in the case of an activated signal FA, for a fine analysis of the triggering condition to a first-in-first-out memory (FIFO memory)  41 , in which they are buffered. 
     The last sampled value preceding the first identified triggering event and the next sampled value following the first identified triggering event, S in  and S in+1  respectively, of the first reference signal S i , and the last sampled value preceding the second identified triggering event and the next sampled value following the second identified triggering event, S im  and S im+1  or respectively S jm  and S jm+1  of the first or respectively second reference signal S i  and respectively S j  are read out from the FIFO memory  41 , by means of a process-control unit, which is not illustrated, of the system for digital triggering, and supplied to a unit  42  for determining the first and second intermediate points Z 1  and Z 2  between the sampled values close to the threshold value S in  and S in+1  together with S im  and S im+1  and respectively S jm  and S jm+1  of the first and respectively second reference signal S i  and respectively S j . The levels of intermediate points Z 1  and Z 2  are calculated in the unit  42  via a given interpolation method, which will not be explained in greater detail in present context, and supplied to a fifth and six comparator  43  and  44  for a more precise determination of the first and second triggering event. 
     A threshold-value comparison of the first intermediate points Z 1  with a threshold value SW i  is implemented in the fifth comparator  43 ; while a threshold-value comparison of the second intermediate points Z 2  is implemented in the sixth comparator  44  with the same threshold value S i  in the case of an identification of a signal impulse with a given impulse length or with a given signal delay; or with another threshold value SW j  in the case of an identification of a signal slope. 
     The outputs Z 1 &gt;SW i  and Z 1 &lt;SW i  corresponding to the number of first intermediate points Z 1  provided respectively for an overshooting and an undershooting of the threshold value SW i , which are activated respectively in the presence of the relevant comparison condition, are evaluated in a subsequent, first evaluation-logic unit  45  for the determination of the more-precise timing point t TR1  of the first triggering event. Similarly, the outputs Z 2 &gt;SW i  and Z 1 &lt;SW i  or respectively Z 2 &lt;SW i  corresponding to the number of second intermediate points Z 2  provided respectively for an overshooting and an undershooting of the threshold value SW i  and respectively SW j , which are activated respectively in the presence of the relevant comparison condition, are evaluated in a subsequent second evaluation-logic unit  46  for the determination of the more-precise timing point t TR2  of the second triggering event. 
     A subsequent subtraction element  47  calculates the time difference Δt between the first and second triggering event from the difference between the timing point t TR2  of the second triggering event and the timing point t TR1  of the first triggering event. This time difference Δt is supplied to a first input  49  of a subsequent seventh comparator  48  and compared with reference to overshooting or undershooting a time-threshold value SW t  present at the second input  50 . For this purpose, the signal present at the third input  33  of the multiplexer  30  is supplied to a third input  51  of the seventh comparator  48 , which indicates a comparison with reference to an overshooting or undershooting of the time threshold SW t . In the event of the comparison condition, a triggering impulse s TR ′, which delays the sampled values of the signals S to be displayed on the digital oscilloscope, which have been buffered since the occurrence of the first triggering event, in the FIFO memory  41 , is activated at the output  52  of the seventh comparator  48  and passes on the evaluation time of the fine analysis instead of the currently pre-amplified and sampled signals S to the recording device  4  of the digital oscilloscope. 
     The unit  42  for determining the first and second intermediate points Z 1  and Z 2  between sampled points S in , S in+1 , S im , and S im+1  close to the threshold, the fifth and sixth comparators  43  and  44 , the first and second evaluation-logic units  45  and  46 , the subtraction element  47  and the seventh comparator provide a unit  55  for fine identification of triggering conditions. 
       FIG. 4  shows the block-circuit diagram of the digital oscilloscope together with the functional units already presented in  FIG. 3  with reference to the system for fine analysis of the triggering conditions. The description of these functional units is therefore not repeated at this point. 
       FIG. 6  presents the method for digital triggering of signals on the basis of two triggering events separated by a time difference. 
