Patent Publication Number: US-2013245977-A1

Title: Test and measurement instrument and method for providing post-acquisition trigger control and presentation

Description:
RELATED APPLICATION DATA 
     This application is a division of copending U.S. patent application Ser. No. 12/576,034, filed Oct. 8, 2009, which claims the benefit of U.S. Provisional Application Ser. No. 61/240,054, filed Sep. 4, 2009, incorporated herein by reference. This application is related to U.S. Ser. No. 12/576,045, filed Oct. 8, 2009, now U.S. Pat. No. 8,024,141 B2, issued Sep. 20, 2011, entitled TEST AND MEASUREMENT INSTRUMENT AND METHOD FOR PROVIDING POST-ACQUISITION TRIGGER CONTROL AND PRESENTATION (Bartlett, et al.), which also claims the benefit of U.S. Provisional Application Ser. No. 61/240,054, filed Sep. 4, 2009. 
    
    
     BACKGROUND 
     This disclosure relates to test and measurement instruments, in particular to test and measurement instruments and methods relating to post-acquisition trigger control and presentation of associated waveforms on a display. 
     Modern digital oscilloscopes can acquire an electrical signal under test and store digital data corresponding to the acquired signal as a data record. Such oscilloscopes can be used to display one or more waveforms while acquiring the electrical signal under test. In addition, the previously-stored digital data from the data record can be viewed as a waveform on a display of the oscilloscope even though acquisition of the electrical signal under test has stopped. While older oscilloscopes would generally acquire a relatively small data record corresponding to an amount of time that could be displayed, advancements in the areas of memory speed, memory capacity, and processor speed have led to newer oscilloscopes having improved functionality in this area. Consider that most digital oscilloscopes now have the capability of storing a significantly larger data record, which corresponds to more time than can reasonably be displayed at once. 
     As a result of the larger data records, additional functionality can be made available to the user. For example, most oscilloscopes allow a user to adjust a horizontal or vertical control, thereby changing a position of the waveform on the display. In addition, some oscilloscopes allow a user to “scroll” through the waveform—particularly after the data record has been acquired. However, since the data record now represents much more time than can be displayed at one time, the user&#39;s time interval of interest may be short compared to the full acquired record, and scrolling through an entire data record can be impractical. This causes difficulty in finding and analyzing the time interval of interest. Moreover, the full record may contain other events of interest that are different from the one event being displayed. 
     Some oscilloscopes provide a search feature to flag events of interest in the data record. But due to the rapid advancements in memory capacities, the size of data records continues to expand, which can hinder or otherwise slow down conventional search techniques. In addition, none of the conventional approaches provide for post-acquisition trigger events that are controlled and displayed intuitively by emulating a live trigger mode using standard trigger controls. 
     SUMMARY 
     An embodiment of the invention can be implemented in a test and measurement instrument, comprising, for example, an input terminal to receive a signal under test, one or more analog-to-digital converters associated with the input terminal, the one or more analog-to-digital converters to receive the signal under test and to produce digital samples from the signal under test, and an acquisition memory to store the digital samples of the signal under test as a data record. A display device draws a waveform associated with the signal under test. A first trigger circuit having an input coupled to the input terminal detects a live trigger event in the signal under test based on first trigger criteria and causes an automatic adjustment of the waveform to conform with a time of the live trigger event. A user may halt the acquisition of the signal under test using an input control. A second trigger circuit detects a post-acquisition trigger event in the data record based on second trigger criteria and causes an automatic adjustment of the waveform to conform with a time of the post-acquisition trigger event. 
     Some embodiments include a method for displaying a waveform associated with a post-acquisition trigger on a test and measurement instrument, the method comprising, for example, acquiring data from a signal under test for storage in an acquisition memory as a data record and displaying a waveform associated with the signal under test while acquiring the data. After halting acquisition of the data record, standard trigger controls may be adjusted to select trigger criteria. A post-acquisition trigger event is detected in the data record based on the trigger criteria, and a position of the waveform is automatically shifted to conform with a time of the post-acquisition trigger event. 
     Another embodiment includes a test and measurement instrument, comprising, for example, an input terminal to receive a signal under test, one or more analog-to-digital converters associated with the input terminal, the one or more analog-to-digital converters to receive the signal under test and to produce digital samples from the signal under test, and an acquisition memory to store the digital samples of the signal under test as a data record. A display device draws a waveform associated with the signal under test. An analog trigger circuit includes an input coupled to the input terminal to detect a live trigger event in the signal under test based on first trigger criteria and causes an automatic adjustment to the waveform to conform with a time of the live trigger event. The test and measurement instrument may also include one or more digital-to-analog converters to receive the digital samples from the acquisition memory and to produce a converted analog signal. The analog trigger circuit may be configured to receive the converted analog signal to detect a post-acquisition trigger event in the data record based on second trigger criteria and to cause an automatic adjustment to the waveform to conform with a time of the post-acquisition trigger event. 
     In yet another example embodiment, a test and measurement instrument comprises an input terminal to receive a signal under test, an acquisition memory to store digital samples of the signal under test as a data record, a display device to draw a plurality of waveforms associated with the signal under test, a detector to detect a first trigger event in the signal under test based on first trigger criteria and to cause an adjustment of at least one of the plurality of waveforms during a live trigger mode to conform with a time of the first trigger event, and a second detector to detect second trigger events in the data record based on second trigger criteria. The test and measurement instrument may include first trigger controls to configure the first trigger criteria or the second trigger criteria, and second trigger controls to configure which of the second trigger events or waveforms are displayed on the display device. The first trigger controls may comprise standard trigger controls and the second trigger controls may comprise post-acquisition mode specific trigger controls. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a test and measurement instrument including an acquisition and trigger unit, a controller, and a display unit according to an example embodiment. 
         FIG. 2  is a block diagram illustrating additional example elements of the acquisition unit, the controller, and the display unit of  FIG. 1 . 
         FIG. 2A  is a block diagram illustrating additional example elements of the trigger control of  FIG. 2 . 
         FIG. 3  is an example plot of a sampled electrical signal in a live-acquisition mode showing waveforms having associated therewith certain trigger-related aspects according to an embodiment of the invention. 
