US 4,536,663 AGranted

Comparator circuit having full supply common mode input

AssigneeMotorola, Inc.

InventorsIra Miller, Robert C. Rumbaugh, John J. Price, Jr.

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Abstract

The input voltage signals to a comparison circuit may vary between levels substantial equal to the first and second supply voltages (e.g. typically 5 volts and ground). A first transistor circuit is coupled to a current mirror circuit and to an output node for supplying a mirrorable current to the current mirror circuit which in turn reduces the voltage at the output node when the first input voltage approaches the upper supply voltage, and supplies a current to the output to increase the voltage thereat when the second input approaches the upper supply voltage. A second transistor circuit is also coupled to the current mirror and to the output for supplying a mirrorable current to the current mirror means so as to reduce the voltage at the output when the second input voltage approaches ground, and supplies current to the output to increase the voltage thereat when the first input voltage approaches ground. The output node has coupled thereto a level shifting transistor and first and second follower transistors.

Claims8

Dependent claims

A circuit for comparing first and second input voltages which may vary between a first supply voltage and a second lower supply voltage, said circuit characterized by being powered by said first and second supply voltages and comprising:

current mirror means coupled to an output of said circuit;
first transistor means coupled to said current mirror means and to said output for supplying a mirrorable current to said current mirror means to reduce the voltage at said output when said first input voltage is slightly less than said second input voltage, and said second input voltage is slightly less than or substantially equal to said first supply voltage, and for supplying current to said output to increase the voltage at said output when said second input voltage is slightly less than said first input voltage, and said first input voltage is slightly less than or substantially equal to said first supply voltage;
and
second transistor means coupled to said current mirror means and to said output for supplying a mirrorable current to said current mirror means to reduce the voltage at said output when said first input voltage is slightly less than said second input voltage, and said first input voltage is slightly greater than or substantially equal to said second supply voltage, and for supplying current to said output to increase the voltage at said output when said second input voltage is slightly less than said first input voltage and said second input voltage is slightly greater than or substantially equal to said second supply voltage.

1 more element

Dependencies are inferred from the claim text.