Teledyne LeCroy AORM - Advanced Optical Recording Measurements - Manual (Page 36)

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ISSUED: June 2013 923133 Rev A
BES BEGINNING EDGE SHIFT
Description
BES provides a measurement of the time between the beginning edge of the subject n in a specified
space/pit pair and the nearest specified clock edge. The measurement is calculated between the points
where the data and clock signals cross selected voltage thresholds. The clock period T can be entered by
the user, or measured from a user supplied clock signal, as described below.
The value calculated depends on the clock and data edges selected, as shown in the table below.
The data slope menu selects the polarity of the subject n pit/space. If Pos (positive) is selected,
the measurement is performed from the beginning edges of positive polarity pits and categorized
by the preceding space. If Neg (negative) is selected, the measurement is performed from the
beginning edges of negative polarity spaces and categorized by the preceding pit. If Both is
selected, the beginning edges of both pits and spaces are used in the calculation and categorized
by the preceding inverse polarity space/pit. The sizes of pits or spaces used in the measurement
are also determined by the range of ‘nT’ values chosen.
DATA SLOPE
CLOCK
EDGE
Pos Neg Both
Positive
time between beginning
edge of positive polarity
subject pit and nearest
positive clock edge time between beginning
edge of negative polarity
subject space and
nearest positive clock
edge time between beginning
edge of subject pits and
spaces to nearest
positive clock edge
Negative
time between beginning
edge of positive polarity
subject pit and nearest
negative clock edge time between beginning
edge of negative polarity
subject space and
nearest negative clock
edge time between beginning
edge of subject pits and
spaces to nearest
negative clock edge
Near
time between beginning
edge of positive polarity
subject pit and nearest
clock edge time between beginning
edge of negative polarity
subject space and
nearest clock edge time between beginning
edge of subject pits and
spaces and nearest
clock edge
The next figure shows the measurement of the beginning edge shift on a single subject 4T pit
preceded by a 3T space. In this example, the clock is specified as the positive edge. For each
space/pit combination, the beginning edge shift is calculated as the time difference between the
beginning pit edge and the clock edge. Additionally, the measurements will be sorted by the
space/pit pairs. For the positive polarity pit example shown in the figure after next, measurements t+ and t-
are for a single beginning edge shift measurement configured for positive edge, or negative edge. If nearest
is selected, the smaller of t- or t+ is used.