         FIG. 4  is an example plot of a sampled electrical signal in a post-acquisition mode showing previously-acquired waveforms of  FIG. 3  according to an embodiment of the invention. 
         FIG. 5  is an example plot of a sampled electrical signal in a post-acquisition mode showing previously-acquired waveforms of  FIG. 3  according to an embodiment of the invention. 
         FIG. 6  is an example plot of a sampled electrical signal in a post-acquisition mode showing a previously-acquired waveform according to an embodiment of the invention. 
         FIG. 7  is an example plot of a sampled electrical signal in a live-acquisition mode showing waveforms having associated therewith trigger-related aspects as selected during the post-acquisition mode. 
         FIG. 8  is a block diagram illustrating additional example elements of the post- acquisition trigger circuit of  FIG. 1 . 
         FIG. 9  is an example plot of a sampled electrical signal showing one or more waveforms in a live-acquisition mode having associated therewith certain trigger-related aspects according to yet another embodiment. 
         FIG. 10  is an example plot of a sampled electrical signal in a post-acquisition mode showing previously-acquired one or more waveforms of  FIG. 9  according to an embodiment of the invention. 
         FIG. 11  is an example plot of a sampled electrical signal in a post-acquisition mode showing the previously-acquired one or more waveforms of  FIG. 9  according to an embodiment of the invention. 
         FIG. 12  is an example plot of a sampled electrical signal in a post-acquisition mode showing the previously-acquired one or more waveforms of  FIG. 9  according to an embodiment of the invention. 
         FIG. 13  is an example plot of a sampled electrical signal in a live-acquisition mode showing the one or more waveforms having associated therewith trigger-related aspects as selected during the post-acquisition mode. 
         FIG. 14  is a block diagram illustrating an example configuration of a memory included in the post-acquisition trigger circuit of  FIG. 8 . 
         FIG. 15  is a block diagram illustrating another example configuration of a memory included in the post-acquisition trigger circuit of  FIG. 8 . 
         FIG. 16  is a block diagram illustrating yet another example configuration of a memory included in the post-acquisition trigger circuit of  FIG. 8 , and its relation to columns of a display. 
         FIGS. 17 and 18  are example plots of sampled electrical signals in a post-acquisition mode showing previously-acquired waveforms and associated trigger related aspects, according to an embodiment of the invention. 
         FIG. 19  is a block diagram illustrating a test and measurement instrument including an acquisition memory, an analog trigger circuit, and various analog-to-digital converters and digital-to-analog converters, according to an example embodiment. 
         FIG. 20  is a flow diagram illustrating a technique for configuring post-acquisition triggers and adjusting a corresponding waveform according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments include, for example, test and measurement instruments and techniques for providing post-acquisition trigger control and presentation of associated waveforms on a display. In particular, in one embodiment, the test and measurement instrument includes a trigger circuit to automatically adjust a waveform to conform with a time of a post-acquisition trigger event. The test and measurement instrument may include a trigger control to configure live trigger criteria for detecting a live trigger event and post-acquisition trigger criteria for detecting the post-acquisition trigger event after the acquisition of waveform data has halted. A user can adjust the post-acquisition trigger criteria and preview how the next live waveform acquisition will appear. When the acquisition of the live waveform(s) resume, the live trigger criteria substantially matches the previous post-acquisition trigger criteria. 
     For example, the trigger control includes a trigger level control to select trigger points associated with the live trigger event and the post-acquisition trigger event. An adjustment to the trigger level control after the acquisition of waveform data has halted can cause a waveform associated with previously acquired data to be automatically adjusted, thereby conforming to a time of the post-acquisition trigger event. Upon resumption of the live-acquisition of data, the live waveform(s) may conform to the newly selected trigger criteria as previewed during the post-acquisition mode. 
     In addition, during the post-acquisition mode, the user may quickly find an unusual waveform by simultaneously viewing multiple trigger events or waveforms associated with a given data record, and then using a range control to progressively increase or decrease the number of trigger events displayed, and/or the number of waveforms displayed. These and other inventive aspects will now be discussed in further detail. 
       FIG. 1  is a block diagram of a test and measurement instrument  100  including an acquisition and trigger unit  105 , a controller  130 , and a display unit  135  according to an example embodiment. The test and measurement instrument  100  may be a digital oscilloscope, for example, and for the sake of brevity but not limitation, will generally be referred to as such. The oscilloscope  100  may have multiple channels or inputs suitable for use with various embodiments as described herein. Although the oscilloscope may have a single input terminal  110 , inventive aspects described are equally applicable to an oscilloscope having four inputs, or any number of inputs. 
     The acquisition and trigger unit  105  of the oscilloscope  100  may include a digital acquisition memory  115 . Although the acquisition memory  115  is shown as a single block, which can represent a single memory, it should be understood that the acquisition memory  115  can include multiple discrete memories. In that scenario, each discrete memory can operate individually with respect to the various inputs  110 , or alternatively, the discrete memories can operate collectively to one or more of the inputs  110 . For example, as certain input terminals  110  are deselected, an increased memory depth can be applied to the remaining selected inputs  110 . It should be understood that the inventive aspects contemplate a data record  117  holding any one of filtered, compressed, unfiltered, or uncompressed raw data. In addition, while one data record  117  is shown, it should be understood that one or more data records  117  may be stored in the acquisition memory  115 . 
     The acquisition and trigger unit  105  can include one or more analog-to-digital converters (ADC)  108  and a live trigger circuit  120 . The live trigger circuit  120  includes an input coupled to one or more of the input terminals  110 , for example, after the ADCs  108 . It should be understood that an alternative embodiment includes the live trigger circuit  120  coupled to one or more of the input terminals  110  before the ADCs  108 . An electrical signal under test is received at one or more of the input terminals  110 . The live trigger circuit  120  can detect a live trigger event in the signal under test based on first trigger criteria selected by the user, and can cause an automatic adjustment of the waveform to conform with a time of the live trigger event. 
