Patent Publication Number: US-2010114516-A1

Title: Method and Apparatus for Time Synchronization of Events for Multiple Instruments

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) from U.S. Provisional Application Ser. No. 61/111,406, filed on Nov. 5, 2008, the contents of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     This disclosure relates to test and measurement instruments, in particular to triggering of multiple test and measurement instruments. 
     An event on a test and measurement instrument can be used to trigger an acquisition on other test and measurement instruments. For example, a first test and measurement instrument can have a trigger output. The trigger output can output a signal indicating that the first test and measurement instrument has detected conditions that can cause an acquisition. 
     Other test and measurement instruments can be coupled to the trigger output of the first test and measurement instrument. These test and measurement instruments can trigger an acquisition in response to the external trigger from the first test and measurement instrument. Thus, the acquisition of multiple instruments can be triggered by events detected by one test and measurement instrument. 
     SUMMARY 
     An embodiment includes a measurement system including a plurality of test and measurement instruments; and a hub coupled to each of the test and measurement instruments. Each of the test and measurement instruments is configured to trigger an acquisition in response to a hub event received from the hub. 
     Another embodiment includes a test and measurement instrument including an input configured to receive an event; and a controller coupled to the input and configured to trigger an acquisition in response to the event and a time associated with the test and measurement instrument and at least one other test and measurement instrument. 
     Another embodiment includes measuring a round-trip time from a hub to a test and measurement instrument; receiving an event from the hub at the test and measurement 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a measurement system according to an embodiment. 
         FIG. 2  is a block diagram illustrating a connection of a test and measurement instrument and a hub in the measurement system of  FIG. 1 . 
         FIGS. 3 and 4  are timing diagrams illustrating measurements of round-trip times for two test and measurement instruments according to an embodiment. 
         FIG. 5  is a timing diagram illustrating an event from a first test and measurement instrument propagating to multiple test and measurement instruments according to an embodiment. 
         FIG. 6  is a timing diagram illustrating an event from a second test and measurement instrument propagating to multiple test and measurement instruments according to an embodiment. 
         FIG. 7  is a diagram illustrating a time relationship of waveforms on a device under test according to an embodiment. 
         FIG. 8  is a diagram illustrating a time relationship of the waveforms of  FIG. 7  with the respective trigger points aligned. 
         FIG. 9  is a diagram illustrating a time relationship of the waveforms offset in time according to an embodiment. 
         FIG. 10  is a block diagram of a hub according to an embodiment. 
         FIG. 11  is a flowchart illustrating an example of a calibration of multiple test and measurement instruments. 
         FIG. 12  is a block diagram of a test and measurement instrument according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments include test and measurement instruments, measurement systems, calibration and measurement techniques, or the like where an event generated on one or more test and measurement instruments can be used to trigger acquisition on any or all of the test and measurement instruments. 
       FIG. 1  is a block diagram of a measurement system according to an embodiment. In this embodiment, a measurement system  10  includes multiple test and measurement 
     The test and measurement instruments  12 - 15  can include any variety of instruments. For example, a test and measurement instrument can include an oscilloscope, a logic analyzer, a network analyzer, a spectrum analyzer, or the like. Any instrument that can acquire data in response to an event can be used as a test and measurement instrument. 
     An event can be any variety of conditions. For example, an event can be a rising edge, a level, a glitch, a pulse width, or the like. In another example, an event can include a packet type, a data sequence, or the like. An event can include a combination of such events. Any occurrence measurable by a test and measurement instrument can be an event. 
     Events can, but need not be consistent between test and measurement instruments. For example, a logic analyzer can detect a particular data sequence on the DUT  11  as an event. An oscilloscope can detect a pulse width. That is, some of the test and measurement instruments  12 - 15  can be monitoring the DUT  11  for different types of events. 
     In particular, in an embodiment, different types of test and measurement instruments  12 - 15  can be coupled together and can trigger based on the same event. For example, assume that test and measurement instrument  12  is a logic analyzer monitoring the DUT  11  for a particular data pattern and test and measurement instrument  13  is an oscilloscope monitoring the DUT  11  for an edge with a particular rise-time. The oscilloscope  13  can detect the edge and transmit the detection event to the hub  18 . The hub  18  can transmit the event to each of the test and measurement instruments  12 - 15 , causing the test and measurement instruments  12 - 15  to acquire data. Alternatively, the acquisition can similarly be triggered by a particular data pattern detected on the logic analyzer  12 . 
