Environmental Engineering Reference
In-Depth Information
1.4 Comparators
Comparators are used extensively in sigma-delta modulators as quan-
tizers. Both voltage-mode and current-mode comparators are available,
as shown in Fig.8.4. The output of clocked comparators updates itself
at the clocking instants only and remains unchanged during clocking
phases, whereas the output of unclocked comparator is transparent to
the inputs.
The switching variable of an ideal voltage-mode comparators is defined
as
and the constitutive equation of the comparator is given by
where is a user-defined voltage. It is evident that a voltage-mode
comparator is a voltage-controlled switch.
The switching variable of a current-mode comparator is given by
where is the input current to the comparator. The constitutive
equation of the current-mode comparator is given by
Current-mode comparators are current-controlled switches.
The switching variable of other types of internally controlled switches,
such as thyristors, can also be defined in a similar way.
2. Switching Instants
It was seen in the preceding section that a change in the polarity of
the switching variable
of an internally controlled switch indicates a
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