     The acquisition and trigger unit  105  can also include a post-acquisition trigger circuit  125 . The trigger circuits  120  and  125  may be implemented by hardware, software, or by any combination thereof. After the acquisition of data has stopped, the post-acquisition trigger circuit  125  can detect a post-acquisition trigger event in the data record  117  based on second trigger criteria selected by the user. The post-acquisition trigger circuit  125  can cause an adjustment of the waveform to conform to a time of the post-acquisition trigger event. These and other aspects of the acquisition memory and trigger circuits will be described in further detail below. 
     The live trigger circuit  120  and the post-acquisition circuit  125 , while shown as two separate circuits, may be implemented with one set of hardware serving both the live trigger circuit function and the post-acquisition circuit function, for example, at different times. Alternatively, the live trigger circuit  120  and the post-acquisition circuit  125  are separate from each other, each of which may include similar circuits as the other. 
     The acquisition and trigger unit  105  may be operatively coupled to the controller  130 . The controller  130  may be operatively coupled to the display unit  135 , and may process the sampled data streams provided by the acquisition and trigger unit  105  for display by the display unit  135 . For example, given desired time per division and volts per division display parameters of the oscilloscope  100 , the controller  130  may modify and then render the raw data associated with an acquired sample data stream to produce a corresponding waveform image having the desired time per division and volts per division parameters. 
       FIG. 2  is a block diagram illustrating additional example elements of the acquisition and trigger unit  105 , the controller  130 , and the display unit  135  of  FIG. 1 . Probes  205  are operatively associated with the other elements of the acquisition and trigger unit  105 . The probes  205  may be any conventional voltage or current probes suitable for respectively detecting one or more electrical signals, such as analog voltage or current signals from a circuit under test (not shown). For example, the probes  205  may be provided by Tektronix®, Inc., such as active probe model numbers P1075, TCP105, among others, which may be used to acquire real time electrical signal information. The output signals of probes  205  are sent to the analog-to-digital converters (ADCs)  208 , which sample and digitize the electrical signals. Thereafter, the digital samples are eventually stored as the data record  117  in the acquisition memory  115 . 
     The acquisition and trigger unit  105  is operatively coupled to the controller  130 . The controller  130  may include, for example, a processor  210 , support circuits  220 , input/output (I/O) circuits  215 , memory  225 , and a trigger control  230 . As such, it is contemplated that some of the processes discussed herein may be implemented as software processes in processor  210 , and some of the processes discussed herein may be implemented within hardware, for example, as circuitry that cooperates with processor  210  to perform various functions. In addition, some of the processes discussed herein may be implemented using a combination of software, hardware, firmware, or other execution or storage means. The information stored in the acquisition memory  115  may be transmitted to the processor  210  or the post-acquisition trigger circuit  125 . In addition, the processor  122  may transmit control information to the acquisition memory  115  or the post-acquisition trigger circuit  125 . 
     The I/O circuits  215  may form an interface between the various elements communicating with the controller  130 . For example, the I/O circuits  215  may comprise an interconnection to a keypad, pointing device, touch screen, external PC, or other peripheral devices adapted to provide user input and output to the controller  130 . The controller  130 , in response to such user input, may control the operations of the acquisition and trigger unit  105 , and to perform various functions, in particular filtering or other compression operations, but also including such operations as data acquisitions or processing, among other possibilities. 
     The memory device  225  is operatively associated with the processor  210 . The acquisition memory  115  and the memory device  225  may include volatile memory, such as SRAM, DRAM, among other volatile memories. These memories may also include non- volatile memory devices, such as a disk drive or a tape medium, among others, or programmable memory, such as an EPROM, EEPROM, or flash memory, among other possibilities. 
     Although the controller  130  of  FIG. 2  is depicted as a general purpose computer or microprocessor that is programmed to perform various control functions in accordance with embodiments of the present invention, the embodiments may be implemented in hardware such as, for example, an application specific integrated circuit (ASIC). As such, it is intended that the controller  130 , as described herein, be broadly interpreted as being equivalently performed by hardware, software, or by any combination thereof. 
     It will be appreciated by those skilled in the art that standard signal processing components (not shown), such as signal buffering circuitry, signal conditioning circuitry, display drivers, and the like are also employed as required to enable the various interface functions described herein. For example, the ADCs  208  sample the electrical signals under test at a sufficiently high rate to enable appropriate processing by the controller  130  or the processing circuits  240  of the display unit  135 . In this regard, the ADCs  208  may sample their respective input electrical signals in accordance with a sample clock provided by an internal sample clock generator (not shown), which may be a part of, for example, the support circuits  220 . 
     Controller  130  provides the waveform data to the display unit  135 . The display unit  135  includes processing circuits  240  for subsequent presentation of the waveform data on a display device  250 . The processing circuits  240  may include data processing circuitry suitable for converting acquired data streams or waveform data into video images or video signals, which are adapted to provide visual imagery (e.g., video frame memory, display formatting and driver circuitry, and the like). The processing circuits  240  interface with a memory  245 , also included in the display unit  135 , which may be arranged in memory planes, and may be configured to store the video images, among other possibilities. The processing circuits  240  and/or the memory  245  provide output signals suitable for use by a display device  250 . User input received through I/O circuits  215  or trigger control  230 , for example, may be used to adjust automatic calibration functions, or to adapt other operating parameters of the processing circuits  240  or of display device  250 . The display device  250  may be configured to display the video images and to shift or otherwise adjust a waveform responsive to trigger events when in a post-acquisition mode, as will further be described in detail below. 
     The live trigger circuit  120  includes an input coupled to one or more of the lines associated with probes  205 , for example, after the ADCs  208 . It should be understood that an alternative embodiment includes the live trigger circuit  120  coupled to one or more of the lines associated with probes  205  before the ADCs  208 . The live trigger circuit detects a live trigger event in the signal under test based on predefined trigger criteria selected by the user using the trigger control  230 . As a result, the live trigger circuit  120  can cause an automatic adjustment of the waveform on the display device  250  to conform to a time of the live trigger event. 
     Conversely, the post-acquisition trigger circuit  125  can be operatively coupled to the acquisition memory  115  and receive the digital samples of the data record  117  after the electrical signal under test has been converted and digitized using the ADCs  208 , and after the acquisition period has stopped. The post-acquisition trigger circuit  125  can detect a post-acquisition trigger event in the data record based on predefined trigger criteria selected by the user using the trigger control  230 . As a result, the post-acquisition trigger circuit  125  can cause an automatic adjustment of the waveform on the display device  250  to conform to a time of the post-acquisition trigger event. 