     In another embodiment, each of the test and measurement instruments  12 - 15  can be the same or substantially similar. For example each test and measurement instruments  12 - 15  can be an oscilloscope. A particular event on one instrument can be used to trigger an acquisition on all of the test and measurement instruments  12 - 15 . Regardless of the type of test and measurement instruments used, in an embodiment, a measurement system  10  can be created having the capabilities of the multiple test and measurement instruments  12 - 15  and synchronizes substantially similar to a single integrated test and measurement instrument. 
     Although four test and measurement instruments have been illustrated, any number of test and measurement instruments can be part of the measurement system  10 . In particular, any number of test and measurements greater than one can be used. 
     In addition, although the hub  18  has been illustrated as being separate from the test and measurement instruments  12 - 15 , in an embodiment the hub  18  can be part of one of the test and measurement instruments  12 - 15 . For example, the hub  18  can be integrated with the test and measurement instrument  12 . The connections to the other test and measurement instruments  12 - 15  can be achieved through external connections to the test and measurement instrument  12 . Regardless, the measurement system  10  can be created where events can be routed through the hub  18 . 
       FIG. 2  is a block diagram illustrating a connection of a test and measurement instrument and a hub in the measurement system of  FIG. 1 . In this embodiment, the communications link  16  includes a communication line  32  and event transmission lines  34  and  36 . The communication line  32  and event transmission lines  34  and  36  can be formed by any variety of connections. For example, the event transmission lines  34  and  36  can be coaxial cables, twisted pair cables, or the like. The communication line  32  can similarly include any variety of connections. 
     The test and measurement instrument  12  can include a communication port  20  coupled to a communication port  26  on the hub  18 . An event output  22  of test and measurement instrument  12  can be coupled to an event input  28  of the hub  18  through the event transmission line  34 . An event input  24  of the test and measurement instrument  12  can be coupled to an event output  30  of the hub  18  through the event transmission line  36 . 
     In an embodiment, the event output  22  can be configured to output an event to the hub  18 . The hub  18  can be configured to receive the event through the event input  28 . The hub  18  can be configured to process the event then transmit the event through the event output  30  to be received by the event input  24 . 
     Although the communication of an event of the test and measurement instrument  12  to and from the hub  18  has been described as separate, the transmission of such events can be over a single communication link. For example, in one embodiment, each of the event input and event output pairs can be coupled by a coaxial cable. In another embodiment, a separate coaxial cable can couple the event inputs to the corresponding event outputs. Regardless, an event can be sent to the hub  18  and an event can be received from the hub  18 . 
     In an embodiment, the event transmission lines  34  and  36  can be formed such that communications over the event transmission lines  34  and  36  can be substantially similar. For example, a time delay through the event transmission line  34  can be substantially similar to a time delay through the event transmission line  36 . Accordingly, as will be described below, a propagation time to the hub  18  can be calculated. 
       FIGS. 3 and 4  are timing diagrams illustrating measurements of round-trip times for two test and measurement instruments according to an embodiment.  FIG. 3  illustrates a timing diagram for test and measurement instrument A while  FIG. 4  illustrates a timing diagram for instrument B. 
     In particular, the timing diagrams represent the timing of a round-trip transmission of an event to and from the hub  18 . For example, referring to  FIG. 3 , an event can be transmitted from test and measurement instrument A through the event output  22  to the hub  18 . After a time 2*T A , the event can be received from the hub  18  through the event input  24 . In particular, the round-trip time to and from the hub  18  can be measured. As will be described in further detail below, the hub  18  can be configured such that during this measurement, the hub  18  returns the event transmitted by the particular test and measurement instrument. 
     In this embodiment, the round-trip time is represented as time 2*T A . Thus, the propagation time to the hub  18  can be approximated as T A . Similarly, a round-trip time 2*T B  for test and measurement instrument B can be measured. In particular, as will be described in further detail below, each test and measurement instrument can be configured to measure the round-trip time between itself and the hub  18 . Accordingly, each test and measurement instrument can measure a time for an event to travel from the test and measurement instrument to the hub  18 . 
       FIG. 5  is a timing diagram illustrating an event from a first test and measurement instrument propagating to multiple test and measurement instruments according to an embodiment. It should be noted that in an embodiment, the round-trip times can be different between different test and measurement instruments. However, with such a measurement, the triggering of the test and measurements instruments can be substantially synchronized. 
