Stacked MOSFET protection circuit
First Claim
1. A protection circuit, comprising:
- first and second MOS transistors being of the same channel type and having a source of the first MOS transistor connected to a drain of the second MOS transistor;
a clamping circuit having first and second terminals, said first terminal being connected to a gate of the first MOS transistor and said second terminal being connected to a drain of the first MOS transistor, the clamping circuit being turned on in a normal state, and in a case where a surge voltage is applied the clamping circuit being turned on to accelerate breakdown of the first MOS transistor; and
a pad of a semiconductor device connected to the drain of the first MOS transistor, wherein said clamping circuit comprises a plurality of diodes having a cathode of each diode connected to an anode of the adjacent diode, wherein a cathode forming end portion on one side of the plural diodes constitute the first terminal of the clamping circuit, and an anode forming end portion on the other side of the plural diodes constitute the second terminal of the clamping circuit.
1 Assignment
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Accused Products
Abstract
Disclosed is a protection circuit capable of avoiding breakdown of a gate insulating film of a MOSFET and having an appropriate snap-back voltage in terms of reliability. In order to prevent breakdown of a gate insulating film of a MOSFET constituting a stacked protection circuit caused by application of a surge voltage between the gate and the drain of the MOSFET, a single or a plurality of diodes or a MOSFET switch is connected between the gate and the drain of the MOSFET for absorbing the surge voltage. The particular construction permits obtaining a large surge tolerance against the surge voltage entering through, for example, the external power source pad, making it possible to form a protection circuit used in I/O'"'"'s tolerant to other power sources having an appropriate snap-back voltage against the external surge in assuring the reliability of the semiconductor device.
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Citations
18 Claims
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1. A protection circuit, comprising:
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first and second MOS transistors being of the same channel type and having a source of the first MOS transistor connected to a drain of the second MOS transistor;
a clamping circuit having first and second terminals, said first terminal being connected to a gate of the first MOS transistor and said second terminal being connected to a drain of the first MOS transistor, the clamping circuit being turned on in a normal state, and in a case where a surge voltage is applied the clamping circuit being turned on to accelerate breakdown of the first MOS transistor; and
a pad of a semiconductor device connected to the drain of the first MOS transistor, wherein said clamping circuit comprises a plurality of diodes having a cathode of each diode connected to an anode of the adjacent diode, wherein a cathode forming end portion on one side of the plural diodes constitute the first terminal of the clamping circuit, and an anode forming end portion on the other side of the plural diodes constitute the second terminal of the clamping circuit. - View Dependent Claims (2, 3, 4, 5)
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6. A protection circuit, comprising:
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first and second MOS transistors being of the same channel type and having a source of the first MOS transistor connected to a drain of the second MOS transistor, a drain of the first MOS transistor being connected to an external power supply terminal;
a switching circuit having first, second and third terminals, said first terminal being connected to a gate of the first MOS transistor, said second terminal being connected to a drain of the first MOS transistor and the external power source terminal, and said third terminal being connected to an internal power source terminal of a semiconductor device, the internal power source terminal being electrically separated from the external power source terminal, the switching circuit acting in a normal operation state to connect the gate of the first MOS transistor to the internal power source terminal and separate the gate of the first MOS transistor from the external power source terminal, and in a case where a surge voltage is applied the switching circuit acting to connect the gate of the first MOS transistor to the external power source terminal and separate the gate of the first MOS transistor from the internal power source terminal to accelerate breakdown of the first MOS transistor, and a pad connected to the drain of the first MOS transistor. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A protection circuit, comprising:
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first and second MOS transistors of a first conductivity type;
third and fourth MOS transistors of a second conductivity type;
first and second diodes;
first and second resistors;
an input/output pad; and
first, second and third power sources, wherein;
a source of the first MOS transistor is connected to a drain of the second MOS transistor;
a source of the third MOS transistor is connected to a drain of the fourth MOS transistor;
each of a drain of the first MOS transistor and a drain of the third MOS transistor is connected to the input/output pad;
a cathode of the first diode is connected to a gate of the first-MOS transistor and to the first power source via the first resistor;
an anode of the first diode is connected to the input/output pad;
an anode of the second diode is connected to a gate of the third MOS transistor and to the second power source via the second resistor;
a cathode of the second diode is connected to the input/output pad;
a source of the fourth MOS transistor is connected to the third power source; and
a source of the second MOS transistor is connected to the ground.
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Specification