A means for sampling the signal x^ over its
limited interval is indispensable for sampbng the
logic values ao, ai, ..., am from the signal x. This
sampling means is called the window comparator.
The window comparator is defined as a logic device
that has two different threshold values VH and Vs
(VH > Vs) with respect to the input level x^ and
produces two different logic output signals Z(x^) E
{ 1, 0) inside and outside of the interval between the
two threshold values as expressed by Eq. (2).