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Appendix B: Algorithms
B–8
TDS 500C, TDS 600B, & TDS 700C User Manual
Timing measurement. The amount of time between the MidRef and Mid2Ref
crossings of two different traces, or two different places on the same trace.
Delay measurements are actually a group of measurements. To get a specific
delay measurement, you must specify the target and reference crossing polarities
and the reference search direction.
Delay = the time from one MidRef crossing on the source waveform to the
Mid2Ref crossing on the second waveform.
Delay is not available in the Snapshot display.
Optical measurement.
Extinction Ratio = (High/Low)
Optical measurement.
Extinction % = 100.0 / Extinction Ratio
Optical measurement.
Extinction dB = 10.0 (log
10
(Extinction Ratio))
Timing measurement. The time taken for the falling edge of a pulse to drop from
a HighRef value (default = 90%) to a LowRef value (default = 10%).
Figure B–2 shows a falling edge with the two crossings necessary to calculate a
Fall measurement.
1. Searching from Start to End, find the first sample in the measurement zone
greater than HighRef.
2. From this sample, continue the search to find the first (negative) crossing of
HighRef. The time of this crossing is THF. (Use linear interpolation if
necessary.)
Delay
Extinction Ratio
Extinction %
Extinction dB
Fall Time