US 6,642,750 B1Granted

Sequencing circuit for applying a highest voltage source to a chip

AssigneeInternational Business Machines Corporation

InventorPatrick Kevin Egan

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Abstract

A sequencing circuit and sequencing method are provided for applying a highest voltage of first and second system supplies to a chip. The sequencing circuit includes a first transistor coupled between the first system power supply and a power supply input to the chip and a second transistor coupled between the second system power supply and a power supply input to the chip. The sequencing circuit includes a comparator for sensing a highest voltage of the first and second system power supplies. The first transistor and second transistor are coupled to an output of the comparator. When the comparator senses that the first power supply voltage is higher than the second power supply voltage, the first transistor is turned on and couples the first power supply voltage to the power supply input to the chip. Alternately, when the comparator senses that the second power supply voltage is higher than the first power supply voltage, the second transistor is turned on and couples the second power supply voltage to the power supply input to the chip.

Claims10

Dependent claims

A sequencing circuit for applying a highest voltage of first and second system power supplies to a chip;

said sequencing circuit comprising:
a first transistor coupled between the first system power supply and a power supply input to the chip;
a second transistor coupled between the second system power supply and the power supply input to the chip;
a comparator for sensing a highest voltage of the first and second system power supplies;
a third transistor connected between a bias reference voltage and the second system power supply;
said first transistor, said second transistor, and said third transistor being coupled to an output of said comparator;
responsive to said comparator sensing the highest voltage of the first system power supply, said first transistor being turned on and coupling the first power supply voltage to the power supply input to the chip;
and
responsive to said comparator sensing the highest voltage of the second system power supply, said second transistor being turned on and coupling the second power supply voltage to the power supply input to the chip;
a bias voltage source coupled to said comparator;
said bias voltage source and said bias reference voltage being powered up before the first system power supply and the second system power supply are powered up and said bias voltage source and said bias reference voltage being powered down after the first system power supply and the second system power supply are powered down.

8 more elements

A sequencing method for applying a highest voltage of first and second power system supplies to a chip;

said sequencing method comprising the steps of:
providing a first transistor coupled between the first system power supply and a power supply input to the chip;
providing a second transistor coupled between the second system power supply and the power supply input to the chip;
providing a third transistor connected between a bias reference voltage and the second system power supply;
sensing a highest voltage of the first and second system power supplies using a comparator;
said comparator having an output coupled to said first transistor, said second transistor, and said third transistor;
providing a bias voltage source coupled to said comparator;
powering up said bias voltage source and said bias reference voltage before the first system power supply and the second system power supply are powered up;
responsive to sensing the highest voltage of the first system power supply, turning on said first transistor and coupling the first power supply voltage to the power supply input to the chip;
responsive to sensing the highest voltage of the second system power supply, turning on said second transistor and coupling the second power supply voltage to the power supply input to the chip;
and
powering down said bias voltage source and said bias reference voltage after the first system power supply and the second system power supply are powered down.

9 more elements

Dependencies are inferred from the claim text.