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Oscilloscope Selection Tip 3:
Acquisition Memory
Part 3 of a 12-part series
Tip 3 Select a scope that has sufficient acquisition memory
to capture your most complex signals with high resolution.
Closely related to a scope's maximum sample rate is its maximum available acquisition
memory depth. Even though a scope may have a maximum sample rate that might be con-
sidered fast enough to capture your highest speed signals, this does not mean that the scope
always samples at this high rate. Scopes sample at their fastest rates when the timebase is
set on one of the faster time ranges. But when the timebase is set to slower ranges to capture
longer time spans across the scope's screen, scopes automatically reduce sample rates based
on the available acquisition memory.
For example, let's assume that an entry-level scope has a maximum sample rate of 1 GSa/s and
a memory depth of 10 k points. If the scope's timebase is set at 10 ns/div in order to capture
Agilent's 2000 and 3000 X-Series 100 ns of signal activity across the scope's screen (10 ns/div x 10 divisions = 100 ns time span),
the scope needs just 100 points of acquisition memory to fill the screen while sampling at its
oscilloscopes optimize your deep maximum sample rate of 1 GSa/s (100 ns time span x 1 GSa/s = 100 samples). No problem!
But if you set the scope's timebase to 10