     As previously mentioned, the live trigger circuit  120  and the post-acquisition circuit  125 , while shown as two separate circuits, may be implemented with one set of hardware serving both the live trigger circuit function and the post-acquisition circuit function, for example, at different times. Alternatively, the live trigger circuit  120  and the post-acquisition circuit  125  are separate from each other, each of which may include similar circuits as the other. 
       FIG. 2A  is a block diagram illustrating additional example elements of the trigger control  230  of  FIG. 2 . Standard controls  232  may include standard trigger level control(s)  235 , standard slope control(s)  237  and/or other standard control(s)  239 . Specific controls  252  may include next control(s)  255 , first control(s)  257 , display-all control(s)  259 , previous control(s)  261 , last control(s)  263 , display N control(s)  265 , event range control(s)  267 , waveform range control(s)  268 , and/or other specific control(s)  269 . 
     The term “standard” as used herein refers to a type of physical controls with which skilled users of oscilloscopes are generally familiar, such as the trigger level control(s)  235  or the slope control(s)  237 . The standard controls  232  can include a knob, a switch, an actuator, or any other suitable interface; however, the term “standard” does not necessarily impart any particular class of function performed by the controls  232 . In other words, in one scenario, the “standard” controls  232  may be used to perform a function generally and immediately recognizable to the skilled user, or alternatively as will be further described herein, the “standard” controls may be used in conjunction with new implementations or embodiments of the present invention, such as in relation to a post-acquisition trigger mode. 
     The term “specific” as used herein refers to a type of physical controls that are specifically used while the oscilloscope is operating in a predefined mode. For example, the specific controls  252  may be used in a post-acquisition mode to further refine or otherwise configure how trigger events or waveforms are displayed on the display device  250 . The specific controls  252  can include a knob, a switch, an actuator, or any other suitable interface. 
     The detailed operational features of each of the control illustrated in  FIG. 2A  will be described in additional detail below in conjunction with, for example,  FIGS. 3-15 . 
       FIG. 3  is an example plot  301  of a sampled electrical signal in a live-acquisition mode showing waveforms  306  having associated therewith certain trigger-related aspects according to an embodiment of the invention. While the example plot  301  shows pulsed waveforms for the sake of explaining one aspect of the invention, the inventive aspects are not limited thereto, and can include any number of possible waveform types, and any number of concurrently displayed waveforms. In the live-acquisition mode, waveforms  306  are continually being drawn as the acquisition and sampling of the electrical signal is ongoing. Each of the waveforms  306  are similar to one another, and when drawn together on example plot  301 , appear as substantially a single waveform  306 . In an alternative embodiment, there could be multiple different types of waveforms (not shown) acquired through different inputs  110  of the digital oscilloscope  100 , and concurrently displayed. 
     The waveforms  306  have associated therewith certain trigger-related aspects. For example, live trigger criteria can be configured by a user. In this example plot, the live trigger criteria includes a trigger point  311 , the position of which can be indicated on the display using a graphical “T” or other suitable marker. The trigger point  311  is associated with “time zero” graphical marker  312  and predefined trigger level  316 . Further, the live trigger criteria associated with the waveforms  306  illustrated in  FIG. 3  includes a rising-edge operating mode, thereby triggering on the rising-edge of the waveforms  306 . The live trigger criteria cause a trigger event at  311 , and the waveforms  306  are displayed at least from the trigger event  311  and onward in time. In other words, the waveforms  306  are displayed live where each waveform  306  is drawn on the display so that the trigger event  311  (determined by the live trigger criteria) is placed at the trigger time  312 . 
     The user may configure the live trigger criteria using standard trigger control(s)  232  (of  FIG. 2A ). For example, the trigger level control  235  can be used to adjust the trigger level  316 . Once the user has decided on the trigger level such as level  316 , the trigger point  311  is selected and the user can use the slope control  237  to choose, for example, the rising-edge operating mode. The waveform will then automatically conform to the live trigger criteria. 
       FIG. 4  is an example plot  401  of a sampled electrical signal in a post-acquisition mode showing previously-acquired waveform(s)  406  according to an embodiment of the invention. When live-acquisition mode is halted, the display  401  will initially look substantially the same as the display  301  associated with the live-acquisition mode, except that new waveforms are not being drawn. In other words, in the post-acquisition mode, a user has manually stopped the live acquisition of data by using, for example, one of the input/output circuits  215  ( FIG. 2 ) of the oscilloscope  100 . While the example plot  401  shows pulsed waveforms for the sake of explaining one aspect of the invention, the inventive aspects are not limited thereto, and can include any number of possible waveform types, and any number of concurrently displayed waveforms. 
     In the post-acquisition mode, acquisition of the electrical signal has been halted, and the waveform(s)  406  are generated and displayed using digital samples from the data record  117  stored in the acquisition memory  115  (of  FIGS. 1 and 2 ). In other words, the input (or channel) of the oscilloscope  100  associated with the waveform(s)  406  is no longer in a live mode, but rather, is in a post-acquisition mode. 
     As shown in  FIG. 4 , the waveform(s)  406  represent only a small portion of the digital samples stored in the data record  117 . The amount of information shown in waveform(s)  406  can be adjusted, for example, by using horizontal or vertical scale controls (not shown). Making such adjustments allows the waveform(s)  406  and the trigger point  411  to “scroll” or otherwise be moved over the range of the display  401  or beyond the edges of the display  401 . Such scrolling does not change the trigger criteria itself. For the sake of illustrating embodiments of the invention, the waveform(s)  406  will not be moved using the horizontal or vertical position controls, and the trigger “time zero”  412  associated with the trigger point  411  will be maintained substantially at a top-center or center position on the display  401 . 
       FIG. 5  is an example plot  501  of a sampled electrical signal in a post-acquisition mode showing previously-acquired waveforms  406  and  506  according to an embodiment of the invention. When the acquisition of data has been halted, and when the user changes a standard trigger control  232 , such as in this case adjusting the trigger level control  235  (of  FIG. 2A ) so that the trigger level  516  is adjusted slightly downward, and adjusting the slope control  237  from the rising-edge to a falling-edge operating mode, the last acquired waveform  506  is redrawn on the display according to the new trigger criteria, which now corresponds to the post-acquisition trigger criteria. 
