Title of Invention: Digital storage oscilloscope with simultaneous primary measurement and derived parameter display on common time axis and method therefor
Abstract: A method for presenting information and a digital storage oscilloscope are disclosed in which primary measurements of a signal are performed and displayed. Parameters are also derived for the signal based upon the primary measurement data. These derived parameters are then also displayed as a function of time on the display, preferably with a common time axis. This enables the oscilloscope operator to correlate features found by reference to the derived parameters directly to the primary measurements of the signal. Moreover, since the data from the primary measurements are stored in the oscilloscope, multi parameter calculation and parameter recalculation can be performed.
Detailed Description: Part PAC: DETAILED DESCRIPTION OF THE INVENTION
Part PAR: FIG. 1 shows a digital storage oscilloscope (DSO) to which the principles of the present invention are applied. Generally, the DSO 100 comprises a display 110, on which the time-dependent data is displayed. A key pad 112 controls the operation of the display 110 and trigger characteristics, for example. An optional printer 114 provides a printout of the display, raw data, or the status of the oscilloscope. Four analog signal input ports 114A-114D connect to probes (not shown). The probes are used to transmit time varying voltage signals to the DSO 100 where they are sampled and digitized. Auxiliary input ports 115 provide alternative inputs or trigger inputs.
Part PAR_2: FIG. 2 is a detailed view of the display 110. It comprises a signal plot region 116 in which the detected voltage of a sampled signal is conventionally plotted on a vertical axis against an horizontal time axis. Status portions 118 of the display 110 identify the display characteristics, horizontal/vertical scale, and the oscilloscope's current settings. A legend region 120 identifies the mapping between the colors used in display and the plotted signals.
Part PAR_3: FIG. 3 shows a display in which information is presented according to the principles of the present invention. The signal plot region 116 of display 110 has a primary measurement display portion 120 in which a primary measurement of the signal under analysis is displayed as in FIG. 2. In the most common example, the primary measurement display portion 120 will show the voltage level of the signal as a function of time on the horizontal axis. According to the invention, the signal plot region 116 of the display 110 also has a derived parameter display portion 122 in which parameters derived from the primary measurements are plotted, also as a function of time. In the preferred embodiment, the horizontal axis for the plotted primary measurement and the derived parameter are the same. This characteristic is illustrated by the dotted lines extending between the waveform of the primary measurement and the derived parameter plot. In this way the plots have a common time axis so that an operator, noticing an anomaly by reference to the derived parameter plot can trace the location of the event to the relevant segment of the primary measurement waveform.
Part PAR_4: In the illustrated example, the derived parameter is the time for which the data of the primary measurement either exceeds a threshold TH, illustrating width jitter. As a result, whereas the vertical axis in the primary measurement display portion 122 is voltage, the vertical axis in the derived parameter display portion 122 is time or signal width. As also illustrated, a closely related measurement is the time that the signal falls below the threshold TH. This alternative parameter plot is indicated by reference numeral 122'.
Part PAR_5: FIG. 4 is a process diagram illustrating the method for generating the display of FIG. 3 in which the derived parameters are based upon the level of the primary measurements relative to some threshold. In the first step 210, the primary measurements are made of the signal. Then the data from the primary measurement is displayed as a function of time in step 212. This yields the primary measurement display portion 120. According to the invention, the data from the primary measurements are also compared to the threshold TH in step 214. The derived parameter, i.e., the length of time that the signal exceeds a threshold for every transition through the threshold TH, is also plotted in step 216, yielding the derived parameter display portion 122. The derived parameter display portion 122 preferably shares a time axis with the primary measurements. The vertical axis, however, represents the time the signal exceeds the threshold rather than voltage as in the primary measurement display portion 120.
Part PAR_6: Preferred embodiments, non-linear interpolation techniques are used such as (sin x)/x and cubic interpolation to enhance the accuracy by which threshold crossings are located in time. Additionally, the use of hysteresis values for threshold crossings and digital low pass filtering are also important to provide better noise immunity in the parameter calculations.
Part PAR_7: FIG. 5 shows another exemplary display of derived parameters with primary measurements, according to the present invention. In this case, as in FIG. 3, the primary measurement portion 120 of the display 110 shows the voltage of the signal as a function of time. The period of this signal, however, is derived from the data of the primary measurement. The derived parameter portion 122 of the display 122 then plots the period for each cycle of the signal. This display is helpful to show the progression of the period over time, allowing the operator to relate the plot of the period to the actual waveform of the primary measurement because of the common time axis. As illustrated by derived parameter display 122', in alternative or complimentary embodiments, the period can be derived beginning at the falling portion of the signal rather than the rising portion as shown in portion 122.
