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Circuit for partial power-down on dual voltage supply integrated circuits

  • US 6,281,724 B1
  • Filed: 11/17/1998
  • Issued: 08/28/2001
  • Est. Priority Date: 11/17/1998
  • Status: Expired due to Term
First Claim
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1. An integrated circuit chip having formed thereon a voltage control circuit, such circuit comprising:

  • a comparator circuit adapted for coupling to first and second voltage sources;

    a switch electrically coupled to the comparator circuit and the second voltage source and controlled by the comparator circuit; and

    a diode electrically coupled between the first voltage source and the switch;

    an output of the first voltage source being fed, through the diode, to an output of the switch, an input of the switch being coupled to an a output of the second voltage source;

    wherein the comparator circuit, switch and diode are arranged to place the switch in a non-conducting condition and the diode in a conducting condition in a first operating mode to couple the first voltage source to the output of the voltage control circuit through the conducting diode while the non-conducting switch isolates the output of the second voltage source from the output of the voltage control circuit during the first operating mode, and to place the switch in a conducting condition and the diode in a non-conducting condition in a second operating mode, the non-conducting diode de-coupling the output of the first voltage source from the output of the voltage control circuit while the conducting switch couples the output of the second voltage source to the output of the voltage control circuit output during the second operating mode;

    wherein the integrated circuit chip includes a substrate having a first type conductivity;

    wherein the switch includes a transistor having;

    a gate connected to an output of the comparator circuit; and

    one of the source/drain regions thereof connected to the voltage of the second voltage source;

    wherein source/drain regions of the transistor are formed in a region of the substrate having a type conductivity opposite to the type conductivity of the substrate;

    wherein the first voltage source is connected to the substrate through a first voltage contact region having the type conductivity opposite to the conductivity of the substrate;

    wherein the diode is a diode formed in the integrated circuit chip;

    wherein the diode, during the first operating mode, the diode being a p-n junction between the substrate and the first voltage contact region and with such junction being forward biased conduction, the first operating mode being when the output of the first voltage source is greater than the output of the second voltage source, electrically couples the first voltage source to the substrate to provide the output for voltage control circuit; and

    wherein the diode, during the second operating mode, the second operating mode being when the output of the first voltage source falls to ground potential and the output of the second voltage source remains unchanged, and with the p-n junction becoming reversed biased, electrically isolating the second voltage source from the first voltage source;

    wherein the switch, during the second operating mode, is placed in a conducting condition.

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