     In other words, the post-acquisition trigger circuit  125  (of  FIG. 1 ) detects a post-acquisition falling-edge trigger event  511  that is nearest to the previous trigger point  411  and adjusts the last-acquired waveform  506  so that the selected falling edge trigger event  511  is now displayed at the trigger time  412 . For example, the post-acquisition trigger circuit  125  detects the post-acquisition falling-edge trigger event  511  in the data record  117  based on the post-acquisition trigger criteria selected by the user, and causes an automatic adjustment (e.g., shifting) of the last acquired waveform  506  to conform with a time of the post-acquisition trigger event  511 . Any of the standard trigger controls  232  can be used to adjust the post-acquisition trigger criteria. In so doing, the post-acquisition trigger circuit  125  can adjust the last acquired waveform  506  to match the newly selected trigger criteria, after the acquisition of data has halted, and using one or more standard trigger control  232 . 
     Further relating to the controls, the trigger control  230  (of  FIGS. 2 and 2A ) is used to configure trigger criteria for both a live trigger event and a post-acquisition trigger event. The trigger control  230  can include standard trigger controls, as previously mentioned. The standard trigger level control  235  varies the voltage on the waveform at which point a trigger event will be generated. The trigger control  230  may include other controls such as the slope control  237 , which allows the user to select the rising-edge or falling-edge operating mode at the selected trigger level. 
     The trigger level control  235  may be used to select one trigger point for the live trigger event and to select another trigger point for the post-acquisition trigger event. In the post-acquisition mode, the post-acquisition trigger circuit  125  can detect a post-acquisition trigger event in the data record based on predefined trigger criteria selected by the user using the trigger control  230 , such as the standard trigger level control  235  and the standard slope control  237 . In this manner, the user can use trigger controls with which he or she has the most familiarity to perform triggering operations both in the live trigger mode and in the post-acquisition trigger mode, i.e., after the acquisition of data has been stopped. 
     The previously acquired waveform(s)  406  are preferably removed when a user adjusts a control during the post-acquisition mode, and the last acquired waveform  506  is displayed according to the post-acquisition trigger criteria. Nevertheless, in an alternative embodiment, the previously acquired waveform(s)  406  can remain on the display  501  to provide a comparison or reference to the automatically adjusted last acquired waveform  506 , among other reasons. Alternatively, the previously acquired waveform(s)  406  can be dimmed, or as mentioned above, removed from the display  501 . In addition, although the waveform  506  is referred to as the “last” acquired waveform, any of the waveforms that were previously acquired can be automatically or manually selected as the waveform  506 , which need not be the “last” acquired waveform, and can then be automatically adjusted based on the post-acquisition trigger criteria. 
       FIG. 6  is an example plot  601  of a sampled electrical signal in a post-acquisition mode showing previously-acquired waveform  506  according to an embodiment of the invention. Here, the last-acquired waveform  506  is displayed without displaying the previously acquired waveform(s)  406 , after the user has selected and applied the post-acquisition trigger criteria. The post-acquisition trigger circuit  125  has found the post-acquisition falling-edge trigger event  511  that was nearest to the previous trigger point  411  and has caused the last acquired waveform  506  to be re-drawn or otherwise re-positioned while in the post-acquisition or stopped mode. 
       FIG. 7  is an example plot  701  of a sampled electrical signal in a live-acquisition mode showing waveform(s)  706  having associated therewith trigger-related aspects as selected during the post-acquisition mode. Specifically, the trigger criteria as selected during the post-acquisition mode, such as trigger point  511 , is shown operating on the waveform(s)  706  in a live-acquisition mode. In other words, the user was able to preview the effect that the post-acquisition trigger criteria would have on live-acquired waveforms, such as waveform(s)  706 . 
     To further appreciate the various live trigger criteria and post-acquisition trigger criteria, and how they can interrelate, consider that the live trigger criteria operating on the waveform(s)  706  can essentially match the post-acquisition trigger criteria as selected and previewed by the user during the post-acquisition mode. In addition, the user can use the same trigger controls to adjust both the live trigger criteria and the post-acquisition trigger criteria. An adjustment to the post-acquisition trigger criteria can automatically change the live-acquisition trigger criteria. Similarly, an adjustment to the live-acquisition trigger criteria can automatically change the post-acquisition trigger criteria. Although the trigger controls used to adjust the live-acquisition and post-acquisition trigger criteria need not be identical, such is the preferred approach for intuitive ease-of-use of the digital oscilloscope  100 . 
       FIG. 8  is a block diagram illustrating additional example elements of the post-acquisition trigger circuit  125  of  FIG. 1 . For example, the post-acquisition trigger circuit  125  may include a first memory  705  and a second memory  710 . While two memories are shown for exemplary purposes, it should be understood that any number of memories may be included in the post-acquisition trigger circuit. Some of the elements shown in  FIG. 8  correspond to elements previously discussed with reference to  FIG. 1 , and therefore, need not be repeated. 
     The first memory  705  can store a trigger point immediately before a previous trigger point, and the second memory can store a trigger point immediately after the previous trigger point. A comparator  715  can compare the trigger point immediately before the previous trigger point to the previous trigger point, and can compare the trigger point immediately after the previous trigger point to the previous trigger point. This technique will be further described with reference to  FIGS. 9 to 13 . 
       FIG. 9  is an example plot  800  of a sampled electrical signal showing one or more waveforms  805  in a live-acquisition mode having associated therewith certain trigger-related aspects according to yet another embodiment. While the example plot  800  shows a sinusoidal wave for the sake of explaining one aspect of the invention, the inventive aspects are not limited thereto, and can include any number of possible waveform types, and any number of concurrently displayed waveforms. In the live-acquisition mode, the one or more waveforms  805  are continually being drawn as the acquisition and sampling of the electrical signal is ongoing. In an alternative embodiment, there could be multiple different types of waveforms (not shown) acquired through different inputs  110  of the digital oscilloscope  100 , and concurrently displayed. 