Part PAR_8: FIG. 6 is a process diagram illustrating the method for generating the display 110 shown in FIG. 5. As discussed in reference to FIG. 4, the primary measurements of the signal are made and displayed in steps 210 and 212. According to the present process, cycles of the waveform of the primary measurements are then identified in step 218 by reference to the data from the primary measurements. Based upon the identification of the cycles and the data, derived parameters are calculated, i.e., the periods of successive cycles, and displayed as a function of time in step 220.
Part PAR_9: FIG. 7 shows another display 110 that is also based upon the cycles of the data from the primary measurements. In this case, the cycle-to-cycle jitter is plotted on the derived parameter portion 122 of the display 110. Specifically, the vertical axis of the derived parameter portion of the display 122 represents the difference between the current cycle period and the previous cycle period (P.sub.n -P.sub.n-1).
Part PAR_10: In alternative embodiments, the derived parameters are based on other cycle parameters such as: the time between the maxima and minima for each cycle, the time between minima and a previous minima for each cycle, the time of a local minima for each cycle, the time of a local maxima for each cycle, the time between local maxima and local minima for each cycle, the frequency of each cycle, the rise time for each cycle, the fall time for each cycle, the overshoot for each cycle, the pre-shoot for each cycle, and the change in pulse-width for each cycle relative to adjacent cycles.
Part PAR_11: Especially when searching for minima and maxima in the primary measurements to generate the parameters, the use of hysteresis values is a useful technique for locating the events of interest. Moreover, non-linear interpolation techniques are also preferably used such as (sin x)/x and cubic interpolation to enhance the accuracy by which peaks or other events are located in time and amplitude.
Part PAR_12: FIG. 8 shows still another display of a derived parameter plot with the primary measurement plot. In this example, the derived parameter is based upon the period of each cycle P.sub.N and the duty cycle width W.sub.N or the time for which the voltage of the signal exceeds some threshold TH. The plot of the derived parameters 122 has a vertical axis that is the duty cycle W.sub.N for a cycle divided by the period for that cycle P.sub.N.
Part PAR_13: The alternative derived parameter plot 122' illustrates that the parameters can also be based on the time each cycle is below the threshold TH.
Part PAR_14: FIG. 9 is a process diagram illustrating the technique for generating a cycle time and threshold-based derived parameter display. Specifically, as in FIG. 6, the primary measurements are made, the plot of the primary measurements is displayed, and the cycles of the primary measurements are identified in steps 210, 212, 218. In each cycle, the data from the primary measurements is also compared to a threshold TH in step 222. The parameters are then calculated and displayed as a function of time in step 224 based on the identified cycles in the signal and the thresholding of the data from the primary measurements.
Part PAR_15: In additional implementations, derived parameter displays based upon the peak variation in the amplitude and/or the duty factor are also plotted with the voltage of the primary measurements.
Part PAR_16: FIG. 10 shows still another embodiment of the plot portion 116 of display 110 according to the present invention. In this case the primary measurement portion of the display 120 plots the data from the primary measurements as a function of time as described previously. Cycles in the signal are identified and then compared against an internal or external time reference. This can either be an absolute time reference or a reference clock 124, as illustrated. The derived parameter portion of the display 122 in the illustrated example is a display of the interval error jitter. This is the difference between the period of the measured signal and the period of the reference clock edges 124. Thus, the vertical axis of the derived parameter plot 122 represents the comparison of these two signals or the signal of the primary measurement against an absolute time reference in different implementations.
Part PAR_17: FIG. 11 is a process diagram showing the method for generating the display as shown in FIG. 10. As in the process diagram of FIG. 9, the primary measurements are made, the data from the primary measurements is plotted and displayed, and cycles of the primary measurements of the signal is identified in steps 210, 212, and 218. Further, the cycles of the primary measurement are compared against an external time base in step 226. This can be an external clock source, or an absolute time reference either generated externally or within the oscilloscope. Then the derived parameters are plotted as a function of time. These derived parameters are based upon the comparison of the cycles of the signal and the time base in step 228.
Part PAR_18: In other implementations, the derived parameters can be based on the phase differences between the cycles of the signal and the absolute time reference, the timing errors between the cycles of the signal and the absolute time reference, phase differences between the cycles of the measured signal and the reference clock, and timing errors between the reference clock and the cycles of the measured signal.
Part PAR_19: FIG. 12 is a block diagram showing the internal organization of the oscilloscope 100 of the present invention. Specifically, the four ports 114A-114B provide inputs to four parallel channels 130A-130D of the oscilloscope. Each channel 130 has an amplifier 132 for providing a high impedance input to the channel. The output to the amplifier goes to a sample-and-hold circuit 134 that temporarily freezes the signal for digitization by analog-to-digital converter ADC1-4136. The digital output of the analog digital converters, 8 bits wide, in one embodiment, is stored to waveform memories 1-4138. These waveform memories typically have from 1 to 16 million, eight bit deep, storage locations. Trigger 142 tracks the output from the amplifiers 132 of the channels 130A-130D to search for a trigger condition. When the trigger condition is found, the time base 140 is activated, which synchronizes the operation of the sample-and-hold circuits 134, analog digital converters 136, and waveform memories 138.
