voltage glitch can be missed altogether if the maximum sampling rate is wider than the
glitch.
When real-time sampling is not sufficient to capture the waveform, equivalent-time sampling
can sometimes be used. Equivalent-time sampling generates the waveform by piecing
together samples from different periods of a periodic waveform. The sample points are taken
at slightly different time intervals so that enough points can be sampled to reconstruct the
waveform adequately. The input signal is required to be periodic for equivalent-time
sampling. The equivalent sample time interval is much smaller allowing for potentially much
more accurate reconstruction of periodic waveforms. To accomplish this task, a delayed
trigger is used in either sequential or random order. For sequential sampling the trigger delay
is a fixed amount. This reconstructs the waveform by capturing different points along the
waveform in time until enough points are stored to reproduce the waveform accurately.
Random repetitive sampling is similar to sequential except that sampling is completed
randomly versus a fixed delay trigger. An example of equivalent-time sampling is illustrated
in
Figure 11.3b
.
It should be noted that equivalent-time sampling is only sufficient to capture repetitive events.
To capture random or nonperiodic events, it is necessary to use real-time sampling. This
causes a problem in high-speed measurements. Equivalent time will average out
nonperiodic events, and real time may not capture them if the sample rate is not high
enough. As illustrated in
Figure 11.3c
for nonperiodic waveform capture, the real-time
sampling rate can determine whether a glitch is captured at all. Random glitches in the
signals can cause system failures. If the sample rate is not sufficient, it becomes extremely
difficult to capture these random events. In cases where the width of the glitch is less than
the sampling rate, signal capture may be missed altogether. Similarly, in
Figure 11.4
, the
actual placement of the edge can be unknown if a sample does not fall on the transition.
Figure 11.5
shows another example of lost information due to inadequate sample rate.
Figure 11.4: How measurement resolution loss occurs when the sampling rate is
inadequate.
Summary :
voltage glitch can be missed altogether if the maximum sampling rate is wider than the glitch. When real-time sampling is not sufficient to capture the waveform, equivalent-time sampling can sometimes be used. Equivalent-time sampling generates the waveform by piecing together samples from different periods of a periodic waveform. The sample points are taken at slightly different time intervals so that enough points can be sampled to reconstruct the waveform adequately.
Tags :
waeform,capture,rate,sample,figure,time,equialenttime,random,points,glitch,eents,realtime,different