     In particular, test and measurement instrument A can generate an event. The event can be delayed by a time T DA . In particular, the time T DA  can be a difference between the time T A  and a maximum of times T A  and T B . T MAX  represents this maximum time. In this embodiment, time T B  is the maximum time T MAX . Each test and measurement instrument can 
     The delayed event is then output from the test and measurement instrument A to the hub  18 . The event takes time T A  to reach the hub  18 . Since the event was delayed by time T DA  and took time T A  to reach the hub, the total time is T DA +T A  or T MAX . Similarly, as each test and measurement instrument can delay locally generated events by a time corresponding to the particular instrument, contemporaneous events from different instruments can arrive at the hub  18  at substantially the same time. That is, regardless of the test and measurement instrument that generated the event, the event can reach the hub  18  a time T MAX  after the event occurred. In other words, the time alignment of events on a DUT  11  can be substantially preserved in the events arriving at the hub  18 . 
     The hub  18  can be configured to propagate the event to each of the test and measurement instruments. However, as the transmission delay time can be different, the event can reach the various test and measurement instruments at different times. For example, after time T A , the event can reach test and measurement A as illustrated. Similarly, after time T B , the event can reach test and measurement B as illustrated. 
       FIG. 6  is a timing diagram illustrating an event from a second test and measurement instrument propagating to multiple test and measurement instruments according to an embodiment. To illustrate the synchronization substantially independent of the source of an event, an event generated by test and measurement B is illustrated similar to the event of test and measurement instrument A in  FIG. 5 . 
     In  FIG. 6 , an event is generated on test and measurement instrument B. As instrument B has the maximum time to the hub  18 , its time T B  is the time T MAX . Thus the delayed event at test and measurement instrument B is substantially not delayed relative to the generated event. However, since the propagation time to the hub is T B , the event still arrives at the hub  18  after time T MAX  since in this example, T B  is the time T MAX . Once at the hub  18 , the event can be propagated to the test and measurement instruments. The events arriving at test and measurement instruments A and B are substantially similar as those illustrated in  FIG. 5  since the event arrived at the hub  18  at substantially the same time. 
       FIG. 7  is a diagram illustrating a time relationship of waveforms on a device under test according to an embodiment. Waveform A represents a waveform on a DUT  11  probed by test and measurement instrument A. Similarly, waveform B represents a waveform on a DUT  11  probed by test and measurement instrument B. The waveforms are illustrated as they existed in time on the DUT  11 . 
     In this embodiment, an edge  44  of waveform A is used as the event. That is, in response to the edge  44 , test and measurement instrument A generates an event similar to event A illustrated in  FIG. 5 . As described above, the event is returned to test and measurement instrument A after a time T MAX +T A . In response to the event, the test and measurement instrument A can trigger an acquisition. Trigger point  40  illustrates the point in time relative to the occurrence of waveform A on the DUT  11  where the event was received and a trigger occurred. 
     Similarly, the same event can be received at test and measurement instrument B where the acquisition of waveform B can be triggered. However, as described above, the time the event takes from the occurrence of the event to the time the event reaches the test and measurement instrument is different for each test and measurement instrument. In this example, the time is T MAX +T B . Thus, test and measurement instrument B triggers an acquisition of waveform B after a time T MAX +T B . Trigger point  42  of waveform B represents this trigger point. For reference, point  46  on waveform B represents the location on waveform B that occurred contemporaneous with the edge  44 . 
       FIG. 8  is a diagram illustrating a time relationship of the waveforms of  FIG. 7  with the respective trigger points aligned. As illustrated, the trigger points  40  and  42  of the waveforms A and B were used to align the waveforms A and B in time. However, as described above, the occurrence of the trigger points in time were not the same. As a result, a time error  48  is introduced between contemporaneous points of the waveforms A and B, such as the edge  44  of waveform A and the point  46  of waveform B. 
       FIG. 9  is a diagram illustrating a time relationship of the waveforms offset in time according to an embodiment. In this embodiment, each of the waveforms A and B has been offset in time from their respective trigger points by the event propagation time particular to the corresponding test and measurement instrument. That is, waveform A has been offset by time T MAX +T A  and waveform B has been offset by time T MAX +T B . Accordingly, the presentation of the waveforms A and B are now aligned in time substantially equivalent to the time alignment on the DUT  11  as illustrated in  FIG. 7 . 
