Comparator circuit
AssigneeMotorola, Inc.
InventorsRobert B. Jarrett, Robert A. Neidorff
Life of this patent
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Abstract
This relates to a comparator circuit for monitoring intelligence on a data bus, which circuit consumes no power until activated by a predetermined voltage on the data bus. An input PNP transistor has a base coupled to the data bus. An emitter resistor and a collector resistor may be scaled to achieve a desired switching threshold. A second PNP transistor has a base coupled to the bus and an emitter coupled to the collector of the first PNP transistor such that the second PNP transistor does not turn on until the first PNP transistor saturates. The collector of the second PNP transistor is coupled to the base of an output NPN transistor and supplies drive thereto when the second PNP transistor is on.
Claims4
A comparator circuit for detecting when an input signal reaches a predetermined threshold, comprising:
- input transistor means having base, emitter and collector terminals, said base terminal being coupled to monitor an input signal;
- impedance means coupled to the emitter and collector terminals of said input transistor means for selectively varying said threshold;
- switching transistor means having base, emitter and collector terminals, said base terminal coupled to said input signal and said emitter terminal coupled to the collector terminal of said input transistor means, said switching transistor means turning on when said input transistor means saturates;
- and
- output circuit means coupled to the collector terminal of said switching transistor means and responsive thereto.
Dependencies are inferred from the claim text.