     The one or more waveforms  805  have associated therewith certain trigger-related aspects. For example, live trigger criteria can be configured by a user. In this example plot, the live trigger criteria includes a trigger point  811 , the position of which can be indicated on the display using a graphical “T” or other suitable marker. The trigger point  811  is associated with “time zero” marker  812  and predefined trigger level  815 . Further, the live trigger criteria associated with the waveforms  805  illustrated in  FIG. 9  includes a rising-edge operating mode, thereby triggering on the rising-edge of the one or more waveforms  805 . The live trigger criteria cause a trigger event at  811 , and the one or more waveforms  805  are displayed from the trigger event  811  and onward in time. In other words, the one or more waveforms  805  are displayed live where each of the one or more waveforms  805  is drawn on the display so that the trigger event  811  (determined by the live trigger criteria) is placed at the trigger time  812 . 
     The user may configure the live trigger criteria using trigger control  230  (of  FIG. 2 ). For example, the trigger level control  235  can be used to adjust the trigger level  815 . Once the user has decided on the trigger level such as level  815 , the trigger point  811  is selected and the user can use the slope control  237  to choose, for example, the rising-edge operating mode, such as shown here. The waveform will then automatically conform to the live trigger criteria. 
       FIG. 10  is an example plot  1000  of a sampled electrical signal in a post-acquisition mode showing previously-acquired one or more waveforms  805  according to an embodiment of the invention. When live-acquisition mode is halted, the display  1000  will initially look substantially the same as the display  800  associated with the live-acquisition mode, except that new waveforms are not being drawn. In other words, in the post-acquisition mode, a user has manually stopped the live acquisition of data by using, for example, one of the input/output circuits  215  ( FIG. 2 ) of the oscilloscope  100 . While the example plot  1000  shows a sinusoidal waveform for the sake of explaining one aspect of the invention, the inventive aspects are not limited thereto, and can include any number of possible waveform types, and any number of concurrently displayed waveforms. 
     In the post-acquisition mode, acquisition of the electrical signal has been halted, and the one or more waveforms  805  are generated and displayed using digital samples from the data record  117  stored in the acquisition memory  115  (of  FIGS. 1 and 2 ). In other words, the input (or channel) of the oscilloscope  100  associated with the one or more waveforms  805  is no longer in a live mode, but rather, is in a post-acquisition mode. 
     As shown in  FIG. 10 , the one or more waveforms  805  represent only a small portion of the digital samples stored in the data record  117 . The lines  820  and  825  signify that the data record represents much more time than the time interval of interest that can be displayed at one time on the display. The amount of information shown in the one or more waveforms  805  can be adjusted, for example, by using horizontal or vertical scale controls (not shown). Making such adjustments allows the one or more waveforms  805  and the trigger point  811  to “scroll” or otherwise be moved over the range of the display  1000  or beyond the edges of the display  1000 . Such scrolling does not change the trigger criteria itself. For the sake of illustrating embodiments of the invention, the one or more waveforms  805  will not be moved using the horizontal or vertical position controls, and the trigger “time zero”  812  associated with the trigger point  811  will be maintained substantially at a top-center or center position on the display  1000 . 
       FIG. 11  is an example plot  1100  of a sampled electrical signal in a post-acquisition mode showing the previously-acquired one or more waveforms  805  according to an embodiment of the invention. When the acquisition of data has been halted, and when the user changes a trigger control, such as in this case adjusting the trigger level control  235  (of  FIG. 2A ) so that the trigger level  915  is adjusted downward, the post-acquisition trigger control circuit  125  the post-acquisition trigger circuit can automatically determine the next post-acquisition trigger point. 
     For example, the previous trigger event  811  is associated with a previous trigger point  811  selected by the user. The first memory  705  (of  FIG. 7 ) of the post-acquisition trigger circuit  125  can store a trigger point  830 , which is immediately before the previous trigger point  811 . The second memory  710  of the post-acquisition trigger circuit  125  can store a trigger point  835 , which is immediately after the previous trigger point  811 . A comparator  715  of the post-acquisition trigger circuit  125  can compare the trigger point  830  immediately before the previous trigger point  811  to the previous trigger point  811 , and can compare the trigger point  835  immediately after the previous trigger point  811  to the previous trigger point  811 . In this manner, the comparator  715  can select the trigger point closest to the previous trigger  811  point as a new trigger point, in this case, trigger point  830 . For further clarification, consider that the distance  840  between point  830  and point  811  is shorter than the distance  845  between point  835  and  811 . Therefore, the trigger point  830  is automatically selected as the new trigger point. 
       FIG. 12  is an example plot  1200  of a sampled electrical signal in a post-acquisition mode showing the previously-acquired one or more waveforms  805  according to an embodiment of the invention. After the acquisition of data has been halted, and after the user has changed a trigger control, such as in this case adjusting the trigger level control  235  (of  FIG. 2A ), one or more of the waveforms  805  is redrawn on the display according to the new trigger criteria, which now corresponds to the post-acquisition trigger criteria. 
     In other words, the post-acquisition trigger circuit  125  (of  FIG. 1 ) detects a post-acquisition rising-edge trigger event  830  that is nearest to the previous trigger point  811  and adjusts one or more of the waveforms  805  so that the selected rising-edge trigger event  911  is now displayed at the trigger time  812 . For example, the post-acquisition trigger circuit  125  detects the post-acquisition rising-edge trigger event  830  stored in the first memory  705  based on the post-acquisition trigger criteria selected by the user, and causes an automatic adjustment (e.g., shifting) of one or more of the waveforms  805  to conform with a time of the post-acquisition trigger event  911 . 
     More specifically, the one or more waveforms  805  is shifted as indicated by the arrow  905  so that the trigger event  911  now corresponds to the trigger criteria as previously selected by the user, and as automatically applied using the comparator  715  of the post-acquisition trigger circuit  125 . Any of the standard trigger level controls  235  can be used to adjust the post-acquisition trigger criteria. In so doing, the post-acquisition trigger circuit  125  can adjust one or more of the waveforms  805  to match the newly selected trigger criteria, after the acquisition of data has halted, and using one or more standard trigger control  230 . 