     Thus, once a calibration has been performed where times such as the transmission time T A , time T MAX , the difference time T DA  have been determined, a given test and measurement instrument can, but need not know the identity of the test and measurement instrument that generated the event. In other words, each test and measurement instrument can be configured to delay its own events such that the time from the occurrence of an event 
     As each test and measurement instrument characterized its connection to the hub  18 , each test and measurement instrument can adjust its acquisition, triggering, presentation of data, or the like to account for the particular return time from the hub. That is, as the events are synchronized at the hub  18 , any remaining time offset introduced can be substantially only dependent on the return path to the particular test and measurement instrument. Accordingly, the test and measurement instrument can account for such difference in time and synchronize the acquired data without information regarding which test and measurement instrument generated the event. 
     Although a time T MAX  has been described as being the maximum of the propagation times to the hub among the test and measurement instruments, the time can, but need not be the maximum. In an embodiment, the time can be greater than the maximum time. The difference times such as time T DA  can still be calculated with respect to the greater time. However, in this embodiment T DB , or the difference time for test and measurement instrument B, which had the maximum time above, can be greater than substantially zero. 
       FIG. 10  is a block diagram of a hub according to an embodiment. In this embodiment, the hub  18  includes a controller  50  and a logic circuit  52 . The controller  50  can be coupled to the test and measurement instruments through communication lines  54  and  56 . Although individual communication lines have been described, a single communication system among the test and measurement instruments can be used. 
     The logic circuit  52  is configured to combine events received from the test and measurement instruments. For example, event transmission lines  58  and  60  can provide events to the logic circuit  52 . After any processing, combination, or the like, the event can be propagated to the various test and measurement instruments through event transmission lines  62  and  64 . 
     In an embodiment, the hub  18  can be configured as an aggregator of events. That is, the logic circuit of the hub  18  can be can be configured to propagate any event that the hub  18  receives. For example, the logic circuit  52  can include a logical OR of any received event. Thus, any event will generate an output event propagated to the test and measurement instruments. 
     However, in another embodiment, the hub  18  can be configured to combine events together. For example, the logic circuit  52  can include a logical AND of any received event. 
     Although a logical OR function and a logical AND function have been described above, any combination of events can be used. For example, a multi-gate logic system can be used to combine the events. In another example, a state machine can be used with the various events from the test and measurement instruments as inputs. 
     In particular, it should be noted that a test and measurement instrument can, but need not have any information regarding the combination of events in the logic circuit  52 . A test and measurement instrument can be configured to trigger on any event received from the hub  18 . As described above, the test and measurement instrument need not know the source of the event. 
     In an embodiment, the event received from the hub  18  can, but need not be the sole condition for triggering an acquisition. For example, the event received from a hub  18  can be combined just as any other event in the triggering system of the particular test and measurement instrument. Thus, an even more complex trigger can be generated than that resulting in the event received from the hub  18 . 
       FIG. 11  is a flowchart illustrating an example of a calibration of multiple test and measurement instruments. As described above, the maximum of the propagation times to the hub  18  or greater can be used to substantially synchronize events reaching the hub  18 . Thus, the individual test and measurement instruments need not know the source of any received event. 
     In an embodiment, to remove a need to know the source, a calibration can be performed. For example, in  80  a round-trip time of an event to and from the hub  18  can be measured for a first test and measurement instrument. In particular, the test and measurement instrument can be configured to cause the hub  18  to enter a configuration mode where the hub  18  returns an event received from the test and measurement instrument back to the test and measurement instrument. 
     For example, the test and measurement instrument can control the hub  18  to disregard any events received from other test and measurement instruments. As described above, if the logic circuit  52  of the hub  18  includes a logical AND operation, the other inputs to the logical AND operation can be set to a high level. Similarly, with a logical OR operation, the other inputs can be set to a logical low level. In another example, a state machine in the logic circuit  52  can be set to a state that disregards events from other test and measurement 
     Accordingly, the test and measurement instrument can generate an event and measure a time between that event and an event received from the hub  18 . As described above, events from the hub  18  can come from a variety of sources; however, in this calibration mode, the only event that will be propagated is an event from the test and measurement instrument currently performing a calibration. The round-trip time can be measured and used as described above. 
     Once the measurement is performed, the test and measurement instrument can pass control of the hub to another test and measurement instrument in  82 . In  84  the measurement in  80  and the passing of control in  82  can be repeatedly performed until there are no remaining test and measurement instruments coupled to the hub. Accordingly, each test and measurement instrument will have measured the round-trip time and can calculate the propagation time to the hub  18 . 
