Abstract:
A test and measurement instrument includes a trigger system for controlling an acquisition system to acquire digital signal samples. The trigger system is selectively responsive to a trigger circuit for detecting a trigger event associated with an input signal, and to circuitry for detecting various sequences or combinations of anomalies. Further, selected sequences and combinations of the anomalies may be combined across a plurality of channels of the test and measurement instrument, or across multiple instruments, thereby allowing more sophisticated triggering criteria to be defined.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally concerns an oscilloscope architecture providing detection of anomalous events, and more specifically concerns an oscilloscope architecture for simultaneously monitoring an input signal to detect multiple different types and combinations of anomalies.  
       BACKGROUND OF THE INVENTION  
       [0002]     In a conventional digital real time oscilloscope, an A/D converter digitizes an analog input signal, and the resulting digital signal samples are stored in memory. The analog input signal is also applied to a trigger circuit that detects a trigger event in the input signal. Storage of the digitized signal samples into memory is performed in response to the detection of a trigger event. Rasterizer circuitry then places the digital signal samples into a form suitable for display. The resultant waveform data can then be drawn on a display device such as a Liquid Crystal Display (LCD).  
         [0003]     Well-known trigger circuits for oscilloscopes are responsive to any one of several types of anomalous events. Such anomalies include, but are not limited to, narrow pulses or glitches, pulses that are lower than expected (runt pulses), a rise time or fall time that is slower that expected, an input signal falling within or outside of a “window”, or insufficient setup and hold time of a signal with respect to a clock. Thus, an oscilloscope can be set to detect any one of these anomalous events and generate a trigger to control acquisition of digital signal samples of the input signal.  
         [0004]     Commonly assigned U.S. Pat. No. 5,841,286 (Stoops) discloses monitoring circuitry that continuously monitors an input signal on an oscilloscope for a number of distinct anomalies in parallel. The monitoring circuitry of Stoops counts these anomalies and presents a summary of them to the user. These anomalies may be optionally routed, via an OR gate, into the oscilloscope trigger system so that they may be used to trigger a data acquisition cycle. Finally, the Stoops patent discloses how the anomaly detection circuitry from many channels can be combined, via an OR gate, and routed into the oscilloscope trigger system so that any anomalistic event on any input channel can be used to trigger a data acquisition cycle. The &#39;286 Stoops patent is described in terms of an older analog oscilloscope. While the &#39;286 Stoops patent works well for its intended purpose, it cannot recognize certain triggering conditions that a user of today&#39;s oscilloscopes may need.  
         [0005]     Some limitations of existing arrangements include instances where a user might not be interested in detecting all runt signals occurring on a tri-state bus, since at least some of them are very likely to occur when the bus is not asserted. This condition cannot be distinguished from normal operation using the prior art monitoring circuitry. Another limitation is where a user wants to trigger on setup and hold violations, but only after a glitch has just been detected. In yet another limitation, a user may want to trigger on anomalous events on any of three input channels, but may want to exclude runts on one channel. In addition, the user may not be interested in triggering on any anomalous events unless a fourth channel is asserted, indicating that the device under test is active.  
       SUMMARY OF THE INVENTION  
       [0006]     A test and measurement instrument includes a trigger system for controlling an acquisition system to acquire digital signal samples. The trigger system is selectively responsive to a trigger circuit for detecting a trigger event associated with an input signal, and to circuitry for detecting various sequences or combinations of anomalies. Further, selected sequences and combinations of the anomalies may be combined across a plurality of channels of the test and measurement instrument, or across multiple instruments, thereby allowing more sophisticated triggering criteria to be defined.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The following drawing may be useful for understanding the invention.  
         [0008]      FIG. 1  is a block diagram of a test and measurement instrument embodying the present invention; and  
         [0009]      FIG. 2  is a block diagram of a trigger programmable logic circuit suitable for use with multiple channels in the test and measurement instrument of  FIG. 1 . 
     
    
       [0010]     To facilitate understanding, identical reference numerals have been used, where appropriate, to designate identical elements that are common to the figures.  
       DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0011]     The present invention is discussed in the context of a signal quality monitoring circuit that may be implemented in a Test and Measurement Instrument, such as a Digital Storage Oscilloscope (DSO), a logic analyzer, or the like. Such oscilloscopes and logic analyzers are manufactured by Tektronix, Inc. of Beaverton, Oreg.  
         [0012]      FIG. 1  is a block diagram of a Test and Measurement Instrument  100  embodying the present invention. Although Test and Measurement Instrument  100  will be discussed in terms of a digital real-time oscilloscope, the teachings of the present invention should not be considered as being limited to an oscilloscope.  
