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Protective circuit for insulated gate field effect transistor integrated circuits

  • US 4,264,941 A
  • Filed: 02/14/1979
  • Issued: 04/28/1981
  • Est. Priority Date: 02/14/1979
  • Status: Expired due to Term
First Claim
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1. A protective circuit for CMOS integrated circuits having a substrate of a first conductivity type, one or more diffusions contained within the substrate which are of conductivity type opposite the substrate in which are formed one or more MOS transistors of the same channel type as the conductivity of the substrate and one or more MOS transistors formed within the substrate of a channel type opposite the conductivity type of the substrate comprising:

  • (a) an input and an output terminal;

    (b) a terminal adapted to be connected to a first operating potential;

    (c) a terminal adapted to be connected to a second operating potential;

    (d) a first diode having a first and second electrode, the first electrode being coupled to the input terminal and the second electrode being coupled to the terminal which is adapted to be connected to the first operating potential;

    (e) a second diode having a first and a second electrode, the first electrode being coupled to the terminal adapted to be connected to the second operating potential and the second terminal being coupled to the input terminal;

    (f) a first transistor having a base and an emitter and a collector coupled between the first electrode of the first diode and the second electrode of the first diode, the collector being located in the substrate, the base being a diffusion located within the substrate of a conductivity type opposite the conductivity type of the substrate and the emitter being a diffusion of a conductivity type the same as the substrate which is contained within the base diffusion;

    (g) means coupled to the base of the first transistor for biasing the transistor into conduction when a potential is applied between the input and one of the other terminals which is of sufficient magnitude to reverse bias the first diode to a predetermined potential;

    (h) a second transistor having a base and an emitter and a collector coupled between the input and the first electrode of the second diode, the emitter being a diffusion of a conductivity type opposite the conductivity type of the substrate, the base being contained within the substrate and the collector being a diffusion of a conductivity type opposite the conductivity type of the substrate; and

    (i) means coupled to the base of the second transistor for biasing the transistor into conduction when a potential is applied between the input and one of the other terminals of sufficient magnitude to reverse bias the second diode to a predetermined potential.

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