     In an embodiment, the test and measurement instrument that initiated the calibration can be configured to determine a maximum of the propagation times to the hub in  86 . Such a maximum can be determined in a variety of ways. For example, the test and measurement instrument can receive the round-trip times for each of the test and measurement instruments. The maximum can be calculated and divided in half to determine the maximum propagation time to the hub. Similarly, the test and measurement instrument can receive the propagation times individually calculated by the corresponding test and measurement instruments, then calculate a maximum. Moreover, the test and measurement instrument can select a time greater that the actual maximum as the maximum time. Thus, as described above, a time that is greater than or equal to the largest propagation time can be calculated and used in the triggering of acquisitions. 
     This maximum time can be communicated to each of the test and measurement instruments. For example, the test and measurement instruments can communicate with each other through the hub, another communication interface, such as an Ethernet interface, or the like. Accordingly, each test and measurement instrument can configure itself based on its own propagation time such that events arrive at the hub substantially simultaneously. As a result, in response to this maximum time, in  88  the test and measurement instruments can trigger an acquisition and the presentation of data can be substantially aligned in time as described above. 
     Although a test and measurement instrument has been described as initiating and/or controlling the calculation of such a maximum time, the maximum time can be calculated in other ways. For example, the hub  18  can initiate a calibration, and communicate to each test and measurement instrument in turn instructions to generate an event. The hub  18  can be configured to collect the various propagation times or round-trip times and communicate the calculated maximum to the test and measurement instruments. Accordingly, the test and measurement instruments can, but need not be aware of any other instruments. 
     Moreover, in an embodiment, such a calibration can be performed in response to various conditions. For example, as described above, the calibration can be initiated by one of the test and measurement instruments. A user can press a calibration button; select a calibration menu item, or the like. In another example, the calibration can be performed in response to the detection of a new test and measurement instrument. That is, a new test and measurement instrument can be coupled to the hub  18 . The new test and measurement instrument can inform the hub  18 , the other test and measurement instruments, or the like of its presence. In response a new calibration can be performed such that the propagation times for each of the test and measurement instruments including the new test and measurement instrument can be measured, combined into a maximum or the like, as described above. 
       FIG. 12  is a block diagram of a test and measurement instrument according to an embodiment. In an embodiment, the test and measurement instrument  100  includes an event generator  101 . The event generator  101  represents the systems that can generate the various events described above. For example, the event generator  101  can include the circuitry, pattern analysis, or the like to detect a transition, match a data pattern, or the like. The test and measurement instrument  100  can have any number of such event generators  101 . 
     The test and measurement instrument  100  includes a first event decoder  102 . The first event decoder  102  is configured to select an event from the first event decoder  102 , combine such events, or the like. The event decoder  102  can be configured to generate an event, propagate an event, or the like. 
     An event from the event decoder  102  can be delayed by the delay  104 . The delay  104  can be adjusted by the controller  110  such that a time through the delay  104  can be the difference time such as time T DA  described above. Thus, the event from the event decoder  102  can be delayed as described above before being output through the event output  22  to a hub  18 . 
     The test and measurement instrument can also include an event input  24  coupled to a second event decoder  108 . The second event decoder  108  can be substantially similar to the 
     Although an event from the event input  24  has been described as being input to the time measurement device  106  through the second event decoder  108 , the event input  24  can be directly coupled to the time measurement device  106 , coupled to a dedicated time measurement device  106  along with the first event decoder  102 , or the like. That is, the round-trip time, propagation time, or the like can be measured with the time measurement device  106  of the trigger circuitry as illustrated, a dedicated timer, or the like. 
     The controller  110  can be configured to trigger an acquisition of the acquisition system  112  in response to an event received through the input  24 . That is, the event received through the input  24  can be used by the controller  110  to trigger an acquisition similar to other events generated by the event decoder  108 . However, as described above, the time alignment of the data to data acquired by other test and measurement instruments can be skewed. Accordingly, the controller  110  can be configured to offset the acquired data in response to a time associated with the test and measurement instrument and at least one other test and measurement instrument. For example, such a time can be the time T MAX +T A  as described above 
     The controller  110  can also be coupled to a communication interface  114 . As a result, the controller can be configured to receive the propagation times, maximum time, or the like associated with the other test and measurement instruments. The controller  110  can then be configured to calculate the delay time for the delay  104 , an offset time for the time base, or the like as described above. 
     Although particular embodiments have been described, it will be appreciated that the principles of the invention are not limited to those embodiments. Variations and modifications may be made without departing from the principles of the invention as set forth in the following claims.