5-7
programmed automatically in auto-trigger.
BAD
X1 attenuator, Channel B. The X1 attenuator is set by default in the
manual trigger mode. The X10 attenuator can be set if the signal is
larger than 5 V or larger than ±5 V. The attenuator setting will be
p-p
programmed automatically in auto-trigger.
Phase Mode Default Settings (continued)
COMMAND
Parameter Set
AAC
AC coupling, Channel A. DC coupling (ADC) can be programmed.
BAC
AC coupling, Channel B. DC coupling (BDC) can be programmed.
AFD
Filter disabled, Channel A. The filter on Channel A can be enable by
the AFE command.
APS
Positive slope, Channel A. The slope on Channel A can be changed
to negative with the ANS command.
BPS
Positive slope, Channel B. The slope on Channel B can be changed
to negative with the BNS command.
BCS
Separate inputs. It is assumed that the Phase measurement is being
made on separate signals. The Common input can be enabled if a
single signal is to be characterized with the BCC command.
Summary
To summarize, the automatic functions are designed to reduce the user’s setup time by
programming the counter’s functions and signal conditioning parameters for typical values
appropriate to the measurement. For example, most pulse parameter measurements are made
on square waves or pulses, which would indicate that the user DC couple the input so as not
to slow down the signal and change its integrity prior to measurement. Therefore, in Pulse
Width and Rise/Fall Time modes, the 2251A defaults to DC coupling.
Because of the default conditions and disallowed set-up parameters on the automatic
functions of the 2251A, care needs to be taken when designing drivers or soft panels to
ensure that correct transitions are made when changing functions or signal conditioning
parameters.
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