         [0013]     Referring to  FIG. 1 , Oscilloscope  100  receives an input Signal Under Test (SUT) via an input terminal  10 . Oscilloscope  100  comprises an Acquisition System  8 , a Trigger System  18 , a Processor  24 , a Display Generator (including a rasterizer)  26 , a Display Device  30 , and Programmable Logic circuitry  90 .  
         [0014]     Acquisition System  8  comprises an A/D Converter  2 , an Acquisition Controller  4 , and an Acquisition Memory  6 . Trigger system  18  comprises Trigger Conditioning circuitry (including a trigger comparator)  12 , a Trigger Latch  16 , and a Switch  22 . Processor  24  may comprise one or more microprocessors or similar devices for processing data between, and controlling the operation of, the Acquisition System  8 , the Trigger System  18 , Display Generator  26 , and Programmable Logic circuitry  90 .  
         [0015]     The SUT at input  10  is digitized by A/D Converter  2 , and the resultant data samples are passed through Acquisition Controller  4 , where they may be processed or decimated prior to storing them in Acquisition Memory  6 . In addition, Acquisition Controller  4  determines which of the data samples will actually be stored in Acquisition Memory  6 , thereby forming an acquired waveform. The SUT at input  10  is simultaneously applied to a Trigger Conditioning circuit and Trigger Comparator circuit  12 , which provides an output trigger signal indicative of the conditioned input signal meeting certain criteria, such as its passing through a selected threshold level in a predetermined direction.  
         [0016]     The trigger signal is applied through Switch  22  to Trigger Latch  16 , which provides a signal to Acquisition Controller  4  for controlling the storage of the acquired waveform. Display Generator  26  then rasterizes the acquired waveform and may add additional information necessary to generate a display image that is displayed on Display Device  30 . At some point, illustratively during or after the generation of this display image, Acquisition Controller  4  and Trigger Latch  16  are reset so that another acquisition cycle can begin.  
         [0017]     As described thus far, Oscilloscope  100  operates in a conventional fashion. That is, the waveform of the input signal is ultimately displayed in response to the input signal meeting predetermined trigger criteria. The SUT at input  10  of Oscilloscope  100  is also connected to an array of Anomaly Detection circuits  50  for detecting anomalies associated with the SUT. As noted above, such anomalies associated with a SUT may include positive or negative glitches, positive or negative runts, slow rise/fall times, window excursions, insufficient setup and hold times of the signal with respect to a clock, and the like. Each of Anomaly Detectors  50   a - 50   h  continuously monitors the input signal for the occurrence of a particular respective anomaly.  
         [0018]     The outputs of Anomaly Detectors  50   a - 50   h  are connected to respective inputs of a Programmable Logic circuit  90 . The output of Programmable Logic circuitry  90  is a signal indicative of a detected occurrence of a preselected event comprising a particular combination or sequence of anomalies. For example, a user may be interested in knowing when a positive glitch is followed by signal exhibiting a slow fall time. The user may program Programmable Logic circuit  90  to detect such a sequence of anomalies, while excluding other anomalies that may occur on the signal under test.  
         [0019]     It is important to note that apparatus according to teachings of the &#39;286 Stoops patent would not be able to exclude certain detected anomalies from producing a trigger signal. Such apparatus may interfere with troubleshooting activities by triggering on occurrences of anomalies that are not important to the user at that time. Moreover, apparatus according to teachings of the &#39;286 Stoops patent would not be able to detect specific sequences of anomalies for producing a desired trigger signal.  
         [0020]     When an anomaly (or combination of anomalies, or sequence of anomalies) associated with the SUT at input  10  is detected by Programmable Logic circuitry  90 , it provides EVENT DETECT OUT information to Trigger Latch  16  via Switch  22 . In the single channel arrangement of  FIG. 1 , the EVENT DETECT OUT signal is used directly as a trigger pulse, indicative of a combination or sequence of anomalies, that can then be used by Acquisition Controller  4  to determine which samples will form an acquired waveform.  
         [0021]     Switch  22  selects either the output of Programmable Logic circuit  90  when a user is interested in detecting combinations of anomalies (e.g., glitches and slow rise/fall times that occur only when runt conditions are not present), or the output of Trigger Conditioning circuitry  12 . Thus, Programmable Logic circuitry  90  provides the ability to recognize potentially complex combinations of anomalies.  
         [0022]     For example, a user might want to trigger on a setup and hold violation, but only after a glitch has just been detected. The present invention allows this combination of anomalous events to be recognized by appropriately programming Programmable Logic circuit  90 .  
         [0023]     Programmable Logic circuit  90  may comprise any combination of conventional logic elements capable of producing a specific output associated with a predetermined combination or sequence of detected anomalies. Such logic elements may, for example, include one or more AND gates, NAND gates, OR gates, flip-flops, programmable logic devices, such as field programmable gate arrays (FPGAs) and the like, or any other conventional logical operator or operators, as well as any combination thereof. Each predetermined combination or sequence of detected anomalies may be based upon design considerations or test conditions associated with a particular circuit being observed.  
