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Time base and Acquisition
The analyzer acquires data by sampling the voltage on each input channel
and comparing it to the threshold voltage to determine whether the input was
a logic high or logic low. The interval at which the input is sampled is called
the
sample period.
Because there is a finite amount of acquisition memory in the HP 54620A/C,
the instrument is optimized to deliver the smallest sample period possible,
while still acquiring enough data to provide at least a full screen of waveform
at any Time/Div (or
time base
) setting. To achieve this goal, the analyzer
must vary the sample period as a function of the time base setting. Other
analyzer functions that depend on the sample period, such as duration
trigger, are therefore affected when the time base setting is changed.
Consider what would happen if the sample period were not varied with
respect to the time base setting. If the sample period remained constant at
2 ns, at 1 s/div, the waveform would occupy a little over 16
µ
s (for 8
Ksamples). Thus, it would not be visible on the screen, because 16
µ
s is only
a small fraction of a single division at this sweep speed. This would defeat the
goal of switching to a larger Time/Div value, which is to see data over a larger
span of time.
However, because acquisition mode, trigger functions, delayed sweep, and
measurement functions depend on the sample period, you must be aware of
the relationships to ensure that you achieve the desired measurement results.
Relationship Between Time base and Analyzer Functions
Figure 35
Ensuring Accurate Measurements
Time base and Acquisition
129
Summary of Contents for 54620A
Page 7: ...6 ...
Page 13: ...12 ...
Page 17: ...16 ...
Page 18: ...1 Getting Started ...
Page 20: ...Using the Logic Analyzer Figure 1 Getting Started 19 ...
Page 52: ...2 Making Analyzer Measurements ...
Page 121: ...120 ...
Page 122: ...3 Solving Problems ...
Page 127: ...126 ...
Page 128: ...4 Ensuring Accurate Measurements ...
Page 150: ...5 Testing Adjusting and Troubleshooting the Analyzer ...
Page 180: ...6 Replaceable Parts ...
Page 193: ...Exploded View of Logic Analyzer Figure 60 Replaceable Parts To order a replacement part 192 ...
Page 196: ...7 Performance Characteristics ...
Page 208: ...8 Messages ...
Page 217: ...216 ...
Page 239: ......
Page 241: ...240 ...