       FIG. 13  is an example plot  1300  of a sampled electrical signal in a live-acquisition mode showing the one or more waveforms  805  having associated therewith trigger-related aspects as selected during the post-acquisition mode. Specifically, the trigger criteria as selected during the post-acquisition mode, such as trigger point  911 , is shown operating on the one or more waveforms  805  in a live-acquisition mode. In other words, the user was able to preview the effect that the post-acquisition trigger criteria would have on live-acquired waveforms, such as the one or more waveforms  805 . 
     To further appreciate the various live trigger criteria and post-acquisition trigger criteria, and how they can interrelate, consider that the live trigger criteria operating on the one or more waveforms  805  essentially match the post-acquisition trigger criteria as selected and previewed by the user during the post-acquisition mode. In addition, the user can use the same trigger controls to adjust both the live trigger criteria and the post-acquisition trigger criteria. An adjustment to the post-acquisition trigger criteria can automatically change the live-acquisition trigger criteria. Similarly, an adjustment to the live-acquisition trigger criteria can automatically change the post-acquisition trigger criteria. Although the trigger controls used to adjust the live-acquisition and post-acquisition trigger criteria need not be identical, such is the preferred approach for intuitive ease-of-use of the digital oscilloscope  100 . 
       FIG. 14  is a block diagram illustrating an example configuration of a memory  750 , which may be included in the post-acquisition trigger circuit  125  of  FIG. 8 . The memory  750  can store information about all post-acquisition trigger events T associated with a previously acquired data record, such as trigger event  1 , trigger event  2 , trigger event  3 , etc., through trigger event T. The information can include a time or place of each of the post-acquisition trigger events. 
       FIG. 15  is a block diagram illustrating another example configuration of a memory  755 , which can be included in the post-acquisition trigger circuit  125  of  FIG. 8 . Because of limited memory space, in some cases only a portion of the trigger events can be saved. For example, the memory  755  can store information about a portion of the post-acquisition events, such as trigger event  1 , trigger event  3 , trigger event  5 , and trigger event N. In other words, the memory  755  may store information about N post-acquisition trigger events, where N is less than the total number of post-acquisition trigger events T associated with the data record. The information can include a time or place of each of the post-acquisition trigger events. 
       FIG. 16  is a block diagram illustrating yet another example configuration of a memory  760 , which can be included in the post-acquisition trigger circuit  125  of  FIG. 8 , and its relation to columns of a display  1600 . The memory  760  may have one memory location for each column of the display  1600 . Each of the memory locations, such as memory location  1 , memory location  2 , memory location  3 , etc., through memory location C, may be associated with a corresponding one of the columns, such as column  1 , column  2 , column  3 , etc., through column N, of the display  1600 . The memory location for each column can store information regarding whether a trigger event occurred at the time or place of the associated column. In this embodiment, the memory  760  need only be as large as the width of the display associated with the display device  250 . In other words, when there is a one-to-one mapping of memory locations to columns, the value of N equals the value of C. A width of a “column” can be larger or smaller than a pixel. In other words, the width of a column can be less than a width of a single pixel, or alternatively, the width of a column can be greater than or equal to the width of a pixel. Interpolation or fractional mapping can be used to map one or more memory locations to each column, or to map a single memory location to one or more columns. 
       FIGS. 17 and 18  are example plots  1700  and  1800  of sampled electrical signals in a post-acquisition mode showing previously-acquired waveforms (e.g.,  1715 ,  1720 , and  1725 ) and associated trigger related aspects, according to an embodiment of the invention. The following description makes reference to both of  FIGS. 17 and 18 . 
     The lines  1750  and  1760  signify that the data record represents much more time than the time interval of interest that can be displayed at one time on the display, for any given waveform. While the example plots  1700  and  1800  show sinusoidal waves for the sake of explaining one aspect of the invention, the inventive aspects are not limited thereto, and can include any number of possible waveform types, and any number of concurrently displayed waveforms. 
     A trigger circuit, such as the trigger circuit  125  of  FIG. 1 , can detect one or more post-acquisition trigger events in the data record based on trigger criteria, as discussed above. A display device, such as display device  250  of  FIG. 2 , can output a display, such as the display  1700  of  FIG. 17  or  1800  of  FIG. 18 . The display device can adjust the display of the one or more post-acquisition trigger events and waveforms associated with a data record in response to one or more configurable trigger controls, such as the standard controls  232  or the specific controls  252  mentioned above with reference to  FIG. 2A . 
     The trigger controls can be configured by a user to cause more than one trigger event, such as trigger events  1770 ,  1775 , or  1780  to be displayed simultaneously with more than one waveform from the same data record, such as waveforms  1715 ,  1720 , and  1725 . For example, the display-all control(s)  259  can cause all post-acquisition trigger events associated with the data record to be simultaneously displayed. Alternatively, the display N control(s)  265  can cause N number of post-acquisition trigger events associated with the data record to be simultaneously displayed. 
     The display device  250  can mark each of the post-acquisition trigger events with a graphical marker, such as marker  1710 , toward a top area or top center area of the display device, and/or the letter T, or some other suitable marker, as shown at  1770 ,  1775 , or  1780 . The graphical marker  1710  corresponds to a trigger time of the post-acquisition trigger event or events. There can be more than one graphical marker corresponding to more than one trigger time of the post-acquisition trigger events, any of which can be simultaneously displayed. 
     In another example embodiment, the event range control(s)  267  is configurable to gradually adjust a range of the number of post-acquisition trigger events (e.g.,  1770 ,  1775 , and  1780 ) associated with the data record to be simultaneously displayed. Alternatively, the waveform range control(s)  268  is configurable to gradually adjust a range of the number of waveforms (e.g.,  1715 ,  1720 , and  1725 ) associated with the data record to be simultaneously displayed. The event range control(s)  267  and the waveform range control(s)  268  can be one in the same range control or controls, or can be different controls. These controls allow the range or ranges to be decreased or otherwise increased or varied until just a single waveform  1725  associated with a single trigger event  1780  is displayed, as shown in  FIG. 18 . 
     In this manner, by simultaneously viewing multiple waveforms from the same data record, and then narrowing the waveforms to a single waveform of interest, any unusual waveform such as  1725  or unusual portion of the waveform such as spike  1790  can be quickly found and viewed. In other words, the user can quickly find the unusual waveform  1725  by reducing the range until just the unusual waveform  1725  is displayed, as shown in  FIG. 18 . 