     In the first procedural stage S 10 , the first and second triggering events are determined by means of a first and second comparator  5  and  10  from a first reference signal Si selected from all of the signals S to be presented on the digital oscilloscope or from an additionally-selected second reference signal S j  by means of a threshold-value comparison with a first threshold-value signal SW i , or respectively, additionally, with a second threshold-value signal SW j , with an accuracy corresponding to the level of the sampling periods of the signals S to be presented on the digital oscilloscope. 
     In procedural stage S 20 , using the first and second triggering event determined in procedural stage S 10 , the number ri of sampling times between the first and the second triggering event of the signals S to be presented on the digital oscilloscope are counted in a counter  17 . 
     In procedural stage S 30 , the number n, determined in procedural stage S 20 , of sampling times between the first and second triggering event is compared with reference to overshooting or undershooting an upper and lower threshold value GW o  and GW u  in order to achieve an unambiguous identification or an unambiguous non-identification of the triggering condition. In this context, the upper and lower threshold values GW o  and GW u  corresponding to the comparison operators “&gt;=”, “&lt;=”, “&gt;” or “&lt;”, which have been selected by the user or by the system for the threshold-value comparison of the time difference Δt between the first and second triggering time, are selected by a superordinate process-control unit of the system for digital triggering. 
     If the threshold-value comparison of the number n of sampling times between the first and second triggering event provides an unambiguous identification of the triggering condition in procedural stage S 40 , a triggering impulse s TR  for the triggering of the signals S to be presented on the digital oscilloscope is generated in the next procedural stage S 50 . 
     If the threshold-value comparison in procedural stage S 60  also fails to provide an unambiguous non-identification of the triggering condition, a fine analysis of the triggering condition is implemented within the framework of a sub-routine S 70 , the purpose of which is to provide an unambiguous retrospective identification or an unambiguous retrospective non-identification of the triggering condition. 
     The sub-routine for fine analysis of the triggering condition, which is executed within the method for digital triggering of signals on the basis of two triggering events separated by a time difference shown in  FIG. 6  as procedural stage S 70 , is described in detail in  FIG. 7 . 
     The first procedural stage S 100  of the sub-routine for fine analysis of the triggering condition illustrated in  FIG. 7  provides the buffering of all sampled values of the signals S to be presented on the digital oscilloscope in a first-in-first-out memory  41  from the time of the identification of the first triggering event. 
     In the subsequent procedural stage S 110 , the levels of the first intermediate point Z 1 , which are disposed between the last sampling time preceding the first triggering event and the next sampling time following the first triggering event of the first reference signal S i , and the levels of the second intermediate point Z 2 , which are disposed between the last sampling Lime preceding the second triggering event and the next sampling time following second triggering event of the first or second reference signal S i  or S j , are determined by means of an interpolation method. 
     In procedural stage S 120 , the timing points t TR1  and t TR2  of the first and second triggering event are determined in a fifth and sixth comparator  43  and  44  and a first and second evaluation-logic unit  45  and  46  by comparing the first and second intermediate values Z 1  and Z 2  with a threshold-value signal SW i  or with an additional threshold-value signal SW j . 
     In procedural stage S 130  the time difference Δt between the first and second triggering event is determined in a subtraction element  47  on the basis of the determined timing points t TR1  and t TR2  of the first and second triggering event and, following this, compared in a seventh comparator  48  with reference to overshooting or undershooting a time-threshold value SW t  in order to achieve an unambiguous identification of the triggering condition or an unambiguous non-identification of the triggering condition. 
     If an unambiguous identification of the triggering condition is present in procedural stage S 140  as a result of the threshold-value comparison in procedural stage S 130 , a triggering impulse s TR ′ for triggering the sampling values of the signals S to be presented on the digital oscilloscope, which have been buffered in the FIFO memory  41  since the identification of the first triggering event, is generated in the final procedural stage S 150 . 
     The invention is not restricted to the embodiment illustrated. In particular, other numerical methods for the determination of more-precise timing points of the first and second triggering event, especially delay-time-optimised methods, are also covered by the invention. 
     While the invention has been described in connection with a number of embodiments and implementations, the invention is not so limited but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims. Although features of the invention are expressed in certain combinations among the claims, it is contemplated that these features can be arranged in any combination and order.