         [0024]     In addition, Programmable Logic circuitry  90  may be programmed to operate according to conditional logic rules, such as, an IF, THEN, ELSE statement. For example, Programmable Logic circuitry  90  may be programmed to produce an EVENT DETECT OUT signal if a specified first trigger combination is followed by a second specified trigger combination, and otherwise to look for a third trigger combination.  
         [0025]     Although  FIG. 1  shows application of the invention to a single channel oscilloscope, it is important to note that the invention may also be applied to a multi-channel oscilloscope. In this case, each channel of a multi-channel Oscilloscope  100  may be provided with an array of Anomaly Detectors  50 , and a Programmable Logic circuit  90 . For example, a four channel Oscilloscope would include a total of four arrays of Anomaly Detectors  50 , and a total of four Programmable Logic circuits  90 . However,  FIG. 2  shows an alternate arrangement for applying the teaching of the subject invention to a multi-channel oscilloscope.  
         [0026]      FIG. 2  is a simplified block diagram showing only those portions of  FIG. 1  that are required to understand this embodiment of the invention. Each channel of and N-channel Oscilloscope  100  has an associated array of Anomaly detectors  50 - 1  through  50 -N. The output signals of all of these Anomaly Detectors are coupled to respective inputs of a single Programmable Logic circuit  90 .  
         [0027]     Each channel contains Acquisition System circuitry  8 , and Trigger Conditioning and Comparator circuitry  12 , as discussed above with respect to  FIG. 1 . All of the channels share common components (not shown in  FIG. 2 ) such as, a common Switch  22  and a common Trigger Latch  16 , which are used by Acquisition Controller  4  of each channel to determine when to stop acquiring data.  
         [0028]     By use of the arrangement of  FIG. 2 , Programmable Logic circuit  90  allows combinations of signals from the various Anomaly Detection circuits from multiple channels to be used to trigger Oscilloscope  100 .  
         [0029]     For example, a first input channel may be setup, via Programmable Logic circuitry  90 , to recognize all anomalies except runts (i.e., disable detectors  50   c  and  50   d  of Anomaly Detect array  50 - 1 ). A second input channel may be setup to recognize all anomalies except slow rise or fall times (e.g., disable detectors  50   f  and/or  50   g  of Anomaly Detector array  50 - 2  (not shown)). A third channel might be setup to recognize all anomalies (i.e., none of the detectors of anomaly Detector array  50 - 3  (not shown) are disabled). Programmable Logic circuit  90  would then take into account each of the prescribed conditions for each channel and produce an EVENT DETECT OUT signal only when all of the conditions are satisfied.  
         [0030]     Anomaly Detection signals from multiple oscilloscopes (not shown), each having circuitry according to  FIGS. 1 and 2 , may be combined as shown in  FIG. 2 . That is, the EVENT DETECT OUT signals produced by Programmable Logic circuits  90  of Oscilloscope  200  or Oscilloscope  300  may be applied to respective Event Detect IN terminals of Programmable Logic circuit  90  of Oscilloscope  100 . Programmable Logic circuit  90  of Oscilloscope  100  would then take into account each of the prescribed conditions for each channel of each connected oscilloscope, and produce an EVENT DETECT OUT signal only when all of the conditions on all of the oscilloscopes are satisfied. The single EVENT DETECT OUT signal may be coupled to Oscilloscopes  200  and  300  to trigger them.  
         [0031]     Alternatively, one skilled in the art will realize that a multi-conductor cable could be used to apply the output signals of Anomaly Detector arrays  50 - 1  through  50 -N of Oscilloscope  200  or Oscilloscope  300  directly to input terminals of Programmable Logic circuit  90  of Oscilloscope  100 . This arrangement would also allow Programmable Logic circuit  90  of Oscilloscope  100  to take into account each of the prescribed conditions for each channel of each connected oscilloscope, and produce a single EVENT DETECT OUT signal only when all of the conditions on all of the oscilloscopes are satisfied. The single EVENT DETECT OUT signal may be coupled to Oscilloscopes  200  and  300  to trigger them.  
         [0032]     It will be appreciated that the invention is not restricted to the particular embodiments that have been described, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims and equivalents thereof. For example, the invention is not restricted to use with a digital oscilloscope, and is also applicable to other test and measurement instruments, such as a logic analyzer. One skilled in the art will realize that one or more of detectors  50   a - 50   h  may be omitted, and detectors for responding to other anomalous events may be provided in addition to, or in lieu of, one or more of detectors  50   a - 50   h.    
         [0033]     While the foregoing is directed to specific embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.