     The term “unusual” as used herein can refer to any portion of the waveform that might be considered to possess an anomaly by the user, or is otherwise of interest to the user. Examples can include unusual variances in a pulse width, a fall time, an undershoot, a spike, a runt, or any other type of anomalous waveform. It should be understood that the waveform  1725  is only representative of a waveform that can have one or more of the mentioned unusual aspects. 
     The waveforms such as  1715 ,  1720 , and  1725  can be from the same data record and simultaneously displayed. The configurable trigger controls can be used to adjust how the waveforms are displayed. For example, the next control(s)  255  (of  FIG. 2A ) can cause a next post-acquisition trigger event  1772  associated with the data record to found and displayed. For example, the next control(s)  255  can cause a waveform, such as  1715 , to automatically shift so that the post-acquisition trigger event  1772  is displayed toward the center column of the display. Alternatively, the next control(s)  255  can cause one or more waveforms such as  1715 ,  1720 , and  1725  to automatically shift to the next post-acquisition trigger event. 
     Similarly, the previous control(s)  261  can cause a previous post-acquisition trigger event  1774  associated with the data record to found and displayed. For example, the previous control(s)  261  can cause a waveform, such as  1715 , to automatically shift so that the post-acquisition trigger event  1774  is displayed toward the center column of the display. Alternatively, the previous control(s)  261  can cause one or more waveforms such as  1715 ,  1720 , and  1725  to automatically shift to the previous post-acquisition trigger event. 
     As additional examples, the first control(s)  257  and last control(s)  263  can find and display the first and last post-acquisition trigger events, respectively. Other standard control(s)  239  or specific control(s)  269  may be used to manipulate how the trigger events or the waveforms are displayed. 
       FIG. 19  is a block diagram illustrating a test and measurement instrument  1400  including an acquisition memory  1415 , an analog trigger circuit  1420 , and various analog-to-digital converters (ADCs)  208  and digital-to-analog converters (DACs)  1412 , according to an example embodiment. Some of the components of the acquisition and trigger unit  1405 , the controller  1430 , and the display unit  1435  correspond to similar components discussed above and a detailed description need not be repeated. The acquisition memory  1415  may acquire one or more digital data samples and store them as at least one data record  1417 . 
     One or more ADCs  208  may be associated with the input terminal(s)  110 . The one or more ADCs  208  may receive a signal under test and produce digital samples from the signal under test, and transfer the digital samples to the acquisition memory  1415 . An analog trigger circuit  1420  may have an input coupled to the input terminal(s)  110 , and can detect a live trigger event in the signal under test based on first trigger criteria and can cause an automatic adjustment to the waveform to conform with a time of the live trigger event. In addition, the acquisition and trigger unit  1405  may include one or more DACs  1412  to receive the digital samples from the acquisition memory  1417  and to produce a converted analog signal, which can be transmitted to the analog trigger circuit  1420  for post-acquisition processing. 
     The analog trigger circuit  1420  is configured to receive the converted analog signal to detect a post-acquisition trigger event in the data record  1417  based on second trigger criteria, and to cause an automatic adjustment to the waveform to conform with a time of the post-acquisition trigger event. In this manner, a single trigger circuit may be used to detect and process live trigger events as well as post-acquisition trigger events. 
     Similar trigger controls and behavior as described in detail above can be used to control the analog trigger circuit  1420  to achieve similar outcomes. For the sake of brevity, a detailed description of the various controls and behavior need not be repeated. 
       FIG. 20  is a flow diagram illustrating a technique for configuring post-acquisition triggers and adjusting a corresponding waveform according to an example embodiment. The procedure may begin by acquiring data from an electrical signal under test at  1000 . The flow then proceeds to  1005  where any live trigger events are detected and the waveform(s) are adjusted accordingly. At  1010 , a determination is made whether live acquisition of data has stopped. This determination can be responsive to user input, or determined automatically. If the live-acquisition mode has not been stopped, then the flow takes the path through ‘B’ and continues to acquire data from the electrical signal under test. 
     Otherwise, the oscilloscope enters the post-acquisition mode, and the flow proceeds along one of two paths  1015  or  1020  based on user input. If the user adjusts the standard trigger controls to select trigger criteria at  1015 , then the flow proceeds to  1030  where a determination is made whether a post-acquisition trigger event is detected. If yes, the flow proceeds to  1035  and a position of a waveform is automatically shifted to conform with a time of the post-acquisition trigger event. Thereafter, the flow proceeds to  1040  where a determination is made whether the live-acquisition of data has been re-started, and based on the determination, either path ‘A’ or ‘B’ can be taken. If no, the flow proceeds through ‘A’ and returns to wait for input from the user. At this point, if the user adjusts the standard trigger controls to search at  1020  for events in the data record, the flow proceeds to  1040 , where a similar determination is made whether the live-acquisition of data has re-started. 
     Embodiments of the invention include a method for acquiring data from a signal under test for storage in an acquisition memory as a data record and displaying a waveform associated with the signal under test while acquiring the data. After acquiring the data record, the user may adjust standard trigger controls to select trigger criteria. A trigger circuit can detect a post-acquisition trigger event in the data record based on the trigger criteria and automatically shift a position of the waveform to conform with a time of the post-acquisition trigger event. A trigger level control can be adjusted to select a first trigger point while acquiring the data, and can be adjusted to select a second trigger point after acquiring the data. Adjusting the trigger level control after acquiring the data can include selecting the second trigger point for the post-acquisition trigger event. When the live acquisition of data resumes, the previously selected post-acquisition trigger criteria can be automatically applied to the live trigger criteria. 
     Although particular embodiments have been described, it will be appreciated that the principles of the invention are not limited to those embodiments. For example, in addition to the post-acquisition trigger features described above, the standard trigger controls can also be used to cause the trigger circuit to search for other types of events, such as defects in the waveform, as stored in the data record, during a post-acquisition mode. This allows users to implement searches of the data record using controls with which they are most familiar. Variations and modifications may be made without departing from the principles of the invention as set forth in the following claims.