Teledyne LeCroy AORM - Advanced Optical Recording Measurements - Manual (Page 54)

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ISSUED: June 2013 923133 Rev A
EDGSH EDGE SHIFT
Description
Edge Shift provides a measurement of the difference between the width of pits, spaces, or both,
and their ideal widths. These ideal widths are integer multiples of the clock period ‘T’. The width
of the pit or space is determined by the time between crossings of the selected voltage threshold
(see pwid).
When a single n is specified for the Edge Shift custom parameter, for each pit-width value calculated,
the Edge Shift is calculated as:
( )
T n w edgsh
i i i
⋅ − =
when absolute time units are specified
or
( )
T
T n w edgsh
i i i
% 0 . 100
⋅ ⋅ − =
when percent is specified,
where n
i
is the n that makes the width closest to nT (i.e., n is the n category to which the width belongs).
Thus:
( ) ( )
T n w T n
i i i
⋅ + < ≤ ⋅ −
5 . 0 5 . 0
where T is the configured period. It is very important for this parameter calculation that you enter
exactly the ideal T.
For ‘nT Table’ Show mode, or custom mode with one n specified, the value displayed for the n
th index
is the average of all of the edge shift values calculated that belong to that index:
T
T n
N
w
edgsh
n
i
n
% 0 . 100
⋅
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⋅ − =
∑
Where N
n
is the number of pits belonging to the n th index. When edge shift is configured as a custom
parameter with a range of n, the overall edge shift is calculated and displayed as the weighted average
of the edge shift values calculated above:
( )
∑
∑
⋅
=
n
n n
overall
N
N edsh
edgsh
The measurement calculation is compliant with the definition of Edge Shift as defined by ISO/IEC
JTC1.23.14517 Section 22.4.
Display Options
ORM parameter calculations can be displayed, histogrammed, and trended in a variety of ways.