Browse Prior Art Database

Three State Window Comparator

IP.com Disclosure Number: IPCOM000114184D
Original Publication Date: 1994-Nov-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Maciver, MA: AUTHOR

Abstract

Conventional window comparators use two comparators with two reference voltages to define a window for comparison with an external signal voltage.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 67% of the total text.

Three State Window Comparator

      Conventional window comparators use two comparators with two
reference voltages to define a window for comparison with an external
signal voltage.

      If the output from the window comparator interfaces to a
microprocessor/microcontroller, then the external component count can
be halved.

      Described is a method for reducing the component count and
expanding the function of the window comparator to provide three
valid states on the one (window) comparator output.

      Comparators often rely on a fixed reference voltage for
comparison with an external signal.  An artificial window can be
created by modulating the reference voltage.  The state of the
comparator can be determined during each half cycle of the modulation
by the micro-controller (Fig. 1).

      If the comparator output does not change state during the
period of modulation, then the signal voltage, Vsig, is outwith the
window.  In this condition, the comparator output may be either high
or low, in a conventional comparator role (Figs. 2 and 3).

      If the comparator output alternates during each half cycle,
then Vsig is within the window voltage.  This alternating output is
the third state, and can be decoded within the microcontroller using
a low-pass filter, implemented in software (Fig. 4).

      For convenience, the modulating voltage may be a square wave
generated by the microcontroller.  This simplifies the low pass
filter si...