Teledyne LeCroy SDA II - Manual (Page 18)

Serial Data Analysis II Software
The value of y
k
is the correction value for the kth iteration of the computation and x
k
is the error
between the kth data edge and the corresponding clock edge. Notice that the current correction factor is
equal to the weighted sum of the current error and all previous correction values. The multiplier value is
set to one in the SDA, and the value of n is the PLL cutoff divisor set from the Serial Data Analysis IIdialog.
The cutoff frequency is Fd/n, where Fd is the data rate. This filter is related to its analog counterpart
through a design process known as impulse invariance and is only valid for cutoff frequencies much less
than the data rate. For this reason, the minimum PLL cutoff divisor setting is 20 in the SDA.
The factor n determines the number of previous values of the correction value y used in the computation
of the current correction value. This is theoretically infinite; however, there is a practical limit to the
number of past values included.
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