Acquisition Modes
TDS 620A, 640A, & 644A User Manual
3Ć5
Hi Res Mode
In Hi Res mode, the digitizing oscilloscope averages all samples taken during
an acquisition interval to create a record point. That average results in a
higher-resolution, lower-bandwidth waveform.
This mode only works with real-time, non-interpolated sampling. If you set the
time base so fast that it requires real-time interpolation or equivalent-time
sampling, the mode automatically becomes Sample, although the menu
selection will not change.
A key advantage of Hi Res is its potential for increasing resolution regardless
of the input signal. Table 3-1 and the equations shown below illustrate how
you can obtain up to 15 significant bits with Hi res mode. Note that the resolu-
tion improvements are limited to speeds slower than 400 ns/div. Also, resolu-
tions above 15 bits are not allowed by internal hardware and computation
limitations.
Si = Sampling Interval for TDS 500A =
4
ns
ą
D
t = Sample Interval
=
Time
ń
Div
Number Of Points/Div
= = 100
ns
Nd = Number of points per decimation interval
=
D
t
Si
= 25
Resolution Enhancement (bits) =
0.5
LOG
2
(
Nd
)
2 extra bits
Table 3-1: Additional Resolution Bits
Time Base Speed
Bits of Resolution
400 ns and faster 8 bits
1
m
s to 2
m
s 9 bits
5
m
s to 10
m
s 10 bits
20
m
s to 50
m
s 11 bits
100
m
s to 200
m
s 12 bits
500
m
s 13 bits
1 ms to 2 ms 14 bits
5 ms and slower 15 bits
Envelope Mode
Envelope mode lets you acquire and display a waveform record that shows
the extremes in variation over several acquisitions. You specify the number of
acquisitions over which to accumulate the data. The oscilloscope saves the
highest and lowest values in two adjacent intervals similar to the Peak Detect
mode. But Envelope mode, unlike Peak Detect, gathers peaks over many
trigger events.
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