Tektronix CSA8000B - Manual (Page 153)

Measuring Waveforms
CSA8000B & TDS8000B User Manual 3- 79
Reference Levels Method. You can choose the method that the instrument uses to
determine a second group of levels when taking time-related measurements.
These levels are the High, Mid, and Low references. For example, the measure-
ment system takes risetime from the waveform-edge segment that transitions
from the Low to the High reference levels.
The instrument provides the following calculation methods; refer to Figure 3--21
as you read about each method:
1. Relative Reference is calculated as percentage of the High/Low range.
2. High Delta Reference is calculated as absolute values from the High Level.
3. Low Delta Reference is calculated as absolute values from the Low Level.
4. Absolute Reference is set by absolute values in user units.
5. AOP (not shown) measures the Average Optical Power of the waveform and
uses it as the Mid Ref level. See Pulse Crossings and Mid-reference Level
AOP on page B--58 for more information.
Reference level calculation methods
High (50 mV)
High reference
Mid reference (0 mV)
Low reference
Low (--50 mV)
90%
10% 90 mV
10 mV
--40 mV
40 mV
90 mV
10 mV
50% 50 mV 50 mV 0 mV
Figure 3- 21: Reference-level calculation methods
The High and Low levels from which the reference levels are calculated in
methods 1 -- 3 above are the levels established using the selected High/Low
tracking method described in High/Low Tracking Method on page 3--77.