Part PAR_20: In one implementation, the sample-and-holds 134, analog-to-digital converters 138, and waveform memories 138 continuously freeze, digitize, and store the data that is descriptive of the voltage of the signals transmitted to ports 114A-114B by the probes when the trigger 142 is merely armed. The waveform memories 138 are addressed in the form of a circular buffer. Only after the trigger condition is found does the trigger 142 and time base 140 hold the contents of the waveform memory and thereby sample the waveform at the triggering event.
Part PAR_21: Central processing unit (CPU) 150 controls the overall operation of the oscilloscope 100. Specifically, data captured in the waveform memories 138 of the channels 130A-130B are transferred by the CPU 115 into slots in a local memory 152 via bus 148. In the preferred embodiment there are eight slots #1-#8 in the local memory 152. This allows the oscilloscope to save up to eight separate events captured by the waveform memories 138. For example, the four channels could be operated to simultaneously sample four signals. The CPU 150 transfers their contents to slots 1 through 4 of the local memory 152. Thereafter, the channels 130A-130B would be free to capture up to 4 more additional signal events, storing them in slots 5 through 8 of the local memory 152 before any overwriting is necessitated.
Part PAR_22: Under operator control, the CPU 150 selects the data in local memory slots 1 through 8 for processing and transfer to a video frame buffer 154. Specifically under operator control, the data in slots 1 and 5 could be selected for display. This data is then processed using non-linear interpolation techniques, sin(x)/x or cubic for example, and the resulting display data transferred to video buffer 154 which provides the data to display 110.
Part PAR_23: FIG. 13 is a schematic diagram illustrating the mapping of the data in the slots of the local memory 152 to the display 110. As the CPU 150 operates on the primary measurement data in any one of slots 1 through 8 in the local memory 152, the CPU stores the derived parameters back to a vacant slot. In this way, the derived parameters utilize a slot in the local memory 152 that could otherwise be used by the channels to perform another signal acquisition. Briefly, as described in reference to FIGS. 4 through 11, the CPU identifies cycles in the data of the primary measurements, thresholds the primary measurements possibly using non-linear interpolation to improve accuracy and hysteresis/low pass filtering for noise immunity, and/or other operations to generate the derived parameters.
Part PAR_24: One advantage of using the storage oscilloscope architecture is the fact that multiple parameters can be calculated from the same primary measurement data and stored for simultaneous display, for example. Moreover, parameter recalculation is possible where the original applied threshold, for example, used to generate the parameters is modified after observation of the parameter display.
Part PAR_25: FIG. 13 illustrates an example situation in which a triangular waveform is stored in slot 1, which was generated from signal acquisition. The data in the array of slot 1 is indicated by reference numeral 157. The second array from slot 7 is indicated by reference numeral 155 holding parameter derived from the data in array 157. In the illustrated example, the derived parameters relate to the period of the triangular signal stored in array 155 of slot 1. The dotted lines 156 extending between the two arrays illustrate that the data for the primary measurements and the derived parameters are stored with analogous temporal organizations. For example, array location n in the array 155 holds parameters derived from data in array location n in array 155.
Part PAR_26: In the preferred embodiment, array 155 holding the derived parameters is packed with the period-based data. Each location that corresponds to the same cycle of the primary measurements in array 154 holds the measure of the period in the derived parameter array. Although being somewhat wasteful in storage space, this allows the existing oscilloscope zoom and scan features to operate normally. Even when expanding or contracting the scale using normal oscilloscope functions, the horizontal axis of the primary measurement data and the derived parameters remain synchronized to a common time axis.
Part PAR_27: While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described specifically herein. Such equivalents are intended to be encompassed in the scope of the claims.


{'bibliographic_information': "{'Patent Number': '061956171', 'Series Code': '9', 'Application Number': '0371556', 'Application Type': '1', 'Art unit': '287', 'Application Filing Date': '19980309', 'Title of Invention': 'Digital storage oscilloscope with simultaneous primary measurement and derived parameter display on common time axis and method therefor', 'Issue Date': '20010227', 'Number of Claims': '10', 'Exemplary Claim Number(s)': '1', 'Primary Examiner': 'Shah; Kamini', 'Number of Drawing Sheets': '10', 'Number of figures': '13'}", 'source_file': './grant/2001/pftaps20010227_wk09.txt', 'source_data': 'USPTO-Grant'}