TDS 620A, 640A, & 644A User Manual
2Ć19
Acquisition
Acquisition is the process of sampling the analog input signal, converting it
into digital data, and assembling it into a waveform record. The oscilloscope
creates a digital representation of the input signal by sampling the voltage
level of the signal at regular time intervals (Figure 2-4).
Input Signal Sampled
Points
Digital
Values
+5.0 V
–5.0 V
+5.0 V
–5.0 V
0 V 0 V 0 V 0 V
Figure 2-4: Acquisition: Input Analog Signal, Sample, and Digitize
The sampled points are stored in memory along with corresponding timing
information. You can use this digital representation of the signal for display,
measurements, or further processing.
You specify how the digitizing oscilloscope acquires data points and as-
sembles them into the waveform record.
The trigger point marks time zero in a waveform record. All record points
before the trigger event make up the pretrigger portion of the the waveform
record. Every record point after the trigger event is part of the posttrigger
portion. All timing measurements in the waveform record are made relative to
the trigger event.
Each time it takes a sample, the oscilloscope digitizer produces a numeric
representation of the signal. The number of samples may be larger than the
number of points in your waveform record. In fact, the oscilloscope may take
several samples for each record point (Figure 2-5).
Samples For a
Record Point
Interval for One Waveform Record Point
Figure 2-5: Several Points May be Acquired for Each Point Used
Sampling and
Digitizing
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