Tektronix 11A34 User Reference Supplement page 26

Adding and Subtracting Waveforms
waveforms without rMriclion. The reason for this lies in the manner in which
samples are taken and usad by the mainframe. Each plug-in compaztmant
an assdated sampler in the 11401 or 11402. Samples ara taken simultaneously
from that of another plugin unit accurately by virtue of this simultaneity.
Thus noise and other signals
Signals from different channekwith.in a plug-in unit are sampled at different
times. Signals that are entirely repetitive and related to the
maybe successfully added or subkactad in spite of this. However, signals that
are not repdive or related to the trigger will not be sampled at the same
signals to ba added or subtracted be sekted from different plug-in
in unit because its hardware subtracts the signals at its two inputs, passing only
Even when using channels from different
two problems limit the accuracy of sums or differences:
2
The solution to both problems is to invoke averaging. The averaging prom
suppresses all signals and noise unrelated to the trigger.
consists of same points that are "older" than others. Although samples
may be taken simultaneously, thera is a chance that a correct sample may
and displayed.
Delay differmces between channels of different plug-m uni& due to probe
cable length differences are normally removed by deskewing the probes
and the assodated amplifier channel. Samples are still taken
simultaneously, but the display is manipulated to remove time
to their proper tkne relatio&ip,~but there is no way for signals unrelated
to the trigger to be corrected with this deskwing technique. High-
to the trigger will be canceled when
has